In vitro effects of bethanechol on abomasal and duodenal smooth muscle preparations from dairy cows with left displacement of the abomasum and from healthy dairy cows.

This study investigated the effects of bethanechol (BeCh) on abomasal and duodenal smooth muscle preparations from dairy cows with left displacement of the abomasum (LDA) and from healthy dairy cows, and determined the role of muscarinic acetylcholine receptor subtypes 2 and 3 (M(2) and M(3)) in mediating contraction. Concentration-response curves for BeCh, with or without prior incubation with an M(2) antagonist (AF-DX 116) or an M(3) antagonist (4-DAMP), were established and evaluated. BeCh induced a significant, concentration-dependant increase in the contractility variables for all locations in both groups of cows. The inhibiting effect of 4-DAMP was stronger than that of AF-DX 116, which suggested that contractions were mediated by M(3) and to a lesser extent by M(2). The basal tone of abomasal smooth muscle was reduced in cows with LDA, which indicated hypotonia. The use of BeCh as a prokinetic drug in cows with gastrointestinal motility disorder warrants further investigation.