Receptor subtype for vasopressin-induced release of nitric oxide from rat kidney

Chronic activation of vasopressin V2 receptor signalling lowers renal medullary oxygen levels in rats

AIM

In the present study, we aimed to elucidate the effects of chronic vasopressin administration on renal medullary oxygen levels.

METHODS

Adult Sprague Dawley or vasopressin-deficient Brattleboro rats were treated with the vasopressin V2 receptor agonist, desmopressin (5 ng/h; 3d), or its vehicle via osmotic minipumps. Immunostaining for pimonidazole and the transcription factor HIF-1α (hypoxia-inducible factor-1α) were used to identify hypoxic areas. Activation of HIF-target gene expression following desmopressin treatment was studied by microarray analysis.

RESULTS

Pimonidazole staining was detected in the outer and inner medulla of desmopressin-treated rats, whereas staining in control animals was weak or absent. HIF-1α immunostaining demonstrated nuclear accumulation in the papilla of desmopressin-treated animals, whereas no staining was observed in the controls. Gene expression analysis revealed significant enrichment of HIF-target genes in the group of desmopressin-regulated gene products (P = 2.6*10(-21) ). Regulated products included insulin-like growth factor binding proteins 1 and 3, angiopoietin 2, fibronectin, cathepsin D, hexokinase 2 and cyclooxygenase 2.

CONCLUSION

Our results demonstrate that an activation of the renal urine concentrating mechanism by desmopressin causes renal medullary hypoxia and an upregulation of hypoxia-inducible gene expression.

Endogenous nitric oxide reduces the efficacy of the endothelin system to maintain blood pressure during high epidural anaesthesia in conscious dogs

BACKGROUND AND OBJECTIVE

During high epidural anaesthesia, endothelin only contributes minimally to blood pressure stabilization. This phenomenon could result from the inhibitory action of nitric oxide on the endothelin system. To clarify this, we studied the interaction between nitric oxide and endothelin during high epidural anaesthesia in conscious dogs, in comparison to the interaction of nitric oxide and vasopressin.

METHODS

Six animals were used in 45 individual experiments randomly arranged as follows: N-omega-nitro-arginine-methylester 0.3-10 mg kg-1 under physiological conditions or during high epidural anaesthesia (lidocaine 1%) and N-omega-nitro-arginine-methylester (l-NAME) 0.3-10 mg kg-1 after preceding endothelin (Tezosentan(R)) or vasopressin (beta-mercapto-beta,beta-cyclo-penta-methylene-propionyl-O-Me-Tyr-Arg-vasopressin) receptor blockade under physiological conditions or during high epidural anaesthesia. During control experiments normal saline was injected either intravenously (n = 5) or into the epidural space (n = 4).

RESULTS

N-omega-nitro-arginine-methylester increased mean arterial pressure dose-dependently in all groups. However, this effect was substantially reduced in the presence of the endothelin receptor antagonist compared to N-omega-nitro-arginine-methylester alone, both under control conditions (7 +/- 3 vs. 21 +/- 3 mmHg; P < 0.05) and during high epidural anaesthesia (17 +/- 3 vs. 30 +/- 1 mmHg; P < 0.05). Blockade of vasopressin showed no similar relationship with N-omega-nitro-arginine-methylester.

CONCLUSIONS

The diminished increase in mean arterial pressure after injection of N-omega-nitro-arginine-methylester only during endothelin receptor blockade indicates that endogenous nitric oxide inhibits the action of endothelin during high epidural anaesthesia and might thus explain the reduced efficacy of endothelin in maintaining blood pressure during high epidural anaesthesia.

Vasopressin for the septic burn patient

BACKGROUND

Exogenous arginine vasopressin (VP) has been increasingly used in the hemodynamic management of critically ill patients with septic shock, but its use in septic burn patients has not been systematically examined.

PURPOSE

To review our experience with the use of VP in septic burn patients.

METHODS

Retrospective review of all patients who received VP at a tertiary care adult regional burn centre. Only patients who strictly met the American College of Chest Physicians/Society of Critical Care Medicine Consensus Criteria for sepsis at the time of VP initiation were analysed.

RESULTS

There were 30 septic burn patients treated on 43 distinct occasions with VP. This group had a mean (+/-S.D.) age of 49+/-19 years, a mean % TBSA burn of 41+/-15% and a 37% incidence of inhalation injury. A significant increase in mean arterial pressure (MAP), a significant decrease in heart rate (HR), and a trend towards increased urine output (UO) occurred following initiation of VP. When VP was added to an existing infusion of norepinephrine (NE), there was a significant NE sparing effect. VP was implicated in the death of one patient who developed diffuse upper gastrointestinal necrosis while on VP. Other complications in patients treated with VP included peripheral ischemia (2), skin graft failure (1) and donor site conversion (1). In all complications, VP had been administered in combination with prolonged NE infusions (mean of 10 microg/min over a mean of 177 h).

CONCLUSION

VP is a useful adjunctive pressor that spares NE requirements in septic burn patients, but its use is not without risks, particularly when VP is combined with sustained moderate to high infusions of NE.

Arginine vasopressin-mediated cardiac differentiation: insights into the role of its receptors and nitric oxide signaling

Despite the existence of a functional arginine vasopressin (AVP) system in the adult heart and evidence that AVP induces myogenesis, its significance in cardiomyogenesis is currently unknown. In the present study, we hypothesized a role for AVP in cardiac differentiation of D3 and lineage-specific embryonic stem (ES) cells expressing green fluorescent protein under the control of atrial natriuretic peptide (Anp) or myosin light chain-2V (Mlc-2V) promoters. Furthermore, we investigated the nitric oxide (NO) involvement in AVP-mediated pathways. AVP exposure increased the number of beating embryoid bodies, fluorescent cells, and expression of Gata-4 and other cardiac genes. V1a and V2 receptors (V1aR and V2R) differentially mediated these effects in transgenic ES cells, and exhibited a distinct developmentally regulated mRNA expression pattern. A NO synthase inhibitor, L-NAME, powerfully antagonized the AVP-induced effects on cardiogenic differentiation, implicating NO signaling in AVP-mediated pathways. Indeed, AVP elevated the mRNA and protein levels of endothelial NO synthase (eNOS) through V2R stimulation. Remarkably, increased beating activity was found in AVP-treated ES cells with down-regulated eNOS expression, indicating the significant involvement of additional pathways in cardiomyogenic effects of AVP. Finally, patch clamp recordings revealed specific AVP-induced changes of action potentials and increased L-type Ca2+ (ICa,L) current densities in differentiated ventricular phenotypes. Thus, AVP promotes cardiomyocyte differentiation of ES cells and involves Gata-4 and NO signaling. AVP-induced action potential prolongation appears likely to be linked to the increased ICa,L current in ventricular cells. In conclusion, this report provides new evidence for the essential role of the AVP system in ES cell-derived cardiomyogenesis.

Vasopressin V1 receptors contribute to hemodynamic and sympathoinhibitory responses evoked by stimulation of adenosine A2a receptors in NTS

Activation of adenosine A2a receptors in the nucleus of the solitary tract (NTS) decreases mean arterial pressure (MAP), heart rate (HR), and renal sympathetic nerve activity (RSNA), whereas increases in preganglionic adrenal sympathetic nerve activity (pre-ASNA) occur, a pattern similar to that observed during hypotensive hemorrhage. Central vasopressin V1 receptors may contribute to posthemorrhagic hypotension and bradycardia. Both V1 and A2a receptors are densely expressed in the NTS, and both of these receptors are involved in cardiovascular control; thus they may interact. The responses elicited by NTS A2a receptors are mediated mostly via nonglutamatergic mechanisms, possibly via release of vasopressin. Therefore, we investigated whether blockade of NTS V1 receptors alters the autonomic response patterns evoked by stimulation of NTS A2a receptors (CGS-21680, 20 pmol/50 nl) in α-chloralose-urethane anesthetized male Sprague-Dawley rats. In addition, we compared the regional sympathetic responses to microinjections of vasopressin (0.1–100 ng/50 nl) into the NTS. Blockade of V1 receptors reversed the normal decreases in MAP into increases (−95.6 ± 28.3 vs. 51.4 ± 15.7 ∫Δ%), virtually abolished the decreases in HR (−258.3 ± 54.0 vs. 18.9 ± 57.8 ∫Δbeats/min) and RSNA (−239.3 ± 47.4 vs. 15.9 ± 36.1 ∫Δ%), and did not affect the increases in pre-ASNA (279.7 ± 48.3 vs. 233.1 ± 54.1 ∫Δ%) evoked by A2a receptor stimulation. The responses partially returned toward normal values ∼90 min after the blockade. Microinjections of vasopressin into the NTS evoked dose-dependent decreases in HR and RSNA and variable MAP and pre-ASNA responses with a tendency toward increases. We conclude that the decreases in MAP, HR, and RSNA in response to NTS A2a receptor stimulation may be mediated via release of vasopressin from neural terminals in the NTS. The differential effects of NTS V1 and A2a receptors on RSNA versus pre-ASNA support the hypothesis that these receptor subtypes are differentially located/expressed on NTS neurons/neural terminals controlling different sympathetic outputs.

The effects of arg-vasopressin on osteoblast-like cells in endothelial nitric oxide synthase-knockout mice and their wild type counterparts

In the present study, we investigated whether nitric oxide (NO) could be involved in the effects of arg-vasopressin (AVP) on osteoblast-like cells. Cells derived from endothelial nitric oxide synthase (eNOS)-knockout mice and their wild type (WT) counterparts, and an osteosarcoma cell line (SaOS-2) were used. AVP (10-100 pmol/l) increased proliferation of osteoblast-like cells from WT mice. The effect was abolished by an AVP V1-receptor antagonist. AVP increased proliferation of cells from eNOSKO mice only when a NO donor, SNAP, was added. A nitric oxide synthase-inhibitor, L-NAME, antagonized the increase in cell proliferation in response to AVP in SaOS-2 cells. In conclusion, this study indicates that NO is involved in the effects of AVP on cell proliferation in osteoblast-like cells.

Endothelium-dependent, vasopressin-induced contractions in rabbit renal arteries

OBJECTIVES

To identify and quantify the stimulatory and inhibitory activity of endothelial factors on Arginine vasopressin (AVP)-induced contractions.

METHODS

In a standard organ bath set-up for isometric force recording, rabbit isolated renal artery rings were exposed to cumulative concentrations of AVP. Experiments were performed in the presence or absence of functional endothelium, or in the presence of N-Nitro-L-Arginine 10 microM (L-NNA) (NO-synthase inhibitor).

RESULTS

Arginine vasopressin induced a maximal contractile response of 6.5 +/- 0.1 mN in vessels with and 6.3 +/- 0.3 mN in vessels without endothelium. The preincubation with l-NNA resulted in an enhanced response to AVP of 12.6 +/- 0.8 mN (P < 0.05). The augmentation of the AVP induced contractile response by NOS inhibition, which was not seen in preparations after the removal of the endothelium, suggests an endothelium dependent factor that is co-released with NO. The unknown nature of this endothelium dependent contractile factor was not influenced by indomethacin 100 microM (cyclooxygenase inhibitor), meclofenamic acid 20 microM (cyclooxygenase and lipoxygenase inhibitor), or bosentan 100 microM (endothelin antagonist). Charybdotoxin 0.1 microM (inhibitor of Ca2+ -activated K+ channels) specifically increased the contractile force in preparations with and without endothelium, or in the presence of l-NNA to 11.2 +/- 0.4 mN, 14.0 +/- 0.8 mN, and 19.0 +/- 0.8 mN, respectively (P < 0.05 compared with the experiments without charybdotoxin). SR 49059 (vasopressin 1 receptor (V1) antagonist) antagonized the effects of AVP, whereas SR 121463 B (V2 antagonist) was ineffective. In contrast to the results obtained with AVP, desmopressin (V2 agonist) showed no effect.

CONCLUSION

The completely V1 dependent AVP-induced contraction is partly inhibited by the stimulated release of NO. This was only demonstrable in endothelium intact vessels in the presence of l-NNA and not after removal of the endothelium. This strongly suggests the involvement of an unknown endothelium V1 receptor dependent contractile factor that is not influenced by inhibition of the prostaglandin, lipoxygenase, or endothelin pathway, or by blockade of the V2 receptor.

Nitric oxide in responses of regional kidney blood flow to vasoactive agents in anesthetized rabbits

To determine whether differential release of nitric oxide underlies the diversity of regional kidney blood flow responses to vasoactive agents, this study examined how nitric oxide synthase blockade with IV N(G)-nitro-L-arginine (L-NNA), and also IV L-NNA plus co-infusion of glyceryl trinitrate, affected responses to renal arterial boluses and infusions of vasoactive agents. L-NNA, but not vehicle, or L-NNA plus glyceryl trinitrate, increased mean arterial pressure (35%) and reduced renal blood flow (20%), cortical perfusion (11%), and medullary perfusion (54%). L-NNA plus glyceryl trinitrate, but not L-NNA alone, blunted renal vasodilatation in response to boluses of bradykinin and acetylcholine, abolished increased medullary perfusion after bolus angiotensin II, and enhanced reductions in medullary perfusion, and to a lesser extent those in renal blood flow and cortical perfusion, during norepinephrine infusion. Neither L-NNA, nor L-NNA plus glyceryl trinitrate, affected responses to infusions of angiotensin II, [Phe(2),Ile(3),Orn(8)]-vasopressin, or endothelin-1. The data indicate roles for nitric oxide in angiotensin II-induced increases in medullary perfusion and in protecting medullary perfusion from norepinephrine-induced vasoconstriction. However, differential engagement of nitric oxide synthase cannot completely account for the diversity of responses of regional kidney perfusion to vasoactive agents. Effects of nitric oxide synthase blockade on renal vascular responses to vasoactive agents were revealed only when glyceryl trinitrate was co-infused to restore resting nitrergic vasodilator tone. This may reflect interactions between nitric oxide and other vasodilator mediators, in modulating renal hemodynamic responses to vasoactive agents.

Increased contraction to noradrenaline by vasopressin in human renal arteries

OBJECTIVE

Arginine vasopressin (AVP) not only acts directly on blood vessels through vasopressin V1 receptor stimulation but also may modulate adrenergic-mediated responses in animal experiments. The aim of the present study was to assess whether subpressor concentrations of AVP could contribute to an abnormal adrenergic contractile response of human renal arteries.

METHODS

Renal artery rings were obtained from 27 patients undergoing nephrectomy. The rings were suspended in organ bath chambers for isometric recording of tension.

RESULTS

AVP (10(-10) mol/l) and the vasopressin V1 receptor agonist [Phe2, Orn8]-vasotocin (10(-10) mol/l) produced a leftward shift of the concentration-response curve to noradrenaline (half-maximal effective concentration decreased from 1.1 x 10(-6) mol/l to 3.1 x 10(-7) mol/l). The enhancement of noradrenaline-induced contractions was inhibited by the vasopressin V1 receptor antagonist d(CH2)5Tyr(Me)AVP (10-8 mol/l) and unaffected by endothelium removal or pretreatment with the inhibitor of nitric oxide (NO) synthase NG-monomethyl-l-arginine (l-NMMA). The vasopressin V2 receptor agonist 1-desamino-8-D-arginine vasopressin (dDAVP) (10(-10)-10(-8) mol/l) did not modify contractile responses to noradrenaline. In the presence of the dihydropyridine calcium antagonist nifedipine (10(-6) mol/l), vasopressin failed to enhance the contractile response to noradrenaline.

CONCLUSIONS

The results demonstrate that subpressor concentrations of vasopressin potentiate the contractile effects of noradrenaline without intervention of the NO system. The effects appear to be mediated by vasopressin V1 receptor stimulation, which brings about an increase in calcium entry through dihydropyridine-sensitive calcium channels.

Vasopressin and shock

Vasopressin (antidiuretic hormone) is emerging as a potentially major advance in the treatment of a variety of shock states. Increasing interest in the clinical use of vasopressin has resulted from the recognition of its importance in the endogenous response to shock and from advances in understanding of its mechanism of action. From animal models of shock, vasopressin has been shown to produce greater blood flow diversion from non-vital to vital organ beds (particularly the brain) than does adrenaline. Although vasopressin has similar direct actions to the catecholamines, it may uniquely also inhibit some of the pathologic vasodilator processes that occur in shock states. There is current interest in the use of vasopressin in the treatment of shock due to ventricular fibrillation, hypovolaemia, sepsis and cardiopulmonary bypass. This article reviews the physiology and pharmacology of vasopressin and all of the relevant animal and human clinical literature on its use in the treatment of shock following a MEDLINE (1966-2000) search.

Enhanced renal vasoconstrictor responsiveness to vasopressin after renal denervation

Previous studies from our laboratory and others demonstrated a relative insensitivity of the renal vasculature to the vasoconstrictor influences of arginine vasopressin (AVP). Experiments were therefore conducted to identify the possible roles of renal sympathetic withdrawal and V2-vasopressinergic receptor-mediated vasodilation in this response. Renal hemodynamic responses to AVP or saline vehicle were examined in the presence or absence of either selective V1-vasopressinergic-receptor blockade or nonselective vasopressinergic-receptor antagonism in conscious intact and renal-denervated rats. Our results indicate that renal denervation profoundly augmented AVP-induced renal vasoconstriction, whereas no differences were observed in the responses to V1-receptor blockade versus combined V1, V2-receptor antagonism. These findings are consistent with a role for renal sympathoinhibition in mediating the relative insensitivity of the renal bed to the vasoconstrictor effects of AVP in conscious rats but do not support a modulatory influence of V2-receptor activity in this response.

AVP inhibits LPS- and IL-1beta-stimulated NO and cGMP via V1 receptor in cultured rat mesangial cells

The present study examined how arginine vasopressin (AVP) affects nitric oxide (NO) metabolism in cultured rat glomerular mesangial cells (GMC). GMC were incubated with test agents and nitrite, and intracellular cGMP content, inducible nitric oxide synthase (iNOS) mRNA, and iNOS protein were analyzed by the Griess method, enzyme immunoassay, and Northern and Western blotting, respectively. AVP inhibited lipopolysaccharide (LPS)- and interleukin-1beta (IL-1beta)-induced nitrite production in a dose- and time-dependent manner, with concomitant changes in cGMP content, iNOS mRNA, and iNOS protein. This inhibition by AVP was reversed by V1- but not by oxytocin-receptor antagonist. Inhibition by AVP was also reproduced on LPS and interferon-gamma (IFN-gamma). Protein kinase C (PKC) inhibitors reversed AVP inhibition, whereas PKC activator inhibited nitrite production. Although dexamethasone and pyrrolidinedithiocarbamate (PDTC), inhibitors of nuclear factor-kappaB, inhibited nitrite production, further inhibition by AVP was not observed. AVP did not show further inhibition of nitrite production with actinomycin D, an inhibitor of transcription, or cycloheximide, an inhibitor of protein synthesis. In conclusion, AVP inhibits LPS- and IL-1beta-induced NO production through a V1 receptor. The inhibitory action of AVP involves both the activation of PKC and the transcription of iNOS mRNA in cultured rat GMC.

Discovery of novel selective hypotensive vasopressin peptides that exhibit little or no functional interactions with known oxytocin/vasopressin receptors

1. Arginine-vasopressin (VP) has both vasoconstricting and vasodilating action. We report here the discovery of four novel selective hypotensive VP analogues: d(CH2)5[D-Tyr(Et)2,Arg3,Val4]AVP; d(CH2)5[D-Tyr(Et)2,Lys3,Val4]AVP and their iodinatable Tyr-NH2(9) analogues. 2. Bioassays in rats for activities characteristic of neurohypophysial peptides showed that the four VP peptides possessed little or no V1a, V2 or oxytocin (OT) receptor agonistic or antagonistic activities. 3. In anaesthetized rats, these peptides (0.05-0.10 mg kg(-1) i.v.) elicited a marked fall in arterial blood pressure. 4. Blockade of cholinoceptors, adrenoceptors and bradykinin B2 receptors, and inhibition of prostaglandin synthesis had little effect on their vasodepressor action. 5. Classical V1a, V2 and OT receptor antagonists did not block the vasodepressor response. 6. L-NAME, 0.2 mg kg(-1) min(-1), markedly suppressed the hypotensive response to ACh but not the vasodepressor response to the hypotensive VP peptides. However, the duration of the vasodepressor response was shortened. Very high doses of L-NAME attenuated both the vasodepressor response and the duration of action. 7. These findings indicate that the vasodepressor action of these VP peptides is independent of the peripheral autonomic, bradykinin and PG systems and is not mediated by the known classical OT/VP receptors. NO does not appear to have an important role in their vasodepressor action. 8. The discovery of these novel VP peptides could lead to the development of new tools for the investigation of the complex cardiovascular actions of VP and the introduction of a new class of hypotensive agents. The two iodinatable hypotensive VP peptides could be radiolabelled as potential markers for the localization of the receptor system involved.

Arginine vasopressin inhibits interleukin-1 beta-stimulated nitric oxide and cyclic guanosine monophosphate production via the V1 receptor in cultured rat vascular smooth muscle cells

BACKGROUND

It has been reported that various vasoactive substance modulate cytokine stimulated nitric oxide (NO) production in many cell types.

OBJECTIVE

To examine the effects of arginine vasopressin (AVP) on the production of NO and cyclic GMP (cGMP), and on inducible nitric oxide synthase (INOS) in cultured rat vascular smooth muscle cells (VSMC).

DESIGN

Because VSMC possess the V1 receptor which clauses vascular contraction and respond to various cytokines for producing NO, we used rat VSMC and selected interleukin-1 beta (IL-1 beta) as a potent stimulator of NO production among various cytokines. We also measured cGMP production, which is the final mediator of NO-induced vascular relaxation, in order to evaluate the physiologic meaning of the present study.

METHODS

VSMC were incubated with test agents for 24 h except for a time-course study. Nitrite as a stable end product of NO was measured in the medium. Intracellular cGMP contents were assayed by enzyme immunoassay. INOS messenger RNA expression was analyzed by Northern blotting.

RESULTS

AVP inhibited IL-1 beta-induced nitrite production in a dose- and time-dependent manner with concomitant changes in intracellular cGMP contents. On the other hand, AVP did not affect nitrite and cGMP production in the absence of IL-1 beta. Inhibition of nitrite and cGMP production by AVP was reversed by administration of the specific V1 receptor antagonist [1-(beta-mercapto-beta,beta- cyclopentamethylene propionic acid), 2-(O-methyl)-tyrosine] -Arg8-vasopressin) but not by the oxytocin (OXT) receptor antagonist [d(CH2(5)), TyrMe2, Orn8]-Vasotocin. Administration of the V1 receptor antagonist or OXT receptor antagonist alone did not affect IL-1 beta-stimulated nitrite and cGMP production. Although administration of AVP inhibited IL-1 beta-induced INOS messenger RNA expression, administration of the V1 receptor antagonist but not of the OXT receptor antagonist reversed this inhibition.

CONCLUSION

It is suggested that AVP inhibits IL-1 beta-induced NO and cGMP production via the V1 receptor but not via the OXT receptor in VSMC. AVP can cause vascular contraction not only through direct action but also through indirect action by inhibiting NO production under some inflammatory conditions.