CHOLECYSTOKININ DOES NOT ACT ON THE EFFERENT PATHWAY OF CHOLINERGIC AND ADRENERGIC-NERVES TO INHIBIT RUMINAL CONTRACTIONS IN SHEEP (OVIS-ARIES)

The effect of exogenous cholecystokinin-octapeptide (CCK-8) on ruminal contractions and the role of efferent pathways of cholinergic and adr energic nerves on the effect were studied in sheep. Intravenous infusi on of CCK-8 at 11.4 and 45.6 pmol/kg/min significantly inhibited the f requency and amplitude of ruminal contractions in conscious sheep. Aft er bilateral cervical vagotomy, intravenous infusion of CCK-8 at 45.6 mol/kg/min had no detectable effect on amplitude of ruminal contractio ns induced by electric stimulation to the cervical vagus nerve (1 msec , 20 Hz, 5 mA, for 10 sec at 1-min intervals) in anesthetized sheep. T he amplitude of contractile responses of ovine ruminal muscle strips t o acetylcholine at 5 x 10(-5) M was not inhibited by CCK-8 applied sim ultaneously at 1 x 10(-9) M. Intravenous infusion of phentolamine at 5 3.0 nmol/kg/min, propranolol at 101.4 nmol/kg/min, or their combined i nfusion did not alter the inhibitory action of CCK-8 at either dose on ruminal contractions in conscious sheep. These results suggest that C CK-8, which does not act on the efferent pathway of cholinergic and ad renergic nerves, may reflexively inhibit reticuloruminal contractions via vagal afferent fibers in sheep.