SOME BASES OF DIFFERENCES IN VASCULAR-RESPONSE TO SYMPATHETIC ACTIVITY - VARIATIONS ON A THEME

Three general patterns of sympathetic control of vascular tone are described. These are patterns of neuromuscular organization and are distinguished on the basis of both anatomical and functional criteria derived from in vitro studies. They are specific types of relationships between the contractile system of the blood vessel wall, particularly the individual vascular smooth muscle cells, and the postganglionic adrenergic neural terminations. Their adequate description includes a detailed consideration of the transmitter mechanism that links the two types of cells. In general, these patterns vary with vessel diameter and function. In each instance the different neuromuscular organization reflects a different functional role of the blood vessel. Although for convenience, three basic patterns of neuroeffector organization are presented, these are disparate examples selected from the two extremes and probably the middle of a wide-ranging continuum. They have been recognized by parallel structural and functional investigation, the results of which complement each other. In this review of primarily in vitro studies, after the description of these three basic types, additional factors are discussed that contribute to the variation in functional behavior of individual blood vessels and presumably, as a consequence, entire regional beds.