AJP - Renal Physiology, Vol 251, Issue 2 257-F265, Copyright © 1986 by American Physiological Society
Renal reabsorption and utilization of hydroxybutyrate and acetoacetate in starved rats
M. Barac-Nieto
Are there increases in the renal reabsorption (R) and utilization (Q) of
ketoacids during starvation? R and Q of D-3-hydroxybutyrate and
acetoacetate were measured in anesthetized normally fed (C) and 3-day
starved (S) rats, using clearance and arteriovenous extraction methods. R
was nearly complete in both groups at low filtered ketoacids loads (less
than 2mumol/g X min). At higher filtered loads, R of the two ketoacids
increased in proportion to their filtered loads (r2 greater than 0.95) but
with significantly steeper slopes in the S than in the C group; fractional
R of the two ketoacids were significantly higher in the S than in the C
animals. Saturable and nonsaturable components for ketoacid reabsorption
were evident, but only the nonsaturable component was significantly
increased with starvation. Increased R of ketoacids during starvation was
in the absence of changes in the initial rates of hydroxybutyrate influx
into isolated rat renal brush-border membrane vesicles. Thus the
rate-limiting step for ketoacid reabsorption through the nonsaturable
pathway may not be located at the luminal membrane of the proximal cells.
The increases in R of ketoacids in the S group were associated with
simultaneous decreases in the net rates of renal utilization of the two
ketoacids. Thus increased renal conservation of ketoacids is a transport
and not a metabolic event. Overall, during complete starvation, both the
increased R and the decreased renal Q of the ketoacids contribute to
increase the availability of these metabolites to other organs.
