Serum inflammatory responses of transcortin binding activities and of total and free corticosterone and progesterone levels in developing rats: a kinetic approach.

The kinetics of the inflammatory responses of 5 serum parameters involved in specific protein-hormone interactions were studied, namely: transcortin (CBG) binding activities; total corticosterone (B), main ligand of CBG; unbound corticosterone (free B); total progesterone (P4), main competitor of B for binding on CBG; and the free P4. The studies were performed in developing animals, i.e. on rats given a single turpentine injection at 1, 10, 21 or 90 days of post-natal age. The responses showed similar trends at all ages, but age-dependent differences in kinetics and reactivities. Common characteristics were 3-5-fold increases of the hormone parameters as soon as 4-8 h after the injection, and 2-3-fold decreases in CBG activities. A remarkable age-dependent difference was the contrast of early CBG decrease in adults (4 h after turpentine) to the delayed occurrence of this reaction in immatures (8-24 h after turpentine). On the other hand, the increase of free B lasted for 72 h in neonates, but only 40 h in rats treated at 21 or 90 days. Age-dependent characteristics were seen also in reactivities: the peak increases in the hormone levels were highest in the young, while the peak decreases of CBG were most marked in the mature animals. The results suggest that the regulatory mechanisms governing the mutual effects of hormonal activities and CBG synthesis might depend on the stage of development.