EFFECTS OF PIPERITENONE OXIDE ON THE INTESTINAL SMOOTH-MUSCLE OF THE GUINEA-PIG

We investigated the effects of piperitenone oxide (PO), a major consti tuent of the essential oil of Mentha x villosa, on the guinea pig ileu m. PO (30 to 740 mu g/ml) relaxed basal tonus without significantly al terating the resting membrane potential. In addition, PO relaxed prepa rations precontracted with either 60 mM K+ or 5 mM tetraethylammonium in a concentration-dependent manner. At concentrations from 0.1 to 10 mu g/ml PO potentiated acetylcholine-induced contractions, while highe r concentrations (>30 mu g/ml) blocked this response. These higher PO concentrations also inhibited contractions induced by 60 mM K+. PO als o blocked the components of acetylcholine contraction which are not se nsitive to nifedipine or to solutions with nominal zero Ca2+ and EGTA. These results show that PO is a relaxant of intestinal smooth muscle and suggest that this activity may be mediated at least in part by an intracellular effect.