EFFECT OF ADRENAL ENUCLEATION ON SODIUM EXCRETION IN RAT

After the adrenal glands are removed without their capsules, so-called adrenal enucleation, rats initially retain Na, and, after adrenal regeneration, escape from salt retention. To define the renal mechanisms involved in this alteration in salt handling, clearance and micropuncture techniques were used in 3 groups of saline-expanded rats that were sham-operated (S), enucleated (AE) or escaped after adrenal regeneration (E). Na excretion was clearly blunted after AE, 5.5 .mu.eq/min vs. 20.5 for S and 18.7 for E. Although glomerular filtration rate (GFR) and filtered load of Na were lower in AE rats, the delivered load of Na 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 Na 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 Na was reabsorbed by the AE rats while over 30% of the excreted Na was added in this tubular segment in the other groups. 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 Na retention, the effect is probably related to some alteration in adrenal hormone production. Na excretion in markedly expanded normal rats also appears to be determined by the net addition of Na in the collecting duct.