NONADRENERGIC NONCHOLINERGIC NEURON STIMULATION IN THE CAT LOWER ESOPHAGEAL SPHINCTER

Both electrical field stimulation and nicotine produced non-adrenergic non-cholinergic (NANC) relaxation of the circular muscle strips from the cat lower esophageal sphincter in the presence of 5 mu M guanethid ine and 5 mu M scopolamine. Low-frequency stimulation (2 Hz, 0.2 ms du ration, supramaximal current intensity, 20-s train) provoked a transie nt relaxation, while at high-frequency stimulation (20 Hz) a slow rest oration to the resting tone was observed. Blockade of nitric oxide (NO ) synthesis by 1 mM N-omega-nitro-L-arginine decreased by 20% the ampl itude of the 20 Hz-induced relaxation and changed the pattern of relax ation, making it similar to the sustained relaxation evoked by exogeno usly applied vasoactive intestinal peptide (VIP). After chymotrypsin ( 4 U/ml), the pattern of the high-frequency-induced relaxation resemble d that of the low-frequency-induced relaxation. Similarly, chymotrypsi n changed the shape of nicotine-provoked relaxation, increasing the sp eed of restoration to the resting tone. We suggest that the fast relax ation elicited in cat lower esophageal sphincter by electrical field s timulation or nicotine is initiated by NO. The slow restoration to the resting tone in the case of high-frequency- or nicotine-induced relax ation seems to be due to the release of VIP or VIP-like peptides. The possibility of participation of another transmitter(s) involved in NAN C relaxation should not be excluded.