Effect of ganglionic blockade on catecholamine secretion in exercised dogfish.

Abstract

A brief bout of vigorous exercise results in significant increases in plasma epinephrine (E) and norepinephrine (NE) in the dogfish, Squalus acanthias. Since the presence of a functioning sympathetic nervous system in dogfish is in doubt, experiments were undertaken to show whether or not exercise-induced catecholamine (CA) secretion is under autonomic neurogenic control. Changes in plasma E and NE in a control group of exercised fish were compared with changes in fish exercised while under the influence of ganglionic blockade. Ganglionic blockade was induced in dogfish by hexamethonium infusion before exercise. CA secretion in response to a subsequent bout of exercise was significantly reduced without impairment of the ability of the fish to exercise. The pattern of systemic arterial pressure response to exercise and recovery (initial decrease during exercise followed by a prompt recovery to control level) was not significantly altered by ganglionic blockade. It is concluded that in dogfish some fraction of CA secretion capacity is possibly or potentially under neurogenically related control. Apparently the fraction of CA secretion under such control is not essential for performing exercise. The pattern of CA secretion accompanying the events of exercise and recovery in dogfish suggests that CA may play a more important role in recovery from exercise than in its performance.