ADRENERGIC RECEPTORS IN CORONARY ARTERIES *

Teleologically, the activity of vascular smooth muscle is directed toward two distinct and sometimes conflicting goals. The first is the control of total peripheral resistance so that arterial pressure will be sufficient to maintain adequate perfusion of all of our parts, yet not so great tha t i t will blow out our tubes. This system operates for the welfare of the whole organism. The second goal is concerned with the needs of the individual organs. Distribution of blood flow must be adjusted to meet fluctuations in the requirements of our various parts. These two goals find a clear parallelism in those of our Democratic and Republican parties, respectively. I t is the “Republican” focus on individuality which forms the context of the studies that I will describe. Blood vessels are equipped with three distinct control systems which are capable of local regulation of flow to meet the individual requirements of specific regions: 1. Neurogenic control may be a highly individualized phenomenon. Not only does the total amount of innervation vary from tissue to tissue’ but the pattern of neurogenic influence on the different organs is specific for the type of situation to which the whole organism is responding.’ 2. Local humoral regulation is an exceptionally effective mechanism for individualization of flow since, by virtue of the vasodilator response of resistance vessels to local metabolites3 and local pO2,* each tissue can regulate its own blood flow. 3. Finally, individuality of control is effected through differences in behavior among vascular smooth muscles in different parts of the body. Smooth muscles from various sites differ in: (a) degree of spontaneous myogenic tone, (b) capability for autoregulation, and (c) individuality of “receptors.” The observation that cerebral resistance vessels fail to respond to reasonable concentrations of catecholamines, whereas renal resistance vessels are highly responsive to these neurohumoral agent^,^ is interpreted as an indication tha t there is a marked disparity in the populations of adrenergic receptors in vascular smooth muscle a t these two sites. A final basis for individuality, which is emphasized in the current study, is that, in addition to differences in populations of adrenergic receptors in various sites of the body, there are qualitative differences in these receptors in vascular smooth muscle from various tissues. In the present study the relative sensitivity of alpha and beta adrenergic receptors to epinephrine and to norephinephrine was evaluated in vascular smooth muscle from resistance vessels in coronary and skeletal muscle.