Decreased responsiveness of pituitary-adrenal axis to stress in vitamin A-depleted rats.

The functional ability of pituitary-adrenocortical system in relation to adequacy of vitamin A-nutriture was studied by comparing magnitude of its response to stress in vitamin A-depleted rats with that in normal animals. Repeated 4 h-daily immobilizations provoked a significant increase in urinary excretion of free plus conjugated transcortin-bindable corticosteroids with a concomitant rise in serum and adrenal content of free corticosteroids. In the vitamin A-depleted rats stress-evoked increase in urinary excretion and, serum and adrenal level of corticosteroids was less marked than those in the normal animals. The serum ACTH response to the stress was also decreased in the vitamin A-depleted rats. These results suggest that stress-induced activation of the pituitary-adrenocortical axis is significantly reduced in the vitamin A-depleted rats and that this depression is due, in part, to reduction of hypophyseal secretion of ACTH.