Pharmacological Properies of Pteleprenine, a Quinoline Alkaloid Extracted from Orixa japonica, on Guinea-pig Ileum and Canine Left Atrium

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Abstract
We have investigated the pharmacological properties of pteleprenine, a quinoline alkaloid, on contractile responses of the guinea‐pig ileum and on inotropic responses of the canine left atrium. Although pteleprenine (0·1–1 μM) had no effect on the contraction of the ileum induced by acetylcholine at 10 μM it significantly inhibited acetylcholine‐induced contraction of the ileum. Pteleprenine (0·1–10 μM) reduced nicotine induced‐contraction of the ileum in a concentration‐dependent manner yet had no maximum relaxant effect even at a concentration of 10 μM From Schild analysis the pA2 of pteleprenine on the guinea‐pig ileum was found to be 6‐6. The contraction of the ileum induced by 10 μM 1,1‐dimethyl‐4‐phenylpiperazinium, a specific agonist of nicotinic acetylcholine. receptors, was concentration‐dependently suppressed by 10 nM‐10 μM pteleprenine. In contrast, 0.1–10 μM pteleprenine did not antagonize the acetylcholine‐ and nicotine‐induced negative inotropic contractile responses of the canine left atrium. These results show that pteleprenine has inhibitory action against nicotinic acetylcholine receptors in the guinea‐pig ileum but not in the canine left atrium. Our findings also suggest that pteleprenine might be a novel lead compound as a nicotinic receptor antagonist.