The Role of ACTH and Adrenal Glucocorticoids in the Salt Appetite of Wild Rabbits [Oryctolagus cuniculus (L)

Abstract

The selective appetites of wild rabbits for 500 mEq/1 solutions of NaC1, KC1, MgC1(2), and CaC1(2) were studied in intact and adrenalectomized rabbits during daily treatment with either 4 IU long acting ACTH, 1.0 or 2.5 mg cortisol acetate, or 2.5 mg corticosterone. The animals were individually caged and external sodium balances performed. In intact rabbits, cortisol or corticosterone produced a significant stimulation of NaC1 appetite. The response to concurrent dosage of cortisol and corticosterone was less than half of that obtained with ACTH which produced a comparable alteration of blood glucocorticoid levels but a 10-fold increase in NaC1 intake. CaC1(2) intake was increased in intact rabbits by cortisol treatment but not by corticosterone or ACTH. Adrenalectomized rabbits maintained on daily steroid replacement therapy of 0.1 mg deoxycorticosterone acetate and 0.75 mg cortisone acetate showed a normal pattern of electolyte, food, and water intake. Under these conditions ACTH produced a 4-fold increase in NaC1 intake. Further addition of cortisol and corticosterone to steroid replacement therapy produced an increase in NaC1 intake comparable to their effect on normal rabbits. Thereupon supplementation with ACTH resulted in an increase to a level at least as great as that found in ACTH treated, normal rabbits. The effects of ACTH and glucocorticoids on NaC1 appetite were synergistic. Sodium balance showed that increases in NaC1 intake were not the result of the treatment initially producing a body sodium deficit, which was then corrected by increased intake. The results provide further evidence for the hypothesis that NaC1 appetite may be hormonally regulated, and demonstrate that ACTH is capable of stimulating NaC1 intake by a previously unsuspected non-adrenal pathway.