Glucocorticoids stimulate rabbit proximal convoluted tubule acidification

Glucocorticoids have an important role in renal acidification; however, a direct effect of glucocorticoids on proximal convoluted tubule (PCT) acidification has not been directly demonstrated. In the present in vitro microperfusion study PCT from animals receiving dexamethasone (600 μg/kg twice daily for 2 d and 2 h before killing) had a significantly higher rate of bicarbonate absorption than did controls (92.0±13.3 vs 59.9±3.2 pmol/mm · min, P < 0.01). To examine if glucocorticoids had a direct epithelial action, dexamethasone was added to the bath, of PCT perfused in vitro. After 3 h of incubation in paired experiments 10^-6 M and 10^-5 M dexamethasone resulted in an ∼ 30% stimulation in the rate of bicarbonate absorption. 10^-7 M dexamethasone and 10^-6 M aldosterone had no effect on bicarbonate absorption. The stimulation of acidification by 10^-5 M dexamethasone was blocked by actinomycin D and cycloheximide. These data are consistent with a direct effect of glucocorticoids on PCT acidification, and this effect is depen-dent upon protein synthesis.