Neonatal dexamethasone administration. II. Persistent alteration of circadian serum anterior pituitary hormone rhythms in rats.

Newborn male rats were treated SC with dexamethasone phosphate (100 microgram) or dexamethasone acetate (100 microgram) on postnatal day 1, dexamethasone phosphate (5.0 microgram) opn postnatal days 1, 2, 3, or the corresponding drug vehicle. All animals were sacrificed 65-70 days later at previously determined daily trough and peak times of serum LH, TSH, and corticosterone: 0700 and 0100 h for LH, 0700 and 1300 h for TSH, and 0700 and 1900 h for corticosterone. None of the three dexamethasone treatment regimens affected the circadian variation of serum LH or corticosterone. Dexamethasone phosphate (100 microgram) altered the normal circadian rhythm of serum TSH in the adult animals, but the other two dexamethasone treatments did not affect the TSH rhythm. Basal 0700 h serum levels of FSH, PRL, and GH were also measured in these animals; none of the dexamethasone treatments altered the levels of these hormones compared to levels in the vehicle-injected controls.