Early and delayed effects of hydrocortisone and onapristone on intestinal brush-border enzymes and their sialylation and on thymus growth in suckling rats.

The antigestagen-antiglucocorticoid onapristone (ZK 98.299) was tested on three glucocorticoid-sensitive systems after hydrocortisone (HC) administration to suckling male rats, by determining onapristone (ZK)-induced inhibition of HC-provoked (1) increase of activities of intestinal brush-border enzymes, (2) desialylation of brush-border components and (3) thymolysis. HC acetate (75 mg/kg body weight (b.w.)) was injected s.c. on postnatal days 9 and 10, and ZK (150 mg/kg b.w.) on days 9, 10 and 11. The animals were killed on day 12 for assessing the early effect, or on days 15-17 for determining the delayed effect of HC and ZK. In all three systems the glucocorticoid effects were antagonized by ZK. The most sensitive to HC were systems 1 and 3, which exhibited both the early and the delayed effects. The most sensitive to the counteraction of ZK against administered HC was system 1, where HC was antagonized in both its early and delayed effects, whereas only delayed antagonistic action against administered HC was found in system 2. ZK alone had an early inhibitory effect on the activities of several brush-border enzymes and produced an early increase in thymus weight, accompanied by an increased DNA-protein ratio. No delayed effects of ZK alone on the three systems were observed.