Converting a stomach to a uterus: the microscopic structure of the stomach of the gastric brooding frog Rheobatrachus silus.

Rheobatrachus silus is a rare aquatic frog of eastern Australia. The female ingests the eggs after fertilization and broods them in the stomach until fully formed. "Gastric brooding" takes place in the fundus and proximal part of the body of the stomach, which dilates to accommodate the growing young. The surface epithelium becomes attenuated and the cells contain fewer mucus droplets. The acini of the glands are less numerous because of stretching, and they contain oxyntic cells that show evidence of profound suppression or regression. Morphometric studies on the limited number of samples show that the oxyntic cells are attenuated with few surface projections, sparse tubulovesicular reticulum, and a few pepsinogen granules and mitochondria. Eight days after ejection of the young, and 4 days after feeding commences, the lining shows a return of gastric pits and glands. The oxyntic cells show many surface projections and a proliferation of the tubulovesicular reticulum and mitochondria. These findings suggest that the eggs, tadpoles, and juvenile frogs release a substance, or substances, that inhibit acid secretion immediately after the eggs are ingested and that persist throughout brooding.