椙村 益久

The immunoglobulin heavy chain binding protein (BiP) is an endoplasmic reticulum (ER) chaperone that facilitates the proper folding of newly synthesized secretory and transmembrane proteins. Here we report that BiP mRNA was expressed in the supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the hypothalamus in wild-type mice under basal conditions. Dual in situ hybridization in the SON and PVN demonstrated that BiP mRNA was expressed in almost all the neurons of arginine vasopressin (AVP), an antidiuretic hormone. BiP mRNA expression levels were increased in proportion to AVP mRNA expression in the SON and PVN under dehydration. These data suggest that BiP is involved in the homeostasis of ER function in the AVP neurons in the SON and PVN.

Familial neurohypophysial diabetes insipidus (FNDI) is caused by mutations in the gene locus of arginine vasopressin (AVP), an antidiuretic hormone. Although the carriers are normal at birth, polyuria and polydipsia appear several months or years later. Previously, we made mice possessing a mutation causing FNDI and reported that the mice manifested progressive polyuria as do the patients with FNDI. Here, we report that decreases in AVP mRNA expression in the supraoptic nucleus were accompanied by shortening of the AVP mRNA poly(A) tail length in the FNDI mice, a case in which aggregates accumulated in the endoplasmic reticulum (ER) of the hypothalamicAVP neurons. Expression levels of AVP heteronuclear RNA in the supraoptic nucleus, a sensitive indicator for gene transcription, were not significantly different between FNDI and wild-type mice. Incubation of hypothalamic explants of wild-type mice with ER stressors (thapsigargin and tunicamycin) caused shortening of the poly(A) tail length of AVP and oxytocin mRNA, accompanied by decreases in their expression. On the other hand, an ER stress-reducing molecule (tauroursodeoxycholate) increased the poly(A) tail length as well as the expression levels of AVP andoxytocin mRNA.These data reveal a novel mechanism by which ER stress decreases poly(A) tail length of neurohypophysial hormones, probably to reduce the load of unfolded proteins. Copyright © 2011 by The Endocrine Society.

It is well known that glucoprivation induces the release of counterregulatory hormones such as glucagon, and that the response is attenuated when the stimuli are repeated. Glucoprivation also activates orexigenic neurons and induces hyperphagic responses, although it remains unclear whether these responses are attenuated in repeated glucoprivation. In this study, we examined time course changes in feeding as well as activities of orexigenic neuropeptide Y (NPY) neurons in repeated glucoprivation in rats. Either 2-deoxy-d-glucose (2DG), which blocks glucose utilization, or isotonic saline (control) was injected subcutaneously to rats for 14 days, and food consumption for 1 and 2 h after injection was monitored throughout the experiment. While 2DG injection induced robust feeding responses during the first 1 h after injection, the response was gradually attenuated and the food consumption was significantly less on days 12-14 compared to that on day 1. On the other hand, food consumption during 2 h after 2DG injection was not changed significantly for 14 days. The transcriptional activities of NPY neurons in the arcuate nucleus and C1/A1 region of the hindbrain, measured by intronic in situ hybridization, were significantly enhanced after repeated 2DG injection for 14 days, while the feeding responses to intracerebroventricular injection of NPY were significantly less in the 2DG-repeated group compared to the saline-repeated group. It is thus demonstrated that repeated glucoprivation delayed hyperphagic responses while activating NPY neurons in rats. Our data also suggest that decreased feeding responses to NPY might be at least partially responsible for the delayed response. © 2010 Elsevier Inc.

Our recent animal and human studies revealed that chronic hyponatremia is a previously unrecognized cause of osteoporosis that is associated with increased osteoclast numbers in a rat model of the human disease of the syndrome of inappropriate antidiuretic hormone secretion (SIADH). We used cellular and molecular approaches to demonstrate that sustained low extracellular sodium ion concentrations ([Na(+)]) directly stimulate osteoclastogenesis and resorptive activity and to explore the mechanisms underlying this effect. Assays on murine preosteoclastic RAW 264.7 cells and on primary bone marrow monocytes both indicated that lowering the medium [Na(+)] dose-dependently increased osteoclast formation and resorptive activity. Low [Na(+)], rather than low osmolality, triggered these effects. Chronic reduction of [Na(+)] dose-dependently decreased intracellular calcium without depleting endoplasmic reticulum calcium stores. Moreover, we found that reduction of [Na(+)] dose-dependently decreased cellular uptake of radiolabeled ascorbic acid, and reduction of ascorbic acid in the culture medium mimicked the osteoclastogenic effect of low [Na(+)]. We also detected downstream effects of reduced ascorbic acid uptake, namely evidence of hyponatremia-induced oxidative stress. This was manifested by increased intracellular free oxygen radical accumulation and proportional changes in protein expression and phosphorylation, as indicated by Western blot analysis from cellular extracts and by increased serum 8-hydroxy-2'-deoxyguanosine levels in vivo in rats. Our results therefore reveal novel sodium signaling mechanisms in osteoclasts that may serve to mobilize sodium from bone stores during prolonged hyponatremia, thereby leading to a resorptive osteoporosis in patients with SIADH.

Osmotic demyelination syndrome (ODS) is a serious demyelinating disease in the central nervous system usually caused by rapid correction of hyponatremia. In an animal model of ODS, we previously reported microglial accumulation expressing proinflammatory cytokines. Microglia and astrocytes secreting proinflammatory cytokines and neurotrophic factors are reported to be involved in the pathogenesis of demyelinative diseases. Therefore, to clarify the role of microglial and astrocytic function in ODS, we examined the time-dependent changes in distribution, morphology, proliferation, and mRNA/protein expression of proinflammatory cytokines, neurotrophic factors, and matrix metalloproteinase (MMP) in microglia and astrocytes 2 days (early phase) and 5 days (late phase) after the rapid correction of hyponatremia in ODS rats. The number of microglia time dependently increased at demyelinative lesion sites, proliferated, and expressed tumor necrosis factor (TNF)-alpha, interleukin (IL)-1 beta, IL-6, inducible nitric oxide synthase, and MMP2, 9, and 12 at the early phase. Microglia also expressed leukemia inhibitory factor (a neurotrophic factor) and phagocytosed myelin debris at the late phase. The number of astrocytes time dependently increased around demyelinative lesions, extended processes to lesions, proliferated, and expressed nerve growth factor and glial cell line-derived neurotrophic factor at the late phase. Moreover, treatment with infliximab, a monoclonal antibody against TNF-alpha, significantly attenuated neurological impairments. Our results suggest that the role of microglia in ODS is time dependently shifted from detrimental to protective and that astrocytes play a protective role at the late phase. Modulation of excessive proinflammatory responses in microglia during the early phase after rapid correction may represent a therapeutic target for ODS. (C)2010 Wiley-Liss. Inc.

Rapid correction of chronic hyponatremia can lead to osmotic dennyelination syndrome (ODS), a severe demyelination disease. The microglia that accumulate in the demyelinative lesions may play a detrimental role in the pathogenesis of ODS by producing proinflammatory cytokines, suggesting that they may be a target for therapeutic intervention. Here, we investigated whether minocycline, a selective and potent inhibitor of microglial activation, could protect against ODS in rats. We induced hyponatremia by liquid diet feeding and dDAVP infusion. Rapid correction of the hyponatremia 7 days later resulted in neurologic impairment with severe demyelinative lesions. Activated microglia accumulated at the site of demyelination. Treatment with minocycline within 24 hours of rapid correction, however, was protective: rats exhibited minimal neurologic impairment, and survival improved. Histologic analysis showed that minocycline inhibited demyelination and suppressed the accumulation of microglia at the site of demyelination. Real-time RT-PCR and immunohistochemical analyses showed that minocycline inhibited the activity of microglia and the expression of inflammatory cytokines (e.g. IL-1 beta, inducible nitric-oxide synthase, and TNF-alpha), monocyte chemoattractant protein-1, and matrix metalloproteinase-12 in microglia. These results demonstrate that minocycline can protect against ODS by inhibiting the activation and accumulation of microglia at the site of demyelinative lesions, suggesting its possible use in clinical practice.

There is a high prevalence of chronic hyponatremia in the elderly, frequently owing to the syndrome of inappropriate antidiuretic hormone secretion (SIADH). Recent reports have shown that even mild hyponatremia is associated with impaired gait stability and increased falls. An increased risk of falls among elderly hyponatremic patients represents a risk factor for fractures, which would be further amplified if hyponatremia also contributed metabolically to bone loss. To evaluate this possibility, we studied a rat model of SIADH and analyzed data from the Third National Health and Nutrition Examination Survey (NHANES III). In rats, dual-energy X-ray absorptiometry (DXA) analysis of excised femurs established that hyponatremia for 3 months significantly reduced bone mineral density by approximately 30% compared with normonatremic control rats. Moreover, micro-computed tomography (mu CT) and histomorphometric analyses indicated that hyponatremia markedly reduced both trabecular and cortical bone via increased bone resorption and decreased bone formation. Analysis of data from adults in NHANES III by linear regression models showed that mild hyponatremia is associated with increased odds of osteoporosis (T-score -2.5 or less) at the hip [odds ratio (OR) = 2.85; 95% confidence interval (CI) 1.03-7.86; p<.01]; all models were adjusted for age, sex, race, body mass index (BMI), physical activity, history of diuretic use, history of smoking, and serum 25-hydroxyvitamin D [25(OH)D] levels. Our results represent the first demonstration that chronic hyponatremia causes a substantial reduction of bone mass. Cross-sectional human data showing that hyponatremia is associated with significantly increased odds of osteoporosis are consistent with the experimental data in rodents. Our combined results suggest that bone quality should be assessed in all patients with chronic hyponatremia. (C) 2010 American Society for Bone and Mineral Research.

Familial neurohypophysial diabetes insipidus (FNDI) is a rare disease that is inherited in an autosomal dominant manner. In a previous study, we made a mouse model for FNDI, which showed progressive polyuria accompanied by inclusion bodies in the arginine vasopressin (AVP) neurons formed by aggregates in the endoplasmic reticulum. The present study was conducted to determine whether the activities of AVP neurons are related to the phenotype progression in the FNDI model. In the first experiment, female heterozygous mice were administered either desmopressin (dDAVP) or a vehicle (control) subcutaneously with osmotic minipumps for 30 days. The dDAVP treatment significantly decreased the urine volume, AVP mRNA expression, and inclusion bodies in the AVP neurons. Urine volume in the dDAVP group remained significantly less than the control for 14 days even after the minipumps were removed. In the second experiment, the males were fed either a 0.2% Na or 2.0% Na diet for 6 mo. Urine AVP excretion was significantly increased in the 2.0% Na group compared with the 0.2% Na group for the first 2 mo but gradually decreased thereafter. Throughout the experiments, urine volume increased progressively in the 2.0% Na group but not in the 0.2% Na group. Immunohistochemical analyses revealed that inclusion bodies in the AVP cells had significantly increased in the 2.0% Na compared with the 0.2% Na group. These data demonstrated that activation of AVP neurons could accelerate the aggregate formation as well as the progression of the polyuria in the FNDI model mice.

The mammalian target of rapamycin (mTOR) has been implicated in the regulation of physiological functions such as cell growth and proliferation, and glucocorticoids reportedly inhibit mTOR signaling in peripheral tissues. Recent studies suggest that the mTOR signaling in the hypothalamus plays a critical role in maintaining energy homeostasis. In this study, we examined whether the mTOR signaling in the hypothalamus is involved in the regulation of neuropeptide Y (Npy) gene expression in the arcuate nucleus by glucocorticoids. In the hypothalamic organotypic cultures, the incubation with rapamycin significantly inhibited the mTOR signaling which was shown by decreases in the levels of phosphorylated p70S6K1 and S6. Similar to the action of the mTOR inhibitor rapamycin, dexamethasone (DEX), a synthetic glucocorticoid, also inhibited the mTOR signaling in the hypothalamic explants. Analyses of the explants with in situ hybridization demonstrated that the DEX or rapamycin alone significantly increased Npy gene expression in the arcuate nucleus, but that there were no additive effects of DEX and rapamycin on the expression. These data suggest that glucocorticoids upregulate the Npy gene expression in the arcuate nucleus by inhibiting mTOR signaling, at least in part.

While the hypothalamus has been implicated in the regulation of energy balance, the central mechanisms and neural circuit that coordinate the feeding response to energy deficit have not been fully clarified. To better understand the role of the hypothalamus in mediating hyperphagic responses to food deprivation or glucoprivation, we examined the feeding responses in rats in which the medial hypothalamus (MH) was isolated from the rest of the brain. The isolation of the MH was performed with a Halasz's knife cut, and experiments were performed 7 days after the operation. Food consumption between 9:00 a.m. and 11:00 a.m. in rats which had been fasted overnight was significantly increased compared to that in rats which had access to food ad libitum before the measurement in both the sham and MH-isolated groups, and the absolute values of food consumption in fasted rats were not significantly different between the groups. On the other hand, while an injection of 2-deoxy-d-glucose, which blocks glucose utilization, significantly increased food consumption for 2h after injection compared to a saline injection in the sham group, it did not increase food intake compared to saline injection in the MH-isolated groups. Thus, it is demonstrated that glucoprivation is not an effective stimulus to induce feeding in MH-isolated rats.

The adipocyte-derived hormone adiponectin plays an important role in modulating energy homeostasis through peripheral tissues and the central nervous system. Several studies have reported that adiponectin exists in cerebrospinal fluid and that adiponectin receptors are expressed in the hypothalamus, including the paraventricular nucleus (PVN), which plays a key role in controlling pituitary hormone secretion. Furthermore, it has been reported that magnocellular arginine vasopressin (AVP) neurones within the PVN express adiponectin receptors. These findings suggest a central role of adiponectin in the modulation of neuroendocrinological functions. In the present study, we investigated the effect of centrally-administered adiponectin on AVP release in conscious rats. Intracerebroventricular (i.c.v.) administration of adiponectin significantly reduced the basal plasma AVP concentration in a dose-dependent manner, with a maximal effect being obtained 10 min after administration. The plasma AVP increase in response to either hyperosmolar or hypovolaemic stimulation was also significantly attenuated by an i.c.v. injection of adiponectin. Treatment with AMP-activated protein kinase (AMPK) inhibitor compound C (100 nmol, i.c.v.) partially reversed the inhibitory effects of adiponectin on AVP release. These findings suggest that central adiponectin plays an inhibitory role in the osmoregulation and baroregulation of AVP release, that the AMPK pathway is at least partly involved in the action of adiponectin, and further suggest a novel physiological or pathophysiological role for central adiponectin in water balance via inhibition of AVP release.

Maternal diabetes during pregnancy increases the risk of congenital malformations such as neural tube defects (NTDs). Although the mechanism of this effect is uncertain, it is known that levels of nitric oxide synthase (NOS) and nitric oxide are elevated in embryos of a mouse model of diabetes. We postulated that overproduction of nitric oxide causes diabetes-induced congenital malformations and that inhibition of inducible NOS (iNOS) might prevent diabetic embryopathy. Mice were rendered hyperglycaemic by intraperitoneal injection of streptozotocin. The incidence of congenital malformations including NTDs was evaluated on gestational day 18.5. We assessed the involvement of iNOS in diabetes-induced malformation by administering ONO-1714, a specific inhibitor of iNOS, to pregnant mice with streptozotocin-induced diabetic mice and by screening mice with iNOS deficiency due to genetic knockout (iNos (-/-)). ONO-1714 markedly reduced the incidence of congenital anomalies, including NTDs, in fetuses of a mouse model of diabetes. It also prevented apoptosis in the head region of fetuses, indicating that iNOS is involved in diabetes-related congenital malformations. Indeed, no NTDs were observed in fetuses of diabetic iNos (-/-) mice and the incidence of other malformations was also markedly reduced. We conclude that increased iNOS activity during organogenesis plays a crucial role in the pathogenesis of diabetes-induced malformations and suggest that inhibitors of iNOS might help prevent malformations, especially NTDs, in diabetic pregnancy.

It is well known that maternal diabetes causes various congenital malformations. Although there are many reports that folic acid (FA) administration in pregnancy reduces the risk of birth defects including neural tube defects (NTDs), a precise analysis on the preventive effect of FA against diabetic embryopathy has not been done yet. In this study, we analyzed the preventive effects of FA on congenital malformations including NTDs, cardiovascular, and skeletal malformations using a diabetic mouse model. Female mice were rendered hyperglycemic by streptozotocin and then mated. Pregnant diabetic mice were treated daily with FA (3 mg/kg body weight) or saline between gestational days (GD) 6 and 10. On GD 18, fetuses were examined for congenital malformations. FA did not affect plasma glucose levels. In the DM control group, the incidence of NTDs, cardiovascular, and skeletal malformations was 28.4%, 28.5%, and 29.7%, respectively. In the FA-treated group, the corresponding proportions reduced to 6.0%, 2.5% and 12.5%, respectively. A whole-mount TUNEL revealed an increased apoptosis in the hindbrain region of embryos from DM control group on day 9.5, and the apoptosis was decreased by FA treatment. Maternal plasma homocysteine levels on GD 9.5 were significantly lowered in DM control group compared with those in non-DM group, and FA treatment did not show a significant effect. These results indicate that FA is effective for the prevention of various diabetic embryopathy including NTDs, cardiovascular, and skeletal malformations, and suggested that this effect is independent from homocysteine metabolism and possibly mediated by decreasing the abnormal apoptosis during organogenesis.

Epidemiological studies have shown that the risks of fetal malformation such as neural tube defects increase in diabetic pregnancy. To explore the mechanism of fetal malformation induced by diabetes, cDNA subtraction using mouse embryos (E9.5) of diabetic dams and those of controls was performed to identify differentially expressed genes. The expression level of genes identified by cDNA subtraction was further verified by quantitative RT-PCR using E8.5 embryos, and differential expression of 4 genes, Brcc3, Commd3, Ddx1, and SET was confirmed. We also analyzed the expression level of neural tube defect-related genes, and found that Folbp1, EphrinA5 and Sox10 were differentially expressed. Altered expression of these genes mostly persisted throughout the later stages of the development (E10.5-14.5). Hierarchical clustering analysis showed correlation between expression levels of these genes, suggesting that these genes cooperatively play a role in embryonic development. Our results suggest that an altered gene expression profile in embryos underlies the development of congenital malformation in diabetic pregnancies.

Previous studies have shown that the secretion of oxytocin and vasopressin from the posterior pituitary always accompanies systemic hyperosmotic stimuli in rats, and that oxytocin and vasopressin mRNAs consistently increase in response to prolonged hyperosmotic stimuli. Hence, it has been widely interpreted that oxytocin and vasopressin secretion and gene expression are closely coupled. In the present study, we used both vasopressin and oxytocin intron- specific probes to measure vasopressin and oxytocin heteronuclear RNA (hnRNA) levels, respectively, by in situ hybridisation in the rat supraoptic nucleus (SON) in conjunction with radioimmunoassays of vasopressin and oxytocin peptide levels in plasma and in the posterior pituitary in normally hydrated rats and after 1-5 days of salt loading. Increased oxytocin secretion in response to hyperosmotic stimuli exceeded vasopressin secretion at every time point studied. Vasopressin hnRNA in the SON increased to near maximal levels within minutes after the hyperosmotic stimulus, and was maintained throughout all 5 days of salt loading. By contrast, oxytocin hnRNA did not significantly change from control levels until approximately 2 days after hyperosmotic stimulation, and was not maximal until 3 days. In summary, increases in oxytocin gene transcription in response to osmotic stimuli are dramatically delayed compared to increases in vasopressin gene transcription under the same conditions. These data indicate that oxytocin gene transcription is not as closely correlated with pituitary peptide secretion as is vasopressin gene transcription, and suggests that there is a fundamental difference in excitation-secretion-transcription coupling mechanisms that regulate these two closely related genes in the rat magnocellular neurones in the SON.

Osmotic demyelination is a serious disease caused by rapid correction of hyponatremia. In humans, demyelinative lesions occur preferentially in the central pons, and thus are termed central pontine myelinolysis. Although accumulation of microglia has been reported in such demyelinative lesions, their role in the pathogenesis of osmotic demyelination remains unclear. We examined the expression of cytokines in microglia that accumulated in the demyelinative lesions in a rat model of osmotic demyelination. Hyponatremia was induced in rats by a combination of dDAVP infusion and liquid diet feeding. After 7 days, serum sodium levels were rapidly corrected by hypertonic saline injection. The rats developed severe motor deficits, and marked demyelinative lesions were found in the midbrain and cerebral cortex. In the area of the demyelinative lesions, massive accumulations of microglia were observed that expressed the proinflammatory cytokines TNF-alpha and IFN-gamma as well as NOS. In contrast, in hyponatremia corrected rats treated with lovastatin, which is known to inhibit microglial infiltration in various animal models of CNS disease, neurological impairments and the degree of demyelination were significantly ameliorated. Lovastatin also reduced the accumulation of microglia and decreased the expression of TNF-alpha in the demyelinative lesions. These results indicate that microglia play a detrimental role in the pathogenesis of osmotic demyelination by producing proinflammatory cytokines, and further suggest that lovastatin may be useful in repressing the demyelination. (c) 2006 Elsevier Inc. All rights reserved.

Central pontine myelinolysis (CPM) is a rare but serious demyelinative disease that is associated with rapid correction of chronic hyponatremia. Disruption of the blood-brain barrier (BBB) following a rapid increase in serum sodium concentration is considered to play a critical role in the pathogenesis of osmotic demyelination. We investigated the protective effect of dexamethasone (DEX) on osmotic demyelination in rats. After rapid correction of chronic hyponatremia, rats displayed serious neurologic impairments and demyelinative lesions were observed in various brain regions. Conversely, DEX-treated rats exhibited minimal neurologic impairments and demyelinative lesions were rarely seen in the brain. A marked extravasation of endogenous immunoglobulin G and Evans blue dye were observed in the brains of rats that did not receive DEX, indicating disruption, of the BBB, but this was not observed in DEX-treated rats. These results indicate that DEX is effective in preventing osmotic demyelination by inhibiting BBB disruption, and suggest that DEX might be useful for the, prevention of CPM in clinical practice. (c) 2006 Elsevier Inc. All rights reserved.

Increased renal alpha-ENaC and NCC abundance and elevated blood pressure are independent of hyperaldosteronism in vasopressin escape. Am J Physiol Renal Physiol 291: F49-F57, 2006. First published January 31, 2006; doi:10.1152/ajprenal.00390.2005.-Previously, we demonstrated that rats undergoing vasopressin escape had increased mean arterial blood pressure (MAP), plasma and urine aldosterone, and increased renal protein abundance of the alpha-subunit of the epithelial sodium channel (ENaC), the thiazide-sensitive Na-Cl cotransporter (NCC), and the 70-kDa band of gamma-ENaC (Song J, Hu X, Khan O, Tian Y, Verbalis JG, and Ecelbarger CA. Am J Physiol Renal Physiol 287: F1076-F1083, 2004; Ecelbarger CA, Knepper MA, and Verbalis JG. J Am Soc Nephrol 12: 207-217, 2001). Here, we determine whether changes in these renal proteins and MAP require elevated aldosterone levels. We performed adrenalectomies (ADX) or sham surgeries on male Sprague-Dawley rats. Corticosterone and aldosterone were replaced to clamp these hormone levels. MAP was monitored by radiotelemetry. Rats were infused with 1-deamino-[8D-arginine]-vasopressin (dDAVP) via osmotic minipumps (5 ng/h). At day 3 of dDAVP infusion, seven rats in each group were offered a liquid diet [water load (WL)] or continued on a solid diet (SD). Plasma aldosterone and corticosterone and urine aldosterone were increased by WL in sham rats. ADX-WL rats escaped, as assessed by early natriuresis followed by diuresis; however, urine volume and natriuresis were somewhat blunted. WL did not reduce the abundance or activity of 11-beta-hydroxsteroid dehydrogenase type 2. Furthermore, the previously observed increase in renal aldosterone-sensitive proteins and escape-associated increased MAP persisted in clamped rats. The densitometry of immunoblots for NCC, alpha-and gamma-70 kDa ENaC, respectively, were (% sham-SD): sham-WL, 159, 278, 233; ADX-SD, 69, 212, 171; ADX-WL, 116, 302, 161. However, clamping corticosteroids blunted the rise at least for NCC and gamma-ENaC (70 kDa). Overall, the increase in aldosterone observed in vasopressin escape is not necessary for the increased expression of NCC, alpha-or gamma-ENaC or increased MAP associated with "escape."

Renal sodium reabsorption is a key determinant of final urine concentration. Our aim was to determine whether differences existed between aged and young rats in their response to water restriction with regard to the regulation of abundance of any of the major distal renal sodium transporter proteins. Male Fisher 344 x Brown Norway (F344 x BN) rats of 3-, 10-, 24-, or 31 months of age (3M, 10M, 24M, or 31M) were either water restricted (WR) for 5 days or control ( ad libitum water). Major renal sodium transporters and channel subunits were evaluated by immunoblotting and immunohistochemistry. Age did not significantly affect plasma arginine vasopressin or aldosterone levels, but renin activity was only 8% in 31M-WR rats relative to 3M-WR (P<0.05). Extreme aging ( 31M) led to decreased outer medullary abundance of the bumetanide-sensitive Na-K-2Cl cotransporter and decreased cortical abundance of the beta- and gamma-subunits (70-kDa band) of the epithelial sodium channel ( ENaC) (P<0.05). Water restriction significantly (P<0.05) increased the abundance of Na-K-2Cl cotransporter (NKCC2) and Na - Cl cotransporter (NCC) across ages. However, these increases were significantly blunted as rats aged. Mean band densities were increased in WR rats ( relative to age controls) by 54 and 106% at 3M, but only 25 and 29% at 24M and 0 and 6% at 31M for NKCC2 and NCC, respectively. Aged F344 x BN rats have reduced basal distal tubular renal sodium transporter abundances and blunted upregulation during water restriction, which may contribute to decreased urinary concentrating capacity.

Central pontine myelinolysis (CPM) is a serious demyelination disease commonly associated with the rapid correction of hyponatremia. Although its pathogenesis remains unclear, the disruption of the blood-brain barrier (BBB) as a consequence of a rapid increase in serum sodium concentration is considered to play a critical role. Since glucocorticoids are known to influence BBB permeability and prevent its disruption as a result of hypertension or hyperosmolarity, we investigated whether dexamethasone (DEX) could protect against osmotic demyelination in an animal model of CPM. Hyponatremia was induced in rats by liquid diet feeding and dDAVP infusion. Seven days later, the animals' hyponatremia was rapidly corrected by injecting a bolus of hypertonic saline intraperitoneally. Rats subjected to this treatment displayed serious neurological impairment and 77% died within 5 days of rapid correction of their hyponatremia; demyelinative lesions were observed in various brain regions in these animals. On the other hand, rats that were treated with DEX (2 mg/kg, 0 and 6 h after hypertonic saline injection) exhibited minimal neurological impairment and all were alive after 5 days. Demyelinative lesions were rarely seen in the brains of DEX-treated rats. A marked extravasation of endogenous IgG was observed in the demyelinative lesions in the brains of rats that did not receive DEX, indicating disruption of the BBB, but was not observed in DEX-treated rats. Furthermore, Evans blue injection revealed a significant reduction in staining in the brains of DEX-treated rats (P < 0.05). These results indicate that early DEX treatment can prevent the BBB disruption that is caused by the rapid correction of hyponatremia and its associative demyelinative changes, and suggest that DEX might be effective in preventing CPM. (C) 2004 Elsevier Inc. All rights reserved.

We describe a novel missense mutant of arginine vasopressin (AVP)-dependent neurohypophyseal diabetes insipidus in an autosomal dominant family. A 54-year-old woman was admitted to our hospital because of thyroidectomy for thyroid cancer. After thyroidectomy she was found to have hypernatremia and polyuria and polydipsia both of which had been present from childhood. She had no obstructive hydronephrosis. Her father, father's younger sister and her third son also had polyuria and polydipsia. Basal plasma AVP concentration at normal plasma osmolality was normal but did not respond to increased plasma osmolality despite hyperosmolality during infusion of hypertonic saline infusion, indicating that plasma AVP secretion was impaired. Sodium concentration in urine and urine osmolality were low and increased after nasal administration of DDAVP. There was a diminished but bright signal of pituitary posterior gland on magnetic resonance T1 weighted image. Molecular genetic analysis demonstrated that the patient and her son had a single heterozygous missense mutation (G-->A) at nucleotide 1829 in 1 AVP allele, yielding an abnormal AVP precursor with lacking Glu-47 in its neurophysin II moiety. The abnormal AVP precursor may be related to the impaired AVP secretion.

Effects of peripheral administration of melanotan II (MTII), a melanocortin agonist, on insulin sensitivity and glucose tolerance were examined in Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Subcutaneous administration of MTII with osmotic mini-pumps decreased food intake and body weight in OLETF rats. MTII group showed more sensitivity to insulin compared with that allowed to eat ad libitum or pair-fed group in insulin tolerance tests on day 9. MTII group also showed significantly lower glucose values than ad libitum group in glucose tolerance tests on days 11 and 23. Thus, MTII increased insulin sensitivity and improved glucose tolerance in OLETF rats.

Leukemia inhibitory factor (LIF) is a cytokine of the interleukin-6 family exhibiting diverse physiological functions during inflammatory stress. It is well known that syndrome of inappropriate secretion of antidiuretic hormone (SIADH) is often associated with inflammatory disease, and cytokines produced at inflammatory foci are thought to stimulate arginine vasopressin (AVP) release. In the present study, we investigated the effects of centrally administered LIF on AVP release in conscious rats. Intracerebroventricular administration of LIF (0.01-1.0 microg/rat) significantly increased the plasma AVP concentration, and its effect was observed from 5 to 60 min after the injection. LIF did not cause significant changes in plasma Na+, total protein and blood pressure. There were no significant changes in the plasma AVP concentration after intravenous injection of LIF (1.0, 3.0 microg/rat). These results indicate that LIF plays a stimulatory role in the regulation of AVP release, and suggest the possibility that LIF may be involved in the pathogenesis of SIADH.

Although arginine vasopressin (AVP), an antidiuretic hormone, has been widely acknowledged to play an important role in cardiovascular regulation via V1a receptors (V1aR), its precise significance remains unclear. In this study, we investigated the effects of long-standing high plasma AVP status on cardiovascular regulation in the AVP-overexpressing transgenic (Tg) rat. Adult male homozygous Tg rats were compared with age-matched normal Sprague-Dawley rats as controls. There were no significant differences in mean arterial blood pressure (BP; MABP) or heart rate between Tg and control rats in the basal state. Subcutaneous injection of AVP significantly increased MABP in controls but did not cause any apparent increase in MABP in Tg rats. BP recovery from hemorrhage-induced hypotension was significantly delayed in Tg compared with control rats. Pretreatment with a selective V1aR antagonist, OPC-21268, which is thought to restore the downregulation of V1aR, markedly improved both of these impaired responses. Northern blot analysis confirmed that decreased expression of V1aR mRNA and pretreatment with V1aR antagonist significantly restored the downregulation of V1aR mRNA. These results suggest that the Tg rat has decreased sensitivity to the hypertensive effect of AVP due to downregulation of V1aR, which may function as an adaptive mechanism to maintain normal BP against chronic hypervasopressinemia. In addition, impaired restoration of BP after hemorrhage-induced hypotension in Tg rats supports a physiological role of AVP in cardiovascular regulation.

Tuberoinfundibular peptide of 39 residues (TIP39) is a recently discovered neuropeptide identified on the basis of its ability to activate the PTH2 receptor, and it is thought to be the brain PTH2 receptor's endogenous ligand. The PTH2 receptor is highly expressed in the hypothalamus, suggesting a role in the modulation of neuroendocrinological functions. PTHrP, which also belongs to the PTH-related peptides family, stimulates arginine vasopressin (AVP) release. In the present study, therefore, we investigated the effect of centrally administered TIP39 on AVP release in conscious rats. Intracerebroventricular administration of TIP39 (10-500 pmol/rat) significantly suppressed the plasma AVP concentration in dehydrated rats, and the maximum effect was obtained 5 min after administration ( dehydration with 100 pmol/rat TIP39, 4.32 +/- 1.17 pg/ml; vs. control, 8.21 +/- 0.70 pg/ml). The plasma AVP increase in response to either hyperosmolality [ip injection of hypertonic saline (HS), 600 mosmol/kg] or hypovolemia [ ip injection of polyethylene glycol ( PEG)] was also significantly attenuated by an intracerebroventricular injection of TIP39 ( HS with 100 pmol/rat TIP39, 2.65 +/- 0.52 pg/ml; vs. HS alone, 4.69 +/- 0.80 pg/ml; PEG with 100 pmol/rat TIP39, 4.10 +/- 0.79 pg/ml; vs. PEG alone, 6.19 +/- 0.34 pg/ml). Treatment with naloxone [1.5 mg/rat, sc injection], a nonselective opioid receptor antagonist, significantly reversed the inhibitory effects of TIP39 on AVP release. These results suggest that central TIP39 plays an inhibitory role in the osmoregulation and baroregulation of AVP release and that intrinsic opioid systems are involved in its mechanism.

GH secretagogue (GHS) is a small, synthetic compound that has the potential to stimulate GH release via its specific receptors (GHS-R). Ghrelin is a novel 28-amino acid peptide recently isolated from human and rat stomach, and it is thought to be the endogenous ligand for GHS-R. Ghrelin has a variety of physiological functions such as the stimulation of GH release or the increase of food intake by activating NPY neurons. In the present study, we investigated the effects of ghrelin on AVP release in conscious rats. Intracerebroventricular (icv) administration of ghrelin increased the plasma AVP concentration in a dose-dependent manner (1-1000 pmol/rat), and its effect was observed as late as 60 min after the administration. Icv injection of ghrelin caused no significant change in plasma osmolality, plasma volume, or arterial blood pressure. Iv administration of ghrelin (10 nmol/rat) also increased the plasma AVP concentration, which was accompanied by a significant decrease in arterial blood pressure. Pretreatment with antiserum against NPY significantly reduced the plasma AVP increase induced by icv administration of ghrelin. These results suggest that ghrelin plays a stimulatory role in AVP release, which is possibly mediated by NPY neurons.