Significance of the biphasic developmental pattern of the hypothalamo-pituitary-adrenocortical system in the rat

One group of neonatal rats was injected with metopirone at 2-5 days and the second group at 7-10 days of age. At 14 and 21 days all rats treated with metopirone had reduced body and adrenal weights in comparison with their saline-treated littermates. At 21 days the smallest adrenals were in the rats treated with metopirone at 7-10 days. Metopirone increased resting and stress levels of adrenal and plasma corticosterone in the 14-day-old rats and the response to stress by the adrenal corticosterone increase in the 21-day-old rats. The differential effect of metopirone applied in two developmental periods was indicated.