Abstract

We tested the hypothesis that the biochemical properties of cardiac beta-adrenergic receptors (beta AR), as determined by standard in vitro methods, limit physiological responsiveness of dogs to beta AR stimulation during peak exercise. Accordingly, we measured oxygen consumption, left ventricular dP/dt at 40 mmHg developed pressure, heart rate, and cardiac output during maximal dynamic exercise in 13 adult mongrel dogs. These studies were followed by biochemical analysis of beta AR in membrane homogenates of left ventricle from the same animals using saturation binding and agonist competition curves for <125I> cyanopindolol. There was a substantial range in both biochemical and physiological variables within this population of normal dogs. However, there were no significant correlations between biochemical descriptors of cardiac beta AR and any physiological variables measured during exercise. These results suggest that receptor-effector coupling and maximal cardiac performance during intense sympathetic stimulation of peak exercise are limited by factors other than the biochemical properties of cardiac beta AR. Verf.-Referat