Kanako Miyagi

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.

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.

Role of High Glycogen in Underperfused Diabetic Rat Hearts with Added Norepinephrine

The relationship between cardiac dysfunction and glycogen level and/or duration of diabetes was examined during underperfusion (2 ml/min/g heart weight) with 10(-6)M norepinephrine (NE) in isolated 1- and 6-week streptozotocin-diabetic rat (diabetes mellitus, DM) hearts and non-DM hearts. Glycogen levels in non-DM and 1- and 6-week DM hearts were 85, 120, and 206 mumol/g dry weight, respectively, in the subendocardium. About 13 min after the start of underperfusion with NE, the diastolic tension in 1-week DM hearts began to increase when the glycogen level had decreased to half; in 6-week DM hearts, glycogen decreased more markedly without greater lactate accumulation, but these glycogen levels were still higher (104 mumol/g dry weight) than those in 1-week DM hearts and the diastolic tension did not increase. About 17 min after the onset of underperfusion, the glycogen decreased to the 13-min level of 1-week DM hearts (64 mumol/g dry weight) and the diastolic tension began to increase. Until 20 min after the onset of underperfusion, the injury was less in 6-week than in 1-week DM hearts. However, after 60-min underperfusion with NE, when the glycogen level was markedly low in both groups ( < 20 mumol/g dry weight), diastolic tension was increased twice as much in 6-week DM as in 1-week DM hearts and was related to the decreased subendocardial ATP level. The results indicate that the markedly high glycogen content in diabetic hearts probably helps delay the start of the increase in left ventricular (LV) stiffness during underperfusion with NE. Ultimately, however, the degree of the injury depends on the duration, i.e., the severity, of the diabetes.

Effects of glutathione S‐transferase inhibitors on nitroglycerin action in pig isolated coronary arteries

1. The present study was designed to clarify the role of glutathione S‐transferase (GST) in the vasorelaxation response and development of tolerance to nitroglycerin (GTN) using GST inhibitors.

Acceleration of stiffness in underperfused diabetic rat hearts by glyburide, a KATP channel blocker, and its prevention by levcromakalim and insulin

OBJECT To clarify the role of the KATP channels in myocardial dysfunction during underperfusion with norepinephrine (NE) in the diabetic heart, particularly the heart treated with sulphonylurea derivatives. METHODS Isolated 6-week streptozotocin-diabetic rat hearts with a balloon in the left ventricle (LV) were paced and perfused with normoxic Krebs-Henseleit solution. Agents were infused for 15-25 min before as well as during 60-min underperfusion (2 ml/min/g heart weight) with 10(-6) M NE. Regional myocardial flow distribution was measured using dye microspheres. The effects of ex vivo glyburide (10(-6) M, a sulphonylurea anti-diabetic drug and a specific KATP channel inhibitor) on contractile dysfunction and abnormal regional myocardial energy metabolism were examined during underperfusion with NE in the absence of presence of levcromakalim (10(-4) M, a selective K+ channel opener) and insulin (2 mU/min/g heart weight). RESULTS The flow rate was greater in the LV subendocardium than the subepicardium during normal perfusion, and smaller at 60-min underperfusion with NE. The LV diastolic tension and pressure during underperfusion with NE increased more rapidly in the presence of glyburide. At 60-min underperfusion with NE, the diastolic pressure elevation was still higher in the glyburide-treated heart, and decreases in tissue ATP, creatine phosphate (CP), energy charge, phosphorylation potential and CP/inorganic phosphate (P(i)) ratio, and increases in AMP, P(i) and lactate were more marked in the glyburide-treated heart, particularly in the LV subendocardium. Thus, ex vivo glyburide enhanced the increase in LV stiffness and abnormal myocardial energy metabolism during underperfusion with NE in diabetic hearts. These changes were reduced by levcromakalim to the level during underperfusion with NE without glyburide. Insulin did not prevent the glyburide-induced earlier exacerbation of the increase in LV stiffness during underperfusion with NE, but reduced the detrimental effects 20 min after the onset of underperfusion. CONCLUSIONS KATP channels in the diabetic myocardium probably open during underperfusion with NE, and it helps delay the initiation of the increase in cardiac stiffness. Glyburide may have harmful effects in the ischemic diabetic heart; the myocardial KATP channel blockade during underperfusion with NE enhanced the increase in LV stiffness and abnormal myocardial energy metabolism. The glyburide-induced detrimental effects in the ischemic diabetic heart are prevented by levcromakalim and partly by insulin.

Underperfusion Injury in Diabetic Rat Hearts: Effects of Norepinephrine and/or Insulin on Stiffness Increase and Abnormal Energy Metabolism

Diabetic hearts were more susceptible than nondiabetic hearts to flow reduction and readily exhibited an increase in left ventricular diastolic stiffness in isolated rat hearts. Norepinephrine during underperfusion exacerbated the injury and improved the reperfusion injury, particularly in diabetic hearts, while the positive inotropic response was decreased by the progression of diabetes. The increase in stiffness correlated closely with ATP depletion and lactate accumulation in the subendocardium, which was metabolically more susceptible than the subepicardium. The correlation curves, however, were not coincidental: the critical ATP level was significantly higher in diabetic hearts. The markedly high glycogen content in diabetic hearts probably helps delay the start of underperfusion injury. The degree of injury depended on the degree and duration of underperfusion with norepinephrine and on the severity of diabetes. In vivo and ex vivo insulin prevented the injury.