Abstract
In sheep, both beta (β)-endorphin (1 and 2 μg kg −1) and gamma (γ)-endorphin (2 μg kg −1) administered into the third cerebral ventricle caused a significant depression of rumen motility. The amplitude of the first rumen contraction appearing immediately after the end of infusion was diminished and the average amplitude of primary rumen contractions was decreased. In contrast, γ-endorphin (1 μg kg −1) enhanced the mean amplitude of these primary contractions. The effects of endorphins were completely prevented by intracerebroventricular (i.c.v.) naloxone (12.5 μg kg −1) or 6-hydroxydopamine (6-OHDA 18.2 μg kg −1) pretreatment. These results suggest that a central inhibitory opioid system is involved in the endorphin-induced inhibition of forestomach motility and has an adrenergic character in sheep. Central chemical sympathectomy by 6-hydroxydopamine (6-OHDA) also caused increase of the mean frequency of the rumen contractions and completely prevented inhibitory intracerebroventricular endorphin induced effects on the forestomach motility. They confirm the physiological role of endogenous opioid peptide (EOP) in important functions of small ruminants.
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