Action of Serotonin (5-Hydroxytryptamine) on Vagal Afferent Impulses in the Cat

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Abstract
Serotonin given intraven. to cats at a dose of 50-100 [mu]g./kg. always causes an abrupt fall in blood pressure, bradycardia and respiratory arrest. Ganglionic block reverses the blood pressure response to serotonin and diminishes or abolishes bradycardia; the period of respiratory arrest, however, is prolonged. Local anesthetics given intraven. in high doses before serotonin antagonize the blood-pressure fall and bradycardia, as well as respiratory arrest. Action potentials derived from single inspiratory active vagus fibers of the cat under artificial respiration show a marked increase in frequency after serotonin injn., thus giving evidence of direct action of serotonin on pulmonary stretch receptors. These results indicate that serotonin in the cat has a peripheral point of attack on autonomic sensory nerve endings in the cardiopulmonary region; it causes a von Bezold-Jarisch reflex in the cat.