Control of canine ACTH by corticosteroids: an integral feedback effect of steroids

These experiments were designed to test whether the pattern of change in plasma corticosteroid or the total corticosteroid dose is important in determining the degree of inhibition of adrenocorticotropic hormone (ACTH) responses to stress by corticosteroid intermediate-delayed feedback. Five conscious dogs were studied. The ACTH response to induced hypoglycemia was measured after no prior corticosteroid feedback signal or after a corticosteroid feedback signal produced by infusion, two bolus injections, or three bolus injections of cortisol and corticosterone. The total corticosteroid dose (45 micrograms/kg) and the total interval of steroid treatment (60-30 min before hypoglycemia) were the same in all three cases of corticosteroid treatment. Changes in plasma glucose concentration during induced hypoglycemia were not altered by corticosteroid treatment. The plasma ACTH response to hypoglycemia was inhibited by all three patterns of treatment with corticosteroids. The inhibition of ACTH response was not significantly altered among the patterns of treatment with corticosteroids. The data suggest that the integrated (total) or the mean change in plasma corticosteroid concentration over time determines the degree of inhibition of stimulated ACTH in this time domain.