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PubMed1997

The effect of intravenous vasopressin on gastric myoelectrical activity in human subjects.

UNLABELLED: Vasopressin's role in the sensation of nausea is incompletely understood. In this study, our goals were to investigate whether high intravenous vasopressin levels in normal subjects would induce nausea and vomiting and to determine the electrogastrographic (EGG) pattern which would develop at these concentrations. METHODS: EGG recordings were made on five fasting healthy subjects (three females, mean age: 27 years). Vasopressin was infused (0.15 or 0.3 U kg-1 h-1) for 1 h after a 30-min baseline recording. Serum vasopressin levels were measured every 15 min. Symptoms of nausea, cramping, retching, vomiting and bloating were graded from 0 to 5 (0 = none, 5 = most severe). Normal saline at the same rate was then infused for 1 h, with recording of symptoms and measuring blood levels of vasopressin as done previously. RESULTS: EGG data showed a 43% reduction in the percentage of normal slow waves (96-53%) at a vasopressin rate of 0.3 U kg-1 h-1. A 29% reduction (88-59%) occurred at 0.15 U kg-1 h-1. The EGG dominant frequency decreased by 0.8 cpm (3.07-2.25) for the high dose, while only 0.2 cpm reduction (2.9-2.7) occurred at the lower dose. Bradygastria (< 2.4 cpm) rather than tachygastria (> 3.7 cpm) was the predominant abnormality with the high dose. Symptoms of nausea correlated with the infusion of vasopressin and significantly increased with the higher dose. CONCLUSIONS: (i) At supraphysiological vasopressin levels, nausea was present in 80% of subjects but there was no retching or vomiting, (ii) bradygastria was the predominant dysrhythmia at these high vasopressin concentrations, (iii) increasing vasopressin levels correlated symptomatically with increases in nausea.

Adult↗
PubMed1988

Vasopressin: sexual dimorphism in secretion, cardiovascular actions and hypertension.

We have investigated the issue of sexual dimorphism in the secretion of vasopressin, its pressor action, and the development of deoxycorticosterone (DOC)-salt hypertension. In normal human subjects on controlled salt intake, the basal secretion of vasopressin, indicated by plasma vasopressin levels and urinary excretion of vasopressin, was higher in men than in women and in blacks than in whites. Basal vasopressin secretion also was higher in male than in female rats. This effect was not associated with a difference in the metabolic clearance of the hormone. The sex-related difference in vasopressin release in rats was abolished by gonadectomy and restored by treatment of males with testosterone and females with ovarian hormones. The pressor responsiveness to vasopressin was higher in male than in randomly cycling female rats. Finally, DOC-salt hypertension, which is dependent on vasopressin, developed more rapidly in male than in female rats. Although there was no sex-related difference in the extent to which plasma vasopressin levels were elevated, pressor responsiveness to vasopressin was greater and baroreflex sensitivity was attenuated to a lesser extent in hypertensive males than in hypertensive females. Thus, it seems likely that gonadal hormones play a significant role in cardiovascular regulation.

Animals↗
PubMed2000

Pentobarbital, but not propofol, suppresses vasopressin-stimulated heat shock protein 27 induction in aortic smooth muscle cells.

BACKGROUND: Although it is known that systemic blood pressure decreases after the administration of pentobarbital or propofol, the mechanisms underlying the cardiovascular effects of these anesthetics are still poorly understood. The authors previously showed that vasopressin stimulates the induction of heat shock protein (HSP) 27, a low-molecular-weight HSP, by a protein kinase C-dependent manner in aortic smooth muscle A10 cells. It is recognized that HSP27 may act as a chaperone like high-molecular-weight HSPs such as HSP70. HSP27 is reportedly associated with agonist-induced contraction of vascular smooth muscle cells. The authors examined the effects of pentobarbital and propofol on the vasopressin-stimulated HSP27 induction in A10 cells. METHODS: Cultured A10 cells were pretreated with pentobarbital or propofol and then stimulated by vasopressin or 12-o-tetradecanoylphorbol 13-acetate (TPA). The effect of vasopressin on HSP70 was evaluated by Western blot analysis and compared with its effect on HSP27. The concentrations of HSP27 were determined by a specific immunoassay. The effect of pentobarbital on the expression levels of mRNA for HSP27 by vasopressin was evaluated by Northern blot analysis. RESULTS: Vasopressin induced HSP27 but had little effect on HSP70. At concentrations used clinically, pentobarbital inhibited the accumulation of HSP27 by vasopressin or TPA. Pentobarbital reduced the levels of mRNA for HSP27 induced by vasopressin. In contrast, propofol affected neither the vasopressin- nor TPA-induced HSP27 accumulation. CONCLUSIONS: These results suggest that pentobarbital suppresses the vasopressin-stimulated HSP27 induction in vascular smooth muscle cells. This inhibitory effect is probably exerted at a point downstream from protein kinase C.

Anesthetics, Intravenous↗
PubMed2003

Should vasopressin replace adrenaline for endotracheal drug administration?

OBJECTIVE: Arginine vasopressin was established recently as a drug of choice in the treatment of cardiac arrest and in retractable ventricular fibrillation; however, the hemodynamic effect of vasopressin following endotracheal drug administration has not been fully elucidated. We compared the effects of endotracheally administered vasopressin vs. adrenaline on hemodynamic variables in a canine model, and we investigated whether vasopressin produces the same deleterious immediate blood pressure decrease as did endotracheal adrenaline in the canine model. DESIGN: Prospective controlled study. SETTING: Animal laboratory in Tel-Aviv University, Israel. SUBJECTS: Five adult mongrel dogs weighing 6.5-20 kg. INTERVENTIONS: Dogs were anesthetized; each dog was intubated orally, and both femoral arteries were cannulated for the measurement of arterial pressure and for sampling blood gases. Each dog was studied four times, 1 wk apart, by using the same protocol for injection and anesthesia: endotracheal placebo (10 mL NaCl 0.9%,), endotracheal vasopressin (1 units/kg), endobronchial adrenaline (0.1 mg/kg), and endotracheal adrenaline (0.1 mg/kg). Following placebo, vasopressin, and adrenaline instillation, five forced manual ventilations were delivered with an Ambu bag. Each dog was its own control. MEASUREMENTS AND MAIN RESULTS: Following placebo or drug administration, heart electrocardiography and arterial pressures were continuously monitored with a polygraph recorder for 1 hr. Endotracheal vasopressin produced an immediate increase of diastolic blood pressure (from 83 +/- 10 mm Hg [baseline] to 110 +/- 5 mm Hg at 1 min postinjection). This response lasted >1 hr. In contrast, both endotracheal and endobronchial administration of adrenaline produced an early and significant (p <.05) decrease in diastolic and mean blood pressures. The diastolic blood pressure increase from 85 +/- 10 mm Hg to 110 +/- 10 mm Hg took an ill-afforded 55 secs following endotracheal adrenaline. Diastolic blood pressure was significantly (p <.05) higher following vasopressin compared with adrenaline administration in both routes. CONCLUSIONS: Vasopressin accomplishes its hemodynamic effect, particularly on diastolic blood pressure, more rapidly, vigorously, and protractedly and to a significant degree compared with both endotracheal and endobronchial adrenaline. Evaluation of the effects of endotracheal vasopressin in a closed chest cardiopulmonary resuscitation model is recommended.

Animals↗
PubMed2004

The discovery of novel vasopressin V1b receptor ligands for pharmacological, functional and structural investigations.

Until recently, pharmacological studies dealing with vasopressin receptor isoforms were severely hampered by the lack of selective agonists or antagonists that recognize the pituitary V(1b) vasopressin receptor. By contrast, many selective vasopressin-related compounds are available for characterization of the vasopressor (V(1a)) or antidiuretic (V(2)) vasopressin receptor subtypes. Recently, SSR149415, a selective nonpeptide molecule, was discovered with nanomolar affinity for mammalian V(1b) receptors and good selectivity for the other vasopressin and oxytocin receptor isoforms. This molecule exhibits potent antagonist properties both in vitro and in vivo. We also designed synthetic peptides derived from [deaminocysteine(1),arginine(8)]vasopressin (dAVP), modified in position 4 by various amino acid residues. Some of these, d[cyclohexylalanine(4)]AVP or d[lysine(4)]AVP, have a high affinity and an excellent selectivity for the human V(1b) receptor subtype. However, they exhibit a mixed V(1b)/V(2) pharmacological profile for the rat vasopressin receptor isoforms. Whatever the species considered, these peptides behave as agonists both in bioassays performed in vitro and in vivo. The d[cyclohexylalanine(4)]AVP was tritiated and represents the first selective radiolabelled ligand available for studying the human V(1b) receptors. The discovery of these new selective V(1b) agonists and V(1b) antagonist allows an accurate pharmacological characterization of all the vasopressin receptor isoforms. As emphasized in this review, attention to the vasopressin and oxytocin receptor species differences is of critical importance in studies with all vasopressin and oxytocin ligands.

Animals↗
PubMed1984

Regulation by adenosine of the vasopressin-sensitive adenylate cyclase in pig-kidney cells (LLC-PK1L) grown in defined media.

LLC-PK1L cells, a kidney-derived cell line, had sustained growth in a defined medium. When compared to the parent cell line growing with 10% fetal bovine serum, LLC-PK1L cells had about 100-times fewer vasopressin receptors. Upon modifications of the cell culture medium, the vasopressin response of the adenylate cyclase could be increased by more than 10-fold with a parallel increase in vasopressin receptor number. Using cells with high or low receptor densities, the stimulatory and inhibitory effects of N6-L-2-phenylisopropyl-adenosine on the modulation of the adenylate cyclase responsiveness to vasopressin were investigated. When high concentrations of GTP were added, low concentrations of phenylisopropyladenosine inhibited the enzyme, while higher concentrations were found to be stimulatory. The adenylate cyclase activity stimulated by vasopressin could only be inhibited by phenylisopropyladenosine under these conditions in membranes with high receptor density; only the increase in enzyme activity due to high GTP concentration was inhibitable. The analysis of the dependency of the adenylate cyclase activity as a function of the vasopressin concentration showed that, besides reducing the maximum velocity of the system for vasopressin, the addition of phenylisopropyladenosine generated an heterogeneity in the adenylate cyclase response to vasopressin (as judged by a curvilinear Eadie plot). A high-affinity component in the adenylate cyclase response appeared when phenylisopropyladenosine was added. The growth of the cells in a medium containing adenosine deaminase gave results identical to those obtained for control cells. However, growing the cells with both phenylisopropyladenosine and adenosine deaminase abolished the inhibitory effects of the former on the adenylate cyclase and greatly reduced its stimulatory action. Under these conditions, the vasopressin response of the adenylate cyclase was not further regulated by phenylisopropyladenosine. These results indicate a role of adenosine on vasopressin response, especially at low physiological concentrations of the hormone where a high-affinity component of the hormonal response could be demonstrated.

Adenosine↗
PubMed2000

Discovery and design of novel and selective vasopressin and oxytocin agonists and antagonists: the role of bioassays.

Synthetic oxytocin and vasopressin agonists and antagonists have become important tools for research and were instrumental in the identification of the four known receptor subtypes, V1a, V2, V1b (V3) and oxytocin, of these peptide hormones. However, the relative lack of receptor selectivity, particularly of the antagonists, has limited their usefulness as experimental probes and their potential as therapeutic agents. We now present some findings from our continuing studies aimed at the design of more selective oxytocin and vasopressin agonists and antagonists and a structure-activity relationship update on our recently discovered novel hypotensive vasopressin peptides. Bioassays have been, and continue to be, of critical importance in leading to the discovery of the novel agonists, antagonists and hypotensive peptides reported here. This paper highlights three main aspects of these studies. (1) Replacement of the tyrosine2 and/or phenylalanine3 residues in the V2 agonist deamino,[Val4,D-Arg8]arginine-vasopressin (dVDAVP) by thienylalanine resulted in selective V2 agonists with strikingly high potencies. However, the peptide solutions were unstable and lost activity over time. These highly potent V2 agonists, which are devoid of vasopressor activity, are promising leads for improving drugs for treating diabetes insipidus, enuresis and coagulation disorders. (2) Diaminopropionic acid and diaminobutyric acid substitution at position-5 in oxytocin and in V1a antagonists yielded, respectively, the first specific antagonist for the oxytocin receptor, desGly-NH2,d(CH2)5[D-Trp2,Thr4,Dap5]OVT and the first specific antagonist for the vasopressin V1a receptor, d(CH2)5[Tyr(Me)2,Dab5]AVP. The availability of single receptor subtype-specific or selective antagonists will enhance our ability to delineate receptor functions. Utilising these new receptor specific probes, we were able to show that the uterotonic action of vasopressin is mediated principally by oxytocin and not by V1a receptors. (3) Replacement of the phenylalanine3 residue in the V1a/V2/oxytocin antagonist, d(CH2)5[D-Tyr(Et)2,Val4]AVP, with arginine3 yielded the novel, selective, hypotensive vasopressin peptide, d(CH2)5[D-Tyr(Et)2,Arg3,Val4]AVP (Peptide I). Bioassay characterisations of Peptide I show that its vasodepressor action is independent of the peripheral autonomic, bradykinin, nitric oxide and prostaglandin systems and is not mediated by the known classical oxytocin and vasopressin receptors. These findings suggest the existence of a new vasopressin receptor subtype that may be relevant to the vasodilating action of vasopressin in regional vascular beds. Iodinatable hypotensive peptides have been synthesised and could be developed as markers for the putative new receptor. Ongoing structure-activity relationship studies on Peptide I have led to more potent and selective hypotensive peptides for use as new research tools and as leads for the development of a new class of antihypertensive agents.

Amino Acid Sequence↗
PubMed2000

The role of steroid hormones in the regulation of vasopressin and oxytocin release and mRNA expression in hypothalamo-neurohypophysial explants from the rat.

Vasopressin and oxytocin release from the neural lobe, and the vasopressin and oxytocin mRNA contents of the supraoptic and paraventricular nuclei are increased by hypertonicity of the extracellular fluid. The factors regulating these parameters can be conveniently studied in perifused explants of the hypothalamo-neurohypophysial system that include the supraoptic nucleus (but not the paraventricular nucleus) with its axonal projections to the neural lobe. Vasopressin and oxytocin release and the mRNA content of these explants respond appropriately to increases in the osmolality of the perifusate. This requires synaptic input from the region of the organum vasculosum of the lamina terminalis. Glutamate is a likely candidate for transmitting osmotic information from the organum vasculosum of the lamina terminalis to the magnocellular neurones, because agonists for excitatory amino acid receptors stimulate vasopressin and oxytocin release, and because increased vasopressin release and mRNA content induced in hypothalamo-neurohypophysial explants by a ramp increase in osmolality are blocked by antagonists of both NMDA (N-methyl-D-aspartate) and non-NMDA glutamate receptors. Osmotically stimulated vasopressin release is also blocked by testosterone, dihydrotestosterone, oestradiol and corticosterone. Both oestrogen and dihydrotestosterone block NMDA stimulation of vasopressin release, and in preliminary studies oestradiol blocked AMPA stimulation of vasopressin release. Thus, steroid inhibition of osmotically stimulated vasopressin secretion may reflect inhibition of mechanisms mediated by excitatory amino acids. Recent studies have demonstrated numerous mechanisms by which steroid hormones may impact upon neuronal function. Therefore, additional work is warranted to understand these effects of the steroid hormones on vasopressin and oxytocin secretion and to elucidate the potential contribution of these mechanisms to regulation of hormone release in vivo.

Animals↗
PubMed1986

Studies of vasopressin in the human cerebrospinal fluid.

The development of sensitive radioimmunoassays has permitted measurement of the low concentration of vasopressin in the human cerebrospinal fluid. There is accumulating evidence to suggest that vasopressin is involved in a variety of brain functions. As an effective blood-cerebrospinal fluid barrier to vasopressin has been demonstrated, the concentration of vasopressin in the cerebrospinal fluid probably reflects the release of vasopressin within the brain. In human subjects without intracranial disease, the concentration of vasopressin in the cerebrospinal fluid is in the range 0.5-2.0 pg/ml with only little diurnal variation. Intracranial disorders associated with increased intracranial pressure may cause increased cerebrospinal fluid vasopressin concentrations, whereas degenerative brain diseases are associated with low concentrations. Only little is known about the physiologic stimuli which alter the concentration of vasopressin in cerebrospinal fluid. The concentration in cerebrospinal fluid is not influenced by a number of stimuli that cause release of vasopressin into the blood, i.e. changes in plasma osmolality, postural changes, and nausea. Elevation of the intracranial pressure, changes in the composition of the cerebrospinal fluid, electrical stimulation of the hypothalamus, and severe hemorrhage provoke an increase in cerebrospinal fluid vasopressin level.

Animals↗
PubMed1994

Effects of vasopressin on haemodynamics in portal hypertensive rats receiving clonidine.

The effects of clonidine, vasopressin or a combination of both substances on splanchnic and systemic haemodynamics were measured in conscious rats with portal vein stenosis. Clonidine alone significantly decreased portal pressure, portal tributary blood flow and cardiac index, but did not change arterial pressure. Vasopressin alone significantly increased arterial pressure and significantly decreased portal pressure, portal tributary blood flow and cardiac index. Changes in portal tributary blood flow, arterial pressure and cardiac index were significantly higher with vasopressin than with clonidine alone. Vasopressin infusion in rats pretreated with clonidine significantly increased arterial pressure and significantly decreased portal pressure, portal tributary blood flow and cardiac index. Changes in arterial and portal pressures and portal tributary blood flow were significantly higher with combined therapy than with clonidine alone. Changes in arterial and portal pressures and portal tributary blood flow did not differ between combined therapy and vasopressin alone. Changes in cardiac index were significantly higher with combined therapy than with clonidine or vasopressin alone. Hepatic artery blood flow was not affected by either clonidine or vasopressin but significantly declined with combined therapy. In conclusion, this study suggests that a combination of vasopressin and clonidine accentuates the portal hypotensive action of clonidine but not the action of vasopressin. Moreover, this study suggests that a combination of vasopressin and clonidine may have deleterious effects on systemic and hepatic artery vascular beds.

Animals↗
PubMed1997

Vasopressin and oxytocin release during prolonged environmental hypoxia in the rat.

BACKGROUND: The mechanism causing peripheral oedema in hypoxaemic chronic obstructive pulmonary disease has not been established. Vasopressin, a powerful antidiuretic hormone involved in salt and water homeostasis, is released in response to acute hypoxia. However, the effect of prolonged hypoxaemia on hypothalamic and pituitary release of the magnocellular hypothalamic hormones, vasopressin and oxytocin, has not previously been studied. METHODS: Male Wistar rats were randomly allocated to either normobaric, hypoxic (10% O2) or control (21% O2) environmental chambers. An initial series of experiments examined plasma vasopressin concentration, osmolality, sodium concentration, packed cell volume (PCV), and weight gain at weekly intervals (n = 4-6) for six weeks. The maximum increase in plasma vasopressin concentration and PCV occurred after five weeks. In a second experiment vasopressin and oxytocin concentrations in the hypothalamus, pituitary gland, and plasma were measured in eight control and eight hypoxic rats after five weeks in the environmental chambers. RESULTS: In rats exposed to environmental hypoxia PCV increased (p < 0.001) and weight gain decreased (p < 0.05) compared with controls. The plasma vasopressin concentration increased progressively from a baseline of 1.36 (0.2) pmol/l (n = 6) to a maximum of 4.38 (0.8) pmol/l (n = 6; p < 0.01) during the first five weeks of environmental hypoxia (difference 3.02 (95% CI 1.18 to 4.86)). Plasma osmolality and sodium concentration were unchanged in hypoxic rats compared with controls during the six week period. The hypothalamic vasopressin concentration was increased (p < 0.001) after five weeks of environmental hypoxia (91.6 (4.8) pmol/ hypothalamus) compared with controls (57.4 (5.1) pmol/hypothalamus), the difference being 34.2 pmol/hypothalamus (95% CI 21.6 to 46.5). The pituitary vasopressin concentration was unchanged. In hypoxic rats hypothalamic oxytocin (59.6 (3.2) pmol/hypothalamus) was greater (p < 0.01) than in controls (42 (3.8) pmol/hypothalamus), a difference of 17.6 pmol/ hypothalamus (95% CI 8.7 to 26.5). Similarly, the plasma oxytocin concentration was increased (p < 0.05) in hypoxic rats (6.78 (1.2) pmol/l) compared with controls (3.3 (0.8) pmol/l), a difference of 3.48 pmol/l (95% CI 0.89 to 6.07). The pituitary oxytocin concentration was unchanged in the two groups. CONCLUSIONS: These results demonstrate an increase in hypothalamic production of vasopressin and oxytocin in rats during prolonged hypoxaemia. Increased plasma concentrations of neurohypophysial hormones would be expected to impair sodium and water homeostasis in patients with hypoxaemia. However, the absence of change in the plasma osmolality and sodium concentrations in this study and previous clinical investigations suggests that compensatory mechanisms modulate the actions of both vasopressin and oxytocin. A reduction in renal blood flow or decreased renal responsiveness to the neurohypophyseal hormones may be involved.

Animals↗
PubMed1997

Role of plasma vasopressin as a mediator of nausea and gastric slow wave dysrhythmias in motion sickness.

The possible role of vasopressin in nausea and gastric dysrhythmias in motion sickness was tested by electrogastrography in 14 subjects during circular vection (60 degrees/s) and vasopressin infusion. Tachygastria was expressed as the signal percent >4.5 cycles/min. Vection evoked nausea scores of 2.6 +/- 0.2 (0 = none to 3 = severe) in 10 subjects with increases in tachygastric activity (15 +/- 2 to 45 +/- 3%) and plasma vasopressin (4.5 +/- 1.5 to 8.4 +/- 2.5 pg/ml) that were blocked by atropine but not indomethacin. Four asymptomatic subjects had no tachygastria or vasopressin release. Vasopressin at 0.2 U/min (plasma level = 322.1 +/- 10.3 pg/ml) evoked nausea (2.6 +/- 0.4) and increases in tachyarrhythmic activity (41 +/- 5%) that were blunted by atropine but not indomethacin. There were no differences in nausea or dysrhythmias with vasopressin infusion in subjects who noted nausea during vection versus those who did not. To conclude, vection evokes nausea, dysrhythmias, and vasopressin release in motion sickness-susceptible humans via cholinergic prostaglandin-independent pathways. Supraphysiological vasopressin infusions evoke nausea and dysrhythmias by similar pathways to equal degrees in motion sickness-susceptible and -resistant subjects. Thus central but not peripheral actions of vasopressin may contribute to nausea and slow wave disruption with vection. Blunting of both the release and action of vasopressin by atropine may explain its beneficial action in motion sickness.

Adult↗
PubMed1985

Vasopressin in plasma and ventricular cerebrospinal fluid during dehydration, postural changes, and nausea.

The responses of plasma and ventricular cerebrospinal fluid (CSF) vasopressin concentration to dehydration, postural changes, and induction of nausea were studied in 21 patients with hydrocephalus of various etiology. The 24-h dehydration test evoked a significant increase in plasma osmolality and vasopressin concentration, whereas the concentration of vasopressin in CSF was unchanged. Head-up tilt to 50 degrees for 45 min with a tilt bed resulted in a modest increase of plasma vasopressin in patients who did not develop presyncopal symptoms, but no changes were seen in CSF vasopressin. Induction of nausea by subcutaneously injected apomorphine provoked a marked (20- to 50-fold) rise in plasma vasopressin concentration within 15 min, and the plasma concentration was significantly increased above base-line values for 60-120 min. Despite the prolonged period of high plasma vasopressin concentration CSF vasopressin was not influenced by the apomorphine injection. The findings suggest that the concentration of vasopressin in the CSF is controlled by mechanisms other than the well-known osmotic and nonosmotic stimuli of vasopressin release into the blood.

Adult↗
PubMed1981

Multiple sites for interaction of prostaglandin and vasopressin in toad urinary bladder.

The interaction of vasopressin with prostaglandins were examined in the toad bladder by determining water flows, cAMP levels, and cAMP-dependent protein kinase activity. Both water flow and activation of cAMP-kinase in response to vasopressin were enhanced after prostaglandin inhibition, consistent with inhibition of vasopressin-induced cAMP generation by endogenous prostaglandins. On the other hand exogeneous PGE stimulated cAMP generation. PGE1 (10(-7) M) alone did not increase water flow but activated kinase more than vasopressin only. Addition of PGE1 (10(-7) M) and vasopressin inhibited water flow as compared with vasopressin along but increased the kinase ratio above that with vasopressin only. PGE2 (10(-5) M) increased the cAMP content and kinase ratio even more than vasopressin but again resulted in no water flow. Addition of vasopressin and PGE2 (10(-5) M) increased water flow but did not alter cAMP content or the kinase ratio compared with PGE2 alone. Similar results were obtained with PGE1. Accordingly, prostaglandin dissociates cAMP levels and kinase ratio from the hydroosmotic response, suggesting that PGE2 inhibits steps distal to cAMP. Consistent with this, in bladders pretreated with naproxen or meclofenamate, PGE2 (10(-8) to 10(-6) M) inhibited the response to submaximal doses of cAMP (5 mM) or 8-bromo-cAMP (0.03 mM). Furthermore, pretreatment with naproxen significantly enhanced the response to cAMP (5 mM). These studies provide evidence for vasopressin-PGE interaction at the site of cAMP generation and also at a step(s) unrelated to cAMP generation.

Animals↗
PubMedDate not supplied

No role of ATP-sensitive potassium channels in the vasoconstriction produced by vasopressin.

The contribution of ATP-sensitive potassium channel (KATP channel) blockade in the vasoconstriction produced by vasopressin was studied. All experiments were performed using rat thoracic aorta cut in 4-mm rings, denuded from their endothelium and mounted into 20-ml organ baths. Glibenclamide (0.01-10 microM), a KATP channel antagonist, did not induce any measurable contraction, nor did it reduce the maximum contraction induced by vasopressin and phenylephrine. The specific inhibition of lemakalim-induced (a KATP channel activator) relaxation by vasopressin was investigated. Lemakalim (0.01-0.3 microM) relaxed both vasopressin (0.1 microM) and phenylephrine (0.3 microM) preconstricted vessels. However, in contrast to what would be expected from KATP blockade by vasopressin, rings preconstricted with vasopressin were more sensitive to the relaxant action of lemakalim, compared to phenylephrine preconstricted vessels (log[EC50] of -7.82 +/- 0.01 and -7.10 +/- 0.02, respectively, p < 0.05). Dose-response curves to papaverine (3-30 microM) in rings preconstricted with vasopressin and phenylephrine were comparable. When aortic rings were pretreated with lemakalim (0.1 microM), the maximum active tension induced by vasopressin was reduced (2.68 +/- 0.23 in control conditions vs. 0.62 +/- 0.08 g on pretreated vessels, p < 0.001), whereas that by phenylephrine was slightly increased. In order to explain the stronger relaxant action of lemakalim against vasopressin-induced constriction, the contribution of calcium influx through L-type calcium channels in the constriction of aortic rings to vasopressin and phenylephrine was compared.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1987

Diabetes insipidus with renal resistance to vasopressin in the desoxycorticosterone-treated dog: a possible role for prostaglandins.

We examined the release of vasopressin and the renal response to exogenous vasopressin before and during desoxycorticosterone acetate (DOCA) administration in the dog. As treatment with DOCA produced potassium loss, urine volume increased, urinary osmolality decreased, and urinary PGE2 tended to increase. The increase in urine volume was accompanied by increases in serum sodium, in plasma osmolality and in plasma arginine vasopressin. The threshold for vasopressin release measured during polyuria was higher than control but the rate of vasopressin release was unchanged. The DOCA-induced polyuria was not affected by treatment with vasopressin which further increased plasma vasopressin. Treatment with indomethacin which corrected the increase in urinary PGE2 excretion but not the hypokalemia, restored the renal responsiveness to vasopressin, decreased the secretion of vasopressin, and corrected the polyuria and the hypernatremia. These findings suggest that DOCA-induced polyuria is attributable to a decrease in renal responsiveness to vasopressin which may be mediated in part by an increase in the renal synthesis of prostaglandins.

Animals↗
PubMedDate not supplied

Effects of luminal vasopressin on intracellular calcium in microperfused rat medullary thick ascending limb.

Recent evidence suggests that vasopressin exerts a regulatory influence on transport processes in the rabbit cortical collecting duct via both the basolateral and luminal membranes. The present study was undertaken to examine whether luminal vasopressin receptors, coupled to changes in intracellular calcium, were also present in microperfused rat medullary thick ascending limb (mTAL), a key element of the urine concentrating mechanism. Addition of 1 nM vasopressin to the luminal microperfusate elicited a small but significant and sustained rise in intracellular calcium, from basal values of 100.1 +/- 20.1 to 169.6 +/- 24.1 nM after 250 s. The effect observed following luminal addition of vasopressin was dose-dependent, with a larger increment of 190.2 +/- 32.2 nM evoked by addition of 1 microM vasopressin. Addition of 1 nM oxytocin to the lumen did not cause a significant increase in intracellular calcium concentration, consistent with the response to vasopressin being mediated by specific luminal vasopressin receptors. In the absence of calcium in the bath and lumen together or in the bath alone, a residual response to 1 microM luminal vasopressin was still evident, suggestive of a small component of release of calcium from intracellular stores. Selective calcium removal from the luminal microperfusate alone left the response intact. These data are congruous with a model of vasopressin-induced entry of calcium which occurs via the basolateral membrane following ligand binding to the apical membrane. These findings, coupled with earlier observations in the collecting duct, suggest that a fundamental re-assessment of where and how vasopressin, and perhaps other hormones, acts in the kidney may be required.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1997

Osmoregulation of plasma vasopressin in three cases with adrenal insufficiency of diverse etiologies.

Neurohypophyseal function was studied by hypertonic saline infusion with plasma vasopressin measurement in 3 patients with adrenal insufficiency before and after cortisol replacement. Although each patient had different causes of adrenal insufficiency, all showed impaired water excretion before replacement. The first patient with isolated adrenocorticotropin deficiency had marked hyponatremia and inappropriate vasopressin secretion which was normalized after replacement, indicating vasopressin hypersecretion during hypoadrenocorticism. The second patient had combined anterior and posterior pituitary deficiency due to postpartum hypopituitarism and showed completely absent vasopressin secretion, with her polyuria being masked before cortisol replacement, suggesting a vasopressin-independent intrarenal mechanism of antidiuresis. The third patient with panhypopituitarism due to a pituitary tumor also had preexisting diabetes insipidus with defective vasopressin secretion. In this case, however, plasma vasopressin was found to be elevated when adrenal insufficiency and hyponatremia subsequently developed. Together, these results indicate that vasopressin hypersecretion does occur during adrenal insufficiency, but that the accompanying urinary diluting defect may be attributable either to vasopressin-dependent or to vasopressin-independent mechanisms.

Adrenal Insufficiency↗