title: Vasopressin resistance in potassium depletion: role of Na-K pump.
abstract: Resistance to the hydrosmotic effects of vasopressin has been described in K depletion. It is not clear whether other effects of vasopressin, notably its effects on the Na-K pump in the collecting duct, are similarly affected. Adrenalectomized male Sprague-Dawley rats were allocated to either a normal K (NK) or low-K (LK) diet. Na-K pump activity (pmol.mm-1.h-1) in cortical collecting duct (CCD) and medullary collecting duct (MCD) was determined at 21 days after allocation to the dietary groups before and after exogenous vasopressin (0.1 U twice daily for 3 days). In animals on NK diet, vasopressin (AVP) led to a doubling of Na-K pump activity in the CCD from 502 +/- 47 to 1,144 +/- 41 pmol.mm-1.h-1 (P < 0.01). In K-depleted animals, which had a higher baseline Na-K pump activity, an increase was also observed from 1,056 +/- 97 to 1,239 +/- 65 pmol.mm-1.h-1 (P < 0.05), but this increase was quantitatively less, with the change being 183 vs. 642 pmol.mm-1.h-1 in K-replete rats. The findings in the MCD were similar; in rats on a NK diet, AVP led to a significant increase in Na-K pump activity from 498 +/- 29 to 830 +/- 28 pmol.mm-1.h-1 (P < 0.01). With K depletion, this directional change was preserved, increasing from 1,380 +/- 49 to 1,556 +/- 45 pmol.mm-1.h-1 (P < 0.05), but was quantitatively less than in K-replete rats, the change being 176 vs. 332 pmol.mm-1.h-1.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Medicine, Northwestern University Medical School, Chicago, Illinois.
authors.forename: S K
authors.initials: SK
authors.lastname: Mujais
authors.forename: Y
authors.initials: Y
authors.lastname: Chen
authors.forename: N A
authors.initials: NA
authors.lastname: Nora
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology*; D004351:Drug Resistance; D007672:Kidney Cortex; D007679:Kidney Medulla; D007685:Kidney Tubules, Collecting / Q000473:pathology; D008297:Male; D011191:Potassium Deficiency / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects / Q000502:physiology*
chemical_list: D001127:Arginine Vasopressin; D000251:Adenosine Triphosphatases; D000254:Sodium-Potassium-Exchanging ATPase