Physiological disposal of the potential alkali load in the diet of
the rat; steps to achieve acid-base balance.
Lin, Shih-Hua, Surinder Cheema-Dhadli, Sorasak Chayaraks, Ching-Bun,
Chen, Manjula Gowrishankar, and Mitchell L Halperin.
Renal Division, National Defense Medical Center, Taipei, Taiwan,
ROC, Renal Division, St. Michael's Hospital, University of Toronto,
Toronto, Canada, Renal Division, Department of Pediatrics, University
of Alberta, Edmonton, Canada.
APStracts 5:0043F, 1998.
Purpose: To provide a better understanding of the physiological role
of endogenous net organic acid production in rats consuming their
usual diet. Methods: Balance studies were performed over 24 hr; urine
was collected in the day and night portions of the diurnal cycle. A
supplemented low-electrolyte diet (LED) was fed to determine if
urinary organic anions were identical to those in the diet. A
titration procedure was developed to determine the pK of titratable
groups in the urine of rats studied with and without an acid load.
Results: Although normal rats excreted net acid (NAE), the latter was
inversely related to the amount of food consumed. The rates of
excretion of bicarbonate (HCO3-), citrate, unmeasured organic anions,
and NH4+ were higher in the night portion of the diurnal cycle. NAE
rose dramatically when alkali intake was decreased by consuming the
LED. Dietary and urinary organic anions were not identical because
rats fed the LED supplemented with potassium citrate excreted <10 %
of this alkali load as citrate and < 25 % as HCO3-. In the 24 hr
after 3000 [mu]mol NH4Cl was given intraperitoneally, H+ did not
appear to be retained, yet NAE rose by only close to 2000 [mu]Eq. The
rate of excretion of titratable groups with a pK in the 3-5 pH range
fell by close to 1000 [mu]Eq; most of these changes occurred in the
first 7 hr after NH4Cl was given.
Conclusions: Rat chow provides a large net alkali load. There appears
to be two types of endogenous acid production, a form associated with
a rise in NAE (e.g., sulfuric acid) and dietary alkali-driven
endogenous net acid production which titrates this alkali; renal
excretion of organic anions makes these acids end-products of
metabolism.
Received 22 October 1997; accepted in final form 12 February
1998.
APS Manuscript Number F338-7.
Article publication pending Am. J. Physiol. (Renal Physiology).
ISSN 1080-4757 Copyright 1998 The American Physiological Society.
Published in APStracts on 19 February 1998