Pertussis toxin prevents homologous desensitization of adenylate cyclase in cultured renal epithelial cells

The biochemical mechanisms of adenylate cyclase desensitization in arginine vasopressin-responsive epithelial cells remain unclear. Preincubation of cultured rabbit renal cortical collecting tubular cells with arginine vasopressin leads to a 30-100% decline in arginine vasopressin-stimulated adenylate cyclase activity. This loss of adenylate cyclase activity is time- and arginine vasopressin concentration-dependent. Preincubation with arginine vasopressin does not result in significant changes in basal, NaF-, forskolin-, isoproterenol- or cholera toxin-stimulated adenylate cyclase activity. Preincubation of cells with chlorophenylthio-cAMP, forskolin, and cholera toxin does not result in loss of arginine vasopressin-stimulated adenylate cyclase activity. Since products of cyclo-oxygenase inhibit arginine vasopressin action, cells were preincubated with indomethacin. Arginine vasopressin-induced adenylate cyclase desensitization is not reversed by indomethacin. By contrast, incubation with pertussis toxin prevents arginine vasopressin-induced adenylate cycle desensitization. These data demonstrate that arginine vasopressin induces homologous desensitization in membranes from cultured rabbit cortical collecting tubular cells and suggest that this desensitization is mediated, at least in part, by pertussis toxin substrate. These observations provide a unifying mechanism for desensitization of adenylate cyclase-coupled hormone receptors.     

Central injections of arginine vasopressin prolong extinction of active avoidance

Behavioral and physiological effects of arginine vasopressin (AVP) were examined following intracerebroventricular (ICV) injection in the rat. ICV injections prolonged extinction of active avoidance at doses of 1.0 and 10.0 ng/rat and this effect was blocked by peripheral injection of the vasopressor antagonist of vasopressin [dPtyr(Me)AVP] at a dose of 30 micrograms/kg (SC). However, 1.0 ng of AVP ICV failed to alter systemic blood pressure and also failed to produce taste aversions in a one or two bottle test. Results suggest that central AVP has a central action independent of systemic changes in blood pressure, but that the receptor mediating this action is functionally similar to the AVP V1 (vasopressor) receptor.     

Mechanism of polyuria and natriuresis in atrioventricular nodal tachycardia.

A woman with tachycardia associated with polyuria was investigated. Electrophysiological analysis showed that the tachycardia was an atrioventricular nodal re-entrant tachycardia. Programmed stimulation was then used to provoke and sustain the tachycardia for 40 minutes. Polyuria, with an appreciable increase in free water clearance, was observed. This was associated with reduction in plasma and urinary arginine vasopressin concentrations. Appreciable natriuresis also developed. These results support the hypothesis that the polyuria with increased free water clearance and the natriuresis occurring during sustained tachycardia in man are due to inhibition of secretion of vasopressin and the release of natriuretic factor.     

Arginine vasopressin and a vasopressin antagonist peptide: Opposite effects on extinction of active avoidance in rats

Systemic injection of arginine vasopressin (AVP) (1 μ/rat) significantly prolonged extinction of a pole-jump, active avoidance response in rats; lateral ventricular injection of 1000-fold less AVP (1 ng/rat) produced similar results. A new AVP analogue, [1-deaminopenicillamine-2-(O-methyl)-tyrosine]arginine vasopressin (dPTyr-(Me)AVP), is known to antagonize behavioral and vascular effects of exogenous AVP at molar ratios of 5:1. At a dose of 100 μ/rat (subcutaneously) dPTyr-(Me)AVP produces, by itself, a behavioral effect opposite to that of exogenous AVP, namely a facilitation of extinction. Injections of dPTyr-(Me)AVP into the lateral ventricle were ineffective except at a dose of 10 μg/rat. These results confirm previous reports of the effect of vasopressin on delaying extinction of avoidance behavior, but suggest a site of action distant from the lateral ventricle.     

Stimulation of testicular ornithine decarboxylase activity by arginine vasopressin

Intratesticular injection with arginine vasopressin caused stimulation of ornithine decarboxylase activity in the testes of immature rats. The increase in ornithine decarboxylase activity in response to arginine vasopressin was dose and time dependent. Maximal stimulation of ornithine decarboxylase activity occurred at 2 h after injection with 0.1 micrograms of arginine vasopressin. It was observed that stimulation of ornithine decarboxylase activity occurred in seminiferous tubules and in Leydig cells of the testis in response to arginine vasopressin.     

Involvement of the ventrolateral medulla in the mediation of pressor responses of the rat to afferent vagal stimulation

Electrical stimulation of afferent vagal fibres evoked a pressor response in rats after transection of the spinal cord. The pressor response was accounted for by an increased release of vasopressin because it was abolished by the intravenous injection of a vasopressin antagonist. Bilateral electrolytic lesions at the sites of the caudal ventrolateral medulla markedly reduced the pressor response to afferent vagal stimulation but not that to carotid occlusion. It is concluded that the area of the caudal ventrolateral medulla is involved in mediation of the vasopressin-induced pressor response to afferent vagal stimulation.     

Testosterone response in arginine vasopressin desensitized immature rat testis

Direct injection of arginine vasopressin into immature rat testis inhibited basal testosterone synthesis. Simultaneous injection of arginine vasopressin with luteinizing hormone, norepinephrine or cholera toxin inhibited these agonists - induced testosterone response. In arginine vasopressin - desensitized testis, cAMP response to luteinizing hormone, norepinephrine and cholera toxin was not disturbed. However, testosterone response to luteinizing hormone, norepinephrine or cholera toxin was drastically reduced in arginine vasopressin-desensitized testis. This shows that the increased cAMP generated by luteinizing hormone, norepinephrine or cholera toxin in arginine vasopressin desensitized testis did not cause increase in steroidogenesis. This could be due to a lesion in steroidogenic pathway beyond cAMP generation caused by arginine vasopressin.     

Renal vasopressin receptor expression and function in rats following spaceflight.

It has been suggested there is a decreased renal responsiveness to vasopressin following spaceflight and that this may be the mechanism for the increased urine flow that is observed following return to normal gravity. In the present study, we have therefore measured vasopressin receptor expression and activity in kidneys taken from rats 1 and 14 days following spaceflight of 15 days duration. Measurements of renal vasopressin V(2) and V(1a) receptor mRNA expression by quantitative RT-PCR demonstrated little difference at either 1 day or at 14 days following return from space. Evaluation of (3)H-labeled arginine vasopressin binding to membranes prepared from kidneys indicated that the majority of the vasopressin receptors were V(2) receptors. Furthermore, the data suggested that binding to vasopressin V(2) or V(1a) receptors was unaltered at 1 day and 14 days following spaceflight. Similarly, the ability of vasopressin to stimulate adenylate cyclase suggested no change in vasopressin V(2) receptor activity in these animals. These data suggest that, whatever changes in fluid and electrolyte metabolism are observed following spaceflight, they are not mediated by changes in vasopressin receptor number or vasopressin-induced stimulation of adenylate cyclase.     

Stimulative effect of guanylylimidodiphosphate on the vasopressin-induced increment of osmotic water flow of the toad bladder.

The effect of guanylylimidodiphosphate [Gpp(NH)p] on vasopressin-induced osmotic water flow across the bladder of the toad, $\text{Bufo}\text{bufo}\text{japonicus}$ was examined. Gpp(NH)p significantly enhanced vasopressin-induced osmotic water flow of the bladder at a concentration of 1 × 10^?5M, while it showed no effect on the water flow without vasopressin. Gpp(NH)p alone could not enhance cyclic AMP-induced osmotic water flow of the toad bladder. Adenylylimidodiphosphate [App(NH)p] could not enhance vasopressin-induced osmotic water flow of the bladder at a concentration of 1 × 10^?5M. The results suggest that Gpp(NH)p can enhance the physiological effect of vasopressin by stimulating vasopressin activation of adenylate cyclase during substrate and hormone depletion of the toad bladder.     

Effects of lithium on the hypothalamo-pituitary-adrenal axis

The effect of lithium on the hypothalamo-pituitary-adrenal axis was studied in vivo and in vitro. The levels of plasma vasopressin, ACTH and corticosterone increased after the administration of lithium (LiCl 4 mmol/kg BW, 11 days) in rats, while the tissue vasopressin concentration in the median eminence, the rest of the hypothalamus and the posterior pituitary was decreased. The CRF concentration in the posterior pituitary increased markedly, but it did not change significantly in the median eminence or the rest of the hypothalamus. The elevated plasma ACTH level might be at least partly due to the increased vasopression secretion. Lithium stimulated ACTH secretion per se and also enhanced vasopressin-induced ACTH secretion in cultured pituitary cells and in half pituitary incubations, while it did not affect CRF-induced ACTH secretion. Lithium inhibited CRF-induced cAMP accumulation in half pituitary incubations, while lithium and vasopressin did not affect cAMP accumulation per se or even when administered together. The results suggest that lithium-induced ACTH release is via a cAMP-independent mechanism. Thus, it is possible that lithium stimulates ACTH release by acting directly on the corticotroph, stimulating vasopressin release and potentiating vasopressin-induced ACTH release.     

Glucocorticoid amplifies vasopressin-induced phosphoinositide hydrolysis in aortic smooth muscle cells

It has been reported that glucocorticoid modifies phosphoinositide (PI) hydrolysis stimulated by vasoactive agents in vascular smooth muscle cells. In the present study, we investigated the point at which glucocorticoid affects vasopressin-induced PI hydrolysis in primary cultured rat aortic smooth muscle cells. The pretreatment with dexamethasone significantly amplified the formation of inositol trisphosphate (IP₃) induced by vasopressin in a dose-dependent manner in a range of 1 pM to 10 nM. The effect of dexamethasone was dependent on the time of pretreatment up to 8 h. Dexamethasone had little effect on the number of vasopressin receptor and its affinity to vasopressin. The pretreatment with dexamethasone also amplified the formation of IP₃ induced by NaF, a GTP-binding protein activator, or angiotensin II. 12-O-Tetradecanoylphorbol-13-acetate, a protein kinase C (PKC)-activating phorbol ester, significantly reduced the dexamethasone-induced enhancement of IP₃ formation stimulated by vasopressin, angiotensin II or NaF. 4α-Phorbol-12, 13-didecanoate, a PKC-nonactivating phorbol ester, had little effect on the enhancement by dexamethasone. These results strongly suggest that glucocorticoid amplifies vasopressin-induced PI hydrolysis at a point downstream from GTP-binding protein in primary cultured rat aortic smooth muscle cells, and that the activation of PKC has a negative feedback effect on the amplification by glucocorticoid of vasopressin-induced PI hydrolysis.     

Long-term facilitation of social recognition in rats by vasopressin related peptides: a structure-activity study.

The effect of several vasopressin-related peptides was investigated in the social recognition paradigm, that consists of two successive encounters of a resident and a juvenile rat. The decrease of social investigation time of the resident rat during the second encounter served as a measure for social recognition. Single administration (3.0 micrograms, s.c.) of the vasopressin (AVP)-related peptides AVP-(1-8), AVP-(1-7) or AVP-(1-6), injected just after the first encounter, resulted in social recognition after 24 hours. Such an effect was not observed after placebo treatment or an injection with AVP-(1-5), [pGlu4, Cyt6]AVP-(4-8), [pGlu4, Cyt6]-AVP-(4-9), AVP-(7-9) or oxytocin-(1-6)-NH2. The peptide AVP-(1-6) was also active when administered in a dose of 0.3 micrograms in contrast to other peptides. Thus, vasopressin related peptides induce long term facilitation of social recognition and this action resides in the covalent ring structure of vasopressin. This effect resembles the vasopressin-induced facilitation of particular memory processes, as revealed with other behavioral paradigms.     

Central cardiovascular effects of mammalian neurohypophyseal peptides in conscious rats

To confirm and extend the results of previous studies which demonstrated central cardiovascular effects of vasopressin in anesthetized rats, we determined blood pressure and heart rate changes for 30 minutes after intracerebroventricular injections of arginine vasopressin, arginine vasotocin and oxytocin in conscious rats. As compared to sham injections, significantly greater increases in either systolic or diastolic blood pressure were noted over the 30 minutes which followed the injection of 0.15, 1.0 or 10.0 nM of either vasopressin or vasotocin. In animals given vasopressin, plasma levels of the peptide were determined. There was a substantial increase in plasma vasopressin only after the highest dose. Overall blood pressure responses to doses of oxytocin as high as 100 nM were not significantly different than sham injections. Heart rate following both vasopressin and vasotocin was increased at 0.15 nM, was initially decreased then increased at 1.0 nM and was substantially decreased after the 10.0 nM dose. There was a significant increase in heart rate at the 10.0 nM and 100 nM doses of oxytocin. Dose response curves for systolic blood pressure and heart rate 20 minutes after injection were similar for vasopressin and vasotocin. We conclude that arginine vasopressin has significant central pressor and tachycardic effects in conscious rats, and it is related, at least in part, to the tail structure of the peptide, which is shared with arginine vasotocin.     

Vasopressin administration to neonatal rats reduces antidiuretic response in adult kidneys

Neonatal rats who had been given injections of vasopressin on days 1–7 after birth exhibited polyuria as adults. In vivo antidiuresis bioassays demonstrated that their kidneys were deficient in their ability to concentrate urine in response to stimulation with vasopressin. The kidneys also showed a reduction in vasopressin-induced cyclic AMP production, although parathyroid hormone- and calcitonin-induced levels were normal. This suggests a specific deficit in vasopressin receptor-adenylate cyclase function. In contrast, the neonatal treatment had no effect on the sensitivity of the adult vasculature to the hypertensive effects of vasopressin. These results show that short exposures to high levels of vasopressin early in development can produce a long-term defect in vasopressin responsiveness that is specific to the kidney.     

Platelet aggregation and vasopressin receptors in patients with diabetes mellitus

Plasma vasopressin, vasopressin-induced platelet aggregation, and platelet vasopressin receptors were investigated in 10 normal subjects and 14 diabetic patients free of microangiopathy. Basal plasma vasopressin concentration was identical in two groups. Platelet aggregation induced by vasopressin as well as by epinephrine was not significantly altered in the diabetic patients. However, exploration of platelet V1-vasopressin receptors revealed in the diabetic group a dramatic reduction in the number of binding sites without alteration of the receptor affinity for tritiated vasopressin. Thus vasopressin-induced platelet aggregation in uncomplicated diabetes mellitus remains normal despite a decrease in the number of vasopressin receptors presumably due to alterations of the platelet membrane structure.     

Effects of Rho-kinase inhibitor on vasopressin-induced chronic myocardial damage in rats

The aim of this study was to develop a new model of vasopressin-induced chronic myocardial damage based on sustained ST-segment depression in electrocardiogram (ECG) with progression of myocardial fibrosis in rats. Furthermore, using this model, we examined the prophylactic potential of fasudil, a Rho-kinase inhibitor, against myocardial damage induced by vasopressin. In 10-week old male Donryu rats, intravenous administration of arginine vasopressin (0.5 iu/kg) induced significant ST-segment depression. Two days and one week after the administration of vasopressin, ST-segment depression was -0.19 +/- 0.02 and -0.14 +/- 0.02 mV, respectively. Fasudil (10 and 30 mg/kg, p.o.) significantly attenuated the ST-segment depression induced by vasopressin. One week after the administration of vasopressin, the percent area of myocardial fibrosis in control animals (0.42 +/- 0.11%, p < 0.01) was significantly greater than that in normal animals (0.05 +/- 0.01%). Fasudil (10 and 30 mg/kg) significantly prevented the development of the fibrosis. We present a new model of chronic myocardial damage based on sustained ST-segment depression with progression of myocardial fibrosis in rats, and suggest that this model may be useful to investigate the treatment of chronic angina. Inhibition of Rho-kinase is efficacious in preventing the ECG change and development of fibrosis induced by vasopressin in this model.     

Phorbol ester inhibition of the hormone-stimulated phosphoinositide cycle in WRK-1 cells.

WRK-1 rat mammary tumour cells respond to vasopressin with increased accumulation of inositol phosphates as well as increased precursor incorporation into phosphatidylinositol. The phorbol ester, phorbol 13-myristate 12-acetate (PMA) inhibits by 80% both inositol phosphate accumulation and increased precursor incorporation. This inhibition is much less evident at early times (2 min) than at later times (25 min). The vasopressin-induced rise in cytosolic free Ca2+ is inhibited in a similar manner. Oleoylacetylglycerol is inactive with respect to inhibition of vasopressin-induced increases in incorporation of 32P into phosphoinositides. PMA has no effect on vasopressin binding at saturating concentrations of the hormone and does not affect the binding affinity.     

Only through the brain nuclei, arginine vasopressin regulates antinociception in the rat

The effect of arginine vasopressin (AVP) on rat antinociception was investigated. Intraventricular injection of 50 or 100 ng AVP dose-dependently increased the pain threshold; in contrast, intraventricular injection of 10 μl anti-AVP serum decreased the pain threshold; both intrathecal injection of 200 ng AVP or 10 μl anti-AVP serum and intravenous injection of 5 μg AVP or 200 μl anti-AVP serum did not influence the pain threshold. Pain stimulation reduced AVP concentration in hypothalamic paraventricular nucleus (PVN), and elevated AVP concentration in hypothalamic supraoptical nucleus (SON) and periaqueductal gray (PAG), but no change in AVP concentration was detected in pituitary, spinal cord and serum. The results indicated that AVP regulation of antinociception was limited to the brain nuclei.