Gastric emptying and gastrointestinal transit during lactation in rats.

Female sex hormones can influence gastrointestinal function. To understand whether postpartum changes in female sex hormones may affect such function, gastric emptying and gastrointestinal transit were measured in rats on days 1-2, 10, 15, and 21 of lactation, on day 7 postweaning, and at the nonpregnant diestrous stage. Gastric emptying and gastrointestinal transit were assessed in conscious rats 15 min after intragastric instillation of a test meal containing charcoal and (51)Cr. The results showed that gastric emptying was increased throughout the first 2 wk of lactation, with a gradual decrease as lactation proceeded toward weaning, and returned to the level of the virgin rats by 1 wk postweaning. Gastrointestinal transit was greater in the early stage of lactation and was related to gastric emptying (P < 0.001). Increases in gastric emptying and intestinal length were correlated with lactation (P < 0.001) and plasma prolactin levels (P < 0.05) but not with plasma progesterone or estradiol levels. We concluded that the sex steroid hormones associated with lactation do not mediate a change in gastric emptying and gastrointestinal transit during lactation.