5-Carboxamide tryptamine, a compound with high affinity for 5-hydroxytryptamine1 binding sites, dilates arterioles and constricts arteriovenous anastomoses.

The effects of 5-carboxamide tryptamine, which activates non-5-hydroxytryptamine2-'atypical' receptors for 5-hydroxytryptamine (5-HT) in the dog saphenous vein, was studied on the complete distribution of cardiac output and common carotid blood flow in anaesthetized pigs. The drug was infused for 10 min at the rate of 0.025, 0.1 and 0.4 micrograms kg-1 min-1 either intravenously (cardiac output distribution) or intra-arterially (carotid distribution). 5-Carboxamide tryptamine decreased arterial blood pressure due to a reduction of cardiac output. This reduction was confined to its arteriovenous anastomotic component; the component used for the tissue perfusion (nutrient part) in fact increased. Similar changes were observed in the carotid blood flow distribution. Vasodilation was observed in several tissues, but the skin, ears and stomach responded most prominently. The effects of 5-carboxamide tryptamine on the carotid distribution were not significantly modified by cyproheptadine (1 mg kg-1). It is concluded that, like 5-HT, 5-carboxamide tryptamine constricts arteriovenous anastomoses and dilates arterioles by activating non-5-HT2-'atypical' receptors. These 'atypical' 5-HT receptors appear to be of the 5-HT1 type since both 5-carboxamide tryptamine and BEA 1654, a new piperazine derivative, produced similar vascular effects in the carotid bed of the pig and also showed a high and selective affinity for the 5-HT1 binding sites.