Vasopressin-induced Antidiuresis Research Articles

Combined Proteomics and Pathways Analysis of Collecting Duct Reveals a Protein Regulatory Network Activated in Vasopressin Escape

Low sensitivity is characteristic of many proteomics methods. Presented here is an approach that combines proteomics based on difference gel electrophoresis (DIGE) with bioinformatic pathways analysis to identify both abundant and relatively nonabundant proteins in inner medullary collecting duct (IMCD) altered in abundance during escape from vasopressin-induced antidiuresis. Rats received the vasopressin analog dDAVP by osmotic minipump plus either a daily water load (vasopressin escape) or only enough water to replace losses (control). Immunoblotting confirmed the hallmark of vasopressin escape, a decrease in aquaporin-2, and demonstrated a decrease in the abundance of the urea transporter UT-A3. DIGE identified 22 mostly high-abundance proteins regulated during vasopressin escape. These proteins were analyzed using pathways analysis software to reveal protein clusters incorporating the proteins identified by DIGE. A single dominant cluster emerged that included many relatively low-abundance proteins (abundances too low for DIGE identification), including several transcription factors. Immunoblotting confirmed a decrease in total and phosphorylated c-myc, a decrease in c-fos, and increases in c-jun and p53. Furthermore, immunoblotting confirmed hypothesized changes in other proteins in the proposed network: Increases in c-src, receptor for activated C kinase 1, calreticulin, and caspase 3 and decreases in steroid receptor co-activator 1, Grp78/BiP, and annexin A4. This combined approach proved capable of uncovering regulatory proteins that are altered in response to a specific physiologic perturbation without being detected directly by DIGE. The results demonstrate a dominant protein regulatory network in IMCD cells that is altered in association with vasopressin escape, providing a new framework for further studies of signaling in IMCD.

Attenuation of vasopressin-induced antidiuresis in poorly controlled type 2 diabetes.

Renal resistance to vasopressin has been demonstrated in type 1 diabetes and in type 2 diabetes with nephropathy. However, renal response to vasopressin in type 2 diabetes without nephropathy has not been studied. We studied 10 subjects with poorly controlled type 2 diabetes (PCDS; Hb A(1c) >9%), 10 subjects with well-controlled type 2 diabetes (WCDS; Hb A(1c) <7%), and 10 matched nondiabetic control subjects (NDCS) during a euglycemic 8-h water deprivation test. None of the subjects had nephropathy. Water deprivation caused similar rises in plasma vasopressin concentrations in all three groups, but the rise in urine osmolality in PCDS (280.3 +/- 49.7 to 594.4 +/- 88.5 mosmol/kgH(2)O) was lower than in WCDS (360.7 +/- 142.8 to 794.1 +/- 77.3 mosmol/kgH(2)O, P < 0.001) or NDCS (336.0 +/- 123.3 to 786.5 +/- 63.3 mosmol/kgH(2)O, P = 0.019). Total urine output was higher in the PCDS than in WCDS and NDCS (P < 0.05). Linear regression analysis showed that, in PCDS, the osmotic thresholds for thirst (291.9 +/- 4.6 mosmol/kgH(2)O) and vasopressin release (291.1 +/- 2.9 mosmol/kgH(2)O) were higher compared with WCDS (286.6 +/- 1.8 and 286.0 +/- 3.6 mosmol/kgH(2)O, respectively) and NDCS (286.0 +/- 2.4 and 284.1 +/- 4.7 mosmol/kgH(2)O, respectively) (between groups P < 0.001 for both variables). Under conditions of euglycemia, PCDS have impaired renal response to vasopressin and elevated osmotic threshold for thirst and vasopressin release in response to dehydration. Under conditions of chronic hyperglycemia, these abnormalities may significantly contribute to the development of dehydration in PCDS.

Synergistic effects of nitric oxide and prostaglandins on renal escape from vasopressin-induced antidiuresis.

Recent results from our laboratories indicate that renal escape from AVP-induced antidiuresis is accompanied by marked downregulation of kidney aquaporin-2 (AQP2) and AVP V2 receptors. The present studies evaluated the effect of nitric oxide (NO) and PG synthesis blockade on escape from antidiuresis. dDAVP-infused rats were water loaded (WL) for 5 days. l-NAME, an NO synthesis inhibitor, or diclofenac, a cyclooxygenase inhibitor, was infused subcutaneously beginning 1 day before WL. As early as 2 days after WL, urine volume increased and urine osmolality decreased, indicating the onset of escape. Endogenous NO synthesis, measured as urinary NO2 + NO3 excretion, was significantly increased in the WL group compared with the non-WL controls during all 5 days of WL. l-NAME (20 mg. kg(-1). day(-1)) markedly decreased urine volume on days 4 and 5 of WL, indicating inhibition of the escape phenomenon. Kidney AQP2 protein was significantly increased by this dose of l-NAME as well. A lower dose of l-NAME (10 mg. kg(-1). day(-1)) or diclofenac (2.5 mg. kg(-1). day(-1)) did not significantly affect the escape phenomenon by itself, but the combination of l-NAME and diclofenac showed a marked inhibitory effect on the escape phenomenon, which was also accompanied by a significant increase in kidney AQP2 expression. These results therefore suggest that renal NO and PG both play important roles in escape from AVP-induced antidiuresis by acting synergistically to downregulate kidney AQP2 expression.

Role of aquaporin-2 gene expression in hyponatremic rats with chronic vasopressin-induced antidiuresis

In a state of chronic arginine vasopressin (AVP) excess, the action of antidiuresis has been attenuated, resulting in some water diuresis. This state has been termed an "AVP escape" phenomenon. The present study was designed to determine what mechanisms underlie this attenuation in renal concentrating ability, which is found in chronic AVP excess, both in the presence and absence of volume expansion. Two groups of experimental rats were established. One group received solid chow with water ad libitum. The second group received chow, which was offered as a liquid diet. Both groups received subcutaneous administration of 1-deamino-8-D-arginine vasopressin (dDAVP) at 5 ng/h for the entire observation period of one week. Over the course of the observation period, tissue levels of aquaporin-2 (AQP-2) mRNA and protein were measured. Levels of AVP V2 receptor were monitored, both by measuring mRNA levels and by ligand-binding studies using [3H]AVP. Tissue levels of cAMP also were determined. Experimental rats with the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) had severe hyponatremia below 120 mmol/L, and impaired urinary concentrating ability, during the seven-day observation period. In contrast, the dDAVP-excess rats, given solid chow, maintained maximally concentrated urine and normal levels of serum sodium. The down-regulation of AVP V2 receptor function was comparable in the two groups. The maximal binding capacity (Bmax) fell to the nadir on day 2 and was thereafter suppressed at approximately 60% of control rats during the experiment. Up-regulation of AQP-2 mRNA expression was found, but this up-regulation was significantly less in the SIADH rats compared with the dDAVP-excess rats (153.5 +/- 29.8% vs. 323.7 +/- 23.8% on day 7, P < 0.05). This differential response between these two groups was affirmed by measured differences in AQP-2 protein levels, both in tissue and in urinary excretion. These results indicate that the attenuated regulation of the AQP-2 gene leads to the decrease in urinary concentrating ability in the experimental SIADH rats, suffering from hypervolemic state, compared with the normonatremic rats receiving AVP. Either hypervolemia or hypotonicity may diminish the post-receptor signaling of AVP in renal collecting duct cells, under the chronic AVP excess state found in SIADH.

Vasopressin V2 Receptor Binding Is Down-Regulated during Renal Escape from Vasopressin-Induced Antidiuresis

This study evaluated whether renal escape from vasopressin-induced antidiuresis is associated with alterations of vasopressin V2 receptor binding in the kidney inner medulla. A radioligand binding assay was developed using a novel iodinated vasopressin V2 receptor antagonist to analyze vasopressin V2 receptor binding in kidney inner medullary tissue from three groups of rats: normal rats maintained on ad libitum water intake, rats treated with 1-deamino-[8-d-arginine]vasopressin (DDAVP), and rats treated with DDAVP that were also water loaded to induce renal escape from antidiuresis. Analysis of the binding data showed that DDAVP treatment reduced vasopressin V2 receptor binding to 72% of normal levels. Water loading induced a marked further down-regulation of vasopressin V2 receptor binding. This receptor down-regulation began by day 2 of water loading, which correlated with the initiation of renal vasopressin escape; by day 3 of water loading, vasopressin V2 receptor expression fell to 43% of DDAVP-treated levels. No differences in vasopressin V2 receptor binding affinities were found among the three groups. This study demonstrates that vasopressin V2 receptor binding capacity is down-regulated during renal escape from vasopressin-induced antidiuresis and suggests that both vasopressin-dependent mechanisms as well as vasopressin-independent mechanisms associated with water loading are involved in this receptor down-regulation.

Vasopressin V2 Receptor Binding Is Down-Regulated during Renal Escape from Vasopressin-Induced Antidiuresis1

This study evaluated whether renal escape from vasopressin-induced antidiuresis is associated with alterations of vasopressin V2 receptor binding in the kidney inner medulla. A radioligand binding assay was developed using a novel iodinated vasopressin V2 receptor antagonist to analyze vasopressin V2 receptor binding in kidney inner medullary tissue from three groups of rats: normal rats maintained on ad libitum water intake, rats treated with 1-deamino-[8-D-arginine]vasopressin (DDAVP), and rats treated with DDAVP that were also water loaded to induce renal escape from antidiuresis. Analysis of the binding data showed that DDAVP treatment reduced vasopressin V2 receptor binding to 72% of normal levels. Water loading induced a marked further down-regulation of vasopressin V2 receptor binding. This receptor down-regulation began by day 2 of water loading, which correlated with the initiation of renal vasopressin escape; by day 3 of water loading, vasopressin V2 receptor expression fell to 43% of DDAVP-treated levels. No differences in vasopressin V2 receptor binding affinities were found among the three groups. This study demonstrates that vasopressin V2 receptor binding capacity is down-regulated during renal escape from vasopressin-induced antidiuresis and suggests that both vasopressin-dependent mechanisms as well as vasopressin-independent mechanisms associated with water loading are involved in this receptor down-regulation.

Escape from vasopressin-induced antidiuresis: role of vasopressin resistance of the collecting duct.

Previously, we demonstrated that escape from vasopressin-induced antidiuresis ("vasopressin escape") in rats is associated with a large, selective decrease in whole kidney expression of aquaporin-2, the vasopressin-regulated water channel. Here, we show that isolated perfused inner medullary collecting ducts (IMCDs) from vasopressin-escape rats desamino-[D-arginine]vasopressin (DDAVP)/water-loaded have dramatically reduced vasopressin-dependent osmotic water permeabilities [46% of control rats (DDAVP alone)], which coincides with a fall in inner medullary aquaporin-2 protein abundance as measured by immunoblotting in the opposite kidney. Furthermore, we demonstrate in IMCD suspensions that cAMP accumulation in response to DDAVP is substantially reduced in the vasopressin-escape rats both in the presence and absence of the phosphodiesterase inhibitor IBMX. By immunoblotting, we show that the abundance of two proteins important in cAMP generation: the stimulatory heterotrimeric G protein subunit Gs and adenylyl cyclase type VI, do not change. We conclude that vasopressin escape is associated with relative vasopressin resistance of the collecting duct cells manifested by decreased intracellular cAMP levels. The decreased cAMP levels can contribute to the demonstrated decrease in collecting duct water permeability in two ways: 1) by causing a decrease in aquaporin-2 expression and 2) by limiting the acute action of vasopressin to increase collecting duct water permeability.

Studies of renal aquaporin-2 expression during renal escape from vasopressin-induced antidiuresis.

In animal models of the syndrome of inappropriate antidiuresis (SIADH), sustained administration of vasopressin and water results in free-water retention and progressive hyponatremia for several days, which is then followed by escape from the vasopressin-induced antidiuresis. With the onset of vasopressin escape, water excretion increases despite sustained administration of vasopressin, allowing water balance to be re-established and the serum sodium to be stabilized at a steady, albeit decreased, level. Studies from our laboratories have investigated whether this escape phenomenon can be attributed to altered regulation of aquaporin water channels. After four-day pre-treatment with 1-deamino-[8-D-arginine]-vasopressin (dDAVP) by osmotic minipump, rats were divided into control (continued dDAVP) and water-loaded (continued dDAVP plus a daily oral water load) groups. A significant increase in urine volume in the water-loaded rats was observed by the second day of water loading, indicating escape from antidiuresis. The onset of escape coincided temporally with a marked decrease in renal aquaporin-2 protein (measured by semi-quantitative immunoblotting), which began at day 2 and fell to 17% of control levels by day 3. In contrast, there was no decrease in the renal expression of aquaporins 1, 3, or 4. The marked suppression of whole kidney aquaporin-2 protein was accompanied by a concomitant suppression of whole kidney aquaporin-2 mRNA levels. Immunocytochemical localization and differential centrifugation studies demonstrated that trafficking of aquaporin-2 to the plasma membrane remained intact during vasopressin escape. Additional studies have indicated that the observed down-regulation of aquaporin-2 expression also occurs in the renal cortex as well as the inner and outer medullas, and can be reversed simply by water restriction despite maintenance of hyponatremia. Our results therefore suggest that escape from vasopressin-induced antidiuresis is attributable, at least in part, to a vasopressin-independent and osmolality-independent decrease in aquaporin-2 water channel expression in the renal collecting duct. Similar mechanisms likely contribute to the phenomenon of escape from antidiuresis seen clinically in patients with SIADH as well.

Recent Advances in the Discovery and Development of Vasopressin Antagonists: Peptide and Nonpeptide Vta and V2 Receptor Antagonists

Abstract: Arginine. vasopressin (AVP) (antidiuretic harmone) exerts its action through three membrane-bound G-protein-coupled receptor subtypes (VI a, renal V2, and V3). The vasopressin-induced antidiuresis (via V2 receptors coupled to aquaporins) helps maintain normal plasma osmolality and salt (NaCl) balances. The human V1, V2 and V3 (V lb) recep­ receptors and water selective membrane proteins (aquaporins) in the kidney have been cloned. Recent advances are the discovery and development of selective non-peptide antagonists (without agonist activity) that have been shown to be aquaretic agents in animals and humans. This review covers the characterization of vasopressin receptors V la, V2 and V3 (V1 b) (function, cloning, species variations, molecular modeling) and the discovery of non-peptide small molecules (of diverse structural types) that are potent AVP receptor antagonists. Animal and clinical studies of non-peptide AVP antagonists OPC-21268, OPC-31260, SR-49059, YM087 and VPA-985 are reported.

Role of renal aquaporins in escape from vasopressin-induced antidiuresis in rat.

The purpose of this study was to investigate whether escape from vasopressin-induced antidiuresis is associated with altered regulation of any of the known aquaporin water channels. After 4-d pretreatment with 1-deamino-[8-D-arginine]-vasopressin (dDAVP) by osmotic mini-pump, rats were divided into two groups: control (continued dDAVP) and water-loaded (continued dDAVP plus a daily oral water load). A significant increase in urine volume in the water-loaded rats was observed by the second day of water loading, indicating onset of vasopressin escape. The onset of escape coincided temporally with a marked decrease in renal aquaporin-2 protein (measured by semiquantitative immunoblotting), which began at day 2 and fell to 17% of control levels by day 3. In contrast, there was no decrease in the renal expression of aquaporins 1, 3, or 4. The marked suppression of whole kidney aquaporin-2 protein was accompanied by a concomitant suppression of whole kidney aquaporin-2 mRNA levels. Immunocytochemical localization and differential centrifugation studies demonstrated that trafficking of aquaporin-2 to the plasma membrane remained intact during vasopressin escape. The results suggest that escape from vasopressin-induced antidiuresis is attributable, at least in part, to a vasopressin-independent decrease in aquaporin-2 water channel expression in the renal collecting duct.

Renal Handling of Lithium and the Effects of Mannitol and Arginine Vasopressin in man

1. A study has been undertaken in six healthy male subjects to clarify whether post-proximal segments of the nephron contribute to the renal handling of lithium under conditions of maximal forced osmotic load diuresis and arginine vasopressin-induced antidiuresis. Increments in the fractional clearance of free water, as a measure of effect at the proximal tubule, were positively correlated with incremental changes in flow rate, factored for glomerular filtration rate (mean r = 0.80 +/- 0.12, P < 0.001), and fractional excretion of lithium (mean r = 0.84 +/- 0.06, P < 0.001). Changes in flow rate and fractional excretion of lithium were also closely correlated with one another (mean r = 0.81 +/- 0.06, P < 0.001), and the mean slope of these regression lines was not significantly different from unity (1.18; 95% confidence interval 0.76-1.59). These results show that, under conditions of maximal hydration, mannitol-induced changes in proximal tubular function were closely correlated with induced changes in the fractional excretion of lithium. 2. Infusion of arginine vasopressin alone (0.5 m-units/min) caused a marked reduction in both fractional clearance of free water (10.7% +/- 1.2% to -1.2% +/- 0.2%, P < 0.001) and flow rate factored for glomerular filtration rate (14.0 +/- 1.5 to 0.8 +/- 0.2%; P < 0.001) while the fractional excretion of lithium showed only a small non-significant decrease (25.3% +/- 2.0% to 23.3% +/- 2.2%). A similar dissociation was noted between fluid and lithium excretion when arginine vasopressin was superimposed on mannitol infusion with reductions in the fractional clearance of free water (12.7% +/- 1.0% to -0.9% +/- 0.7%, P < 0.001) and flow rate (18.6% +/- 1.5% to 5.7% +/- 1.0%; P < 0.001), while the fractional excretion of lithium showed a significant increase (28.4% +/- 1.7% to 33.1% +/- 2.4%; P < 0.05). The lack of correlation between fluid and lithium excretion, in the presence of arginine vasopressin with or without mannitol, indicates that the late distal tubule and collecting duct have little or no significant capacity to reabsorb lithium. 3. These findings, taken as a whole, strengthen the view that renal tubular handling of lithium is primarily a proximal event.

Acute Effect of Parathyroid Hormone on Urine Concentration in the Rat

1. It has been demonstrated that parathyroid hormone can increase adenylate cyclase activity in the rat papilla, produce a small antidiuretic effect and in vitro can interfere with the action of arginine vasopressin on water transport. Clearance studies were performed in the anaesthetized water diuretic thyroparathyroidectomized rat to evaluate further the effect of parathyroid hormone on urine concentration in the presence and absence of arginine vasopressin. 2. A maximal phosphaturic concentration of rat parathyroid hormone (2 micrograms/kg) reduced urine flow from 125 +/- 7 to 81 +/- 9 microliters/min within 10 min (P < 0.01). Addition of a maximal antidiuretic concentration of arginine vasopressin (100 ng/kg) produced a delayed and diminished antidiuretic response when compared with a group of rats not pretreated with parathyroid hormone (47 +/- 5 compared with 27 +/- 5 microliters/min; P < 0.01). However, a supramaximal arginine vasopressin concentration (1000 ng/kg) produced a maximal antidiuretic effect in the presence of parathyroid hormone. 3. To evaluate further the inhibitory effect of parathyroid hormone on arginine vasopressin-induced antidiuresis, parathyroid hormone (2 micrograms/kg) was administered to one group of rats and a minimally effective arginine vasopressin concentration (7.5 ng/kg) to another group, which produced a similar antidiuretic effect. However, the subsequent effect of a maximal antidiuretic arginine vasopressin concentration (100 ng/kg) was again significantly blunted in the group pretreated with parathyroid hormone. 4. Parathyroid hormone produced only a small increase in mean plasma calcium concentration, and glomerular filtration rate was not altered by either hormone.(ABSTRACT TRUNCATED AT 250 WORDS)

Hyponatremia: epidemiology, pathophysiology, and therapy.

Despite several decades of research interest and productivity, many aspects of hyponatremia and hypo-osmolar disorders remain incompletely understood. Among these aspects are questions relating to the morbidity and mortality actually attributable to hyponatremia, possible hormonal and gender-associated risk factors underlying susceptibility to neurologic complications from hyponatremic encephalopathy, the stimuli to arginine vasopressin secretion in some atypical subsets of patients with the syndrome of inappropriate antidiuretic hormone secretion and other hyponatremic disorders, the contributions of natriuresis and natriuretic peptides to hyponatremic states, the pathologic determinants of brain demyelination that sometimes follow rapid correction of hyponatremia, and appropriate treatment guidelines for patients with acute and chronic hyponatremia. The recent literature confirms that acceptable answers to these questions and others are still not available, and a better understanding of basic issues regarding the pathophysiology of hyponatremia is needed. Several recent advances stand out as being likely to enhance our future understanding of hyponatremia and hypo-osmolar states. First are studies of cellular mechanisms of volume regulation in kidney and brain tissue in response to changes in osmolality. Many, though clearly not all, clinical observations can be better understood by considering them in the conceptual framework provided by knowledge of cell and body fluid compartment volume regulation. Second is the elucidation of several important protein structures via complementary DNA cloning, including the arginine vasopressin V1 and V2 receptors, several organic osmolyte transporters, and the CHIP28 water channel. Future application of these new tools to carefully designed and executed physiologic studies will likely add considerable new knowledge to our understanding of hyponatremia. Third is the development and increasing application of nuclear magnetic resonance spectroscopy and imaging methods that will allow more detailed analyses of acute changes in brain metabolism during hyponatremia and following correction. Finally, the recent development of nonpeptide antagonists to arginine vasopressin V1 and V2 receptors should enable clinical studies to assess more accurately the contribution of arginine vasopressin-induced antidiuresis to hyponatremia and more importantly holds the promise of more effective therapies for hyponatremic patients.

The role of vasopressin and atrial natriuretic factor in postoperative fluid retention after the Fontan procedure

The Fontan procedure results in right atrial distention and is complicated by fluid retention. Since systemic fluid balance may be hormonally mediated in part and related to right atrium size, we measured plasma atrial natriuretic factor and plasma arginine vasopressin levels in 19 patients undergoing the Fontan procedure and in 12 control patients undergoing other types of heart operations. Preoperative plasma atrial natriuretic factor levels were higher in patients undergoing the Fontan procedure than in control patients (95 +/- 16 pg/ml preoperatively versus 50 +/- 8 pg/ml; p less than 0.05) and increased in patients undergoing the Fontan procedure to 330 +/- 48 pg/ml by postoperative day 2 (p less than 0.05) but not in control patients. Increased plasma atrial natriuretic factor levels could enhance capillary transudation, but elevated plasma atrial natriuretic factor levels should also enhance diuresis and prevent fluid retention. Vasopressin levels, however, were also increased in patients undergoing the Fontan procedure (from 9 +/- 2 pg/ml preoperatively to 144 +/- 37 pg/ml at end of operation) and were higher and remained elevated longer than in control patients undergoing heart operations (37 +/- 7, 20 +/- 4, 16 +/- 6 pg/ml on postoperative days 1, 2, and 3 to 10 for the Fontan group compared with 15 +/- 4, 4 +/- 1, 4 +/- 2 pg/ml for control patients). Vasopressin levels were highest in the Fontan group with the most severe fluid retention and effusions (for example, 51 +/- 10 pg/ml versus 23 +/- 4 pg/ml, on postoperative day 1). Increased vasopressin and atrial natriuretic factor could act synergistically to result in the development of effusions after the Fontan procedure when atrial natriuretic factor-induced capillary transudation is combined with vasopressin-induced antidiuresis.

Vasopressin and oxytocin secretion in chronically hyposmolar rats

Neurohypophysial secretion of vasopressin (AVP) and oxytocin (OT) was studied in rats maintained under hyposmolar conditions for 10-24 days. Graded intravenous infusions of hypertonic saline solutions had no consistent effect on plasma AVP and OT levels until plasma sodium concentration ([Na+]) exceeded 130 mM, after which levels of both hormones increased as an exponential function of plasma [Na+]. Detectable increases in plasma AVP and OT began at significantly lower plasma [Na+] in hyposmolar rats than in normosmolar control rats (10.8 mM lower for AVP and 18.4 mM lower for OT). AVP and OT secretion in hyposmolar rats was also markedly blunted in response to nonosmotic stimuli, including acute and chronic hypovolemia and systemic administration of cholecystokinin. Cessation of 1-desamino-8-D-arginine vasopressin-induced antidiuresis resulted in an appropriately rapid correction of plasma [Na+] to normal levels within 24 h. Consequently, although chronic hyposmolarity caused a moderate downward resetting of the osmotic thresholds for AVP and OT secretion, it did not cause sustained deficits in osmoregulation. These results suggest that osmoreceptor activity is regulated to maintain extracellular fluid and plasma osmolality within narrow absolute ranges rather than responding to relative changes in osmolality.

Two distinct pathophysiological mechanisms in congenital nephrogenic diabetes insipidus.

V1 and V2 vasopressin receptor functions were studied in 2 patients with congenital nephrogenic diabetes insipidus. V1 receptor-mediated functions (increase in urinary prostaglandin E2 excretion and plasma cortisol levels) and Gs (guanine nucleotide-binding stimulatory protein) activity of erythrocyte membranes were normal in both patients. After infusion of 0.4 micrograms/kg dDAVP, a 57-yr-old male patient had no increase in plasma factor VIII coagulant, ristocetin cofactor, or fibrinolytic activity or change in von Willebrand factor multimers. In addition, he had no vasodilatory response to dDAVP, a response that occurs in normal subjects and patients with central diabetes insipidus. In contrast, a 25-yr-old female patient had normal hemostatic and vasodilatory responses to the infusion of dDAVP. These observations indicate that the cellular abnormalities in patients with congenital nephrogenic diabetes insipidus may be either at the V2 receptor or in the postreceptor (and Gs activity) cascade of events that mediate vasopressin-induced antidiuresis. Therefore, heterogeneity exists in the biochemical cause(s) of congenital nephrogenic diabetes insipidus in man.

Augmentation by aprotinin of the renal response to vasopressin

We contrasted the renal effects of vasopressin in Brattleboro rats with and without pretreatment with aprotinin (20,000 KIU kg-1). In both treatment groups, vasopressin injected at 3 mU kg-1 sec caused in conscious rats elevation of urine osmolality and reduction of urine flow and urinary excretion of total solutes. However, these effects of vasopressin were significantly greater in aprotinin pretreated rats than in rats without aprotinin treatment. In ketamine-pentobarbital-anesthetized rats without aprotinin pretreatment, vasopressin infused at 2 mU kg-1 hr-1 elevated urinary kinin excretion but did not affect urine flow rate or osmolality; in contrast, in aprotinin-pretreated rats, the same dose of vasopressin did not increase urinary kinins but caused elevation of urinary osmolality and reduction of urine flow, solute excretion, and glomerular filtration rate. Aprotinin pretreatment in anesthetized rats also blunted the rise in kinin excretion elicited by vasopressin at a higher dosage, 5 mU kg-1 hr-1, but did not potentiate the vasopressin-induced antidiuresis. We conclude that aprotinin facilitates the expression of the antidiuretic effect of vasopressin at a low, but not at a high dosage. This effect of aprotinin may be a consequence of: renal kallikrein inhibition which prevents augmentation of renal kinins in response to increased vasopressin levels, or other unrecognized properties of aprotinin.

The effect of vasopressin on renal tubular 22Na efflux in the rat.

1. Paired tracer microinjections of [3H]inulin and 22Na were performed at late proximal and early distal puncture sites in water diuresis and during vasopressin-induced antidiuresis in anaesthetized rats. Vasopressin caused a sixfold increase in Na and a fourfold increase in K excretion without significant changes in renal haemodynamics. 2. 22Na-recovery from late proximal injections increased nearly fivefold (from 0.98+/- 0.16 to 4.76 +/- 0.66%, P less than 0.001). A significant correlation could be detected between changes in sodium excretion and changes in late proximal 22Na recovery. Vasopressin had no significant effect on 22Na recovery from early distal injections. 3. These results suggest that vasopressin inhibits active salt reabsorption within the loop of Henle.

Effect of vasopressin on renal kallikrein excretion.

In an attempt to investigate a possible interaction between vasopressin and the renal kallikrein-kinin system, renal function and urinary kallikrein excretion were monitored in trained conscious dogs and in anesthetized rats in water diuresis and in vasopressin-induced antidiuresis. Vasopressin elevated urinary kallikrein excretion in a dose-dependent way in both species, with concomitant increases in urinary osmolality and electrolyte excretion. A significant increase in kallikrein excretion was observed with a dose of vasopressin as low as 2 mU . kg-1 . h-1 in the dog and 3 mU . kg-1 . h-1 in the rat without a change in renal hemodynamics. In the rat vasopressin-induced changes in kallikrein excretion were positively correlated with changes in sodium and potassium excretion and negatively correlated with changes in free water clearance. It is concluded that vasopressin over its normal physiological range of concentration stimulates renal kallikrein secretion.

Antidiuretic agonism and antagonism of some O-alkylated analogues of vasopressin containing 2-O-alkylated tyrosine

A series of 2-O-alkylated tyrosine analogues of lysine-vasopressin and desamino-lysine and arginine-vasopressin were synthesized and tested for antidiuretic activity in the water-loaded anaesthetized rat. The analogues displayed only weak antidiuretic activities. When they were infused in the rats together with lysine vasopressin it was found that 1-deamino-[2-O-ethyltyrosine]-lysine-vasopressin inhibited the vasopressin-induced antidiuretic response. The antagonistic properties were further evaluated in long-term experiments on conscious non-hydrated rats with implanted minipumps. The analogues inhibited the vasopressin-induced antidiuresis at antagonist:agonist ratios of 0.5 and 1.0.