Sphincter Relaxation

Abstract. The effect of rabbit vasoactive intes-tinal polypeptide (VIP) antiserum on in vitro relaxation of the lower esophageal sphincter (LES) was studied in 10 cats. The stomach and esophagus were opened along the lesser curvature of the stomach and stripped of mu-cosa. Consecutive strips were cut and mounted in a 2.5-ml muscle chamber. They were perfused with Tyrode's solution and oxygenated continuously. After equilibration for 1 h, perfusion was stopped and one strip from the lower esophageal sphincter region was incubated in so-lution that contained 12-25 parts of VIP antiserum per 1,000 of Tyrode's solution, while a second strip was in-cubated in a solution ofnormal rabbit serum at the same concentration. A third strip was maintained in Tyrode's solution for the duration of the experiment. After a 1-h incubation, the strips were stimulated with 6-s square wave trains of 0.1-, 0.2-, 0.4-, and 0.8-ms pulses at 1, 2, and 5 Hz. These stimulation parameters produced LES relaxation that was completely blocked by tetrodotoxin but not by atropine or phentolamine. The strips incubated in Tyrode's solution or in normal serum relaxed reliably and consistently at all levels of stimulation. In the an-tiserum-treated strips, LES relaxation in response to all stimuli was significantly inhibited. Strips treated with normal serum were relaxed in a dose-dependent fashion by l-7 and 10-6M VIP, whereas the antiserum inhibited the relaxation induced by l0-7 M, but not by 10-6 M, VIP. Stimulation with two successive 15-min trains of electrical pulses (2 ins, 5 Hz) separated by 30 min of rest released increasing amounts of VIP into the bathing so-lution. VIP released during the second train of electrica