Gastric emptying and gastric-intestinal transit in rats with varying ovarian hormone status

Basal and stimulated gastric emptying and gastrointestinal (GI) transit in rats of varying ovarian hormone status were compared to define direct ovarian hormone effects on GI function. Thyrotropin-releasing hormone (TRH) was used to evoke vagal GI motility stimulation. Adult female Sprague-Dawley rats were anesthetized (equithesin), ovariectomized, and implanted with 28-day estrogen (E), progestrone (P), E+P, or vehicle (V) pellets; males were also studies. On Day 26, fasted rats were anesthetized (urethane). Nonabsorbable C-14 polyethylene glycol-4000 in saline was gavaged at t = 0. At t = 5 minutes, TRH or saline was administered intracisternally. At t = 30 or 60 minutes, the GI tract was removed, ligated, sectioned, and counted. Gastric emptying was expressed as 100% minus the ration of gastric to total counts; GI transit was expressed as geometric center of radioactivity. In saline-treated rats, gastric emptying and GI transit at 60 minutes varied significantly among ovarian hormone-treated groups, with E lower and males elevated. TRH significantly increased both variables at both times in all groups. Results are consistent with acceleration of upper GI function in the absence of E, possibly contributing to GI symptoms during menopause and late luteal phase.