EATING LOWERS DEFECATION THRESHOLD IN PIGS THROUGH CHOLINERGIC PATHWAYS

The effect of atropine on defecation threshold was compared to placebo pre- and postprandially in four 20- to 30-kg pigs. Stepwise balloon d istention was performed 10 cm from the anal verge with a 5-cm latex ba lloon. Volume was increased in steps of 10 ml up to 200 ml of air or u ntil the balloon was defecated (defecation threshold). Dependent measu res were balloon volume, rectal pressure, rectal compliance, and an in dex of distention-induced contractile activity. Under placebo conditio ns, the volume and pressure to elicit defecation were significantly lo wer after feeding (p < 0.05). The distention-induced contractile activ ity significantly increased near the defecation threshold, but pre- an d postprandial conditions were not different. No differences were seen between pre- and postprandial rectal compliance curves. Atropine abol ished the postprandial decrease in defecation threshold, but did not a ffect rectal compliance. The increase in contractile activity at defec ation threshold seen with placebo was abolished by atropine. These res ults show that eating lowers the defecation threshold in terms of dist ention volume and rectal pressure, and demonstrate that these changes are mediated through cholinergic pathways.