Effects of dopamine receptor agonists on food intake and rumen motility in dwarf goats

Abstract

In ruminants, the dopaminergic regulation of feeding behaviour has not been investigated. Therefore, the effects of dopamine receptor agonists and antagonists on food intake and forestomach motility were studied in dwarf goats. Goats treated i.v. with bromocriptine (1 micrograms or 2.5 micrograms/kg body wt/min during 10 min) ate less food than when treated with saline. This inhibitory effect on food intake could not be prevented by the peripheral dopamine receptor antagonist domperidone (0.5 mg/kg body wt i.v.). In contrast, dopamine (i.v. 20 micrograms/kg body wt/min during 15 min), levodopa (i.v. 40 micrograms/kg body weight during 10 min), apomorphine (i.v. 2 micrograms/kg body wt/min during 10 min) and lisuride (i.v. 0.2 microgram/kg body wt/min during 15 min and 0.5 microgram/kg body wt during 10 min) failed to modify food intake. Given in association with benserazide, a decarboxylase inhibitor (i.v. 20 micrograms/kg body wt/min during 10 min), levodopa was still inactive as an anorectic agent. Levodopa, bromocriptine and lisuride administered at similar dose rates to those which were used in the food intake experiments, induced some clinical signs including inhibition of forestomach contractions. The inhibition of rumen contractions induced by these drugs was completely antagonized by domperidone pretreatment. These results, together with earlier in vivo and in vitro observations, suggest that the inhibitory effects of dopamine receptor agonists on forestomach contractions are due to interactions with peripheral dopaminergic receptors. The change in smooth muscle tension, which leads to a change in the signals transmitted via vagal afferents to the central nervous system, probably does not modify feeding behaviour in dwarf goats.(ABSTRACT TRUNCATED AT 250 WORDS)