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Diabetes & Metabolism
Vol 25, N° 3  - août 1999
p. 213
Doi : DM-08-1999-25-3-1262-3636-101019-ART60
Original articles


Original Article

Original Article

Diabetes & Metabolism1999; 25: 213
© Masson, Paris, 1999

M. Ahloulay(1)(4), F. Schmitt(2), , M. Déchaux(3), , L. Bankir(1)
(1)INSERM Unité 367, Institut du Fer à Moulin, Paris, France.
(2)Laboratoire de Biochimie, Hôpital Necker-Enfants Malades, Paris, France.
(3)Laboratoire de Physiologie, C.H.U. Necker-Enfants Malades, Paris, France.
(4)Département de Biologie, Faculté des Sciences, Université ChouaïbDoukkali, El Jadida, Maroc.


In diabetes mellitus (DM), the high urine flow rate suggests that urinary concentratingcapacity is impaired. However, several studies have shown that vasopressin is elevated inDM and the consequences of this elevation have not yet been characterized. This studyreevaluated renal function and water handling in male Wistar rats withStreptozotocin-induced DM, and in control rats. During five weeks after induction of DM,urine was collected in metabolic cages and a blood sample was drawn during the third week.Control rats (CONT) were studied in parallel. On week 3, urine flow rate was tenfoldhigher in DM than in CONT rats and urinary osmolality was reduced by half along with amarkedely higher osmolar excretion (DM/CONT = 5.87), due for a large part toglucose but also to urea (DM/CONT = 2.49). Glucose represented 52 % oftotal osmoles (90.3 ± 6.5 mmol/d out of 172 ± 14 mosm/d).Free water reabsorption was markedly higher in DM rats compared to CONT(326 ± 24 vs 81 ± 5 ml/d). In other rats treated in thesame way, urinary excretion of vasopressin was found to be markedly elevated(15.1 ± 4.1 vs 1.44 ± 0.23 ng/d). In DM rats, glucoseconcentration in urine was 17 fold higher than in plasma, and urea concentration14 fold higher. Both urine flow rate and free water reabsorption were positivelycorrelated with the sum of glucose and urea excretions (r = 0.967 and0.653, respectively) thus demonstrating that the urinary concentrating activity of thekidney increased in proportion to the increased load of these two organic solutes. Theseresults suggest that vasopressin elevation in DM contributes to increase urinaryconcentrating activity and thus to limit water requirements induced by the metabolicderangements of DM. The possible deleterious consequences of sustained high level ofvasopressin in DM are discussed.

Key words : Diabetes mellitus. , streptozotocin. , vasopressin. , solute-free waterreabsorption. , solute excretion. , kidney hypertrophy. , glucose. , glucagon. , glomerularfiltration rate.


Hormone antidiurétique et activité de concentration urinaire dans le diabète sucré

Le débit urinaire élevé observé dans le diabète sucré (DS) suggère quel'activité de concentration de l'urine est diminuée dans cette pathologie. Cependant,plusieurs études ont bien établi que les taux d'hormone antidiurétique (ADH) sontélevés dans le DS. Les conséquences de cette élévation n'ont pas été étudiées.Nous avons donc évalué la fonction rénale et le bilan de l'eau chez des ratsprésentant un diabète expérimental induit par la streptozotocine (DS) et chez des ratscontroles (CONT). L'urine a été collectée dans des cages à métabolisme pendant cinqsemaines après l'induction du DS, et un échantillon de sang a été prélevé à latroisième semaine. Les rats CONT ont été étudiés en parallèle. A la troisièmesemaine, le débit urinaire était dix fois plus élevé chez les rats DS que chez lesrats CONT et l'osmolalité était deux fois plus basse. L'excrétion osmolaire étaitparticulièrement augmentée (DS/CONT = 5,87), en grande partie en raison duglucose urinaire, mais aussi de l'augmentation d'excrétion d'urée(DS/CONT = 2,49). Le glucose représentait 52 % des osmoles totales(90 ± 6 mmol/j sur 172 ± 14 mosm/j). La réabsorptiond'eau libre était quatre fois plus élevée chez les rats DS que chez les CONT(326 ± 24 contre 81 ± 5 ml/j). L'excrétion urinaired'ADH, mesurée dans une autre série de rats traités de façon identique, a montré unetrès forte augmentation due au DS (15,1 ± 4,1 contre1,44 ± 0,23 ng/j). Chez les rats DS, le glucose était concentré17 fois plus dans l'urine que dans le plasma, et l'urée 14 fois plus. Le débiturinaire et la réabsorption d'eau libre étaient tous les deux positivement corrélésavec la somme des excrétions de glucose et d'urée (r = 0,967 pour le débiturinaire et r = 0,653 pour la réabsorption d'eau libre), démontrant ainsi quel'activité de concentration urinaire était augmentée en proportion de l'augmentation dela charge urinaire en ces deux solutés organiques. Ces résultats suggèrent quel'élévation de l'ADH dans le DS contribue à augmenter l'activité de concentrationurinaire face à une augmentation importante de la charge en solutés à excréter etdonc, qu'elle limite les besoins en eau de l'organisme induits par les perturbationsmétaboliques du diabète. Les conséquences potentiellement néfastes de cetteélévation d'ADH sont discutées.

Mots clés : Diabète. , streptozotocine. , ADH. , eau-libre. , hypertrophie rénale. , glucose. , glucagon. , filtration glomérulaire.

Because urine flow rate is markedly increased in diabetes mellitus (DM), it is usuallyassumed that urinary concentrating capacity is impaired by glucose-induced osmoticdiuresis. Now, several studies have established that vasopressin (or antidiuretic hormone,ADH) is enhanced in patients with type I and type II DM [1, 2, 3], as well as in severalexperimental or genetic animal models of DM [4, 5, 6]. The mechanism responsible foran enhanced release of vasopressin is not yet understood. It does not seem to depend onthe elevation of plasma glucose, nor on that of urea or other known osmoles [7]. On the other hand, theconsequences of this rise in vasopressin secretion have not yet been investigated.

The present study was undertaken to better evaluate water handling in rats withStreptozotocin-induced DM and to understand the pathophysiological consequences of therise in vasopressin secretion. The excessive rate of glucose production in DM results, atleast in part, from the stimulation of gluconeogenesis by glucagon no longercounterbalanced by insulin. Because amino acids are the main substrate forgluconeogenesis, a significant ureagenesis takes place, associated with gluconeogenesis,and leading to a marked increase in urea excretion accompanying that in glucose. Becausevasopressin is the hormone controlling urinary concentrating activity, and because urea isknown to be involved in the urine concentrating mechanism, the present study also examinedthe relationships between water handling by the kidney and its relations with glucose andurea excretion. This study reveals that, contrary to the usual belief, urinaryconcentrating capacity is not impaired in DM. It is actually markedly enhanced whenconsidering the increased amount of solute-free water reabsorbed in the kidney in relationto the elevated solute excretion. The rise in vasopressin secretion observed in DM iscertainly responsible for this improved capacity to reabsorb water. It appears to be anappropriate adaptation that limits water requirements induced by osmotic glucose diuresis.However, considering the consequences of a sustained increase in vasopressin level onrenal function reported in recent studies, it may be assumed that the high vasopressinsecretion might be deleterious for the kidney in the long term.


Rats and experimental protocol­ Male Wistar rats (Iffa Credo,Lyon, France) weighing 240 to 265 g were used in this study. They were placedindividually in metabolic cages (Techniplast, Varese, Italy) in a room with 70 %humidity and constant temperature, and had free access to tap water and normal rat food (M25 Extralabo, Provins, France, containing 23 % protein) during the whole study.

Streptozotocin (STZ) (Sigma Chemical Co., St Louis, MO, USA), 20 mg/ml, wasfreshly prepared in 0.1 mol/L of citrate buffer (pH 4.5). After 3 days ofaccustumation to the cages and basal measurements (see below), six rats received a singlei.p. injection of STZ, 65 mg/kg BW (800 μl/rat). Four control rats (CONT)received only citrate buffer. Two days later, glucose was measured in blood (collectedfrom the tail after a small incision with a razor blade) and urine of the 6 STZ rats.They all exhibited blood glucose values above 10 mmol/L and glycosuria. Rats did notreceive insulin treatment during this study. Body weight (BW), water and food intake, andurine flow rate and osmolality were measured once a week for two consecutive days, oneweek before (basal) and for 5 weeks after induction of diabetes. Three weeks afterthe induction of diabetes, and after the weekly two day urine collection, a blood sample(≈ 300 μl) was taken from the jugular vein under ether anesthesia. Ratswere sacrificed after completion of the measurements of the 5th week and kidneys, liverand heart were removed and weighed.

Biochemical measurements­ Urine volume was evaluated bygravimetry assuming urine density to be equal to that of water. Osmolality in urine andplasma was measured with a freezing point osmometer (Roebling, Berlin, Germany).Creatinine and protein concentrations were measured with an automatic multiparametricanalyser (HITASHI 717, Tokyo, Japan). Concentrations of urea (Urea Kit Biomerieux, Lyon,France), glucose (Sigma Diagnostics, St Louis, MO, USA), sodium and potassium(flame-emission photometry, Instrumentation Laboratory, Paris, France) were also assessedin plasma and urine samples.

Glucagon and vasopressin­ In separate series of control anddiabetic rats used for other purposes in our laboratory we determined the plasmaconcentrations of glucagon (n = 8 per group) and the urinary excretion ofvasopressin (n = 6 per group) 3 weeks after vehicle or STZadministration. For plasma glucagon determination, blood was collected in tubes containingaprotinin and EDTA and centrifuged immediately, and plasma was frozen (-20°C) untilassay. Plasma glucagon was measured by radioimmunoassay using a commercial kit (PharmaciaSerono, Biodata, Italy). For the measurement of urinary vasopressin excretion, rats wereplaced in metabolic cages two weeks after induction of diabetes, and two 24 h urinecollection was performed during the last two days of the 3rd week. Urine flow rate wasmeasured and aliquots were frozen (-20°C) until assay. Urinary vasopressin was measuredby radioimmunoassay with a kit from Nichols Institute (Diagnostics B.V. San Juan,Capistrano, CA, USA).

Calculations and statistics­ Creatinine clearance, absoluteand fractional excretion of different solutes, glucose reabsorption, and free waterreabsorption were calculated according to usual formulas. The results obtained on twoconsecutive days of each week were averaged for each rat, and group means were calculatedfor each week. Results are expressed as means ± SEM. Statistical significanceof the differences observed between control and diabetic rats was evaluated by Student's ttest.


Figures 1  and 2  display the changesobserved during the entire experiment (5 weeks). One DM rat died under anesthesia,just after the blood collection performed at the end of the third week. Results concerningDM rats during weeks 4 and 5 were thus obtained on only 5 rats. Mostparameters increased abruptly during the first and second week, and reached a relativesteady state thereafter. Results observed during the third week were chosen forstatistical comparisons between the two groups, as shown in Table I . As expected, plasmaglucose concentration was markedly elevated in DM rats (Fig. 1) . Although their foodintake almost doubled, DM rats gained little weight during the 5 weeks of observation(8 ± 21 g) as compared to healthy rats (116 ± 11 g,p < 0.001). A considerable (six fold) increase in osmolar excretion wasobserved. Glucose accounted for a large part of this increase (Table I) and made upapproximately half of all urinary solutes in the diabetic rats (Table I) . Urea, sodium andpotassium excretions were more than doubled in DM compared to CONT rats (Table I) . These increasesare slightly higher than that observed for food intake, probably because the markedlyslower growth of DM vs healthy rats resulted in the excretion of a larger fraction of thesolutes ingested with the food.

Urinary flow rate and fluid intake increased 8 - 10 fold with a similartime course as that observed for osmolar excretion (Fig. 2) . Extrarenal waterlosses (the difference between fluid intake and urine output) amounted to &ap;10 ml/d in control rats and were not significantly altered in DM rats. A significant&ap; 40 % fall in urine osmolality was observed and osmotic pressure stabilizedaround 900 mosm/kg H2O vs &ap; 1,600 mosm/kg H2O inCONT rats (Fig. 2)(Table I) . In spite of themarked increase in urine flow rate and fall in urine osmolality, free water reabsorptionwas about 4 fold higher in DM than in CONT rats (Table I) . This is explainedby the fact that the load of osmoles concentrated in the urine was much larger (seefurther).

As shown in Figure 3 ,besides the marked increase in plasma glucose, plasma urea was also increased (from8.2 ± 0.6 in CONT to 13.9 ± 1.1 mmol/l in DM,p < 0.02). Plasma Na and K concentrations were unchanged (not shown) and therise in plasma osmolality observed in DM rats was accounted for entirely by that inglucose and urea concentrations. The changes in renal function induced by DM included a87 % increase in creatinine clearance (3.56 ± 0.10 ml/min in DM vs1.91 ± 0.02 in CONT rats at week 3 after STZ administration,p < 0.001) and a significant proteinuria (62.8 ± 11.3 mg/d vs16.4 ± 1.3 in CONT rats, p < 0.001) (Fig. 4) .

Table II  showsglucose handling by the kidney in the two groups of rats. Calculation of the amount ofglucose reabsorbed in DM rats provides an evaluation of the maximum transport capacity ofproximal tubules in vivo. This amounts to 60 ± 4 mmol/d, i.e., four timesthe amount of glucose filtered in control rats. In spite of this massive reabsorption, asmuch as 82 ± 6 mmol of glucose are excreted per day by DM rats. Thisexcretion is achieved with a marked elevation of glucose concentration in urine withrespect to plasma Table II and Fig. 5 , and seefurther).

In order to study the relationship between water handling and solute excretion, theresults obtained during week 2, 3, and 4 in all individual rats with DM (mean of2 days for each week) were plotted together in Figure 6 . This Figure revealsthat the rise in urine flow rate and the fall in urine osmolality observed in DM aresignificantly correlated with the rise in the excretion of glucose and urea, the two majorsolutes resulting from hypercatabolism in the liver. It also reveals that free waterreabsorption is positively correlated with glucose and urea excretion (although thecorrelation coefficient is somewhat weaker than for urine flow rate). Actually, asdepicted for week 3 in Figure 6, the kidney of DM rats excretes a considerably greater osmolar load than that of CONTrats. Although urine osmolality is slightly lower and urine flow rate much higher in DMthan in CONT rats, the concentration of this load is achieved at the price of a muchgreater amount of free water reabsorption (Fig. 6) . Would the kidneynot concentrate glucose and urea in the urine, the amount of water needed to excrete thisextra solute load would be far greater and would enhance fluid intake and urine outputeven far more than observed here.

At the time of sacrifice, DM rats were lighter than CONT rats (291 ± 23 vs373 ± 7 g, p < 0.02). Kidney weight was higher in DM than inCONT rats (2.55 ± 0.04 vs 2.11 ± 0.03 g) and thisdifference appeared even greater when factored by BW (0.89 ± 0.09 vs0.57 ± 0.01 g/100 g BW, p < 0.02) (Fig. 4) . The liver alsoexhibited some hypertrophy (4.88 ± 0.12 vs4.19 ± 0.05 g/100 g BW, p < 0.01) although much lessthan the kidney (+ 16 % vs + 56 %) while the weight of the heartwas unchanged in proportion to body weight (0.35 ± 0.04 vs0.33 ± 0.02 g/100 g BW, NS).

Plasma glucagon concentration in CONT and DM rats, 3 weeks after vehicle or STZadministration, was 104 ± 2 and 160 ± 6 pg/ml,respectively (p < 0.001), representing a 54 % rise in DM rats. As shownin Table III , urinaryexcretion of vasopressin was more than tenfold higher in DM than in CONT rats. But, due tothe marked difference in urine flow rate between the two groups, the concentration ofvasopressin in urine was similar in DM and CONT rats (Table III) .


It has been known since almost twenty years that plasma vasopressin concentration iselevated in diabetes mellitus in humans as well as in experimental models [1, 2, 3, 4, 5, 6]. However, neither the cause ofthis elevation, nor its consequences are presently understood. Because vasopressin isknown to play a crucial role in water conservation, and because water consumption andurine output are markedly elevated in diabetes, this study was undertaken to quantitatemore precisely water handling in experimental diabetes and examine the possibleconsequences of the elevated vasopressin level on this handling. Our results suggest thatthis elevation contributes to limit the increase in water excretion in the face of theconsiderable increase in osmolar excretion due to metabolic disorders of diabetes. Thus,vasopressin elevation in this pathological condition appears to be an appropriateadaptation, at least in its primary consequences. However, previous studies suggest thatthe sustained effects of vasopressin may be detrimental to the kidney. Thus, the delayedconsequences of elevated vasopressin in DM might not be so favourable (see further).

The streptozotocin-induced diabetic rat is a good model of human type 1 diabetes(insulin-dependent diabetes mellitus = IDDM) with respect to its metabolic andhemodynamic disturbances, and its renal complications [8]. In this study, well-knownfindings of this model have been reconfirmed and, for some of them, precisely quantifiedover time during the first five weeks after induction of IDDM, including hyperglycemia andglycosuria, polyuria, hyperphagia, increases in plasma urea and urea excretion, glomerularhyperfiltration, proteinuria, and renal hypertrophy, and increases in glucagon andvasopressin secretion. As could be expected, elevations in food intake and electrolyteexcretion were of similar magnitude. Glucose represented more than half of all urinarysolutes. In all, total osmolar excretion was increased 5 fold.

High vasopressin level in DM: effects on hepatic metabolism and waterconservation­ Urinary vasopressin excretion was 10 fold higher inDM than in CONT rats, suggesting that vasopressin secretion and plasma levels were indeedelevated. Other studies in which vasopressin was measured in plasma, showed thatcirculating levels of vasopressin are about 2-4 fold increased in STZ-induced DM [4, 5, 9]. Most probably, the differencein urinary excretion of vasopressin between DM and CONT rats observed in the present studyis larger than that occurring in plasma concentration for two reasons. First, the largerise in GFR is responsible for a larger amount of plasma vasopressin filtered, and second,the high load of glucose reabsorbed in the proximal tubule probably reduces thereabsorption and/or degradation of small peptides such as AVP, leading to increase theirfractional excretion. Accordingly, the elevation in plasma level of vasopressin wasprobably less intense than that seen in excretion and closer to values reported by otherauthors. Of note, in spite of the great difference in the amount of vasopressin excretedper day, vasopressin concentration in urine was similar in the two groups. This isimportant to note in view of the fact that V1a receptors of vasopressin, known to bepresent in the collecting duct, have recently been shown to be expressed in the luminalmembrane of the cells [10, 11], thus exposing them to theluminal concentration of vasopressin, not to the peripheral concentration.

Two main types of vasopressin receptors are present in the kidney. Type V1a, coupled tocalcium mobilization, is present in mesangial cells [12], interstitial medullary cells[13], and vasa recta [14], and is also found in somenephron segments [15, 16]. Type V2, coupled to adenylylcyclase is the main vasopressin receptor expressed in the collecting duct [15, 16]. V1a receptors are alsoabundantly expressed in other tissues including vascular smooth muscle cells, liver, andblood platelets. Because of the elevation in circulating vasopressin in DM, severalstudies have examined the possibility that vasopressin receptors could be desensitized. Aspecific decrease in the number of V1a receptors without alteration in their affinity hasbeen documented in kidney, liver, and platelets [17, 9, 18]. In contrast, V2 receptordensity and affinity in the kidney are unaltered [9]. These observations suggest thatthe rise in vasopressin observed in diabetes mellitus could induce more intenseV2-mediated antidiuretic effects, without or with less intense V1a-mediated effects on thekidney and other target tissues (depending on the relative magnitude of vasopressinelevation and receptor desensitization). The present discussion will only consider thepossible consequences of vasopressin actions on liver and kidney.

The high abundance of vasopressin receptors in the rat liver enabled the expressioncloning of the first receptor of the vasopressin family (V1a) from this organ [19]. The occupancy of thisreceptor stimulates several metabolic pathways including glycogenolysis, gluconeogenesisand ureagenesis (the latter two pathways are always linked in order to dispose of thenitrogen of the amino radical of amino acids used in gluconeogenesis) [20, 24]. These effects are similar tothose induced by glucagon, although they involve a different second messenger and are thuspotentially additive. The effects of vasopressin have been well demonstrated in vitro, butno data is available, to our knowledge, about the consequences of this hepatic action ofvasopressin in vivo. The marked increase in protein catabolism observed in DM is usallyattributed to the imbalance between elevated glucagon level and fall in insulin (or in itsperipheral actions in type II DM). However, the rise in vasopressin coud alsocontribute to this hypercatabolism, if the desentization of hepatic V1a receptors is notsufficient to fully compensate for the rise in vasopressin level. This is suggested by therecent findings of Bardoux et al ( [25],and see note added in proof). They observed that induction of DM by STZ in homozygousBrattleboro rats, genetically lacking vasopressin, resulted in a less intense glucoseexcretion and liver hypertrophy than in their vasopresssin-replete controls.

The consequences of elevated vasopressin on renal function are more complex than thoseon the liver. The most immediate effects of vasopressin are to favor water reabsorption inthe collecting duct in order to produce concentrated urine. Because urine flow rate ismarkedly increased in DM, it is usually assumed that urinary concentrating ability isimpaired by glucose-induced osmotic diuresis. Actually, this concept is erroneous becausethe large increase in osmotic load to be excreted, and the fact that urine remains largelyhyperosmotic to plasma, impose on the kidney a huge concentrating activity. This isapparent in the results of the present study in which urine concentrating activity isevaluated, not by looking at urine flow rate and osmolality, but by considering a moreappropriate index, solute-free water reabsorption. The amount of free water"spared" in DM rats was 326 ml/day versus only 81 ml/day in controls.This large difference (245 ml/day) reveals that urine concentrating activity was farmore intense in DM than in CONT rats, and enabled them to reabsorb more free water in theface of a greater solute excretion. If DM rats had spared no more free water than did CONTrats, their urine flow rate would have reached 484 ml/d and their urine osmolalitywould have fallen to 355 mosm/kg H2O, i.e. close to plasma osmolality.This considerable amount of additional water was reabsorbed in the collecting ducts as aresult of the rise in plasma vasopressin concentration, resulting in higherV2 stimulation.

In normal (non diabetic) rats, glucagon has been shown to improve urinary concentratingactivity in addition to the effects of vasopressin. In Brattleboro rats infused with aconstant dose of dDAVP (a V2 agonist of vasopressin), an infusion of glucagon inducesan additional, dose-dependent increase in urinary osmolality [26]. The same is true in normalrats with endogenous AVP [27].This effect was attibuted to a direct action of glucagon on sodium reabsorption in thethick ascending limb, the nephron segment responsible for the accumulation of solutes inthe renal medulla [26]. Becauseglucagon is elevated in DM rats [28,29], it is conceivable thatthis hormone, in addition to vasopressin, also participates in the enhancement of urineconcentrating activity described above.

It may be interesting to underline that DM rats with hypercatabolism and hyperphagiaexhibit adaptations in kidney function that are very similar to those described in normalrats fed a high protein intake, including glomerular hyperfiltration and kidneyhypertrophy, increases in plasma concentration and urinary excretion of urea, and in freewater reabsorption [30]. Inboth situations also, the same two hormones, glucagon [31] and vasopressin [32], are elevated (see review in [30, 33]).

Possible adverse consequences of high vasopressin level in DM­According to the observations described in the present study, the elevation of vasopressinsecretion in DM may be considered an appropriate adaptation because V2 actions ofvasopressin limit the additional water needs of the body imposed by the metabolicdisorders of diabetes. However, on the long term, the consequences of high vasopressinlevels on renal function may be less favourable and may contribute to induce or aggravatediabetic nephropathy. This is suggested by observations in normal rats and in rats withchronic renal failure, as described below.

Several studies suggest, indirectly, that vasopressin, by its V2 effects, couldcontribute to the hyperfiltration, albuminuria and renal hypertrophy of DM. Studiesperformed in normal rats showed that the sustained stimulation of V2 receptors,induced by chronic infusion of the selective V2 agonist, dDAVP, induced a markedincrement in glomerular filtration rate (GFR) and in kidney weight [34], and significant increase inalbumin excretion [35](suggesting an increased leakage of macromolecules from the glomerulus). These effects arethought to be an indirect consequence of the vasopressin-dependent intrarenal recycling ofurea, leading to an alteration in the tubuloglomerular feedback control of GFR [36, 34]. On the other hand,vasopressin has been shown to mediate, at least in part, the elevations in GFR and kidneyweight that are induced by high protein intake ( [37, 38] and see review in [30]). These observations suggestthat vasopressin could contribute to the hyperfiltration of diabetes and the subsequentnephropathy. This is confirmed by the lack of hyperfiltration and less intense kidneyhypertrophy observed after induction of DM in Brattleboro rats [25].

Other experiments suggest that vasopressin contributes to the deterioration of renalfunction in experimental models of chronic renal failure [39]. A reduction in vasopressinlevel, brought about by a sustained increase in fluid intake, resulted in a significantreduction in proteinuria, kidney hypertrophy and incidence of glomerulosclerosis in the5/6 nephrectomized rat [40,30]. In the5/6 nephrectomized Brattlebora rats, a chronic infusion of dDAVP markedly aggravatedproteinuria and renal hypertrophy, and increased mortality [39]. Chronic administration of nonpeptide antagonists of either V1a or V2 receptors in rats with adriamycin nephropathysignificantly reduced urinary protein excretion and glomerulosclerosis, suggesting thatboth types of vasopressin receptors lead to adverse effects on the diseased kidney [41] (see note added in proof).

Besides its V2-mediated antidiuretic effects on the kidney, vasopressin may alsoinfluence renal function through its V1a receptors, present in several cell typesincluding glomerular mesangial, collecting duct and interstitial medullary cells. V1astimulation induces contraction of mesangial cells in vitro and is thus susceptible toinfluencing GFR determinants and glomerular permselectivity in vivo. Actually, chronictreatment for 2 weeks in patients with diabetic nephropathy with a selective V1a nonpeptide antagonist, OPC-21268, was recently reported to significantly reduce their albuminexcretion [42]. V1a-mediatedeffects on the collecting duct, resulting from binding of urinary vasopressin to luminalreceptors [10], stimulate theproduction of prostaglandins which, in turn, blunt the antidiuretic V2-mediated effects,thus producing a local feedback regulation of the antidiuretic effects of vasopressin [43, 44]. In DM, the selectivedesensitization of V1a receptors, and the fact that luminal concentration of vasopressindoes not increase, should attenuate this feedback regulation and thus enable a moreintense response to V2 receptor stimulation.

Finally, some results obtained in diabetic patients also suggest a link betweenelevated vasopressin and diabetic nephropathy. In normoalbuminuric insulin-dependentdiabetic patients, intraindividual variations in GFR observed at a few months interval,were shown to be correlated to the simultaneous individual changes in plasma vasopressinlevel [45]. Higher plasma AVPlevels were reported in type II diabetic patients with microalbuminuria than in patientswithout renal complications [42].In the long term, the sustained elevation of vasopressin seen in DM could thus be anadditional factor contributing to glomerulosclerosis and progressive deterioration ofrenal function.

In conclusion, the present results show that the rise in vasopressin secretion observedin DM is certainly a beneficial adaptation that limits water needs in the face of a markedincrease in solute excretion due to the metabolic disorders of DM. However, in the longrun, the consequences of high vasopressin levels on renal function may be less favourablebecause they likely contribute to aggravate metabolic disorders of diabetes and toaccelerate progression of diabetic nephropathy. Studies using newly developed selectiveV1a and V2 recptor antagonists will be useful in further evaluating the role ofvasopressin in the pathophysiology of diabetes mellitus.

(Les tableaux sont exclusivement disponibles en format PDF).

Table I.

(Les tableaux sont exclusivement disponibles en format PDF).

Values are means ± SE, Uosm: urine osmolality;
TcH2O: free water reabsorption. excr.: excretion.
P values by Student's t test between DM and CONT rats.

Tableau II.

(Les tableaux sont exclusivement disponibles en format PDF).

P values by Student's t test between DM and CONT rats.  

Tableau III.

(Les tableaux sont exclusivement disponibles en format PDF).

P values by Student's t test between DM and CONT rats.  

Figure 1.
Evolution of food intake, plasma glucose, and excretion of glucose and urea in ratswith DM (filled circles, n = 6) and control rats (open circles, n = 4)during the 5 weeks of the study. Values are means ± SE (in control rats,SE are smaller than the symbols, and thus, are not visible).

Figure 2.
Evolution of water intake and excretion, urine osmolality, osmolar excretion, andsolute-free water reabsorption (TcH2O) in rats with DM (filledcircles, n = 6) and control rats (open circles, n = 4) during the5 weeks of the study. Values are means ± SE (in control rats, SE, for someparameters, are smaller than the symbols, and thus, are not visible).

Figure 3.
Plasma concentration of total osmoles, glucose, and urea, and of non-urea-non-glucoseosmoles in control and DM rats, three weeks after induction of DM. Values aremeans ± SE of 6 DM and 4 CONT rats. Student's t test: *,p < 0.05, **, p < 0.01, ***, p < 0.001.

Figure 4.
Creatinine clearance, urinary protein excretion, and weight of kidney and liverrelative to body weight in control and DM rats, three weeks after induction of DM. Valuesare means ± SE of 6 DM and 4 CONT rats. Student's t test: **,p < 0.01, ***, p < 0.001.

Figure 5.
Comparison of the concentrations of electrolytes and organic solutes in plasma andurine of rats with DM (means of 6 rats). As can be seen, both urea and glucose aremarkedly more concentrated in urine than in plasma.

Figure 6.
a, b, c) Urine flow rate and osmolality, and free water reabsorption (TcH2O)plotted as a function of the amount of organic solutes (glucose and urea) excreted per dayin DM rats. Data correspond to all measurements performed in 6 DM rats during the3rd, 4th, and 5th weeks of the study. Linear regressions are shown as well as correlationcoefficients. d) Osmolar clearance and its two components, urine flow rate and solute-freewater reabsorption (TcH2O) in control (n = 4) and DM rats(n = 6).


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