Evidence for Adrenergic Nervous Control of Blood Pressure in Teleost Fish

Several control mechanisms collaborate to regulate cardiovascular functions in the teleost fish. The systems involved include nerves, humoral (circulating) agents, and local (paracrine) effects such as release of cardio- or vasoactive substances from endothelial cells. This brief review focuses on the Atlantic cod, Gadus morhua. In this species, as in most teleosts, blood pressure is elevated because of an adrenergic tonus affecting both the heart and the vascular resistance. Histochemical studies using the Falck-Hillarp technique demonstrate catecholamine-containing chromaffin cells in the walls of the posterior cardinal veins of many teleosts, including the cod, and the adrenaline and noradrenaline released from these sites may affect the heart and vascular beds. There is physiological evidence to suggest that circulating catecholamines play a major role in the control of the arteriorarterial branchial vascular resistance in the cod. Histochemical studies of the cod cardiovascular system reveal adrenergic nerves in the heart and blood vessels. Pharmacological studies using the adrenergic neuron-blocking agent bretylium suggest that the adrenergic vasomotor innervation is a major nervous regulator of blood pressure in this species during rest, exercise, and hypoxia.