K infusion corrects thick ascending limb Cl reabsorption in K-depleted rats by an aldosterone-independent mechanism.
Others have provided evidence that thick ascending limb (TAL) NaCl reabsorption is aldosterone dependent in adrenalectomized animals. In rats fed a K-free diet, plasma K concentration ([K]) is reduced and plasma aldosterone concentration [Aldo] is decreased. Because aldosterone release is regulated by extracellular fluid (ECF) [K], the purpose of the present study was to determine whether aldosterone deficiency mediates inhibition of TAL NaCl transport in K-depleted rats (K-Dep). Cl reabsorption was measured in functionally isolated loop segments microperfused in vivo (22 nl/min) using a modified perfusate that minimizes proximal nephron reabsorption. The results of our studies show that the defect in TAL Cl reabsorption in K-Dep rats is quantitatively significant and can be rapidly reversed by the acute systemic infusion of K. However, acute administration of aldosterone, in the presence of sustained K-Dep, failed to reverse the impairment in TAL Cl reabsorption in K-Dep rats. Furthermore, acute infusion of K, in the presence of an aldosterone antagonist, in K-Dep rats rapidly corrected the defect in TAL Cl reabsorption. Additional studies showed that despite normalization of ECF [K] by acute K infusion in K-Dep rats, plasma [Aldo] failed to increase. In contrast, acute infusion of KCl in control rats increased plasma [Aldo] by 46%, but Cl reabsorption was unchanged. In summary, these results provide conclusive evidence that the correction of defective TAL Cl reabsorption in response to the acute administration of K in K-Dep rats occurs via an aldosterone-independent mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)
McKay
A J
AJ
Department of Physiology, University of Ottawa, Ontario, Canada.
Peterson
L N
LN
D000042:Absorption; D000450:Aldosterone / Q000097:blood / Q000494:pharmacology / Q000502:physiology*; D000818:Animals; D002712:Chlorides / Q000493:pharmacokinetics*; D007262:Infusions, Intravenous; D008138:Loop of Henle / Q000378:metabolism*; D008297:Male; D011188:Potassium / Q000097:blood / Q000494:pharmacology*; D011191:Potassium Deficiency / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012016:Reference Values; D013148:Spironolactone / Q000494:pharmacology
D002712:Chlorides; D013148:Spironolactone; D000450:Aldosterone; D011188:Potassium