Effects of pregnancy in rats on cysteamine-induced peptic ulcers: role of progesterone.

After mating with a sexually active male, groups of female Sprague-Dawley rats were injected with cysteamine (400 mg/kg, subcutaneously) at day 0 (controls), day 5 (early-stage pregnancy), and day 18 (late-stage pregnancy) of pregnancy. In contrast to late-stage pregnancy rats, early-stage pregnancy animals showed a decrease of cysteamine-induced gastroduodenal lesions. When subjected to cysteamine injection, both nonpregnant female and male rats treated for eight days with progesterone (300 microg/rat, subcutaneously) showed a reduced incidence of gastroduodenal lesions. No effect was found in animals pretreated with 17beta-estradiol (200 microg/rat, subcutaneously). Furthermore, increased gastroduodenal mucus levels were found in early-stage pregnancy rats and in animals pretreated with progesterone. These results suggest that increased progesterone plasma levels during early-stage pregnancy may be involved in pregnancy-induced gastric and duodenal protection. This effect may be related to an increase in gastric and duodenal mucus production induced by this hormone.