AJP - Renal Physiology, Vol 249, Issue 1 107-F116, Copyright © 1985 by American Physiological Society
Juxtamedullary nephrons during acute metabolic alkalosis in the rat
J. P. Frommer, D. E. Wesson, M. E. Laski and N. A. Kurtzman
The renal handling of bicarbonate during acute metabolic alkalosis was
examined in Munich-Wistar rats using micropuncture techniques. Group I
received an acute bicarbonate load, and fractional delivery of total CO2
(tCO2) (FDtCO2) to the superficial late distal tubule (LD) was
significantly lower than to the base of the papillary collecting duct (B)
(18.4 +/- 1.7 vs. 22.9 +/- 1.5%; P less than 0.01), indicating net addition
of bicarbonate between LD and B. When acutely bicarbonate-loaded rats had
their deep nephrons destroyed with bromoethylamine hydrobromide (BEA)
(group II), net addition of tCO2 between LD and B was abolished and net
reabsorption uncovered (FDtCO2 LD: 28.0 +/- 3.6 vs. B: 17.5 +/- 2.5%; P
less than 0.01). The infusion of amiloride (2.5 mg/kg body wt) to alkalotic
rats treated with BEA (group III) completely inhibited distal bicarbonate
reabsorption but did not reestablish addition (FDtCO2 LD: 27.6 +/- 1.6 vs.
B: 26.1 +/- 3.7%; P = NS). The values obtained for sham-operated animals
(group IV) were the same for group I. The patterns that were observed
between LD and B were reproduced for the four groups of animals when FDtCO2
LD was compared with the fractional excretion of bicarbonate in the urine
of the intact contralateral kidney. These studies suggest that
juxtamedullary nephrons contribute a higher load of bicarbonate than
superficial nephrons to the final urine during acute metabolic alkalosis in
the rat.
