This study was aimed to explore underlying mechanism(s) of cardiovascular effects of piperine. Intravenous administration of piperine caused a dose-dependent (1 to 10 mg/kg) decrease in mean arterial pressure (MAP) in normotensive anesthetized rats; the next higher dose (30 mg/kg) did not cause any further change in MAP. The fall in blood pressure (BP) was followed by small increase in MAP after each dose. In Langendorrf's rabbit heart preparation, piperine caused partial inhibition and verapamil caused complete inhibition of force and rate of ventricular contractions and coronary flow. In rabbit aortic rings, piperine inhibited high K (80 mM) precontractions and partially inhibited phenylephrine (PE), suggesting Ca channel blockade (CCB), which was further confirmed when pretreatment of tissues with piperine caused rightward shift in Ca concentration-response curves, similar to verapamil. In Ca-free medium, piperine (1 to 30 μM) exhibited vasoconstrictor effect. In rat aorta, piperine demonstrated endothelium-independent vasodilator effect and was more potent against high K precontractions than PE. In bovine coronary artery preparations, piperine inhibited high K precontractions completely. These data indicate that piperine possesses a blood pressure-lowering effect mediated possibly through CCB, while consistent decrease in BP was restricted by associated vasoconstrictor effect. Additionally, species selectivity exists in the CCB effect of piperine.
- Calcium antagonist