Opiate antagonists stimulate ruminal motility of conscious goats

The effect of opiate antagonists was determined on the extrinsic ruminal contractions of conscious goats. These contractions normally occur approximately once per minute. Naltrexone (greater than or equal to mg/kg, i.v.) and naloxone caused a significant increase in the frequency of ruminal contractions; morphine (0.8 mg/kg) depressed both frequency and amplitude. Naltrexone (12.5 micrograms/kg) prevented the response to morphine. These results suggest that an inhibitory opioid system is involved in the control of forestomach motility in goats.