Comparison of the cardiovascular responses to intracerebroventricular administration of tryptamine, 5-hydroxytryptamine, tryptophan and 5-hydroxytryptophan in rats

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Abstract
General characteristics of the cardiovascular responses to intracerebroventricular (i.c.v.) injection of tryptamine, 5-hydroxytryptamine (5-HT), tryptophan and 5-hydroxytryptophan (5-HTP) were compared. Relatively small doses of tryptamine and 5-HT (0.005–0.1 μm) produced considerable, long-lasting and dose-dependent pressor effects, which sometimes were followed by prolonged depressor effects. Tryptophan (0.02–0.5 μm) and 5-HTP (0.02–0.2 μm) caused variable and usually slight, but long-lasting, vascular responses or no vascular response. A large dose of tryptamine (0.5 μm) evoked variable vascular effects, while the same dose of 5-HT and 5-HTP evoked marked and prolonged depressor effects. The vascular responses to the drugs were accompanied by variable changes in heart rate. Tryptamine, 5-HT and 5-HTP, in the majority of rats, produced a bradycardia. The present study provides evidence that the cardiovascular response to i.c.v. administration of tryptamine is similar to that of 5-HT, supporting the idea that tryptamine, in addition to 5-HT, participates in the central physiological Regulation of the rat cardiovascular system. The role of tryptophan and 5-HTP by themselves in this Regulation, if any, is of secondary importance.