Adrenal and Plasma Corticosterone and Vitamin A in Rat Adrenal Glands During Postnatal Development

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Abstract
Studies on the maturation of the hypothalamo-pituitary-adrenal system have indicated a period in development during which the newborn rat appears nonresponsive to stress, even though a significant adrenal response to exogenous ACTH at birth occurs. This report presents a series of experiments on some of the parameters of the response of the adrenal gland in the newborn to combined ether stress and exogenous ACTH. Newborn rats were subjected to intravenous injections of saline or ACTH under ether anesthesia. Different groups of animals were tested at 3-day intervals from birth through 21 days of age. The results indicated that in response to stress the newborn did not show a significant elevation in plasma corticosterone until 18 days of age. However, plasma steroid levels were elevated following ACTH injection as early as 3 days of age, following which there ensued a developmental period during which the release of steroid by the adrenal gland was refractory to corticotropin and this refractory period lasted until approximately 15 days of age. In contrast, elevations in adrenal corticosterone concentration were seen with both stress and ACTH as early as 3 days of age and these increases were observed through all ages tested. Thus, there appears to be a clear distinction between synthesis and release of adrenal steroids. In addition, vitamin A content and concentration in the adrenal gland was determined throughout the period of development investigated because the vitamin has been claimed to be implicated in the biosynthesis of the hormone. It was found that the vitamin concentration over the first 12 days post partum paralleled changes in the concentration of corticosterone in the adrenal following ACTH treatment. (Endocrinology80: 910, 1967)