title: Mechanism of potassium depletion during chronic metabolic acidosis in the rat.
abstract: Pair-fed rats on a normal K diet were given either 1.5% NH4Cl or water for 4 days. The acid-fed animals developed metabolic acidosis, negative K balance, and K depletion. Urinary Na excretion and urinary flow were not different between the groups beyond the first day. After the 4 days, isolated kidneys from animals in each of these groups were perfused at normal pH and bicarbonate concentrations. Urinary K excretion was similar between the groups despite the potassium depletion in the acid-fed animals. In contrast, isolated kidneys from animals with comparable K depletion induced by dietary K restriction readily conserved K (fractional excretion 0.35 +/- 0.04 vs. 0.83 +/- 0.09 by the kidneys from acid-fed animals, P less than 0.01). Sodium excretion and urinary flow were similar among the three groups of isolated kidneys. Plasma aldosterone concentrations were greater in the acid-fed rats after the 4 days of NH4Cl ingestion than in the control animals (43 +/- 10 vs. 10 +/- 2 ng/dl, P less than 0.01). Adrenalectomized rats were treated with either normal (4 micrograms/day) or high (22 micrograms/day) aldosterone replacement while ingesting NH4Cl for 4 days. Only in the presence of high aldosterone replacement did the acid-fed adrenalectomized animals develop K depletion. We conclude that chronic metabolic acidosis stimulates aldosterone secretion, and that aldosterone maintains the inappropriately high urinary potassium excretion and K depletion seen in this acid-base disorder.
mesh_terms: D000138:Acidosis / Q000503:physiopathology*; D000315:Adrenalectomy; D000450:Aldosterone / Q000494:pharmacology; D000643:Ammonium Chloride; D000818:Animals; D002908:Chronic Disease; D066298:In Vitro Techniques; D007668:Kidney / Q000187:drug effects / Q000502:physiology / Q000503:physiopathology*; D007700:Kinetics; D008297:Male; D010477:Perfusion; D011188:Potassium / Q000378:metabolism*; D011191:Potassium Deficiency; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism
chemical_list: D000643:Ammonium Chloride; D000450:Aldosterone; D012964:Sodium; D011188:Potassium