What is responsible for the diurnal variation in potassium excretion?
Potassium excretion exhibits a diurnal pattern, with most excretion occurring close to noon in humans. Each component of the K+ excretion rate [urinary K+ concentration ([K+]) and flow rate] was measured and back-calculated to reflect events in the cortical collecting duct (CCD). Our purpose was to determine to what extent each component contributed to this diurnal variation in each 2-h portion of the day. In humans, K+ excretion rose threefold from nadir (0600 h) to peak (1200-1400 h), 18 h after the principal intake of K+. The variation in K+ excretion was due almost exclusively to changes in [K+] in the terminal CCD ([K+]CCD) rather than via changes in flow rate. In rats, the bulk of K+ excretion occurred shortly after eating. Both components of K+ excretion rose after meals; the rise in the [K+]CCD (3.3-fold) predominated at earlier times, and the rise in flow rate occurred later and was primarily a result of a higher rate of excretion of urea. The rise in [K+]CCD did not correlate with aldosterone levels or administration. A very large rise in the [K+]CCD only occurred in the presence of bicarbonaturia; the transtubular potassium concentration gradient was now close to 15 in the morning and evening.
Steele
A
A
Department of Medicine, St. Michael's Hospital, Toronto, Ontario, Canada.
deVeber
H
H
Quaggin
S E
SE
Scheich
A
A
Ethier
J
J
Halperin
M L
ML
D000086:Acetazolamide / Q000494:pharmacology; D000328:Adult; D000818:Animals; D001639:Bicarbonates / Q000652:urine; D002940:Circadian Rhythm; D005260:Female; D006801:Humans; D007684:Kidney Tubules / Q000378:metabolism; D007685:Kidney Tubules, Collecting / Q000378:metabolism; D008297:Male; D008901:Mineralocorticoids / Q000494:pharmacology; D009994:Osmolar Concentration; D011188:Potassium / Q000378:metabolism / Q000652:urine*; D051381:Rats
D001639:Bicarbonates; D008901:Mineralocorticoids; D000086:Acetazolamide; D011188:Potassium