Search

Corticosterone-free (adrenalectomized, ADX) and intact rats were offered experimentally compounded diets in which 65% of available calories were supplied by a single macronutrient (single-diet study). ADX impaired the intake, weight gain (especially as body fat), and efficient utilization of high-protein and high-fat diets. In contrast, no behavioral, metabolic, or compositional changes could be found among ADX rats maintained on a diet high in carbohydrates. When ADX rats were given separate sources of macronutrients (self-selection study) they did not self-select a high-carbohydrate diet. Instead, they displayed a strong fat avoidance and a relative increase in protein intake, the macronutrient they utilize least efficiently. Separate groups of ADX animals were continuously infused with 25 or 125 micrograms.kg-1.day-1 aldosterone, a specific type I adrenocorticoid receptor agonist. Type I receptor stimulation eliminated all ADX-related deficiencies found in the single-diet and self-selection studies: caloric intake, feeding efficiency, carcass composition, and macronutrient preferences were restored to or beyond the corresponding values of adrenal-intact rats. The normal rat's ability to ingest and utilize macronutrients optimally is dependent on corticosterone's stimulation of type I receptors.

After the adrenal glands are removed without their capsules, so-called adrenal enucleation, rats initially retain sodium, and, after adrenal regeneration, escape from salt retention. To define the renal mechanisms involved in this alteration in salt handling, we have utilized clearance and micropuncture techniques in three groups of saline-expanded rats that were sham-operated (S), enucleated (AE), or escaped after adrenal regeneration (E.) Sodium excretion was clearly blunted after AE, 5.5 mueq/min vs. 20.5 for S and 18.7 for E. Although glomerular filtration rate (GFR) and filtered load of sodium were lower in AE rats, the delivered load of sodium beyond the late distal tubule was not different among the groups: 0.30 neq/min for AE, 0.42 for S, and 0.40 for E. This was a consequence of strikingly greater sodium reabsorption in the loop of Henle and distal tubule in both the S and E rats. In the collecting duct over 50% of the delivered sodium was reabsorbed by the AE rats while over 30% of the excreted sodium was added in this tubular segment in the other groups. These data demonstrate that the impaired natriuresis after adrenal enucleation appears to be due to striking differences in collecting duct function. Since adrenal regeneration in the escape animals reverses this sodium retention, the effect is probably related to some alteration in adrenal hormone production. Sodium excretion in markedly expanded normal rats also appears to be determined by the net addition of sodium in the collecting duct.