AJP - Renal Physiology, Vol 262, Issue 5 762-F769, Copyright © 1992 by American Physiological Society
Transport of beta-hydroxybutyrate and acetoacetate along rat nephrons: a micropuncture study
B. Ferrier, M. Martin, B. Janbon and G. Baverel
Centre National de la Recherche Scientifique, Unite de Recherche Associee 1177, Institut National de la Sante et de la Recherche Medicale, Unite 80, Faculte de Medecine Alexis Carrel, Lyon, France.
The transport of ketone bodies across the luminal membrane of the nephron
was studied by means of micropuncture techniques in rats in normal
acid-base state. The concentration of beta-hydroxybutyrate (beta-HB) and
acetoacetate (AcAc) in plasma, tubular fluid and urine was measured by an
ultramicromethod using enzymatic cycling. At endogenous plasma ketone body
concentration, approximately 80% of the filtered load of beta-HB and AcAc
was reabsorbed in the proximal convoluted tubule, the remaining fraction
being almost completely reabsorbed between the late proximal convoluted and
the distal tubule; under these conditions, the urinary excretion of ketone
bodies was less than 1% of the filtered load. A progressive elevation to
steady-state levels of plasma beta-HB resulted in a progressive reduction
of the fractional reabsorption of beta-HB and AcAc in the proximal
convoluted tubule, which means that reabsorption of ketone bodies in this
nephron segment is saturable. No net secretion of ketone bodies could be
demonstrated along the nephron even at the highest plasma ketone body
concentrations reached. In clearance experiments, the capacity of the rat
kidney for reabsorbing both beta-HB and AcAc was found to be limited by a
maximal tubular capacity (Tm). The data suggest that, in the young Wistar
rat nephron, most of the reabsorption of ketone bodies is carrier mediated.
