Neonatal hydrocortisone: effect of the development of the stress response and the diurnal rhythm of corticosterone.
Neonatal rats were given s.c. injections of 1 mg of hydrocortisone acetate, and the effect on the subsequent development of the pituitary-adrenal response to ether stress and the development of the circadian rhythm in adrenal and serum corticosterone (B) was investigated. Following exposure to ether, adrenal steroids were elevated in 11-day-old controls. The response did not appear in treated animals until 25 days. At this age, the time-course of response to ether in the adrenal was more sluggish in hormone-treated rats. After stress, serum corticoids were high in controls at 20 days; however, this rise did not appear in treated rats until 25 days. Serum corticoids, 5-60 min after ether, tended to be lower in 25-day-old runts than in controls. The diurnal rhythm in serum B first appeared in controls at 27 days and in treated animals at 30 days. The rhythm in adrenal corticoids appeared in both groups at 30 days.