Abstract:

The role of adrenocortical steroids in distal nephron acidification was studied in rats by measuring urine minus blood PCO2 differences (U-B PCO2) in control, sham-operated, and adrenalectomized (ADX) animals. Operations were performed 48 h before experiments. During the experiments, all rats received an infusion of 0.35-0.60 M NaHCO3, leading to urine bicarbonate concentrations in the order of 100-200 mM. Adrenalectomized rats had significantly decreased U-B PCO2 (11.9 ± 1.99 mmHg; 1 mmHg = 133.3 Pa) with respect to sham-operated rats (39.9 ± 1.26 mmHg). In another series, ADX rats received supplements of the adrenal steroids corticosterone, aldosterone, and 18-hydroxycorticosterone 100 min before the experiment. U-B PCO2 increased after hormone administration: corticosterone, 30.0 ± 2.13 mmHg; aldosterone, 26.6 ± 1.74 mmHg; 18-hydroxycorticosterone, 29.0 ± 1.60 mmHg; but none restored these values to normal. Combinations of two hormones were also used; only aldosterone + corticosterone restored U-B PCO2 to normal: 39.0 ± 1.66 mmHg. Renal phosphate excretion (but not urine phosphate levels) decreased significantly in ADX as compared with sham-operated rats. Extracellular volume was not significantly affected in ADX rats, which received ad libitum 0.9% NaCl for drinking. It is concluded that distal tubular acidification, as evaluated by U-B PCO2, is dependent on cortical steroids.