AJP - Renal Physiology, Vol 263, Issue 4 705-F710, Copyright © 1992 by American Physiological Society
Vasopressin resistance in potassium depletion: role of Na-K pump
S. K. Mujais, Y. Chen and N. A. Nora
Department of Medicine, Northwestern University Medical School, Chicago, Illinois.
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)
