Effect of corticosteroids on proximal tubular acidification in the rat

The role of corticosteroid hormones in proximal tubular acidification was studied in control, sham-operated and adrenalectomized (ADX) rats by means of the stopped-flow microperfusion technique and by measurement of tubular acidification kinetics with pH microelectrodes. Rats were adrenalectomized 48 h before experiments, and aldosterone, corticosterone and 18-OH corticosterone (18-OH-B) were given intramuscularly 100 and 40 min before starting the experiments. Stationary proximal luminal pH increased from 6.78 to 7.03 after ADX, while acidification half-times (t1/2) increased from 4.41 to 11.43 s. In consequence, net bicarbonate reabsorption fell from 2.18 to 0.50 nmol/cm2 X s after ADX. The administration of the three hormones stimulated tubular acidification, bicarbonate reabsorption reaching 1.18-1.28 nmol/cm2 X s. These data suggest that proximal tubular acidification is stimulated by both mineralo- and glucocorticoid hormones and by 18-OH-B; their mechanisms of action is discussed on the basis of a recently described model.