The effect of corticosterone and thyroxine on the development of parietal cells was studied in 20-day-old rats. Either corticosterone or thyroxine injection significantly increased the amount of mitochondria, tubulovesicles, and intracellular canaliculi in normal rat pup parietal cells. However, the ultrastructure of parietal cells did not change when rats were adrenalectomized or made hypothyroid by propylthiouracil (PTU) during the first week of life. Corticosterone had the same effect in hypothyroid rats as in normal rats, increasing the volume fraction of mitochondria and the surface density of tubulovesicles and intracellular canaliculi in the parietal cell. However, thyroxine failed to do so in adrenalectomized animals. When 20-day-old adrenalectomized or hypothyroid rats were challenged with secretagogues, there was no increase in maximal acid output over the basal secretory rate, while normal rats showed a 40-50% increase. We conclude that 1) normal parietal cells respond to additional thyroxine or corticosterone with increases in volume fraction of mitochondria and surface density of tubulovesicles and intracellular canaliculi; 2) the dramatic decreases in acid secretion observed in adrenalectomized or PTU-treated rats are not explained by the morphology of parietal cells that remains normal; 3) the effect of thyroxine on the development of acid secretion is mediated by corticosterone; and 4) unlike chief cells the morphological development of parietal cells does not appear to depend on corticosterone or thyroxine after postnatal day 7.
Maximal acid output