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

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 3-30 nmol kg(-1) min(-1) for 30 minutes inhibited both the amplitude and frequency of ruminal contractions in a dose-dependent manner. However, intravenous infusion of Nomega-nitro-L-arginine-methyl ester (L-NAME) at closes of 0.3-3.0 mumol kg(-1) min(-1) did not alter the basal tone of intraruminal pressure and the amplitude of ruminal contractions. The frequency of contractions was slightly inhibited by L.NAME infusion at 1.0 mumol kg(-1) min(-1). The effects of L-NAME were abolished by simultaneous infusion of L-arginine at 30 mumol kg(-1) min(-1). These results suggest that exogenous NO can diminish the ruminal contractions, while endogenous NO is not involved in the regulatory mechanism of basal tune and regular phasic contractions of the rumen in healthy sheep. (C) 2001 Harcourt Publishers Ltd.