ESR1 and duodenal ulcer: Alternatively, estradiol, although not well proven, is believed to stimulate duodenal bicarbonate secretion through intracellular calcium mobilization and stimulation of Cl−/HCO3− anion exchange.31 One study showed that estrogen receptors are expressed in the duodenal mucosa which stimulates duodenal bicarbonate secretion explaining the lower prevalence of duodenal ulcers in premenopausal women compared to men.32