SPATIAL HETEROGENEITY OF BLOOD-FLOW IN THE DOG HEART .1. GLUCOSE-UPTAKE, FREE ADENOSINE AND OXIDATIVE GLYCOLYTIC ENZYME-ACTIVITY/

The spatial heterogeneity of myocardial perfusion and metabolism was s tudied in 11 anaesthetized dogs under resting conditions. In each hear t local myocardial blood flow was assessed using the tracer micro sphe re technique in 256 samples (mean mass: 83.1 mg) taken from the left a nterior ventricular wall. In the same samples, the following biochemic al parameters were determined: accumulation of [H-3]-deoxyglucose (a. measure of glucose uptake), free cytosolic adenosine (S-adenosylhomocy steine accumulation technique, a measure of tissue oxygenation and a p ossible mediator of blood flow regulation), and the specific activitie s of oxidative (citrate synthase, cytochrome-c-oxidase) and glycolytic (hexokinase, phosphoglycerate kinase) enzymes. Capillary density and mitochondrial and myofibril volume densities were determined by morpho metry. Myocardial perfusion in each sample (average 0.77 mi min(-1) g( -1)) varied between 0.1 and 2.5 times the mean (coefficient of variati on 0.30+/-0.02). [H-3]-deoxyglucose was deposited locally in proportio n to perfusion. Samples showing low flow (<0.2 mi min(-1) g(-1)) did n ot exhibit increased levels of cytosolic adenosine. The specific activ ities of the oxidative and glycolytic enzymes, however, were uniformly distributed between low and high flow areas. Furthermore, capillary d ensity and mitochondrial and myofibril densities were similar in high and low flow regions. The results show firstly that local glucose meta bolism in the heart occurs in proportion to local blood flow, suggesti ng that high flow regions have a higher than average metabolic rate. S econdly, regions of low flow are not compromized by critical oxygenati on and most likely have a lower than average oxygen demand and finally , the homogeneous distribution of oxidative and,glycolytic enzymes, as well as the homogeneous myocardial ultrastructure, suggest that areas with high and low blood flow under resting conditions may increase th eir metabolic rate to similar levels when required.