Adrenotensin: An ADM gene product with the opposite effects of ADM

The purpose of the present study was to investigate the effects of putative products of the ADM gene, other than ADM including, prodepin, proADM_45–92 and proADM_153–185 on cat pulmonary arterial (PA) rings with or without precontraction with U46619. Addition of proADM_153–185 (3×10⁻¹⁰−10⁻⁶M) increased tension in a concentration-dependent manner in cat PA rings without precontraction. When vessels were precontracted with U46619, ADM(3×10⁻¹⁰−10⁻⁶M) produced a concentration-dependent vasorelaxant response, whereas proADMus-iss produced a weak concentration-dependent contractile response. Prodepin and proADM_45–92 up to 10⁻⁶M had no activity on PA rings. Since proADM_{1531̄85}, similar to ADM, would be expected to be released in free form following endopeptidase-induced cleavage, the present data suggest proADM undergoes proteolytic processing to release peptides with divergent vascular effects.Thus, the present data also suggest that proADM_153–185 may represent a novel product of the ADM gene and term this putative new substance “adrenotensin”.     

The effect of adrenomedullin on the isolated heart

A novel peptide found in human blood, adrenomedullin (ADM), has been shown to have systematic vasodepressor activity in the rat. However, the direct effects of ADM on cardiac function are unknown. Results of the present study demonstrate that ADM_13–52 possesses marked systemic vasodepressor activity in the anesthetized rat. Although ADM_13–52 modestly decreased peak systolic pressure (PSP) indicating mild negative inotropic activity, the present data suggest that bolus administration of ADM decreases systemic arterial pressure by dilating the systemic vasculature. The present data also suggest that only a portion of the ADM molecule is necessary to produce systemic vasodilation.     

Comparative effects of adrenomedullin,an adrenomedullin analog,and CGRP in the pulmonary vascular bed of the cat and rat

Responses to synthetic human adrenomedullin (ADM), a novel hypotensive peptide initially isolated from human pheochromocytoma cells, an ADM analog (ADM_15–52), and a structurally related peptide, calcitonin gene-related peptide (CGRP), were compared in the pulmonary vascular bed of the cat and rat under constant flow conditions. When tone was increased with U46619, intraarterial injections of ADM (0.03–0.3 nmol), ADM_15–52 (0.03–0.3 nmol), and of CGRP (0.03–0.3 nmol) caused dose-related decreases in pulmonary arterial perfusion pressure. When the relative vasodilator activity of the peptides was compared on a nmol basis, ADM was approximately 10-fold more potent in the cat than in the rat, whereas vasodilator responses to CGRP were very similar in both species. CGRP was slightly more potent than ADM in the rat, whereas ADM was slightly more potent than CGRP in the cat. ADM and ADM_15–52 had similar pulmonary vasodiltor activity in the cat, whereas the full sequence peptide was slightly more potent than ADM_15–52 in the rat. The present data demonstrate that ADM has significant vasodilator activity in the pulmonary vascular beds of the cat and of the rat, and that the relative potency of the vasodilator effects of ADM and ADM_15–52 are different in the two species.     

Agmatine: A novel endogenous vasodilator substance

The purpose of the study was to investigate the effects of agmatine, an endogenous clonidine-displacing substance (CDS), on systemic hemodynamics in the anesthetized rat. Bolus intravenous (i.v.) injections of agmatine decreased systemic arterial pressure (SAP) and systemic vascular resistance in a dose-dependent manner. The development of acute tachyphylaxis to the systemic vasodepressor response to agmatine did not induce cross-tachyphylaxis to the systemic vasodepressor responses to bradykinin, isoproterenol and nitroglycerin. The present data demonstrate agmatine, as a CDS and agonist for imidazoline (I) receptors, possesses marked systemic vasodilator activity in the rat. The present data suggest that activation of I receptors may represent a novel mechanism of vasodilation in vivo.     

Hemopressin, a hemoglobin fragment, dilates the rat systemic vascular bed through release of nitric oxide

The present study was undertaken to investigate the effects of intravenous (i.v.) administration of rat hemopressin (rHP), 30-1000 microg/kg, on systemic arterial pressure (SAP), cardiac output (CO) and systemic vascular resistance (SVR) in the anesthetized rat. Bolus i.v. injections of rHP produced mild decreases in SAP that were dose-dependent. Since CO was not altered, the decreases in SAP reflect reductions in SVR. The systemic vasodilator response to rHP was not subject to tachyphylaxis. The systemic vasodilator response to rHP was abolished by L-nitro-arginine methylester (L-NAME) but was not altered by meclofenamate. In addition, rHP lacked direct contractile and relaxant activity on isolated rat aortic rings (AA) and pulmonary arterial rings (PA). The present data suggest rHP dilates the rat systemic vascular bed through the endogenous release of nitric oxide (NO) independent of the formation of cyclooxygenase products including prostacyclin. It is possible rHP acts as an endogenous vasodilator substance to regulate local blood flow during clinical states of altered red cell turnover, microvascular disease and hemolysis.     

L-Name modulates responses to adrenomedullin in the hindquarters vascular bed of the rat

Responses to synthetic human adrenomedullin (ADM), a novel hypotensive peptide recently discovered in human pheochromocytoma cells, and calcitonin gene-related peptide (CGRP), a structurally related peptide, were investigated in the hintquarters vascular bed of the rat. Under conditions of controlled hintquarters blood flow, intraarterial injections of ADM (0.01–0.3 nmol) and of CGRP (0.03–0.3 nmol) caused dose-related decreases in hindquarters perfusion pressure and decreases in systemic arterial pressure. Following administration of the nitric oxide synthase inhibitor, N^ω-nitro-L-arginine methyl ester (L-NAME), hindquarters vasodilator and systemic depressor responses to ADM were significantly decreased, whereas L-NAME did not significantly decrease the vasodilator response to CGRP in either the hindquarters or systemic vascular beds. Following administration of the cyclooxygenase inhibitor, meclofenamate, vasodilator responses to ADM and to CGRP were not significantly decreased. When the relative vasodilator activity of the two peptides was compared on a nmol basis, responses to ADM were similar to responses with CGRP in the hindquarters vascular bed, whereas ADM was 30–100 fold less potent than CGRP in decreasing systemic arterial pressure. The present data demonstrate that ADM has significant vasodilator activity in the hindquarters vascular bed of the rat, that hindquarters vasodilator and systemic vasodepressor responses to ADM, but not to CGRP, are dependent upon the release of nitric oxide from the endothelium.     

Inhibition of prostaglandin F2α-induced reflex bradycardia and hypotension by meclofenamic acid

Intravenous injection of prostaglandin F_2α (4–15 μg/kg, i.v.) produces an increase in pulmonary arterial pressure in conjunction with reflex bradycardia and hypotension in the anesthetized cat. Meclofenamic acid (30 mg/kg, i.v.) inhibited the bradycardia and the reflex contribution to the systemic hypotension. Neither the PGF_2α-induced pulmonary vasoconstriction nor the direct systemic vasodilator actions of PGF_2α were blocked by meclofenamate. In addition, the reflex responses caused by i.v. veratrine and 5-HT were not inhibited by meclofenamate. These results suggest that meclofenamic acid selectively blocks the afferent mechanism by which PGF_2α induces reflex bradycardia and hypotension in the cat.     

Effect of some acute and prophylactic antimigraine drugs on the vasodepressor sensory CGRPergic outflow in pithed rats

AimsThis study analyzed in pithed rats the effect of several acute and prophylactic antimigraine drugs on the CGRPergic vasodepressor sensory outflow, in an attempt to investigate systemic cardiovascular effects in a model unrelated to migraine.Main methodsMale Wistar pithed rats were pretreated with continuous i.v. infusions of hexamethonium (2 μg/kg.min; to block autonomic outflow) and methoxamine (15–20 μg/kg.min; to maintain diastolic blood pressure at around 130 mmHg). Under these conditions, the effect of both electrical stimulation (0.56–5.6 Hz; 50 V and 2 ms) of the spinal cord (T₉–T₁₂) or i.v. bolus injections of exogenous α-CGRP (0.1–1 µg/kg) were studied in animals pretreated with continuous i.v. infusions of sumatriptan (1–100 μg/kg.min), ergotamine (0.18–0.56 μg/kg.min), dihydroergotamine (1–10 μg/kg.min), magnesium valproate (1000–1800 μg/kg.min), propranolol (100–300 μg/kg.min) or their respective vehicles.Key findingsElectrical stimulation of the spinal cord and i.v. bolus injections of exogenous α-CGRP resulted in, respectively, frequency- and dose-dependent decreases in diastolic blood pressure without affecting heart rate. Moreover, the infusions of sumatriptan, ergotamine and dihydroergotamine, but not of magnesium valproate, propranolol or their respective vehicles, dose-dependently inhibited the vasodepressor responses to electrical stimulation. In contrast, sumatriptan (10 μg/kg.min), ergotamine (0.31 μg/kg.min) and dihydroergotamine (3 μg/kg.min) failed to inhibit the vasodepressor responses to exogenous α-CGRP.SignificanceThe above findings suggest that the acute (rather than the prophylactic) antimigraine drugs attenuate the vasodepressor sensory outflow mainly by prejunctional mechanisms. This may be of particular relevance when considering potential cardiovascular adverse effects by acute antimigraine drugs.     

Differences in the central actions of arachidonic acid and prostaglandin F2α between spontaneously hypertensive and normotensive rats

Prostaglandin F_2α (PGF_2α) is one of the most common metabolites of arachidonic acid (AA) in rat brain. When administered intracerebroventricularly (i.c.v.) to rats, both AA and PGF_2α exert dose-related hypertensive, tachycardic and hyperthermic effects. Metabolic alterations in the endogenous formation of some prostaglandins in the brain-stem of spontaneously hypertensive rats (SHR) have been reported. Therefore the central effects of AA and PGF_2α on blood pressure, heart rate and body temperature were studied both in SHR and normotensive Wistar rats (NR) under urethane-anaesthesia. The hypertensive effect of AA i.c.v. (0.01–100 μg/rat) was larger in magnitude in SHR than in NR, but there was no significant difference in the AA-induced changes of heart rate and body temperature between the groups. Pretreatment of NR with sodium meclofenamate (1 mg/rat i.c.v.) antagonised the central effects of AA indicating that these effects are not due to AA itself but to its conversion to prostaglandins. Unlike the effects of AA, the central hypertensive, tachycardic and hyperthermic responses to PGF_2α (0.5–50 μg/rat i.c.v.) were significantly attenuated in SHR. The present results obtained with AA are compatible with the previous assumption that the synthesis of prostaglandins in the brain of SHR might differ from that in NR. The results also demonstrate that the central effects of PGF_2α are reduced in SHR.     

MDL-646, a new synthetic E1-prostaglandin with local protective effects on the gastric mucosa

The gastric protection, diarrheogenic and arterial hypotensive effects of MDL-646, a PGE₁ derivative, have been studied in rats. The compound administered p.o. or i.v. was able to inhibit the maroscopic damage to gastric mucosa produced by noxious stimuli (ethanol and indomethacin). In the stomach perfusion test with the anesthetized rat, intravenously administered MDL-646 reduced histamine- or pentagastrin-stimulated gastric secretion. After intraduodenal administration (i.d.) doses at least 40–50 times greater were necessary for an antisecretory effect. In conscious rats with chronic gastric fistulas, intragastrically administered (i.g.) MDL-646 affected both acid concentration and volume of unstimulated gastric secretion. In experimental models for gastric lesions, DML-646 was much more potent after oral (p.o.) (15–30 times) than after i.v. administration. (ED₅₀ μg/kg: vs. alcohol lesions, 0.05 p.o. and 0.7 i.v.; vs. indomethacin ulcers, 7.0 p.o. and 195 i.v.). Our data would fit the hypothesis that it was a local effect on the gastric mucosa. The mechanism of this effect is not known. The supposed local activity coupled with the antisecretory effects and the good tolerability make it interesting to test MDL-646 as an anti-ulcer agent in man.     

Cardiovascular actions of python bradykinin and substance P in the anesthetized python, Python regius

The cardiovascular actions of python bradykinin (BK) and substance P (SP) have been investigated in the anesthetized ball python, Python regius. Bolus intra-arterial injections of python BK (0.03-3 nmol/kg) produced concentration-dependent increases in arterial blood pressure, heart rate (HR), and cardiac output concomitant with small decreases in systemic resistance and stroke volume. Intra-arterial injection of 3 nmol/kg python BK produced a tenfold increase in circulating concentration of norepinephrine, but epinephrine levels did not change. BK-induced tachycardia was attenuated (>90%) by the beta-adrenergic receptor antagonist sotalol, and the hypertensive response was attenuated (>70%) by the alpha-adrenergic receptor antagonist prazosin, indicating that effects of python BK are mediated at least in part by activation of the extensive network of adrenergic neurons present in vascular tissues. Bolus intra-arterial injections of python SP in the range 0. 01-30 pmol/kg produced concentration-dependent decreases in arterial blood pressure and systemic peripheral resistance concomitant with increases in cardiac output and stroke volume but with only minor effects on HR. The data suggest that kinins play a physiologically important role in cardiovascular regulation in the python.     

Salinicola peritrichatus sp. nov., isolated from deep-sea sediment

A Gram stain-negative, aerobic and rod-shaped bacterium, strain DY22^T, was isolated from a deep-sea sediment collected from the east Pacific Ocean. The isolate was found to grow in the presence of 0–20.0 % (w/v) NaCl and at pH 4.5–8.5; optimum growth was observed with 0.5–2.0 % (w/v) NaCl and at pH 5.0–7.0. Chemotaxonomic analysis showed the presence of ubiquinone-9 as predominant respiratory quinone and C_16:0, C_19:0 ω8c cyclo and C_12:0 3-OH as major cellular fatty acids. The genomic DNA G+C content was determined to be 59.6 mol%. Comparative 16S rRNA gene sequence analysis revealed that the novel isolate belongs to the genus Salinicola. Strain DY22^T exhibited the closest phylogenetic affinity to the type strain of Salinicola salarius with 97.2 % sequence similarity and less than 97 % sequence similarity with respect to other Salinicola species with validly published names. The DNA–DNA reassociation values between strain DY22^T and S. salarius DSM 18044^T was 52 ± 4 %. On the basis of phenotypic, chemotaxonomic and genotypic data, strain DY22^T represents a novel species of the genus Salinicola, for which the name Salinicola peritrichatus sp. nov. (type strain DY22^T = CGMCC 1.12381^T = JCM 18795^T) is proposed.     

Nociceptin receptor activation produces nitric oxide-mediated systemic hypotension

The purpose of the present study was to investigate the effects of L-N5-(1-iminoethyl)ornithine hydrochloride (L-NIO), an inhibitor of nitric oxide (NO) formation, and [Phe1-psi(CH2NH)-Gly2]Nociceptin(1-13)-NH2 (Phe-NOC), a nociceptin receptor antagonist, on the systemic vasodepressor response to nociceptin in the anesthetized rat. The systemic vasodepressor response to bolus intravenous (i.v.) injections of nociceptin was significantly reduced by L-NIO and Phe-NOC. The present data suggest activation of nociceptin receptors dilates the systemic vascular bed through a NO-dependent pathway. These data also demonstrate Phe-NOC is an efficacious and selective nociceptin receptor antagonist in vivo.     

Gastric antisecretory actions of (15S)-15-methyl prostaglandin E2 methyl ester and natural prostaglandin E2 in rhesus monkeys

The gastric antisecretory actions of (15S)-15-methyl prostaglandin E₂ methyl ester (Me-PGE₂) and Prostaglandin E₂ (PGE₂) were evaluated in the unanesthetized gastric fistula rhesus monkey. Secretion was submaximally stimulated by multiple subcutaneous injections of histamine acid phosphate given every hour for four consecutive hours. When a steady-state plateau of gastric secretion was reached, the PG's were administered as a single bolus dose either intravenously (i.v.) or intragastrically (i.g.). Both PG's inhibited histamine-stimulated gastric secretion. The PG's showed greater sensitivity in inhibiting acid concentration while not affecting volume output. Active i.v. and i.g. antisecretory doses of Me-PGE₂ ranged from 3 to 10 μg/kg, while PGE₂ showed significant antisecretory activity at i.v. bolus doses of 30–100 μg/kg and i.g. bolus dose of 1.0 mg/kg. Thus, Me-PGE₂ is estimated to be at least 10 and 300 times more potent than PGE₂ by the i.v. and i.g. administration routes, respectively. These findings indicate that the rhesus monkey shows some similarities to man in responsiveness to gastric secretory inhibition by E-prostaglandins.     

Impact of the hepatic arterial buffer response on splanchnic vascular responses to intravenous adenosine, isoproterenol, and glucagon

Hepatic arteries (HA) and superior mesenteric arteries (SMA) of cats anesthetized with pentobarbital responded to direct intra-arterial infusion of isoproterenol, adenosine, and glucagon with dose-related vasodilation. In response to intravenous infusion, however, the HA failed to dilate significantly, while the SMA dilated thus elevating portal blood flow. The lack of dilation of the HA was due to the HA buffer response to the elevated portal blood flow, that is, elevation of portal flow causes the HA to constrict. When a clamp was used to return SMA flow to control levels during infusion of the drugs, the HA showed significant dilation to all three agents. Thus, HA vascular responses to i.v. drugs can only be assessed if portal flow is known, since the net effect is dependent upon direct action of the drug on the HA as well as the indirect effect of any drug-induced change in portal flow. None of the agents tested altered the magnitude of the HA buffer response obtained during i.v. infusions, but the effects of other agents on the buffer response remain unknown and must be considered in any tests of i.v. administered drugs. Bolus i.v. injections produce results on the HA flow that are uninterpretable.     

Vasorelaxant effect of C16-PAF and C18-PAF on renal blood flow and systemic blood pressure in the anesthetized rat

The renal vasoactive and systemic hypotensive effects of platelet activating factor (C16:0-PAF and C18:1-PAF) were examined in anesthetized male Wistar rats. Bolus injections of C16-PAF (0.5-25 ng/kg) and C18-PAF (2.5-200 ng/kg) into the arterial circulation of the kidney produced increases in renal blood flow (6-15%) before causing dose-dependent systemic hypotension (2-64 mmHg). The dose-response curves for renal blood flow and systemic blood pressure generated by intrarenal C18-PAF administration were approximately 7 fold to the right of the dose-response curves generated by C16-DPAF. Intrarenal injections of vehicle or the biologically inactive enantiomer C16-DPAF (25-200 ng/kg) did not affect renal blood flow or systemic blood pressure. These results suggest that C16:0-PAF is a more potent renal vasodilator and hypotensive lipid than C18:1-PAF.     

Selective antagonism of the systemic vasodepressor response to PGE1 by d,1–11, 15-bisdeoxy PGE1

Several bisdeoxy PGE₁ analogs are potent, competitive antagonists of PGE₁-induced colonic contractions in the gerbil. The efficacy of these analogs in antagonizing PGE₁-mediated systemic vasodepression has not been previously demonstrated. In this study, serial doses of PGs were administered before, during and after infusion of d,1–11, 15-bisdeoxy PGE₁. Bolus injections of PGE₁ (3.0 μk/kg), PGE₂ (3.0 μg/kg) and PGI₂ (0.3 μg/kg) were administered via the right external jugular vein to male Wistar rats. PGE₁, PGE₂ and PGI₂ decreased systemic arterial pressure 41%, 38% and 38%, respectively. The PGE₁ analog was infused (200 μg/kg/min) through the right common carotid artery. The analog itself had no effect on mean systemic arterial pressure, but maximum reversible inhibition (51%) of PGE₁-mediated vasodepression occurred following a 50 minute infusion. No significant effect of the PGE₁ analog was observed on PGE₂ or PGI₂-mediated vasodepression. These data demonstrate the ability to antagonize PGE₁-mediated vasodepression, and to differentiate the vascular responses to PGE₁ and PGE₂ or PGI₂.     

侧脑室注射肾上腺髓质素增加大鼠心血管相关核团中c-fos的表达并激活脑内一氧化氮神经元

本研究利用Fos蛋白和一氧化氮合酶(nNOS)双重免疫组化方法,观察侧腑脑室注射肾上腺髓质素(adrenomedullin,ADM)对大鼠心血管相关核中c-fos表达及一氧化氮神经元的影响,以探讨ADM在中枢的作用部位并研究其在中枢的作用是否有NO神经元参与。侧脑室注射ADM(1nmol／kg,3nmol／kg)诱发脑干的孤束核、最后区、蓝斑核、臂旁核和外侧巨细胞旁核,下丘脑的室旁核、视上核才腹内侧核以及前脑的中央杏仁核和外侧缰核等多个部位的心血管中枢出现大量Fos样免疫反应神经元。侧脑室注射ADM(3nmol／kg),引起脑干的孤束核、外侧巨细胞旁核,下丘脑的室旁核、视上核内的Fos-nNOS双标神经元增加;ADM(1nmol／kg)亦可引起室旁核、视上核内的Fos-nNOS双标神经元增加,而对孤束核、外侧巨细胞旁核内的Fos-nNOS双标神经元无影响。降钙素基因相关肽(calcitonin gene—related peptide,CGRP)受体拈抗剂CGRP8-37(30nmol／kg)可明显减弱此效应。以上结果表明,ADM可兴奋脑内多个心血管相关核闭的神经元并激活室旁核、视上核、孤束核及外侧巨细胞核内一氧化氮神经元,此效应可能部分山CGRP受体介导。