AJP - Renal Physiology, Vol 256, Issue 1 120-F127, Copyright © 1989 by American Physiological Society
Effect of luminal perfusion on glucose production by isolated proximal tubules
G. T. Nagami and P. Lee
Service, Veterans Administration Medical Center, West Los Angeles, California.
The effects of luminal perfusion on glucose production by the proximal
tubule were examined by use of the technique of in vitro microperfusion
with an ultramicroassay for glucose to measure the net glucose production
rates in isolated mouse midproximal tubule segments. Tubules bathed in
Krebs-Ringer bicarbonate (KRB) buffer containing L-glutamine and acetate
and perfused with KRB buffer at a high flow rate produced glucose at a
lower rate (0.12 +/- 0.02 pmol.min-1.mm-1) than unperfused segments (0.40
+/- 0.03) or segments perfused at a lower flow rate (0.24 +/- 0.03). In
contrast, the estimated rates of glucose utilization were not affected by
luminal perfusion. The inhibition of net fluid reabsorption by perfusion
with a modified KRB buffer containing amiloride or by addition of ouabain
to the bath medium raised glucose production rates to levels equaling or
exceeding those observed in unperfused tubules. The inhibition of glucose
production by luminal perfusion occurred in the presence of multiple
substrates (i.e., glutamine, acetate, lactate, pyruvate, alanine, and
valerate) or nonammoniagenic substrates (i.e., lactate and pyruvate) in the
bath medium. Thus net glucose production is inhibited by luminal perfusion
and the inhibitory effect is dependent on intact fluid reabsorption. The
reduction in net glucose production observed with perfusion does not result
from increased glucose utilization and is not dependent on the presence of
specific substrates.
