Nephron site responsible for the reduced kaliuretic response to mineralocorticoids during hypokalemia in rats.
 Rats with hypokalemia induced by eating a low-K diet have a diminished kaliuretic response to mineralocorticoids.
 The purpose of this study was to determine if this was the due to a lower rate of net secretion of K in the cortical collecting duct (CCD) and/or an enhanced rate of reabsorption of K in the medullary collecting duct (MCD).
 Secondary active secretion of K in the CCD raises the [K] in the lumen as compared to the plasma [TF/P)K).
 If the (TF/P)K is greater than 1, there was secondary active secretion of K in this nephron segment.
 The (TF/P)K in the CCD was measured by microcatheterization of the collecting duct.
 Three groups of rats were studied: rats on a low-K diet with and without the acute administration of DOCA, and rats on a normal-K diet treated with DOCA on a chronic basis.
 Rats on the low-K diet had a (TF/P)K of 0.8 +/- 0.11; this value did not rise to values significantly greater than 1 after the acute administration of DOCA (1.4 +/- 0.35).
 In contrast, chronic administration of DOCA to rats fed a normal-K diet did result in a (TF/P)K which was significantly greater than unity (3.1 +/- 0.39).
 The degree of hypokalemia was not significantly different in these rats.
 The absolute and fractional reabsorption of K in the MCD was not different in the rats on the low-K diet with or without DOCA.
 We conclude that the nephron segment which is responsible for the reduced kaliuretic response to mineralocorticoids is the CCD.
