The dependence of myocardial substrate levels on the arterial oxygen tension in the cat in vivo

Effect of chronic hypoxia and high sucrose diet on body weights and glycolytic enzyme activities in liver, heart, and gastrocnemius of Sprague-Dawley and Wistar rats

Pyruvate kinase and glucosephosphate isomerase activities were measured in liver, heart, and gastrocnemius of Sprague-Dawley and Wistar rats subjected to chronic hypoxia. Animals were fed Purina chow or a high sucrose diet. In terms of changes in body weight, Sprague-Dawleys acclimated better on Purina chow whereas Wistars adjusted better on the high sucrose diet. These two groups had the lowest heart weight:body weight ratios. Only heart enzyme activities were above levels of pair-fed controls in both strains with hypoxia. Diet affected enzyme activities in hypoxic animals: for rats on high sucrose diet, pyruvate kinase activity was greater in all tissues of both strains except gastrocnemius of Sprague-Dawleys; glucosephosphate isomerase was higher in liver of both strains and only gastrocnemius of Wistars.

Myocardial balance of inorganic phosphate and enzymes in man. Effects of tachycardia and ischemia

The effects of atrial pacing on the cardiac balance of inorganic phosphate (P i ) were studied during control, atrial pacing, and recovery periods in 29 patients. Group A (n = 18) who had roentgenographically demonstrated coronary artery disease (CAD) developed angina during pacing, and showed mean myocardial lactate (L) production, abnormal left ventricular end-diastolic pressure (LVEDP) and ST segment depression. Group NA (n = 11), composed of six patients with CAD and five subjects with no demonstrable cardiac disease, had normal lactate metabolism, LVEDP, and ST segments during pacing. In addition, blood levels of two enzymes were determined: creatine phosphokinase (CPK) in nine patients of Group A and six patients of Group NA, and glutamic oxaloacetic transaminase (GOT) in eight patients of each group.

During control, small uptake of P i was observed in both groups. During pacing, Group A showed first a fall and then abolition of mean P i uptake, and during the early recovery period, a small loss of this ion was observed. Although there was a good correlation between L and P i uptakes ( r = 0.86, P < 0.001) throughout the study, P i loss, which occurred in 55% of patients in Group A, appeared to be a less reliable index of myocardial anaerobiosis than L production, which occurred in 72%. No consistent changes in P i balance were observed in Group NA. The only significant enzymatic change was the small but sudden and significant rise of mean CPK levels in coronary sinus (CS) blood above the arterial levels in five patients of Group A during the first 6 min of pacing. These data show that during pacing-induced angina the human heart loses P i . In addition, these preliminary observations on the CS CPK levels during pacing in the angina patients suggest that the stress of tachycardia and ischemia may facilitate the escape of this enzyme from the heart.