Studies of mechanisms of action of secretin and pancreozymin on rumen motility.

Rapid intravenous administration of a single bolus of secretin caused a marked decrease in both amplitude and frequency of rumen contractions, whereas pancreozymin administration caused a decrease in frequency but an increase in amplitude of rumen contractions. Alpha receptor blockade with phenoxybenzamine or beta receptor blockade with propranolol did not alter secretin or pancreozymin effects on rumen motility. Blockade of histamine receptor sites with tripelennamine did not prevent the secretin-induced decrease of rumen motility. A marked similarity in the decreased rumen motility pattern was observed when secretin effects were compared to aminophylline effects.