Effects of acute acid-base disturbances on K+ delivery to the juxtamedullary end-descending limb.
Effects of acute-base disturbances on fractional delivery of potassium to the juxtamedullary end-descending limb were examined by micropuncture in the rat to test the hypothesis that potassium is reabsorbed from the collecting duct and is secreted in juxtamedullary pars recta or descending limb in the renal medulla. In metabolic acidosis, fractional potassium delivery was only slightly reduced compared with control values and was a function of potassium excretion, as the hypothesis predicts. Fractional potassium delivery was sharply reduced both in respiratory acidosis and metabolic alkalosis and was no longer a function of potassium excretion. Although seemingly inconsistent with the recycling hypothesis, the latter finding may be reconciled by the following observations. In respiratory acidosis, vasa recta blood flow nearly doubled, which would lead to vascular washout of interstitial potassium. In metabolic alkalosis, flow rate in the pars recta or descending limb was reduced by 28%, which would limit transepithelial potassium addition. The results indicate complex effects of acid-base disturbances on fractional potassium delivery to the end-descending limb, which can be unified by postulated changes in transepithelial potassium concentration differences across the juxtamedullary pars recta or descending limb. An unexpected observation emerged--fractional delivery of water to the end-descending limb declined as a function of plasma bicarbonate concentration when all groups were combined.
D000137:Acid-Base Imbalance / Q000378:metabolism*; D000138:Acidosis / Q000378:metabolism; D000142:Acidosis, Respiratory / Q000378:metabolism; D000208:Acute Disease; D000471:Alkalosis / Q000378:metabolism; D000818:Animals; D001160:Arterioles; D001784:Blood Gas Analysis; D005260:Female; D007687:Kidney Tubules, Proximal / Q000378:metabolism; D009399:Nephrons / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values; D012079:Renal Circulation; D013431:Sulfates / Q000494:pharmacology
D013431:Sulfates; D011188:Potassium