What is responsible for the diurnal variation in potassium excretion?
Steele, A.; deVeber, H.; Quaggin, S.E.; Scheich, A.; Ethier, J.; Halperin, M.L.
American Journal of Physiology 267(2 Pt 2): R554-R560
1994
ISSN/ISBN: 0002-9513 PMID: 8067468 Document Number: 434404
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-b 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.