Effect of vasoactive intestinal polypeptide and environmental temperature on forestomach electromyographic activity and gastrointestinal contraction in sheep

Abstract

Four crossover design experiments were conducted with sheep to test the hypothesis that vasoactive intestinal polypeptide (VIP) affects gastrointestinal motility with implications for digesta flow. Sheep were shorn and surgically prepared with electrodes implanted on the forestomach, cannulae in the rumen, duodenum or/and ilieum, and a left gastric artery catheter. VIP (1 or 1.5 nmol min−1) or saline (control) was infused for 10 min at half-hour or hour intervals for 4 or 7 d during treatment periods. VIP transiently inhibited electromyographic (EMG) activity of the reticulum, reticulo-omasal orifice (ROO) and omasum for 3 to 8 min during the 10-min infusion periods. VIP infusion extended the duration of ROO opening (P < 0.01). The gastrointestinal lumen pressure pattern was also transiently influenced by VIP, with an increase of quiescent time. Cold exposure of sheep stimulated a relatively higher motility in the ROO and omasum. The results indicate that the inhibitory effect of VIP on the reticulum, ROO and omasum electrical activity is transient; however, its action to extend the duration of opening of the ROO may facilitate digesta passage. Key words: Sheep, vasoactive intestinal polypeptide, electromyographic activity, reticulo-omasal orifice