Effects of nitric oxide donor and nitric oxide synthase inhibitor on ruminal contractions in conscious sheep

Abstract

The present study was planned to evaluate a role of nitric oxide (NO) in the regulation of regular ruminal contractions in conscious sheep. Intravenous infusion of S-nitroso-acethyl- DL -penicillamine (SNAP) at doses of 3–30nmolkg−1min−1for 30 minutes inhibited both the amplitude and frequency of ruminal contractions in a dose-dependent manner. However, intravenous infusion of Nω-nitro-L -arginine-methyl ester (L-NAME) at doses of 0·3–3·0μmolkg−1min−1did not alter the basal tone of intraruminal pressure and the amplitude of ruminal contractions. The frequency of contractions was slightly inhibited byL-NAME infusion at 1·0μmol kg−1min−1. The effects ofL-NAME were abolished by simultaneous infusion of L -arginine at 30μmol kg−1min−1. These results suggest that exogenous NO can diminish the ruminal contractions, while endogenous NO is not involved in the regulatory mechanism of basal tone and regular phasic contractions of the rumen in healthy sheep.