The present studies reveal for the first time that vasopressin induces a marked increase in UAE in healthy rats and humans. This albuminuric effect seems to result from increased glomerular leakage, requires functional vasopressin V(2) receptors, and is, at least in part, mediated by the renin-angiotensin system. These results bring additional support for an involvement of vasopressin in the albuminuria observed in pathological states such as diabetes mellitus or hypertension.

Diabetic nephropathy represents a major complication of diabetes mellitus (DM), and the origin of this complication is poorly understood. Vasopressin (VP), which is elevated in type I and type II DM, has been shown to increase glomerular filtration rate in normal rats and to contribute to progression of chronic renal failure in 5͞6 nephrectomized rats. The present study was thus designed to evaluate whether VP contributes to the renal disorders of DM. Renal function was compared in Brattleboro rats with diabetes insipidus (DI) lacking VP and in normal Long-Evans (LE) rats, with or without streptozotocin-induced DM. Blood and urine were collected after 2 and 4 weeks of DM, and creatinine clearance, urinary glucose and albumin excretion, and kidney weight were measured. Plasma glucose increased 3-fold in DM rats of both strains, but glucose excretion was Ϸ40% lower in DI-DM than in LE-DM, suggesting less intense metabolic disorders. Creatinine clearance increased significantly in LE-DM (P < 0.01) but failed to increase in DI-DM. Urinary albumin excretion more than doubled in LE-DM but rose by only 34% in DI-DM rats (P < 0.05). Kidney hypertrophy was also less intense in DI-DM than in LE-DM (P < 0.001). These results suggest that VP plays a critical role in diabetic hyperfiltration and albuminuria induced by DM. This hormone thus seems to be an additional risk factor for diabetic nephropathy and, thus, a potential target for prevention and͞or therapeutic intervention.One of the major complications of diabetes mellitus (DM) is a progressive nephropathy that develops in about one-third of patients within 10-20 years after the onset of the disease and leads in most cases to end stage renal failure (1). This represents a major problem of public health because a large fraction of dialysis requirements is attributable to DM nephropathy. Although a number of studies have already been devoted to this problem, the factors contributing to diabetic nephropathy are not yet fully identified.A characteristic feature observed in diabetic patients is an elevation of plasma vasopressin (VP), well documented in both type I and type II DM (2-5). This elevation also occurs in animal models of DM, whether experimental or genetically determined (6, 7). Several studies have investigated the possible factors responsible for this increase in VP secretion (3,6,8,9). But they did not succeed in identifying the responsible stimulus for this increase. They revealed a resetting of the osmostat in diabetics but concluded that hyperglycemia was not responsible for this resetting because increasing plasma glucose and osmolality by intravenous infusion of hypertonic dextrose produced no increase in plasma vasopressin in diabetics or in healthy controls (8).Little attention has been given to the possible functional consequences of the rise in plasma VP. To our knowledge, the possible contribution of VP to the renal complications of DM has never been investigated in spite of several previous findings suggesting that this hormone represents a ...

The mechanisms by which arginine vasopressin (AVP) exerts its antidiuretic and pressor effects, via activation of V2 and V1a receptors, respectively, are relatively well understood, but the possible associated effects on sodium handling are a matter of controversy. In this study, normal conscious Wistar rats were acutely administered various doses of AVP, dDAVP (V2 agonist), furosemide, or the following selective non-peptide receptor antagonists SR121463A (V2 antagonist) or SR49059 (V1a antagonist). Urine flow and sodium excretion rates in the next 6 h were compared with basal values obtained on the previous day, after vehicle treatment, using each rat as its own control. The rate of sodium excretion decreased with V2 agonism and increased with V2 antagonism in a dose-dependent manner. However, for comparable increases in urine flow rate, the V2 antagonist induced a natriuresis 7-fold smaller than did furosemide. Vasopressin reduced sodium excretion at 1 g/kg but increased it at doses Ͼ5 g/kg, an effect that was abolished by the V1a antagonist. Combined V2 and V1a effects of endogenous vasopressin can be predicted to vary largely according to the respective levels of vasopressin in plasma, renal medulla (acting on interstitial cells), and urine (acting on V1a luminal receptors). In the usual range of regulation, antidiuretic effects of vasopressin may be associated with variable sodium retention. Although V2 antagonists are predominantly aquaretic, their possible effects on sodium excretion should not be neglected. In view of their proposed use in several human disorders, the respective influence of selective (V2) or mixed (V1a/V2) receptor antagonists on sodium handling in humans needs reevaluation. 19: 172119: -173119: , 200819: . doi: 10.1681 The mechanisms by which arginine vasopressin (AVP) exerts its antidiuretic and its pressor effects are relatively well understood. On the one hand, AVP improves water conservation by increasing the permeability to water of the renal collecting duct (CD), an effect mediated by the V2 receptors (V2R) and permitted by the insertion in the luminal membrane of principal cells of preformed aquaporin 2 (AQP2) molecules. This allows more water to be reabsorbed when these ducts traverse the hyperosmotic medulla. On the other hand, AVP increases blood pressure (BP) by inducing a vasoconstriction through its binding to V1a receptors (V1aR) expressed in vascular smooth muscle cells. For these two different effects, in vivo studies are in good agreement with the expectations based on results obtained in vitro. J Am Soc NephrolIn contrast, the experiments intended to study the effects of AVP on sodium handling in vitro or in vivo provide results that are difficult to reconcile. In the isolated microperfused CD, V2R activation increases sodium transport, 1 an effect that should reduce sodium excretion in vivo; however, in a number of studies, AVP infusion in animals and humans

In addition to its effect on water permeability, vasopressin, through its V2 receptors (AVPR2), stimulates Na reabsorption in the collecting duct by increasing the activity of the amiloride-sensitive sodium channel ENaC. This study evaluated whether dDAVP (a potent AVPR2 agonist) reduces sodium excretion in healthy humans (n ‫؍‬ 6) and in patients with central (C; n ‫؍‬ 2) or nephrogenic (N) diabetes insipidus (DI) as a result of mutations of either the aquaporin 2 gene (AQP2; n ‫؍‬ 3) or AVPR2 (n ‫؍‬ 10). dDAVP was infused intravenously (0.3 g/kg body wt in 20 min), and urine was collected for 60 min before (basal) and 150 min after the infusion. dDAVP markedly reduced both urine flow rate and sodium excretion in healthy individuals. A reduction in sodium excretion was also observed in CDI and NDI-AQP2 patients but not in NDI-AVPR2 patients. The magnitude of the fall in sodium excretion correlated with the rise in urine osmolality and the fall in urine output but not with the simultaneously observed fall in mean BP. These results suggest that the dDAVP-induced antinatriuresis is due to a direct V2 receptor-dependent stimulation of sodium reabsorption in the collecting duct and is not secondary to a hemodynamic effect. In conclusion, this study reveals a potent V2-dependent antinatriuretic effect of vasopressin in humans. The possibility that an inappropriate stimulation of ENaC by vasopressin might lead to significant sodium retention in chronic situations remains to be determined. 16: 192016: -192816: , 200516: . doi: 10.1681 I nappropriate retention of sodium and water by the kidney is thought to be a key factor in several forms of hypertension. Thus, it is important to identify factors that may favor excessive sodium reabsorption by the kidney. Vasopressin is known to promote water conservation by increasing the permeability to water of the collecting ducts (CD), thus allowing osmotically driven water reabsorption along these ducts when dilute distal tubular fluid enters them in the cortex and later when they traverse the hyperosmotic medulla. However, the effect of vasopressin on sodium excretion is less clear. A large number of studies have shown that vasopressin infusion increases sodium excretion in vivo in rats, dogs, and sheep (e.g., references 1-4). This natriuretic effect is difficult to reconcile with the fact that, in vitro, vasopressin stimulates sodium reabsorption in the isolated perfused CD (5,6), in the amphibian bladder (a tissue that shares a number of similarities with the mammalian CD) (7), and in several cell lines issued from these two tissues (8 -10). This effect on sodium reabsorption is inhibitable by amiloride and has been shown to result from activation of the endothelial sodium channel ENaC (11). Moreover, chronic elevation of vasopressin or infusion of its V2 agonist dDAVP (12) has been shown to increase the abundance of mRNA (13) and protein (14) of the ␤ and ␥ subunits of ENaC and to enhance markedly the subsequent functional response (water and sodium reabsorption) to exoge...

In diabetes mellitus (DM), the urine flow rate is increased, and the fluid turnover in the body is accelerated because of the glucose-induced osmotic diuresis. On the other hand, plasma vasopressin (VP) is elevated in both type 1 and type 2 DM. This elevation seems to be due to a resetting of the osmostat. A high VP level is beneficial in the short term because it limits to some extent the amount of water required for the excretion of a markedly enhanced load of osmoles (mainly glucose). However, in the long run, it may have adverse effects by favoring the developement of diabetic nephropathy. VP has been shown in normal rats to induce kidney hypertrophy, glomerular hyperfiltration, and an increase in urinary albumin excretion (features also occurring in association in the period preceding diabetic nephropathy). Moreover, VP has been shown to participate in the progression of renal failure in rats with five-sixths reduction in renal mass. In recent studies, we have shown (1) that creatinine clearance, albuminuria and renal mass increased much less during experimental DM in Brattleboro rats unable to secrete VP than in their VP-replete Long-Evans controls, and (2) that albuminuria was prevented during experimental DM in Wistar rats when a VP nonpeptidic, highly selective V2 receptor antagonist was administered chronically for 9 weeks. Taken together, these results strongly suggest that VP plays a crucial role in the onset and aggravation of the renal complications of DM. The mechanisms by which VP exerts these adverse V2-dependent effects are not yet elucidated. They are most likely indirect and may involve several intermediate steps comprising VP-induced changes in the composition of the tubular fluid in the loop of Henle (due to solute recycling in the renal medulla associated with improved concentrating activity of the kidney), inhibition of the tubuloglomerular feedback control of glomerular function, and alterations in glomerular hemodynamics by the intrarenal renin-angiotensin system.

This study shows that V(2) receptor-mediated actions of vasopressin play a critical role in the albuminuria of diabetes. It also reveals that individual rats, like humans, seem to exhibit an unequal susceptibility to diabetic nephropathy, or at least to albuminuria, a factor considered to be one of its early manifestations.

Chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) has been implicated in the control of blood glucose by its potent effect on expression and signaling of various nuclear receptors. To understand the role of COUP-TFII in glucose homeostasis, conditional COUP-TFII-deficient mice were generated and crossed with mice expressing Cre under the control of rat insulin II gene promoter, resulting in deletion of COUP-TFII in pancreatic ␤-cells. Homozygous mutants died before birth for yet undetermined reasons. Heterozygous mice appeared healthy at birth and showed normal growth and fertility. When challenged intraperitoneally, the animals had glucose intolerance associated with reduced glucose-stimulated insulin secretion. Moreover, these heterozygous mice presented a mild increase in fasting and random-fed circulating insulin levels. In accordance, islets isolated from these animals exhibited higher insulin secretion in low glucose conditions and markedly decreased glucose-stimulated insulin secretion. Their pancreata presented normal microscopic architecture and insulin content up to 16 weeks of study.Altered insulin secretion was associated with peripheral insulin resistance in whole animals. It can be concluded that COUP-TFII is a new, important regulator of glucose homeostasis and insulin sensitivity. Diabetes

In diabetes mellitus, water turnover in the body is enhanced because of the glucose-induced osmotic diuresis and it is usually assumed that the concentrating capacity of the kidney is partially impaired. On the other hand, plasma vasopressin concentration is known to be increased by several fold in patients with Type I (insulin-dependent) diabetes mellitus or Type II (non-insulin-dependent) diabetes mellitus as well as in animal models of experimental or genetic diabetes mellitus [1±6]. This high vasopressin concentration is accompanied by a desensitization of V1 a receptors in liver, kidney and platelets [7,8]. In contrast, renal V2 receptors, responsible for the antidiuretic action of the hormone, are not down-regulated [8].Actually, higher vasopressin in diabetes mellitus probably represents an appropriate adaptation by limiting to some extent the amount of water required Abstract Aims/hypothesis. Although the urine flow rate is considerably higher in diabetes mellitus, water reabsorption is greatly increased to concentrate an increased amount of solutes. Our study evaluated the expression of aquaporins and urea transporters, which are essential to the urinary concentration process. Methods. Northern blot and immunoblot were used to quantify mRNA and proteins for aquaporin-2 (AQP2) as well as urea transporters UT-A1, UT-A2 and UT-B1, in subzones of the renal medulla of rats with streptozotocin-induced diabetes. Results. In these rats, glycaemia, urine flow rate and water reabsorption were respectively fourfold, ninefold and fourfold those of control rats. The AQP2 protein isoforms were significantly up-regulated in outer and inner medulla. In the base and tip of inner medulla, UT-A1 mRNA was significantly up-regulated (three-and 1.3-fold, respectively) as well as the 117 kD protein (ten-and threefold, respectively) whereas the 97 kD protein was not changed or decreased twofold, respectively. This suggests that, in diabetes, the inner medullary collecting duct is endowed with more UT-A1, especially in its initial part. In the case of mRNA and proteins of UT-A2, located in thin descending limbs in the inner stripe of outer medulla, they were respectively not changed and down-regulated in diabetic rats. Conclusion/interpretation. This study shows that in diabetes, the increased expression of AQP2 and UT-A1 in medullary collecting duct is consistent with an improved concentrating activity. In addition, the underexpression of UT-A2 and the overexpression of UT-A1 in the initial medullary collecting duct are reminiscent of the changes seen after experimental reduction of urine concentration or low protein feeding. [Diabetologia (2001) 44: 637±645]