Inhibition of food intake and reticulo-rumen motility of sheep by the alpha-2 adrenoreceptor agonist clonidine.

The investigation of the effect of intravenous clonidine, an alpha-2 adrenoreceptor agonist, was carried out in sheep with recording of forestomach motility for 3 h and intake of chopped hay for 8 h after drug administration. Motility and food intake were inhibited by clonidine at 2 micrograms.kg-1 and at 5 micrograms.kg-1. The effects of the lower dose were prevented by idazoxan, an alpha-2 antagonist, at 0.1 mg.kg-1 but not by prazosin, an alpha-1 antagonist, at 0.1 mg.kg-1. Minor effects of the antagonists alone were noted. Blood glucose concentration was measured in all the experiments and the possibility discussed that changes in concentration, not absolute values, may have contributed to inhibitory effects. Vagal stimulation in anaesthetised sheep indicated that inhibition of motility was a central neural effect, not an effect on forestomach muscle.