Katsuhiko Noguchi

Cardioprotective Effects of Extracts from Psidium guajava L. and Limonium wrightii, Okinawan Medicinal Plants, against Ischemia-Reperfusion Injury in Perfused Rat Hearts

The aim of this study was to determine whether the medicinal herbs growing in Okinawa and possessing a radical-scavenging activity would exert cardioprotective effects against ischemia-reperfusion injury using isolated perfused rat hearts. Effects of the aqueous extracts from Psidium guajava L. and Limonium wrightii at concentrations having an equipotent radical-scavenging activity on myocardial injury produced by global ischemia followed by reperfusion were tested and were further compared with those of quercetin and gallic acid, major antioxidative components of P. guajava L. and L. wrightii, respectively. Both extracts significantly attenuated ischemic contracture during ischemia and improved myocardial dysfunction after reperfusion. Decreases in high-energy phosphates and increases in malondialdehyde in the reperfused hearts were significantly lessened with both plant extracts. Quercetin and gallic acid also exerted similar beneficial effects. These results indicate that P. guajava L. and L. wrightii both have cardioprotective effects against myocardial ischemia-reperfusion injury in isolated rat hearts, primarily through their radical-scavenging actions.

Effect of 1-week treatment with erythropoietin on the vascular endothelial function in anaesthetized rabbits

Chronic administration of erythropoietin (EPO) is often associated with hypertension in animals and humans. The aim of this study was to estimate whether 1‐week treatment with EPO can affect the vascular endothelial function. Rabbits were given with EPO (400 iu kg−1 s.c.) or saline each other day for 1 week. Hypotensive responses to intravenously given acetylcholine (ACh), endothelium‐independent nitric oxide donors (NOC7, nitroprusside and nitroglycerin) and prostaglandin I2 were tested before and after administration of NG‐nitro‐L‐arginine methyl ester (L‐NAME), a specific nitric oxide synthase inhibitor, under pentobarbitone anaesthesia. Blood haemoglobin concentration in EPO group was significantly higher than that in control group, whereas baseline values of aortic pressure, heart rate and femoral vascular resistance were similar. The dose of ACh (172 ng kg−1) requiring for a 15 mmHg hypotension from the baseline in EPO group was apparently higher than that (55 ng kg−1) in control group. On the contrary, hypotensive responses to NOC7, nitroprusside, nitroglycerin and prostaglandin I2 were comparable between two groups. The extent of ACh‐induced hypotension did not correlate with haemoglobin concentration. L‐NAME significantly inhibited the ACh‐induced vasodilating response in control group but did not in EPO group. In another set of rabbits, the same treatment with EPO also decreased vasodilating responses to carbachol, bradykinin and substance P besides ACh as compared with control group. These results indicate that 1‐week treatment with EPO selectively attenuates depressor responses to endothelium‐dependent vasodilators in anaesthetized rabbits, most likely due to inhibition of endothelial nitric oxide synthase.

Analysis for sites of anticoagulant action of plancinin, a new anticoagulant peptide isolated from the starfish Acanthaster planci, in the blood coagulation cascade.

1. Effects of plancinin, a new anticoagulant peptide, on the human blood coagulation cascade were investigated. 2. Plancinin prolonged both activated partial thromboplastin time and prothrombin time, and it significantly inhibited factor X activation by both intrinsic (factor IXa-factor VIIIa-phospholipids-Ca2+) and extrinsic (factor VIIa-tissue factor-phospholipids-Ca2+) tenase complexes and prothrombin activation by prothrombinase complex (factor Xa-factor Va-phospholipids-Ca2+) to 13.8%, 4.8% and 10.5% of control value, respectively. 3. Results indicate that sites of anticoagulant action of plancinin may be located in activation steps of prothrombin and factor X.

Increasing dihydrobiopterin causes dysfunction of endothelial nitric oxide synthase in rats in vivo

An elevation of oxidized forms of tetrahydrobiopterin (BH(4)), especially dihydrobiopterin (BH(2)), has been reported in the setting of oxidative stress, such as arteriosclerotic/atherosclerotic disorders, where endothelial nitric oxide synthase (eNOS) is dysfunctional, but the role of BH(2) in the regulation of eNOS activity in vivo remains to be evaluated. This study was designed to clarify whether increasing BH(2) concentration causes endothelial dysfunction in rats. To increase vascular BH(2) levels, the BH(2) precursor sepiapterin (SEP) was intravenously given after the administration of the specific dihydrofolate reductase inhibitor methotrexate (MTX) to block intracellular conversion of BH(2) to BH(4). MTX/SEP treatment did not significantly affect aortic BH(4) levels compared with control treatment. However, MTX/SEP treatment markedly augmented aortic BH(2) levels (291.1 ± 29.2 vs. 33.4 ± 6.4 pmol/g, P < 0.01) in association with moderate hypertension. Treatment with MTX alone did not significantly alter blood pressure or BH(4) levels but decreased the BH(4)-to-BH(2) ratio. Treatment with MTX/SEP, but not with MTX alone, impaired ACh-induced vasodilator and depressor responses compared with the control treatment (both P < 0.05) and also aggravated ACh-induced endothelium-dependent relaxations (P < 0.05) of isolated aortas without affecting sodium nitroprusside-induced endothelium-independent relaxations. Importantly, MTX/SEP treatment significantly enhanced aortic superoxide production, which was diminished by NOS inhibitor treatment, and the impaired ACh-induced relaxations were reversed with SOD (P < 0.05), suggesting the involvement of eNOS uncoupling. These results indicate, for the first time, that increasing BH(2) causes eNOS dysfunction in vivo even in the absence of BH(4) deficiency, demonstrating a novel insight into the regulation of endothelial function.

Haemodynamic effects of the crude venom from nematocysts of the box-jellyfish Chiropsalmus quadrigatus (Habu-kurage) in anaesthetized rabbits

Haemodynamic effects of saline-extracted venom from nematocysts isolated from tentacles of the box-jellyfish Chiropsalmus quadrigatus (Habu-kurage) were investigated. In anaesthetized rabbits, i.v. injections of the venom produced hypotension following a transient hypertension. Mean femoral arterial blood flow markedly decreased immediately after the injection and femoral vascular resistance increased. Left ventricular dP/dt remarkably decreased after a transient and small increase, and heart rate decreased. Left ventricular end-diastolic pressure markedly elevated. All of the above changes by 0.2-5 microg/kg of the venom expressed as the amount of protein were seen dose-dependently and occurred without tachyphylaxis. In five of seven animals received an injection of the venom at 10 microg/kg, irreversible cardiac arrest occurred. Changes produced by 1 or 2 microg/kg of the venom were significantly attenuated either by heating the venom at 40 degrees C for 10min or by pretreatment with diltiazem. These results indicate that the venom from Habu-kurage has both vasoconstrictor and cardiodepressive effects, and suggest that these thermolabile actions may be due partly to activation of voltage-dependent calcium channels and probably subsequent calcium-overload.

Uneven Changes In Circulating Blood Cell Counts With Adrenergic Stimulation To The Canine Spleen

1. Responses of splenic diameter measured by sonomicrometry to α‐ and β‐adrenoceptor stimulants were estimated together with simultaneously measured systemic arterial and splenic venous concentrations of red blood cells (RBC), white blood cells (WBC) and platelets (PLT) in anaesthetized dogs.

Effects of an Antihypertensive Agent, Nipradilol, on Isolated Coronary Artery of the Dog

Effects of nipradilol on proximal, middle and distal portions of left coronary arteries of the dog were investigated in vitro. Nipradilol (10(-7)-10(-3) M) produced a concentration-dependent relaxation in helical strips of isolated coronary artery under potassium contracture. The relaxation in the middle portions was most pronounced, it was 10% of the equimolar concentrations of nitroglycerin and significantly greater than that of propranolol. In the proximal portions of the coronary arteries, nipradilol (3 X 10(-8)-3 X 10(-7) M) showed a tendency to augment the contractile responses to norepinephrine; in the middle portions it reversed the relaxant responses to norepinephrine into contractile effects in a concentration-dependent manner. In distal portions, nipradilol significantly decreased the relaxant responses of the strips to norepinephrine. The findings demonstrate direct vasodilating and beta-adrenoceptor blocking actions of nipradilol in isolated coronary arteries of the dog.

Cardiovascular effects of Acanthaster planci venom in the rat: Possible involvement of PAF in its hypotensive effect

Cardiovascular effects of the crowns-of-thorns starfish (Acanthaster planci) venom were examined in rats. The crude venom extracted from the spines of A. planci caused systemic hypotension associated with an increase in heart rate and a decrease in renal cortical blood flow when given i.v. The hypotensive effect of the venom was not inhibited by pretreatment with atropine, indomethacin or aprotinin, but was significantly inhibited by SRI 63-441, a platelet activating factor (PAF) antagonist. The venom caused dose-dependent vasorelaxation of the isolated rat aortic ring preparation precontracted by noradrenaline, an effect which was significantly attenuated by pretreatment with SRI 63-441, methylene blue or parabromophenacyl bromide. Denudation of the endothelium also diminished the vasorelaxing effect of the venom. Both the vasorelaxing and the hypotensive effects showed tachyphylaxis. These results suggest the release of PAF or a PAF-like substance from the endothelium by the venom.

Effect of caffeine contained in a cup of coffee on microvascular function in healthy subjects.

Recent epidemiological studies have demonstrated that coffee drinking is associated with reduced mortality of cardiovascular disease. However, its precise mechanisms remain to be clarified. In this study, we examined whether single ingestion of caffeine contained in a cup of coffee improves microvascular function in healthy subjects. A double-blind, placebo-controlled, crossover study was performed in 27 healthy volunteers. A cup of either caffeinated or decaffeinated coffee was drunk by the subjects, and reactive hyperemia of finger blood flow was assessed by laser Doppler flowmetry. In an interval of more than 2 days, the same experimental protocol was repeated with another coffee in a crossover manner. Caffeinated coffee intake slightly but significantly elevated blood pressure and decreased finger blood flow as compared with decaffeinated coffee intake. There was no significant difference in heart rate between caffeinated and decaffeinated coffee intake. Importantly, caffeinated coffee intake significantly enhanced post-occlusive reactive hyperemia of finger blood flow, an index of microvascular endothelial function, compared with decaffeinated coffee intake. These results provide the first evidence that caffeine contained in a cup of coffee enhances microvascular function in healthy individuals.

Haemodynamic and haematologic effects of Acanthaster planci venom in dogs

This study was designed to examine haemodynamic and haematologic effects of the crown-of-thorns starfish venom (Acanthaster planci venom: APV) in dogs. Severe systemic hypotension, thrombocytopenia and leukopenia were induced by APV (1.0 mg protein/kg i.v.), followed by gradual return to the baseline level within 60 min. Hypotension was presumably caused by two factors: an early decrease in systemic vascular resistance and the large reduction in cardiac output due to reduced ventricular filling. Indomethacin, a cyclooxygenase inhibitor, remarkably suppressed systemic hypotension induced by APV. The peak reduction in systemic pressure was associated with concomitant rise of plasma 6-keto-PGF1 alpha, a major stable metabolite of prostacyclin. Thus, the hypotensive effect of APV may be caused primarily by prostacyclin and/or some vasodilating prostaglandins. In contrast, thrombocytopenia and leukopenia were not affected by cyclooxygenase inhibitor, 5-lipoxygenase inhibitor or platelet activating factor (PAF) receptor antagonist. When APV was administered repeatedly, tachyphylaxis was developed in haemodynamic effects, but not in haematologic effects. These findings suggest that APV-induced hypotensive effects may occur mainly through endogenous production of vasodilating prostaglandins including prostacyclin, although APV-induced thrombocytopenia and leukopenia may be caused by other mechanism(s) unrelated to arachidonate metabolites and/or PAF.