Dual mechanism of the stimulant action of N,N-dimethyl-5-hydroxy-tryptamine (bufotenine) on cardiac sympathetic nerves

The indirect sympathomimetic effects of N,N-dimethyl-5-hydroxytryptamine (bufotenine) have been analysed on the rabbit heart perfused in vitro by the Langendorff technique. Comparisons have been made with the effects of 5-hydroxytryptamine (5-HT), which activates tryptamine receptors, and dimethylphenylpiperazinium (DMPP), which stimulates nicotine receptors. Bufotenine, 5-HT and DMPP stimulated the rate and force of cardiac contraction but whereas all were powerful stimulants of cardiac rate, bufotenine and DMPP were much stronger stimulants of atrial and particularly ventricular tension than 5-HT. Responses to 5-HT were markedly reduced by perfusion of hearts with an excess of 5-HT, and those to DMPP, during perfusion with hexamethonium. A combination of 5-HT with hexamethonium was necessary to abolish the effects of bufotenine. The data suggest a dual mechanism of stimulant action of bufotenine on the cardiac sympathetic nerves of the rabbit heart involving activation of receptors sensitive to 5-HT and nicotine receptors.