Localization of the nephron sites responsible for mineralocorticoid escape in rats

Fractional delivery of sodium (FDNA) from the superficial late distal tubule is increased in deoxycorticosterone acetate-(DOCA) treated rats, which may compensate for a presumed mineralocorticoid-stimulated sodium reabsorption in the cortical collecting tubule. In the present study, late proximal (LPT) and early distal tubules (EDT) were micropunctured during volume expansion in control and DOCA-treated rats. Whereas FDNa to the LPT was similar in the two groups, FDNa to the EDT was greater in DOCA-treated than in control rats. Additionally, LPT and deep loop of Henle (LH) were micropunctured in volume-expanded control and DOCA-treated rats. FDNa to the bend of the LH was increased in DOCA-treated rats compared to controls. These findings indicate that in DOCA escape sodium reabsorption is diminished in the pars recta and/or loop of Henle of superficial nephrons and there is increased delivery to the bend of the loop of deep nephrons. We conclude that mineralocorticoid escape is most likely due to increased sodium delivery to the cortical collecting tubule from both deep and superficial nephrons.