Cardiovascular responses to intravenous administration of piperine wer
e investigated in anaesthetized dogs. Piperine produced biphasic effec
ts on the arterial blood pressure, depressor and presser effects. In t
he presence of vagus nerves, low doses of piperine (0.25-0.5 mg kg(-1)
) caused a transient drop in arterial blood pressure, a marked bradyca
rdia and apnea. With higher doses of piperine (1.0-1.5 mg kg(-1)), a t
ransient drop in blood pressure was followed by an overshoot of pressu
re and then a rapid return to normal. Bilateral vagotomy or atropine i
njection (1.0 mg kg(-1)) abolished the bradycardia and the fall of blo
od pressure caused by piperine. Regarding the presser effect, piperine
produced a positive inotropic effect with no chronotropic action. Ver
apamil (0.15 mg kg(-1)), a calcium channel blocking agent, completely
abolished the overshoot of blood pressure. These results suggest that
the depressor effect of piperine is associated with a cholinergic mech
anism whereas the presser effect is related to an influx of Ca++ into
the muscle cells probably into the cardiac and vascular smooth muscle
cells.