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PubMed1983

Vasopressin induces selective desensitization of its mitogenic response in Swiss 3T3 cells.

Prior incubation of quiescent cultures of Swiss 3T3 cells with vasopressin leads to loss of mitogenic stimulation on its subsequent addition in the presence of a synergistic growth factor. This desensitization is selective for vasopressin, requires prolonged incubation (half-maximal desensitization after 12 hr of treatment) for its induction, and is reversed after a 48-hr incubation in the absence of vasopressin. It is elicited by concentrations of vasopressin, and several analogues, similar to those required for stimulation of DNA synthesis. Inhibition of 125I-labeled epidermal growth factor binding and stimulation of 86Rb+ uptake by vasopressin are also selectively decreased in the refractory cells. The vasopressin receptors that mediate mitogenesis in Swiss 3T3 cells are of the pressor type, not coupled to adenylate cyclase. These cells bind [3H]vasopressin in a specific and saturable (Kd = 1 X 10(-8) M) manner. The receptors are down-regulated after prolonged vasopressin treatment; however, this cannot provide a complete explanation of desensitization because cells that are completely refractory to vasopressin retain 60% of their [3H]vasopressin binding sites. Vasopressin refractoriness must therefore occur partly at a post-receptor locus.

Animals↗
PubMed1984

Properties of rat anterior pituitary vasopressin receptors: relation to adenylate cyclase and the effect of corticotropin-releasing factor.

Crude plasma membrane fractions were prepared from female Wistar rat anterior pituitaries. These fractions contained a single population of specific 3H-labeled [8-lysine]vasopressin [( 3H]vasopressin) binding sites with a dissociation of constant (Kd) of 8 +/- 2 X 10(-9) M and maximal binding capacity of 244 +/- 45 fmol/mg of protein. The Kd values for a series of vasopressin structural analogues with selective vasopressor or antidiuretic activities were determined together with the corresponding corticotropin-releasing activities (isolated perfused pituitary cells were used). A good correspondence was found between the two sets of values, suggesting that the detected vasopressin binding sites are the receptors involved in vasopressin-induced corticotropin release. The order of potency of these analogues for the binding to hypophysial receptors was similar to that found for the binding to the receptors involved in the vasopressor response. Corticotropin-releasing factor and angiotensin did not affect vasopressin binding to pituitary membranes. Median eminence extracts inhibited [3H]vasopressin binding with an efficiency very close to that expected from their vasopressin content. Corticotropin-releasing factor activated, and angiotensin inhibited, the adenylate cyclase activity of pituitary membranes. Under the same experimental conditions, vasopressin did not influence adenylate cyclase activity nor did it affect the corticotropin-releasing factor-induced activation. These data support the view that vasopressin is one component of the multifactorial regulation of corticotropin release and that it acts through a cAMP-independent pathway. The potentiation by vasopressin of corticotropin-releasing factor-induced cAMP accumulation in intact cells very likely proceeds through indirect mechanisms, which are not expressed in broken cell preparations.

Adenylyl Cyclases↗
PubMed2000

Regulation of aquaporin-2 trafficking by vasopressin in the renal collecting duct. Roles of ryanodine-sensitive Ca2+ stores and calmodulin.

In the renal collecting duct, vasopressin increases osmotic water permeability (P(f)) by triggering trafficking of aquaporin-2 vesicles to the apical plasma membrane. We investigated the role of vasopressin-induced intracellular Ca(2+) mobilization in this process. In isolated inner medullary collecting ducts (IMCDs), vasopressin (0.1 nm) and 8-(4-chlorophenylthio)-cAMP (0.1 mm) elicited marked increases in [Ca(2+)](i) (fluo-4). Vasopressin-induced Ca(2+) mobilization was completely blocked by preloading with the Ca(2+) chelator BAPTA. In parallel experiments, BAPTA completely blocked the vasopressin-induced increase in P(f) without affecting adenosine 3',5'-cyclic monophosphate (cAMP) production. Previously, we demonstrated the lack of activation of the phosphoinositide-signaling pathway by vasopressin in IMCD, suggesting an inositol 1,4,5-trisphosphate-independent mechanism of Ca(2+) release. Evidence for expression of the type 1 ryanodine receptor (RyR1) in IMCD was obtained by immunofluorescence, immunoblotting, and reverse transcription-polymerase chain reaction. Ryanodine (100 microm), a ryanodine receptor antagonist, blocked the arginine vasopressin-mediated increase in P(f) and blocked vasopressin-stimulated redistribution of aquaporin-2 to the plasma membrane domain in primary cultures of IMCD cells, as assessed by immunofluorescence immunocytochemistry. Calmodulin inhibitors (W7 and trifluoperazine) blocked the P(f) response to vasopressin and the vasopressin-stimulated redistribution of aquaporin-2. The results suggest that Ca(2+) release from ryanodine-sensitive stores plays an essential role in vasopressin-mediated aquaporin-2 trafficking via a calmodulin-dependent mechanism.

Animals↗
PubMed1985

Vasopressin in circulatory control and hypertension.

Recently, there has been an explosion of knowledge on vasopressin, including its neuro-anatomy, biochemistry and physiology. Recent work demonstrates extensive extra-hypothalamic vasopressinergic projections from the SON and PVN. Of particular importance are projections to the cardiovascular medullary centres. Conversely, the SON and PVN receive reciprocal catecholaminergic innervation from autonomic medullary centres. Vasopressin should now be regarded as a peptide hormone with important peripheral effects, as well as a neuropeptide acting as a neurotransmitter or neuromodulator with important CNS actions. The central and peripheral vasopressin systems are not only anatomically differentiated, but, although integrated, may also function independently. There is an important interaction between the central vasopressin system and the autonomic nervous system. Vasopressin has multiple and diverse actions on the cardiovascular system, including direct vasoconstriction, antidiuresis and hence volume control, central actions on cardiovascular neural centres, modulation of the baroreflex and direct cardiac effects. It also acts in concert with the sympathetic nervous system and the renin-angiotensin system as an integrated neurohormonal system in the control of blood pressure. Vasopressin appears to have an important role as a vasoconstrictor agent whenever volume is threatened, such as in dehydration, haemorrhage, adrenal insufficiency and orthostasis. It seems unlikely that vasopressin acts as a direct vasoconstrictor agent in the pathogenesis of any form of experimental or human hypertension. Although plasma vasopressin levels have been reported to be elevated in most forms of hypertension, this correlates best with the severity of hypertension. Furthermore, the levels are not elevated to the pressor range, so that increased vascular reactivity and sensitivity has to invoked. This does not appear to be specific for vasopressin. However, vasopressin may be indirectly involved through volume maintenance or interactions within the CNS. Indeed, its volume retaining properties have probably been underestimated. Whereas in acute situations the vasoconstrictor properties may be of some importance, it is difficult to sustain long-term hypertension without maintenance of an adequate plasma volume. Vasopressin's central actions on the cardiovascular medullary centres, the baroreflex, the autonomic nervous system and catecholamine metabolism may also be involved in some hypertensive processes.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2007

Vasopressin: mechanisms of action on the vasculature in health and in septic shock.

BACKGROUND: Vasopressin is essential for cardiovascular homeostasis, acting via the kidney to regulate water resorption, on the vasculature to regulate smooth muscle tone, and as a central neurotransmitter, modulating brainstem autonomic function. Although it is released in response to stress or shock states, a relative deficiency of vasopressin has been found in prolonged vasodilatory shock, such as is seen in severe sepsis. In this circumstance, exogenous vasopressin has marked vasopressor effects, even at doses that would not affect blood pressure in healthy individuals. These two findings provide the rationale for the use of vasopressin in the treatment of septic shock. However, despite considerable research attention, the mechanisms for vasopressin deficiency and hypersensitivity in vasodilatory shock remain unclear. OBJECTIVE: To summarize vasopressin's synthesis, physiologic roles, and regulation and then review the literature describing its vascular receptors and downstream signaling pathways. A discussion of potential mechanisms underlying vasopressin hypersensitivity in septic shock follows, with reference to relevant clinical, in vivo, and in vitro experimental evidence. DATA SOURCE: Search of the PubMed database (keywords: vasopressin and receptors and/or sepsis or septic shock) for articles published in English before May 2006 and manual review of article bibliographies. DATA SYNTHESIS AND CONCLUSIONS: The pathophysiologic mechanism underlying vasopressin hypersensitivity in septic shock is probably multifactorial. It is doubtful that this phenomenon is merely the consequence of replacing a deficiency. Changes in vascular receptors or their signaling and/or interactions between vasopressin, nitric oxide, and adenosine triphosphate-dependent potassium channels are likely to be relevant. Further translational research is required to improve our understanding and direct appropriate educated clinical use of vasopressin.

Antidiuretic Agents↗
PubMed1983

Effect of vasopressin on prostaglandin excretion in conscious dogs.

A controversy persists around the effect of vasopressin on urinary prostaglandin excretion. In an attempt to explain part of this controversy, in the present study we re-investigated the effect of vasopressin on urinary prostaglandin excretion in conscious dogs after water loading and during hydropenia. In water diuresis, during the administration of arginine vasopressin or 1-deamino-8-D-arginine vasopressin, prostaglandin excretion and urine flow decreased in parallel. Prostaglandin E2 excretion fell from 1086 +/- 454 to 353 +/- 122 and from 754 +/- 216 to 226 +/- 74 pg min-1 as urine flow decreased by 74 and 66% with arginine vasopressin and 1-deamino-8-D-arginine vasopressin, respectively. In hydropenia both arginine vasopressin and 1-deamino-8-D-arginine vasopressin increased prostaglandin E2 excretion (from 85 +/- 15 to 261 +/- 82 pg min-1; and from 115 +/- 33 to 272 +/- 66 pg min-1, respectively), while urine flow remained practically unchanged. The changes in prostaglandin F2 alpha excretion were similar to those observed with prostaglandin E2. Plasma renin activity was reduced during arginine vasopressin infusion but was unaltered during 1-deamino-8-D-arginine vasopressin infusion. These results indicate that, in the conscious dog, urine flow is a major determinant of prostaglandin excretion but they also show that when large changes in urine flow are avoided vasopressin may increase urinary prostaglandin excretion.

Animals↗
PubMed1996

Relationship between vasopressin and opioids in hypoxia induced pial artery vasodilation.

It has been observed that a vasopressin receptor antagonist attenuates hypoxic hyperemia in fetal sheep, whereas methionine enkephalin (Met) and leucine enkephalin (Leu) contribute to hypoxia-induced pial artery dilation in newborn pigs. This study was designed to investigate the relationship between vasopressin and opioids in hypoxia-induced pial artery dilation in the newborn pig by use of the closed cranial window technique. Hypoxia-induced pial artery dilation was attenuated during moderate [arterial Po2 (PaO2) approximately 35 mmHg] and severe hypoxia (PaO2 approximately 25 mmHg) by the vasopressin receptor antagonist, [beta-mercapto-beta beta-cyclopentamethylenepropionyl, 2-O-Me-Tyr2, Arg8]vasopressin (MeAVP, 5 micrograms/kg i.v.; 29 +/- 1 vs. 14 +/- 2 and 37 +/- 2 vs. 18 +/- 2% for moderate and severe hypoxia in absence vs. presence of MeAVP, respectively, n = 7). Hypoxia-induced dilation was accompanied by increased cerebrospinal fluid (CSF) vasopressin concentration (26 +/- 1 vs. 67 +/- 4 and 26 +/- 1 vs. 99 +/- 4 pg/ml for control vs. moderate and control vs. severe hypoxia, n = 5). Vasopressin increased CSF Met (895 +/- 28, 1,147 +/- 63, 1,327 +/- 48, and 1,600 +/- 75 pg/ml for control and 40, 400, and 4,000 pg/ml vasopressin, respectively, n = 7). CSF Leu concentration was similarly increased by vasopressin. Furthermore, MeAVP attenuated the release of Met during moderate hypoxia (910 +/- 38 and 2,682 +/- 49 vs. 911 +/- 38 and 2,110 +/- 84 pg/ml for control and moderate hypoxia in absence and presence of MeAVP, respectively, n = 5). MeAVP had similar effects on hypoxia-induced Leu release. These data show that vasopressin contributes to hypoxia-induced pial artery dilation and that vasopressin increases CSF Met and Leu concentrations. These data also suggest that elevated CSF vasopressin concentrations that occur during hypoxemia result in opioid release, which subsequently contributes to hypoxic pial artery dilation.

Animals↗
PubMed1997

Enhancement by vasopressin of adrenergic responses in human mesenteric arteries.

Vasopressin not only acts directly on blood vessels through V1-receptor stimulation but also may modulate adrenergic-mediated responses in animal experiments in vitro and in vivo. The aim of the present study was to investigate whether subpressor concentrations of vasopressin could modify the constrictor responses to norepinephrine and electrical stimulation of the perivascular nerves in human mesenteric arteries. Human mesenteric artery rings (3-3.5 mm long, 0.8-1.2 mm OD) were obtained from 38 patients undergoing abdominal operations. The arterial rings were suspended in organ bath chambers for isometric recording of tension. Vasopressin (3 x 10(-11) M) enhanced the contractions elicited by electrical stimulation at 2, 4, and 8 Hz (by 100, 100, and 72%, respectively) and produced a leftward shift of the concentration-response curves to norepinephrine (half-maximal effective concentration decreased from 2.2 x 10(-6) to 5.0 x 10(-7) M; P < 0.05) without any alteration in maximal contractions. Vasopressin also potentiated KCl- and calcium-induced contractions. The V1-receptor antagonist 1-[beta-mercapto-beta,beta-cyclopentamethylenepropionic acid-2-O-methyl-tyrosine, 8-arginine]vasopressin (10(-6) M) prevented the potentiation evoked by vasopressin in all cases. The calcium antagonist nifedipine (10(-6) M) did not affect the potentiation of electrical stimulation and norepinephrine induced by vasopressin but abolished KCl-induced contractions. The results suggest that vasopressin, in addition to its direct vasoconstrictor effect, strongly potentiates the responses to adrenergic stimulation and KCl depolarization. Both the direct and indirect effects of vasopressin appear to be mediated by V1-receptor stimulation. The amplifying effect of vasopressin on constrictor responses may be relevant in those clinical situations characterized by increased plasma vasopressin levels.

Adult↗
PubMed1987

Vasopressin activation of phosphatidylinositol metabolism in rat anterior pituitary in vitro and its modification by changes in the hypothalamo-pituitary-adrenal axis.

The ability of vasopressin to stimulate the accumulation of 3H-labelled inositol phosphates was studied in vitro using prelabelled rat anterior pituitary quarters. [8-Arginine] vasopressin activates inositol lipid breakdown in this system in a time- and dose-dependent manner; vasopressin (3 X 10(-7) M) resulted in a 1.8-fold stimulation of inositol phosphate accumulation over control accumulation after 10 min. This response to vasopressin is inhibited by the specific V1 antagonist (CH2)5Tyr(Me)AVP. Both oxytocin and the selective V2 agonist DDAVP also show some agonist activity, but are considerably less potent than arginine vasopressin. Corticotrophin-releasing factor alone had no effect on inositol phosphate production, whilst a high dose given in conjunction with vasopressin resulted in a diminution of the response below that found with the same concentration of vasopressin alone. Anterior pituitaries from vasopressin-deficient Brattleboro rats also show a phosphatidylinositol response to vasopressin. Pituitaries from rats that had been adrenalectomized 4 days earlier showed no increase in inositol phosphate accumulation in response to vasopressin. Daily administration of dexamethasone (40 micrograms/day) reversed this effect of adrenalectomy. This reversal was not seen when dexamethasone (40 micrograms/ml) was added to the incubation medium of adrenalectomized rat pituitary quarters. These results confirm that the rat anterior pituitary contains functional vasopressin receptors capable of activating inositol phospholipid metabolism and that this biochemical response is modified by changes in the hypothalamo-pituitary-adrenal axis.

Adrenalectomy↗
PubMed1996

Role of vasopressin V2 receptor in acute regulation of aquaporin-2.

Aquaporin-2 (AQP-2) has been shown to be a vasopressin-sensitive water channel in collecting duct (CD) cells of the kidney. To prove the role of the vasopressin V2 receptor (V2R) in the regulation of intracellular AQP-2 shuttling, we examined the acute effects of vasopressin and V2R antagonist on the distribution of AQP-2 in the cells. Normal Wistar rats were given continuous infusions of vasopressin, vasopressin V2R antagonist (OPC31260), or both. The kidneys were then processed for immunofluorescent studies with an affinity-purified specific antibody to AQP-2. One hour after the infusion of the V2R antagonist, AQP-2 staining was diffusely distributed in the CD cells from the cortex to the inner medulla. This tendency was not changed by the concomitant infusion with vasopressin. Vasopressin infusion without antagonist, however, induced intensified AQP-2 staining of the apical membrane in the CD cells. The ratio of the fluorescence intensity of the apical to subapical region was determined by confocal laser microscopy. In the inner medulla, this ratio was significantly increased in the vasopressin treatment group (2.26 +/- 0.76) as compared to the V2R antagonist group (1.03 +/- 0.34) and the combined treatment group (0.84 +/- 0.43). The increase in the ratio was also demonstrated in the cortex and the outer medulla in the vasopressin-treated group. In addition, Northern blotting studies clearly revealed that mRNA of AQP-2 in the vasopressin-treated group was increased when compared to the combined treatment animals. Our present results reveal that localization and gene expressions of AQP-2 are acutely regulated via vasopressin V2R.

Animals↗
PubMed2002

Vasopressin induces vascular superoxide via endothelin-1 in mineralocorticoid hypertension.

We have recently reported that endothelin-1 (ET-1), which is increased in the arteries of deoxycorticosterone acetate (DOCA)-salt hypertensive rats, stimulates superoxide production. However, the humoral mechanisms responsible for ET-1-induced superoxide formation in low-renin models of hypertension, such as DOCA-salt hypertension, remain undefined. Vasopressin is known to upregulate vascular preproET-1 gene expression in DOCA-salt rats, an effect that is absent in vasopressin-deficient Brattleboro rats treated with DOCA-salt. The present study tested the hypothesis that vasopressin contributes to ET-1-induced vascular superoxide production in DOCA-salt hypertensive rats. Carotid arterial segments of DOCA, sham (uninephrectomized), or normal (untreated) rats were used for the study. In vitro vasopressin treatment of carotid arteries from normal rats for 24 hours, but not 4 hours, increased both ET-1 and superoxide levels. The increase of vasopressin-induced superoxide was reduced by pretreatment of the vessels with ABT627, a selective ETA receptor antagonist ABT627. Vasopressin, ET-1, and superoxide levels were significant elevated in carotid arteries of DOCA-salt rats compared with sham controls. The selective V1-vasopressin receptor antagonist (beta-Mercapto-beta, beta-cyclopentamethylenepropiony1, O-Me-Tyr2, Arg8 vasopressin, ME-AVP), decreased superoxide both in vasopressin-treated vessels of normal rats and in vessels of DOCA-salt rats, with a concomitant reduction of ET-1 content. These results suggest that vasopressin increases vascular superoxide levels by stimulating ET-1 formation in mineralocorticoid hypertension, and that V1-vasopressin receptors play an important role in this process.

Animals↗
PubMed1986

Does vasopressin sustain blood pressure in conscious spontaneously hypertensive rats?

To investigate the possible role of arginine vasopressin in maintaining high blood pressure of spontaneously hypertensive rats (SHR), the effect of two arginine vasopressin pressor antagonists on mean arterial pressure and the pressor responsiveness to exogenous arginine vasopressin were studied in conscious, freely moving SHR and in Wistar-Kyoto rats (WKY). Intravenous injections of either d(CH2)5Tyr(Me)arginine vasopressin, 10 micrograms/kg, or dPTyr(Me)arginine vasopressin, 20 micrograms/kg, had no effect on mean arterial pressure or heart rate of normohydrated SHR, although both antagonists almost completely abolished the pressor response to exogenous arginine vasopressin. Furthermore, dPTyr(Me)arginine vasopressin was ineffective in eliciting a depressor response, even after 24 or 48 hours of water deprivation. During converting enzyme inhibition with SQ 20881, mean arterial pressure and heart rate remained unchanged following arginine vasopressin blockade in both normohydrated and fluid-restricted animals. alpha-Adrenergic receptor blockade reduced the blood pressure of normohydrated SHR, from 160 +/- 7 to 81 +/- 8 mm Hg. When dPTyr(Me)arginine vasopressin was given during alpha-adrenergic receptor blockade there was a small, transient fall in mean arterial pressure. The pressor responsiveness to exogenous arginine vasopressin was similar in hypertensive and normotensive rats. These results suggest that arginine vasopressin does not function as an important pressor hormone in conscious SHR.

Adrenergic beta-Antagonists↗
PubMed1990

Hyponatremia in rats induces downregulation of vasopressin synthesis.

Hyponatremia due to inappropriate secretion of vasopressin is a common disorder in human pathophysiology, but vasopressin synthesis during hypoosmolality has not been investigated. We used a new method to quantitate synthesis of vasopressin in rats after 3, 7, and 14 d of hyponatremia induced by administering dDAVP (a vasopressin agonist) and a liquid diet. Vasopressin synthesis was completely turned off by 7 d. Vasopressin mRNA levels in the hypothalamus paralleled the reduction in synthesis and were reduced to levels of only 10-15% of the content in control rats. When hyponatremia was corrected by withdrawal of dDAVP, vasopressin mRNA slowly returned to normal over 7 d. The observation that vasopressin synthesis can be so completely turned off leads to several conclusions: under normal physiological conditions the neurohypophysis is chronically upregulated; there must be an osmotic threshold for initiation of vasopressin synthesis (and release); the large store of hormone in the posterior pituitary is essential for vasopressin to be available during times of decreased synthesis; and, finally, some nonosmolar stimulus for synthesis must be present during clinical disorders when vasopressin is secreted (and synthesized) despite hypoosmolality.

Animals↗
PubMed1980

Effects of increases in plasma vasopressin concentration on plasma renin activity, blood pressure, heart rate, and plasma corticosteroid concentration in conscious dogs.

It is known that vasopressin decreases PRA and heart rate and increases blood pressure and plasma corticosteroid concentration. The purpose of this study was to determine the plasma concentration of vasopressin required to produce these effects. Arginine vasopressin was administered iv to five normal conscious dogs as priming injections of 0.1, 0.5, 1.0, 2.5, 5.0, and 10.0 ng/kg, followed by infusions of 0.01, 0.05, 0.1, 0.25, 0.5, and 1.0 ng/kg x min, respectively, for 30 min. These doses produced increases in the plasma vasopressin concentration (+/- SE) of 1.0 +/- 0.8, 2.1 +/- 4.3, 4.3 +/- 1.8, 11.4 +/- 1.0, 19.7 +/- 6.4, and 30.8 +/- 7.8 pg/ml, respectively, from a basal level of 2.7 +/- 0.2 pg/ml. An increase in the plasma vasopressin concentration of 2.1 +/- 0.3 pg/ml suppressed PRA by 19 +/- 5% (P < 0.02); increases of 4.2 +/- 1.8 pg/ml or more suppressed PRA by 34 +/- 12% (P < 0.005). Only the highest dose of vasopressin produced a significant pressor effect (9 +/- 3 mm Hg; P < 0.05) or lowered the heart rate (18 +/- 4 beats/min; P < 0.005). An increase in plasma vasopressin concentration of 19.7 +/- 6.4 pg/ml was required to increase the plasma corticosteroid concentration (1.2 +/- 0.2 to 2.2 +/- 0.4 microgram/dl; P < 0.01); the largest dose of vasopressin increased the plasma corticosteroid concentration from 1.5 +/- 0.1 to 2.4 +/- 0.6 microgram/dl (P < 0.02). Twenty-four-hour water deprivation in the same dogs increased the plasma vasopressin concentration from 2.5 +/- 0.2 to 7.4 +/- 0.6 pg/ml (P < 0.01). Nonhypotensive hemorrhage in another group of dogs increased the plasma vasopressin concentration from 2.5 +/- 0.2 to 47.4 +/- 16.8 pg/ml (P < 0.05). These data indicate that elevations in the plasma vasopressin concentration within the range observed during 24 h of water deprivation and nonhypotensive hemorrhage produced significant decreases in renin secretion and heart rate and elevations in blood pressure and corticosteroid secretion.

Adrenal Cortex Hormones↗
PubMed1981

Characterization of the renal handling of vasopressin in the dog by stop-flow analysis.

The stop-flow technique has been used to characterize the renal handling of vasopressin in the anesthetized dog. To facilitate the measurement of vasopressin in small urine samples by a specific RIA, the plasma vasopressin concentration was elevated by the iv infusion of arginine vasopressin. Under control conditions, the urinary clearance of vasopressin did not differ significantly from the glomerular filtration rate. The data obtained with the stop-flow technique indicate that vasopressin was reabsorbed from or degraded in the proximal nephron and secreted into the distal nephron. Thus, vasopressin excreted in the final urine is the result of glomerular filtration (which is limited to the extent that vasopressin is bound to plasma proteins), proximal reabsorption or degradation of filtered vasopressin, and distal secretion of vasopressin. It is likely that the tubular secretion of vasopressin is an important component of the renal organ clearance of this hormone.

Animals↗
PubMed1983

3H-vasopressin binding to the rat mesenteric artery.

We investigated the binding of 3H-Arg8-vasopressin to membranes from rat mesenteric arteries. Specific binding of 3H-vasopressin was 60-75% of total binding. Binding at 22 C achieved a plateau at 30 min whereas at 4 C binding was significantly slower. Binding was reversible upon addition of 1 microM Arg8-vasopressin after 30 min of incubation. Scatchard analysis indicated a single class of high-affinity binding sites with an equilibrium dissociation constant of 5.1 +/- 0.6 nM and a total binding capacity of 91 +/- 12 fmol/mg protein. Competitive inhibition of 3H-Arg8-vasopressin binding showed an IC50 of 3 nM for Arg8-vasopressin, 14 nM for [I-(beta-mercapto-beta-beta-cyclopentamethylene-propionic, 4-valine, 8-D-arginine]-vasopressin, 31 nM for oxytocin, 52 nM for I-deamino-8-D-arginine-vasopressin, 0.1 microM for [I-deamino-penicillamine, 4-valine, 8-D-arginine]-vasopressin, and 0.8 microM for desglycinamide-deamino-Arg8-vasopressin. Unrelated peptides did not displace 3H-Arg8-vasopressin. We conclude that these binding sites possess characteristics of physiologically relevant vasopressin receptors in vascular smooth muscle of a resistance type vessel.

Animals↗
PubMed1996

Molecular and functional characterization of V1b vasopressin receptor in rat adrenal medulla.

In rat adrenal medulla, PCR experiments reveal the expression of messenger RNA encoding the gene for the V1b vasopressin receptor. Complementary DNA amplified sequences corresponded to the cloned rat pituitary V1b vasopressin receptor. Video microscopy experiments performed on fura-2-loaded adrenal medullary or adrenal glomerulosa cell primary cultures showed that vasopressin dose dependently mobilized intracellular calcium, suggesting that functional vasopressin receptors are expressed in these tissues. The use of d[D-3-Pal]vasopressin, a specific V1b vasopressin agonist, and SR 49059, a specific V1b vasopressin antagonist, revealed that V1b receptors are exclusively expressed in adrenal medulla. Using an indirect immunological approach (plasma membrane localization of dopamine-beta-hydroxylase), we demonstrated that stimulation of rat adrenal medulla V1b receptor leads to catecholamine secretion. More interestingly, PCR experiments performed on rat adrenal medulla RNA revealed that the arginine vasopressin-encoding gene is also expressed in this tissue. In addition, perifusion experiments indicated that [Arg8] vasopressin is released by the adrenal medulla. Together, these data suggest that vasopressin may regulate the adrenal functions by paracrine/autocrine mechanisms involving distinct vasopressin receptor subtypes: V1a in the adrenal cortex and V1b in the adrenal medulla.

Adrenal Medulla↗
PubMed1975

Specificity of oxytocin and vasopressin immunofluorescence.

A total inhibition of immunofluorescence could not be obtained using the technique of preincubating either anti-vasopressin or anti-oxytocin plasmas with their homologous antigens. An alternative test of specificity was therefore developed. Lysine-vasopressin (LVP), arginine-vasopressin (AVP) or oxytocin were covalently bound to CNB-activated agarose beads. These hormone-coupled beads were then either placed immediately on glass slides and treated in the same way as tissue sections for immunofluorescence, or pre-incubated in test-tubes with the antibodies and then prepared for immunofluorescence. Fluorescence was measured quantitatively using a Leitz orthoplan microscope with epi-illumination and a photometer attachment. Without pre-incubation the anti-oxytocin plasmas produced intensive fluorescence on those beads containing their homologous antigen (oxytocin) but only slight fluorescence with the heterologous antigens (AVP or LVP). Anti-vasopressin plasmas produced intensive fluorescence of AVP-, LVP- and oxytocin-containing beads. Because the neurohypophysial hormones were bound to agarose beads, antibodies binding to these hormones could be removed by simple centrifugation. Anti-oxytocin and anti-vasopressin lost their fluorescence capacity after pre-incubation with oxytocin- or vasopressin-containing beads respectively, showing that all the antibodies important for fluorescence were bound to homologous antigens. Pre-incubation of anti-oxytocin or anti-vasopressin with beads coupled to their heterologous hormones completely removed the components binding to the heterologous hormone, leaving antibodies that showed fluorescence only with oxytocin or vasopressin respectively. This purification showed that in contrast to the findings with homologous antigens, not all of the antibody population bound to its heterologous antigen. Using non-purified anti-vasopressin, immunofluorescence was observed in neurohypophyses of homozygous Brattleboro rats. This was evidently due to those antibodies which bind to oxytocin, since the fluorescence was abolished after pre-incubating the antibody-containing plasmas with oxytocin-coupled beads. Immunofluorescence was still observed, however, in the suprachiasmatic nucleus of both Wistar and heterozygous Brattleboro rats, if purified anti-vasopressin was used. This was probably due to either vasopressin storage or production in these hypothalamic cells.

Animals↗