Patterns of alpha-adrenoceptor regulation of the vasculature.

There are patterns in the distribution of the characteristics of vascular alpha-adrenoceptors. Sudden changes in their mechanism occur at particularly sites along the main branches of the aorta; in some regional vascular beds, but not others, there is a progressive reduction in the response that can be elicited through the alpha-adrenoceptor; in smaller blood vessels, alpha- and beta-adrenoceptors may be spatially separated in the vessel wall; in most blood vessels, the inner smooth muscle is more sensitive to alpha-agonists and more dependent on sequestered calcium than the outer. There is little support for a significant physiological role of the proposed gamma-receptor.