Involvement of α‐adrenoreceptors in the regulation of omasal cyclic myoelectrical activity in sheep

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Abstract
In five conscious adult ewes at rest, chronically implanted with electrodes in the musculature of the omasal wall, intravenous (i.v.) infusion for 30 min of .alpha.1- or .alpha.2-adrenergic receptor blockers, prazosin (20 .mu.g/kg/min) and yohimbine (30 .mu.g/kg/min), respectively, had no significant effects on omasal myoelectrical activity. The i.v. adminstration for 15 min of .alpha.1- or .alpha.2-agonists phenylephrine (4 .mu.g/kg/min) or naphazoline (2.5 .mu.g/kg/min), respectively, increased the frequency and the amplitude of groups of myoelectrical discharges of omasum, as well as the duration of its activity. Pretreatment of animals prazosin blocked the responses to phenylephrine. Yohimbine prevented the effects of naphazoline dose-dependently. It is suggested that both .alpha.- and .alpha.2-adrenoreceptors are involved in regulation of the sheep''s omasal motility. This regulation did not seem to be a simple consequence of the changes in the reticular motility.

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