Heterogeneous distribution of adrenergic receptors in coronary arteries and their influence on coronary arterial tone.

In-vitro experiments, using canine large (o.d. 1-2 mm) and small (o.d. 0.4-0.8mm) coronary arteries, were undertaken to determine the functional state of alpha- and beta-adrenergic receptors and their role in regulation of coronary arterial tone. Both large and small coronary arteries of the dog possess alpha and beta adrenergic receptors. Alpha-adrenergic receptors are more numerous on the circumflex vessel than elsewhere. Functionally, beta-adrenergic receptors appear to be dominant under physiological conditions in most types of coronary arteries. In canine coronary arteries, beta-adrenergic receptors have a greater affinity for noradrenaline than adrenaline. Alpha-adrenergic receptors have a greater affinity for adrenaline than noradrenaline. It is concluded that after beta-adrenergic blockade, in both large and small coronary arteries, alpha-adrenergic receptors play an important role in regulation of coronary arterial tone.