title: Does the kidney 'escape' from the kaliuretic action of mineralocorticoids?
abstract: The purpose of this study was to determine if there are renal mechanisms which limit the magnitude of potassium loss during mineralocorticoid-induced hypokalemia. To study the renal effects of mineralocorticoids in vivo, the 'cortical distal nephron' transtubular [K] gradient (TTKG) was calculated by dividing the urine [K] by the urine to plasma osmolality ratio; this in turn was divided by the arterial plasma [K]. Hypokalemia (2.6 +/- 0.1 mM) was induced in rabbits by the daily administration of 5 mg deoxycorticosterone acetate (DOCA) for 9-13 days. Infusion of a K-free isotonic solution into these rabbits resulted in more severe hypokalemia (1.6 +/- 0.1 mM) and a TTKG of 4.3 +/- 0.3. The subsequent infusion of a 60-mM K-containing solution elevated the plasma [K] to 5.1 +/- 0.1 mM and was associated with a significant rise in the TTKG to 5.9 +/- 0.4 (p less than 0.05). A K-free solution was then infused to lower the plasma [K]; when the plasma [K] fell below 4 mM, the TTKG decreased to 4.4 +/- 0.3 (p less than 0.05), and was equal to the preinfusion value. Thus, DOCA-induced hypokalemia diminishes renal K excretion by two mechanisms: first, the lower value for the denominator of the TTKG (the plasma [K]) results in a lower luminal [K] at a given TTKG. Second, the TTKG fell during hypokalemia and thereby decreased the luminal [K] in the cortical distal nephron. Hence the urinary K excretion rate was diminished to a greater extent than that predicted from the fall in the plasma [K] despite continuing mineralocorticoid action.
authors: Department of Medicine, St. Michael's Hospital, Toronto, Ont., Canada.
authors: R M
authors: RM
authors: Zettle
authors: M L
authors: ML
authors: West
authors: C B
authors: CB
authors: Chen
authors: M L
authors: ML
authors: Halperin
mesh_terms: D000818:Animals; D003900:Desoxycorticosterone / Q000494:pharmacology*; D005260:Female; D006929:Hyperaldosteronism / Q000378:metabolism; D007668:Kidney / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D011188:Potassium / Q000097:blood / Q000652:urine*; D011817:Rabbits
chemical_list: D003900:Desoxycorticosterone; D011188:Potassium