Hideyuki Fujioka

Mechanisms underlying arginine vasopressin-induced relaxation in monkey isolated coronary arteries.

OBJECTIVE The present study was undertaken to examine whether arginine vasopressin (AVP) relaxes primate coronary artery and to analyse the mechanisms of its action in reference to endothelial nitric oxide and AVP receptor subtype. METHODS Isometrical tension responses to AVP and desmopressin were recorded in isolated monkey coronary arteries. RESULTS AVP (10(-9) to 10(-7) mol/l) induced a concentration-related relaxation; endothelium-denudation abolished the response. Treatment with N(G)-nitro-L-arginine, but not the D-enantiomer, abolished the endothelium-dependent relaxation, which was restored by L-arginine. Treatment with SR49059 and [Pmp1,Tyr(Me)2]-Arg8-vasopressin, selective inhibitors of V1 receptor subtype, attenuated the relaxant response to AVP, whereas the relaxation induced by sodium nitroprusside was not affected by SR49059. Desmopressin, a V2 receptor agonist, up to 10(-8) mol/l did not elicit relaxation. CONCLUSIONS It is concluded that AVP-induced monkey coronary arterial relaxation is mediated via nitric oxide synthesized from L-arginine in association with stimulation of V1 receptor subtypes in the endothelium.

Relatively selective neuronal nitric oxide synthase inhibition by 7-nitroindazole in monkey isolated cerebral arteries

The selectivity of 7-nitroindazole in inhibiting endothelial and neuronal nitric oxide synthases (eNOS and nNOS) was investigated by comparing its inhibitory action on relaxations mediated by nitric oxide (NO) in response to stimulation of perivascular nerves and in response to histamine in monkey cerebral artery strips. 7-Nitroindazole at 2 x 10(-5) M moderately attenuated the response to transmural electrical stimulation and to nicotine, but did to alter the endothelium-dependent relaxation in response to histamine in cimetidine-treated strips. Raising the concentration of 7-nitroindazole to 10(-4) M abolished the neurogenic response, partially inhibited the histamine-induced relaxation, but did not affect the response to NO. It is concluded that 7-nitroindazole is a relatively selective nNOS inhibitor; however, at high concentrations, it inhibits eNOS in monkey cerebral arteries.

Ginsenoside potentiates NO-mediated neurogenic vasodilatation of monkey cerebral arteries

The aqueous extract of the Panax ginseng (GE) potentiated the relaxation induced by transmural electrical stimulation or nicotine in monkey cerebral arterial strips denuded of the endothelium and partially contracted with prostaglandin F(2 alpha). The response to electrical stimulation was abolished by tetrodotoxin, whereas that to nicotine was suppressed by hexamethonium. N(G)-nitro-L-arginine abolished both of the neurogenic relaxation. Atropine did not alter the potentiating effect of GE. Relaxations induced by exogenous NO were unaffected by GE. The enhancement by GE, of the neurogenic response, appears to be associated with increment in the synthesis or release of NO from the perivascular nerve. Blockade of muscarinic prejunctional inhibition, superoxide scavenging action and phosphodiesterase inhibition are not involved.

Effects of endothelial impairment by saponin on the responses to vasodilators and nitrergic nerve stimulation in isolated canine corpus cavernosum.

Responsiveness to EDRF‐releasing substances and inhibitory nerve stimulation of canine isolated penile corpus cavernosum with and without saponin treatment were investigated. Histological studies demonstrated that saponin did not detach endothelial cells from underlying tissues, but induced degenerative changes in the endothelial cells selectively. In the cavernous strips contracted with phenylephrine, addition of acetylcholine, sodium nitroprusside, ATP and Ca2+ ionophore A23187 induced relaxations, but substance P and bradykinin did not change the muscle tone. Acetylcholine‐induced relaxation was significantly attenuated but not abolished by NG‐nitro‐L‐arginine (L‐NOARG). L‐arginine restored the response inhibited by L‐NOARG. The L‐NOARG resistant relaxation was not influenced by 1H[1,2,4]oxadiazole[4,3‐a]quinoxalin‐1‐one (ODQ) but was suppressed in the strips contracted with K+. Treatment with saponin abolished the relaxation elicited by acetylcholine and A23187 but did not influence the response to nitroprusside and ATP. The ATP‐induced relaxation was attenuated by aminophylline. Transmural electrical stimulation at 2–20 Hz produced endothelium‐independent relaxations which were abolished by tetrodotoxin and L‐NOARG but unaffected by treatment with saponin. In saponin‐treated cavernous strips, the neurogenic relaxation was not affected by acetylcholine, physostigmine, atropine and vasoactive intestinal peptide (VIP) but was abolished by ODQ. It is concluded that acetylcholine‐induced relaxations are endothelium‐dependent and mediated partly by NO and also by other substances from the endothelium. The endothelium‐independent relaxation to ATP is likely to be mediated by P1 purinoceptors. The function of nitrergic nerve does not seem to be prejunctionally modulated by acetylcholine and VIP.

Neurogenic cerebral vasodilation mediated by nitric oxide.

In cerebral arteries isolated from most of mammals, nerve stimulation produces relaxations in contrast to contractions in peripheral arteries. The relaxant mechanism is found to be non-adrenergic and non-cholinergic, but the neurotransmitter is not clarified until recently. Based on several functional and histological studies with isolated cerebral arteries, nitric oxide (NO) is now considered to be a neurotransmitter of the vasodilator nerve and the nerve has been called a nitroxidergic (nitrergic) nerve. Upon neural excitation, calcium influxed through N-type Ca2+ channels activates neuronal NO synthase, and then NO is produced by the enzyme from L-arginine. The released NO activates soluble guanylate cyclase in smooth muscle cells, resulting in relaxation with a cyclic GMP-dependent mechanism. The functional role and neuronal pathway have also been investigated in anesthetized dogs and Japanese monkeys. The nitroxidergic (nitrergic) nerves innervating the circulus arteriosus, including the anterior and middle cerebral and posterior communicating arteries, are found to be postganglionic nerves originated from the ipsilateral pterygopalatine ganglion and tonically dilate cerebral arteries in the resting condition. Our findings suggest that the nitroxidergic (nitrergic) nerve plays a physiologically important role to maintain a steady blood supply to the brain.

Inhibition by adrenomedullin of amine release from adrenergic nerves in dog mesenteric arteries

Adrenomedullin and calcitonin gene-related peptide (CGRP) inhibited the pressor response to transmural electrical stimulation in perfused isolated canine mesenteric arteries. The response was abolished by treatment with either prazosin or tetrodotoxin. Adrenomedullin-(22-52), an adrenomedullin receptor antagonist, reduced the inhibitory effect of adrenomedullin (10(-10) to 10(-8) mol/l), but did not alter the action of CGRP. CGRP-(8-37), a CGRP(1) receptor antagonist, did not affect the inhibition induced by adrenomedullin, but reversed the CGRP-induced inhibition. In helical strips of the arteries, adrenomedullin (up to 10(-8) mol/l) did not influence the contraction induced by noradrenaline, whereas CGRP attenuated the response. Adrenomedullin decreased the release of noradrenaline from adrenergic nerves elicited by transmural electrical stimulation, but CGRP had no effect. Adrenomedullin-(22-52) reversed the decrease in noradrenaline release induced by adrenomedullin. The adrenomedullin-induced relaxation of vascular strips precontracted with prostaglandin F(2alpha) was suppressed by CGRP-(8-37) but was unaffected by adrenomedullin-(22-52). These findings suggest that adrenomedullin impairs noradrenaline release from adrenergic nerves by acting on adrenomedullin receptors located in the nerve terminals, whereas arterial relaxation caused by adrenomedullin and CGRP is due to activation of CGRP(1) receptors in vascular smooth muscle.

Involvement of CYP3A-derived arachidonic acid metabolite(s) in responses to endothelium-derived K+ channel opening substance in monkey lingual artery

In monkey lingual artery strips partially contracted with prostaglandin F2α, acetylcholine‐induced, concentration‐related relaxations were abolished by removal of the endothelium. The response was not significantly influenced by indomethacin but attenuated by NG‐nitro‐L‐arginine (L‐NOARG); the effect of the nitric oxide (NO) synthase inhibitor was reversed by L‐arginine. The response to acetylcholine resistant to L‐NOARG was suppressed in the strips exposed to high K+ media. Charybdotoxin partially inhibited the relaxation, and the remaining relaxation was abolished by additional treatment with apamin, whereas glibenclamide, iberiotoxin or apamin alone was without effect. Relaxations induced by sodium nitroprusside were not influenced by charybdotoxin. The L‐NOARG‐resistant acetylcholine‐induced relaxation was inhibited by metyrapone, proadifen and 17‐octadecynoic acid, non‐selective cytochrome P450 mono‐oxygenase (CYP) inhibitors, and progesterone and ketoconazole, inhibitors selective to CYP3A. The inhibitors did not affect the nitroprusside‐induced relaxation. Selective inhibitors of other CYP isoforms, such as debrisoquine and lauric acid, did not reduce the response to acetylcholine. Reaction mixture containing human liver microsome rich in CYPs, arachidonic acid and NADPH incubated at 37°C and filtrated relaxed endothelium‐denuded monkey lingual artery strips, used as bioassay tissues. This response was abolished in the strips exposed to high K+ media. The response was also suppressed by combined treatment of the assay tissue with charybdotoxin plus apamin, but was not affected by treatment with iberiotoxin. The reaction mixture co‐incubated with ketoconazole failed to relax the strips. It is concluded that the monkey lingual arterial relaxation dependent on the endothelium is mediated by NO and also by a charybdotoxin plus apamin‐sensitive but iberiotoxin‐insensitive Ca2+‐activated K+ channel opening substance(s) that may be a CYP3A‐derived arachidonic acid metabolite(s).

Mechanisms underlying endothelium-dependent, nitric oxide- and prostanoid-independent relaxation in monkey and dog coronary arteries.

Abstract. We compared the mechanisms of vasorelaxation of acetylcholine and of substance P with reference to K+ channels, and analyzed pharmacologically the nature of endothelium-derived substance(s) other than NO and prostanoids in monkey and dog coronary arteries.Coronary arteries were isolated from monkeys and dogs, and the isometric tension of the artery strips was measured.In canine coronary artery strips treated with indomethacin plus NG-nitro-L-arginine (L-NA) and partially contracted with prostaglandin F2α, acetylcholine induced concentration-related relaxation, which was abolished by removal of the endothelium. The relaxation was markedly suppressed but not abolished in the strips exposed to high K+ media. Charybdotoxin plus apamin potently inhibited the relaxation to the similar extent to that by high K+ media, whereas glibenclamide or iberiotoxin had no effect. The relaxation was markedly inhibited by quinacrine, a phospholipase A2 inhibitor, and ketoconazole, a selective cytochrome P450 (CYP) 3A inhibitor, but not by sulfaphenazole, a selective CYP 2C inhibitor. In contrast to acetylcholine, endothelium-dependent and indomethacin-plus-L-NA-resistant relaxation induced by substance P was not inhibited by high K+ media, charybdotoxin plus apamin, or ketoconazole. Quinacrine and AA861, a 5-lipoxygenase inhibitor, inhibited the relaxation induced by substance P. In monkey coronary artery, acetylcholine-induced relaxation resistant to indomethacin plus L-NA was abolished by endothelial denudation and by treatment with high K+ media, charybdotoxin plus apamin, progesterone and ketoconazole, but was not affected by iberiotoxin or sulfaphenazole. Substance P did not relax monkey coronary arteries. It is concluded that endothelium-dependent, nitric oxide- and prostanoid-independent relaxation induced by acetylcholine in monkey and dog coronary arteries are mediated by charybdotoxin plus apamin-sensitive but iberiotoxin-insensitive Ca2+-activated K+ channel opening substance(s), which may be CYP3A-derived arachidonic acid metabolite(s). Contrasting to the response to acetylcholine, endothelium-dependent, indomethacin-plus-L-NA-resistant relaxation induced by substance P in dog coronary artery is not associated with K+ channel opening, and may be mediated by 5-lipoxygenase product(s).

Mechanism of neurogenic relaxation and modification of the response by enteric substances in isolated dog colon

The mechanisms of neurogenic relaxation in the longitudinal muscle of the isolated canine colon and its modification by enteric substances were investigated. Relaxations induced by transmural electrical stimulation with electrical pulses, nicotine or K+ in the muscle strips contracted with bradykinin and treated with atropine were attenuated but not abolished by NG-nitro-L-arginine (L-NA), and the inhibition was reversed by L-arginine. Oxyhemoglobin and ouabain inhibited the response, whereas K+ channel inhibitors, such as glibenclamide, tetraethylammonium, apamin and charybdotoxin, were without effect. In L-NA-treated strips, stimulation-induced relaxations were reduced by ouabain but not by oxyhemoglobin. Among substances tested, only norepinephrine, ATP, vasoactive intestinal peptide (VIP) and galanin produced relaxations. However, alpha- and beta-adrenoceptor antagonists and aminophylline did not alter the response to nerve stimulation. In the strips made unresponsive to VIP and galanin, stimulation-induced relaxations were not influenced. Indomethacin, calcitonin gene-related peptide, cholecystokinin, peptide YY, substance P and serotonin did not modulate the neurogenic response. It is concluded that the relaxation associated with nerve stimulation is mediated by nitric oxide (NO) synthesized from L-arginine and also by substance(s) activating the electrogenic Na+ pump but not that opening K+ channels. Norepinephrine, ATP, VIP and galanin can be excluded as candidate inhibitory neurotransmitters, and the substances used so far are unlikely to modulate inhibitory nerve function.

Detection of Palmaz-Schatz stent by ultrafast CT.

We present a case of Palmaz-Schatz stent in the anterior descending coronary artery in a patient in whom restenosis occurred repeatedly after balloon angioplasty. The location of the stent was confirmed by ultrafast CT. The Palmaz-Schatz stent is barely visible by fluoroscopy and confirmation of its location by fluoroscopy is difficult after failure of stent delivery. However, ultrafast CT enabled the clear detection of a Palmaz-Schatz stent without artifacts and may be valuable in confirming its location.