Effects of deuteration on transamination and oxidation of hyperpolarized 13C-Pyruvate in the isolated heart.

This study was designed to determine the effects of deuteration in pyruvate on exchange reactions in alanine aminotransferase (ALT), lactate dehydrogenase (LDH) and flux through pyruvate dehydrogenase (PDH). Although deuteration of a 13C enriched substrate is commonly used to increase the lifetime of a probe for hyperpolarization experiments, the potential impact of kinetic isotope effects on such substitutions has not been studied in detail. Metabolism of deuterated pyruvate was investigated in isolated rat hearts. Hearts were perfused with a 1:1 mixture of [U-13C3]pyruvate and [2-13C1]pyruvate or a 1:1 mixture of [U-13C3]pyruvate plus [2-13C1, U-2H3]pyruvate for 30 min before being freeze clamped. Another set of hearts received [2-13C1, U-2H3]pyruvate and was freeze-clamped at 3 min or 6 min. Tissue extracts were analyzed by 1H and 13C{1H} NMR spectroscopy. The chemical shift isotope effect of 2H was monitored in the 13C NMR spectra of the C2 resonance of lactate and alanine plus the C5 of glutamate. There was little kinetic isotope effect of 2H in pyruvate on flux through PDH, LDH or ALT as detected by the distribution of 13C, but the distribution of 2H differed markedly between alanine and lactate. At steady-state, alanine was a mixture of deuterated species, while lactate was largely perdeuterated. Consistent with results at steady-state, hearts freeze-clamped at 3 min or 6 min showed rapid removal of deuterium in alanine but not in lactate. Metabolism of hyperpolarized [1-13C1]pyruvate was compared to [1-13C1,U-2H3]pyruvate in isolated hearts. Consistent with the results from tissue extracts, there was little effect of deuteration on the kinetics of appearance of lactate, alanine or bicarbonate, but there was a small, time-dependent upfield chemical shift in the HP[1-13C1]alanine signal reflecting exchange of methyl deuterons with water protons. Together, these results demonstrate that (1) the kinetics of pyruvate metabolism in hearts detected by 13C NMR are not affected by replacement of the pyruvate methyl protons with deuterons and (2) that the loss of deuterium from the methyl position occurs rapidly during the conversion of pyruvate to alanine. The majority of the deuterium atoms are lost on the time-scale of a hyperpolarization experiment.

Ventricular cycle length irregularity affects the correlation between ventricular rate and coronary flow in isolated, Langendorff perfused guinea pig hearts.

INTRODUCTION: Heart rate affects coronary flow, but the mechanism is complex. The relationship between rhythm and flow is unclear, especially in experimental settings used for determining drug actions. The present study examined whether ventricular irregularity influences coronary flow independently of heart rate. METHODS: Guinea pig hearts were perfused (Langendorff mode) at constant pressure. Hypokalemic Krebs solution facilitated spontaneous development of arrhythmias. The ECG, left ventricular and perfusion pressures were recorded, and the coronary flow was measured. Beat-to-beat ventricular cycle length variability was quantified. Hearts were retrospectively allocated to arbitrary 'Low' or 'High' RR variability groups. RESULTS: A positive linear correlation was found between mean ventricular rate and coronary flow. The slope of the regression line was significantly greater in the 'High' versus 'Low' RR variability group, with greater coronary flow values in the 'High' RR variability group in the physiological heart rate range. During regular rhythm, left ventricular pressure exceeded perfusion pressure and prevented coronary perfusion at peak systole. However, ventricular irregularity significantly increased the number of beats in which left ventricular pressure remained below perfusion pressure, facilitating coronary perfusion. DISCUSSION: In isolated hearts, cycle length irregularity increases the slope of the positive linear correlation between mean ventricular rate and coronary flow via producing beats in which left ventricular pressure remains below perfusion pressure. This means that changes in rhythm have the capacity to influence coronary flow independently of heart rate in isolated hearts perfused at constant pressure, which should be noted in drug studies on arrhythmias performed in Langendorff hearts.

Hydroalcoholic extract of Allium eriophyllum leaves attenuates cardiac impairment in rats with simultaneous type 2 diabetes and renal hypertension.

Some species of Allium family have been shown to offer cardioprotection in animal studies. This study aimed at examining possible role of oxidative stress in the cardioprotective effects of hydroalcoholic extract of Allium eriophyllum in rats with simultaneous type 2 diabetes and renal hypertension. Six groups of male Spargue-Dawley rats (8-10 rats each) including a sham-control, a diabetic group, a renal hypertensive group, three groups of animals with simultaneous diabetes and hypertension receiving vehicle, or the extract at 30 or 100 mg/kg/day were used. Four weeks after receiving vehicle or extract, blood pressure, fasting blood glucose, and serum superoxide dismutase and glutathione reductase levels were measured, and isolated heart studies were performed. Systolic blood pressure, fasting blood glucose, coronary effluent creatine kinase-MB, infarct size and coronary resistance of diabetic hypertensive group receiving vehicle were significantly higher than those of the sham-control group and treatment with the extract prevented the increase of these variables. Moreover, rate of rise and decrease of left ventricular pressure, left ventricular developed pressure, rate pressure product and serum levels of superoxide dismutase and glutathione reductase of diabetic hypertensive group receiving vehicle were significantly lower than those the sham-control group, and treatment with the extract prevented the decrease of these variables. The findings indicate that hydroalcoholic extract of A. eriophyllum leaves, possibly by an antioxidant mechanism, protected against simultaneous diabetes and hypertension-induced cardiac dysfunction.

Effects of different time on ischemia/reperfusion injury in isolated rat hearts / 中国药学杂志

METHODS: Male Sprague Dawley rats which were used lor Langendoff isolated heart perfusion were divided into four groups; normal control group (n=6), 120 group (n=1), 130 group (n=8) and 140 group (n=8), these hearts were subjected to global ischemia for 20, 30 and 40 min respectively. Then coronary flow, heart rate, creatinine kinase and lactate dehydrogenase in effluent and the changes of cardiac function parameters were measured in different groups. Infarct and risk areas were measured by planimetry using Image/J software.

Nucleoside transport inhibitor, dipyridamole, induced myocardial protection following hemorrhagic shock in ex vivo perfused rat hearts.

INTRODUCTION: Successful protection against post-resuscitation myocardial injury is not available for trauma patients. Whereas intensive improvement in resuscitation strategies reduce myocardial injury, death among trauma patients are among the highest in the world due to myocardial dysfunction and multiple organ failure. Dipyridamole is a nucleoside transport inhibitor. Recent studies have shown that elevation of serum adenosine caused by dipyridamole improve cardiac function. The purpose of the present study was to examine the myocardial protective effects of dipyridamole therapy following 1 h of hemorrhagic shock. METHODS: Sprague-Dawley rats were used. The study consisted of three phases: Phase I to examine the direct effects of dipyridamole on myocardial function by perfusion of the isolated hearts with Krebs Henseleit buffer (KHB) + dipyridamole on the Langendorff apparatus. Phase II examined the protective effects of dipyridamole following 60 min of hemorrhagic shock (HS) by ex vivo treatment with dipyridimole 20 µg/L for 5 min followed by resuscitation with KHB for 55 min. Phase III: 60 min HS followed by in vivo treatment by injecting 1 ml of (20 µg/L) dipyridamole intra-arterially, and resuscitation for 30 min. Myocardial protection was assessed by measuring left ventricular generated pressure (LVGP) and end diastolic pressures (LVEDP). RESULTS: During ex vivo resuscitation, hearts from dipyridamole treated animals had significantly higher LVGP, and significantly lower LVEDP versus controls. CONCLUSION: Dipyridamole therapy produces protection against post-resuscitation myocardial injury in rats.