Effect of pregnancy on gastric motility in vivo and in vitro in the guinea pig.

Experiments were designed to examine the effects of pregnancy on gastric emptying and on the in vitro contractile response of gastric smooth muscle to cholinergic stimulation. Gastric emptying of a radio-labeled liquid marker (51Cr in saline) was determined at regular intervals (5, 15, 30, and 60 min) in nonpregnant and pregnant (third trimester) guinea pigs. Gastric emptying after 30 min also was determined for animals 1 and 4 days postpartum. The in vitro contractile responses of muscle strips from the fundus, corpus, and antrum of nonpregnant and pregnant animals after stimulation with acetylcholine were analyzed with respect to the maximal force developed and the pD2 value (negative logarithm of the dose that gives a one-half maximal response). The results can be summarized as follows. Pregnancy was characterized by an increase in the amount of marker retained within the stomach at each time point. For nonpregnant animals the time to one-half emptying was approximately 10 min; in pregnant animals this was prolonged to 30 min. Gastric emptying was reduced in animals 1-day postpartum but returned to normal by 4 days after delivery. In contrast, pregnancy had no effect on the maximal contractile response to acetylcholine of muscle strips from the orad and caudad stomach or on their respective pD2 values. The results suggest that pregnancy is associated with decreased gastric emptying of liquids in the guinea pig, but that the delay cannot be attributed to alterations in the maximal force-generating capacity of gastric smooth muscle.