Food intake and rumen motility in dwarf goats. Effects of atipamezole on the inhibitory effects induced by detomidine, medetomidine and romifidine.

The effects of some alpha 2-adrenoceptor agonists and of the alpha 2-adrenoceptor antagonist atipamezole on food intake and ruminal contractions were studied in dwarf goats. Detomidine, 0.2 microgram/kg per min for 10 min, failed to modify food intake during either the first or second observation period (0-30 min and 180-210 min after drug infusion, respectively). Given at a higher dose rate (0.4 microgram/kg per min for 10 min), the drug inhibited food consumption during the first observation period, but stimulated food intake during the second period. A similar pattern was observed after IV infusion with medetomidine (0.2 microgram/kg per min for 10 min), romifidine (0.4 microgram/kg per min for 10 min) or xylazine (1 microgram/kg per min for 10 min). The alpha 2-antagonist atipamezole (2 micrograms/kg per min for 10 min) failed to modify food intake during either the first or second observation period. After treatment with atipamezole, the effects of alpha 2-agonists on feeding behaviour were completely antagonized. The alpha 2-agonists administered at similar dose rates to those used in the food intake experiments induced bradycardia, decreases in body temperature and inhibition of ruminal contractions. The inhibition of ruminal contractions induced by romifidine was partly antagonized by atipamezole pre-treatment. These findings demonstrate that the alpha 2-agonist-induced changes in ruminal contractions do not simply cause changes in feeding behaviour. The drop in body temperature induced by alpha 2-agonists was prevented by atipamezole pre-treatment, whereas the induced bradycardia was not modified by this alpha 2-antagonist.