Some bases of differences in vascular response to sympathetic activity.

Basic patterns of neuroeffector organization vary widely in the vasculature, in general, with vessel diameter and type, and confer distinctive properties. The smaller the vessel, the more intimate the neuroeffector relationship, the more localized the action of the released transmitter, and the more important myogenic conduction compared to transmitter diffusion for the coordination of vascular effector response. Seemingly superimposed upon these basic general patterns are other variable features, conferring upon vessels of similar size and type diversity of function. These variables include sensitivity and magnitude and possible location of alpha- and beta-receptors and their subtypes, presence and nature of intrinsic vascular tone, and the density and pattern of adrenergic innervation to mention the more important. Functional diversity in neuroeffector characteristics can, to some extent, be understood in relation to embryological development, neurotrophic influences, effector regulation of innervation, and the mural response to an increase in intravascular pressure.