Corticosteroid feedback: I. General characteristics, role of adrenal cortex.

The dependence of the basal corticosterone content, the stress-induced response of the pituitary-adrenocortical system (PACS) and ACTH-induced adrenal response on different doses of hydrocortisone has been studied in rats. PACS and adrenal responses were estimated by the corticosterone content in blood. Hydrocortisone was administered intraperitoneally in the dose of 100 micrograms/100 g b.w., 300 micrograms/100 g b.w. and 1200 micrograms/100 g b.w. The following relationships in functioning of corticosteroid feedback are described: 1) The suppression of the amplitude of the stress-induced PACS response is proportional to the logarithm of the administered hydrocortisone dose; 2) logarithm of the inhibition period of the basal corticosterone content and stress-induced PACS response is proportional to the logarithm of the administered hydrocortisone dose; 3) increasing doses of hydrocortisone affect to a greater extent the suppression period of the stress-induced content than of the basal corticosterone one; 4) hydrocortisone administration affects to a lesser extent the amplitude and the suppression period of ACTH-induced adrenal response than of the stress-induced PACS response. The conclusion was made that adrenal glands were involved in ensuring the feedback only at high doses of corticosteroids, contribution making up only a part of that discovered in PACS inhibition.