A pharmacological analysis of the adrenergic and cholinergic mechanisms regulating branchial vascular resistance in the rainbow trout (Salmo gairdneri)

Abstract

The adrenergic and cholinergic mechanisms regulating branchial vascular resistance in the trout have been studied using a whole gill preparation perfused at constant flow under approximately normal afferent and efferent levels of blood pressure. The receptors have been pharmacologically characterized by agonist potency comparisons within individual preparations and by the use of specific antagonists. The predominant response to adrenergic stimulation is vasodilation mediated by β-receptors, but a more rapid vasoconstriction mediated by α-receptors may also occur. The β-adrenoreceptors appear to be of the β₁, variety, as in the homologous coronary vasculature of mammals. The cholinergic receptors of the gills are purely muscarinic in nature and mediate vasoconstriction. The possible functions of the mechanisms are discussed.