Pathogenesis of digitoxin-induced duodenal ulcers in pregnant rats. Roles of gastric acid and duodenal alkaline secretion.

Late-stage pregnant rats (day 17) had higher rates of gastric acid secretion (45-55 mu eq/15 min) as compared to nonpregnant and middle-stage pregnant (day 10) rats (20-25 mu eq/15 min). In contrast, basal rates of duodenal alkaline secretion were significantly lower (2-3 mu eq/15 min) in pregnant rats (day 10 and 17) than those in nonpregnant rats (approximately 5 mu eq/15 min), although the duodenal mucosa responded to acid with a significant rise in HCO3- output in these three groups of rats. In pregnant rats (day 17), a single injection of digitoxin, a Na+ K+-ATPase inhibitor (10 mg/kg, subcutaneously), had no effect on basal acid and alkaline secretions, but significantly blocked the acid-induced HCO3- secretion for more than 18 hr from 6 hr after administration. This drug, when given once daily for four days (10 mg/kg, subcutaneously), produced well-defined ulcers in the proximal duodenum with few lesions in the stomach of female rats, and the severity and incidence were significantly higher in late-stage pregnant rats than in the other two groups of rats. Following repeated administration of digitoxin (10 mg/kg) to late-stage pregnant rats (days 17-20), acid secretion significantly declined after two days of treatment, while the acid-induced HCO3- secretion was significantly attenuated after one day of treatment and remained inhibited during the whole period. These results suggest that an impairment of the mechanisms related to acid-induced HCO3- secretion may be associated with the induction of duodenal ulcers caused by digitoxin in female rats, and the high incidence of these ulcers in late-stage pregnant rats may be due to acid hypersecretion.