Skip to main content
PMC home page
The Journal of Clinical Investigation logoLink to The Journal of Clinical Investigation
. 1983 Oct;72(4):1385–1395. doi: 10.1172/JCI111095

Proximal tubular bicarbonate reabsorption and PCO2 in chronic metabolic alkalosis in the rat.

D A Maddox, F J Gennari
PMCID: PMC370423  PMID: 6415109

Abstract

Studies were undertaken to define the pattern of proximal tubular bicarbonate reabsorption and its relation to tubular and capillary PCO2 in rats with chronic metabolic alkalosis (CMA). CMA was induced by administering furosemide to rats ingesting a low electrolyte diet supplemented with NaHCO3 and KHCO3. Proximal tubular bicarbonate reabsorption and PCO2 were measured in CMA rats either 4-7 or 11-14 d after furosemide injection, in order to study a wide range of filtered bicarbonate loads. A group of nine age-matched control animals, fed the same diet but not given furosemide, was studied for comparison. In a third group of controls, the filtered load of bicarbonate was varied over the same range as in the CMA rats by plasma infusion and aortic constriction. The CMA rats had significant alkalemia and hypokalemia (4-7 d: pH 7.58, HCO3 38.3 meq/liter, K+ 2.1 meq/liter; 11-14 d: pH 7.54, HCO3 38.1 meq/liter, K+ 2.5 meq/liter). Nonetheless, proximal bicarbonate reabsorption was not significantly different from that seen in control rats at any given load of filtered bicarbonate (from 250 to 1,300 pmol/min). In both control and CMA rats, 83-85% of the filtered bicarbonate was reabsorbed by the end of the accessible proximal tubule. These observations indicate that proximal bicarbonate reabsorption is determined primarily by the filtered load in chronic metabolic alkalosis. When single nephron glomerular filtration rate (SNGFR) is reduced by volume depletion in the early postfurosemide period, the filtered load and the rate of proximal bicarbonate reabsorption remain at or below control levels, maintaining metabolic alkalosis. In the late postfurosemide period, however, SNGFR returned to control levels in some instances. In these animals, both the filtered load and rate of proximal reabsorption were increased above the highest levels seen in control animals. The PCO2 gradient between the peritubular capillaries and arterial blood (Pc-Art) was significantly higher in CMA than in control, even though the rate of proximal bicarbonate reabsorption did not differ. Thus, proximal bicarbonate reabsorption did not appear to be the primary determinant of Pc-Art PCO2. PCO2 in the early proximal (EP) tubule was significantly higher than in either the late proximal (LP) tubule or peritubular capillaries in both control and CMA rats. The EP-LP PCO2 gradient correlated directly with proximal bicarbonate reabsorption (P less than 0.05). The small elevation in PCO2 in EP may be related to CO2 generated at this site in the process of bicarbonate reabsorption.

Full text

PDF
1387

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. Alpern R. J., Cogan M. G., Rector F. C., Jr Effects of extracellular fluid volume and plasma bicarbonate concentration on proximal acidification in the rat. J Clin Invest. 1983 Mar;71(3):736–746. doi: 10.1172/JCI110821. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Bank N., Aynedjian H. S. A micropuncture study of renal bicarbonate and chloride reabsorption in hypokalaemic alkalosis. Clin Sci. 1965 Aug;29(1):159–170. [PubMed] [Google Scholar]
  3. Chan Y. L., Biagi B., Giebisch G. Control mechanisms of bicarbonate transport across the rat proximal convoluted tubule. Am J Physiol. 1982 May;242(5):F532–F543. doi: 10.1152/ajprenal.1982.242.5.F532. [DOI] [PubMed] [Google Scholar]
  4. Cogan M. G., Liu F. Y. Metabolic alkalosis in the rat. Evidence that reduced glomerular filtration rather than enhanced tubular bicarbonate reabsorption is responsible for maintaining the alkalotic state. J Clin Invest. 1983 May;71(5):1141–1160. doi: 10.1172/JCI110864. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Cogan M. G., Maddox D. A., Lucci M. S., Rector F. C., Jr Control of proximal bicarbonate reabsorption in normal and acidotic rats. J Clin Invest. 1979 Nov;64(5):1168–1180. doi: 10.1172/JCI109570. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. De Mello Aires M., Malnic G. Micropuncture study of acidification during hypochloremic alkalosis in the rat. Pflugers Arch. 1972;331(1):13–24. doi: 10.1007/BF00587187. [DOI] [PubMed] [Google Scholar]
  7. Deen W. M., Troy J. L., Robertson C. R., Brenner B. M. Dynamics of glomerular ultrafiltration in the rat. IV. Determination of the ultrafiltration coefficient. J Clin Invest. 1973 Jun;52(6):1500–1508. doi: 10.1172/JCI107324. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. DuBose T. D., Jr, Pucacco L. R., Lucci M. S., Carter N. W. Micropuncture determination of pH, PCO2, and total CO2 concentration in accessible structures of the rat renal cortex. J Clin Invest. 1979 Aug;64(2):476–482. doi: 10.1172/JCI109485. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. DuBose T. D., Jr, Pucacco L. R., Seldin D. W., Carter N. W. Direct determination of PCO2 in the rat renal cortex. J Clin Invest. 1978 Aug;62(2):338–348. doi: 10.1172/JCI109134. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Effros R. M., Nioka S. Deficiency of carbonic anhydrase in the vasculature of rabbit kidneys. J Clin Invest. 1983 May;71(5):1418–1430. doi: 10.1172/JCI110895. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Gennari F. J., Caflisch C. R., Johns C., Maddox D. A., Cohen J. J. PCO2 measurements in surface proximal tubules and peritubular capillaries of the rat kidney. Am J Physiol. 1982 Jan;242(1):F78–F85. doi: 10.1152/ajprenal.1982.242.1.F78. [DOI] [PubMed] [Google Scholar]
  12. Gennari F. J., Cortell S., Schwartz W. B. Loss of measured activity of inulin-14C and a corrective technique. J Appl Physiol. 1970 Jan;28(1):105–107. doi: 10.1152/jappl.1970.28.1.105. [DOI] [PubMed] [Google Scholar]
  13. Kunau R. T., Jr, Frick A., Rector F. C., Jr, Seldin D. W. Micropuncture study of the proximal tubular factors responsible for the maintenance of alkalosis during potassium deficiency in the rat. Clin Sci. 1968 Apr;34(2):223–231. [PubMed] [Google Scholar]
  14. Lucci M. S., Pucacco L. R., Carter N. W., DuBose T. D., Jr Direct evaluation of the permeability of the rat proximal convoluted tubule to CO2. Am J Physiol. 1982 May;242(5):F470–F476. doi: 10.1152/ajprenal.1982.242.5.F470. [DOI] [PubMed] [Google Scholar]
  15. Maddox D. A., Bennett C. M., Deen W. M., Glassock R. J., Knutson D., Daugharty T. M., Brenner B. M. Determinants of glomerular filtration in experimental glomerulonephritis in the rat. J Clin Invest. 1975 Feb;55(2):305–318. doi: 10.1172/JCI107934. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Maddox D. A., Price D. C., Rector F. C., Jr Effects of surgery on plasma volume and salt and water excretion in rats. Am J Physiol. 1977 Dec;233(6):F600–F606. doi: 10.1152/ajprenal.1977.233.6.F600. [DOI] [PubMed] [Google Scholar]
  17. Schwartz G. J., Weinstein A. M., Steele R. E., Stephenson J. L., Burg M. B. Carbon dioxide permeability of rabbit proximal convoluted tubules. Am J Physiol. 1981 Mar;240(3):F231–F244. doi: 10.1152/ajprenal.1981.240.3.F231. [DOI] [PubMed] [Google Scholar]
  18. Warnock D. G., Rector F. C., Jr Proton secretion by the kidney. Annu Rev Physiol. 1979;41:197–210. doi: 10.1146/annurev.ph.41.030179.001213. [DOI] [PubMed] [Google Scholar]

Articles from Journal of Clinical Investigation are provided here courtesy of American Society for Clinical Investigation

RESOURCES