Peripheral cardiovascular effects of tabernanthine tartrate in anaesthetized rats

The peripheral cardiovascular effects of tabernanthine tartrate have been studied in anaesthetized rats. Our results confirm that the bradycardic effect of tabernanthine is not inhibited by vagotomy, atropine or propranolol. On the contrary, bivagotomy, atropine treatment, as well as carotid artery occlusion, potentiate the bradycardic effect of tabernanthine. The same is true for its hypotensive action and can be explained by the suppression of a compensatory mechanism involving the central nervous system, the parasympathetic system and/or a baroreflex mechanism. In addition, domperidone and sulpiride, two dopaminolytic drugs, are able to potentiate the decrease in heart rate produced by tabernanthine. In pithed rat, tabernanthine 1 mg/kg, potentiates the increases in systolic blood pressure produced either by norepinephrine or serotonine; conversely the systolic blood pressure responses to angiotensin II are significantly inhibited by tabernanthine 1 mg/kg. Thus, tabernanthine appears to possess a complex cardiovascular mechanism of action, depending probably on a simultaneous stimulation of beta 2-vascular adrenoceptors and alteration of cellular movements of calcium. Part of the direct bradycardic effect, as well as the inhibition of the pressor responses of angiotensin II could be explained by a calcium antagonist action of the alcaloid.