EFFECT OF NITROVASODILATORS ON THE RHYTHMIC CONTRACTIONS OF GUINEA-PIG ISOLATED SPHINCTER OF ODDI

The effects of amyl nitrite (CAS 8017-89-8) isosorbide dinitrate (CAS 87-33-2) and sodium nitroprusside (CAS 14402-89-2), on the acetylcholi ne-induced tachyrhythmia (greater than 9 waves/min) were investigated in the isolated guinea-pig sphincter of Oddi. Acetylcholine (10(-3) mo l/l) produced an initial rapid rise in tension, the peak being followe d by a gradual decrease associated with the initiation of the peristal tic waves. Nitrovasodilators significantly decreased the initial respo nse to acetylcholine. Methylene blue (5 x 10(-5) mol/l), a soluble gua nylate cyclase inhibitor increased the tonic response to acetylcholine and reversed the inhibition caused by nitrovasodilators. The frequenc y and amplitude of peristaltic waves were decreased by nitrovasodilato rs. Methylene blue significantly increased both the frequency and ampl itude of peristaltic waves, however; it did not reverse the inhibition caused by nitrovasodilators tested. Results suggest that nitrates dec rease the acetylcholine-induced contraction and peristaltism of isolat ed guinea-pig sphincter of Oddi and NO released by acetylcholine may p artially suppress its own tonic contractile response.