Receptor mechanisms in the human epicardial coronary artery. Heterogeneous pharmacological response to histamine and carbachol.

We studied isolated ring segments from a number of sites along the course of epicardial coronary arteries from 24 human hearts in order to characterize regional responsiveness to vasoactive agents. Concentration-response curves revealed heightened sensitivity to histamine in the proximal portion of the coronary arteries, and increased sensitivity to carbachol in the distal portion of these same vessels. In contrast, the response to stimulation by calcium or phenylephrine was uniform throughout the length of the vessels examined. These data suggest that regional variations in agonist response reflect heterogeneity in receptor populations along the course of the human epicardial coronary artery.