Modification by domperidone of dopamine- and apomorphine-induced inhibition of extrinsic ruminal contractions in goats.

Goat ruminal strips reacted with an increase in smooth muscle tone after exposure to apomorphine. This rise in tone could be blocked by domperidone, but not by naltrexone. In vivo, both dopamine and apomorphine caused inhibition of extrinsic ruminal contractions. These effects completely prevented by domperidone pretreatment, whereas naltrexone was not an effective antagonist. These results suggest that apomorphine-induced inhibition of rumen motility is due to DA-receptor activation. The extract location of these DA-receptors remains to be determined.