ABSTRACT
The passive distensibility and adrenergic reactivity of the systemic vascular resistance (Rs) in Salmogairdneri have been studied using perfused trunk pre-parations, and the data compared with previous results on the branchial resistance (Rg). At normal levels of efferent blood pressure, Rs is relatively more distensible than Rg in response to afferent pressure increases, but this difference may not be important in vivo, α-adrenergic constrictory receptors predominate in Rs, in contrast to β-adrenergic dilatory receptors in Rg; a significant a-adrenergic tone in Rs is lost during perfusion. Rs is far less sensitive than Rg to circulatory catecholamine levels. It is suggested that the sympathetic nervous system, rather than plasma catecholamines, provides the effective adrenergic control of Rs in vivo.
