Reflex and Direct Cardiopulmonary Effects of 5-OH-Tryptamine (Serotonin)

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Abstract
Serotonin, 5-OH-tryptamine creatinine sulfate, given by rapid intraven. injn. in doses as small as 0.5 [um]g./kg. in chloralosed cats, produces profound reflex cardiopulmonary changes, which include brady-cardia, hypotension and apnea (Bezold-Jarisch reflex). In addition, it produces bronchoconstriction and pulmonary vasoconstriction (increase in right ventricular pressure). The sensory receptors sensitive to 5-OH-tryptamine appear to receive blood from the pulmonary circulation and the ascending aorta; the afferent fibers run mainly in the vagus nerves. The receptors are probably different from veratridine- sensitive receptors, and are blocked by an anti- metabolite of serotonin. It is suggested that some of the cardiopulmonary disturbances seen in patients with pulmonary embolism or eoronary thrombosis might result from local or reflex effects of 5-OH-tryptamine liberated from platelets in the process of blood coagulation.