PINOCYTOSIS PERSISTS IN THE ILEUM OF HYPOPHYSECTOMIZED RATS UNLESS CLOSURE IS INDUCED BY THYROXINE OR CORTISONE

It was previously reported that in rats hypophysectomized at 6 days of age, the apicotubular system that permits the entrance of macromolecules closes spontaneously in the duodenal epithelium. Extending these observations to the ileum, where pinocytosis is nutritionally important in the suckling rat, now reveals that in the absence of the hypophysis, closure of the surface does not occur. Hence, the failure of growth that sets in during the fourth postnatal week appears not to be due to malnutrition consequent on the cessation of intracellular digestion. Treatment of the hypophyseoprivic sucklings with either thyroxine or cortisone from 15 to 23 days causes the disappearance of the apical infoldings, vesicles, and giant vacuole characteristic of the suckling stage. Instead, the cells exhibit all of the ultrastructural features typical of mature ileal epithelium. The effects of the two hormones differed in that cortisone caused a slightly greater lengthening of the microvilli. These results further extend the evidence indicating that either thyroid hormone or glucocorticoid can activate the complete regulatory program that brings about the redifferentiation of the intestinal epithelium from the suckling to the mature type. © 1979.