Regulation of renal bicarbonate reabsorption by extracellular volume

Abstract

AB STR A CT The ability of the kidney to reabsorb bicarbonate is held to be a function of plasma C02 tension, carbonic anhydrase activity, and potassium stores. The effects of alterations of extracellular volume on bicarbonate reabsorption were studied in dogs whose arterial Pco2 was kept constant at 40 mm Hg (range 35-45 mm Hg).The effect of extracellular volume expansion was studied in dogs receiving hypertonic bicarbonate and isotonic saline, isotonic saline alone (two of the animals in this group received HCO to lower the plasma bicarbonate concentration), and isotonic bicarbonate. The results were similar in each group. Extracellular volume expansion depressed bicarbonate reabsorption. This depression was related not to changes in -glomerular filtration rate (GFR) or bicarbonate concentration, but to the increase of fractional sodium excretion. In addition, volume expansion with bicarbonate increased chloride excretion.Bicarbonate loading was performed in tvo groups of dogs in which effective expansion of extracellular volume was minimized by hemorrhage or acute constriction of the thoracic vena cava. Both groups demonstrated enhanced bicarbonate reabsorption relative to that seen in the volume-expanded groups. Release of the caval ligature promptly decreased bicarbonate reabsorption.Plasma potassium decreased in all animals studied, but the changes in bicarbonate reabsorption noted could not be related to the decrease.This study demonstrates that the state of effective extracellular volume is a major determinant of bicarbonate reabsorption by the kidney.

Effects of extracellular fluid volume and plasma bicarbonate concentration on proximal acidification in the rat.

“…Clearance studies in dogs, rats, and man have all demonstrated that ECF volume expansion inhibits fractional bicarbonate reabsorption (3)(4)(5)(6)8). A prevalent view has been that this inhibition occurs in the proximal tubule and is related to increased bicarbonate back leak (20).…”

“…Numerous clearance studies have examined the effect of acutely increasing plasma bicarbonate concentration on bicarbonate absorption (1,(3)(4)(5) (9). The In previous studies, the rate of proton secretion was examined as a function of luminal bicarbonate concentration (9).…”

“…Numerous clearance and micropuncture studies have attempted to examine the effects of systemic bicarbonate concentration and ECF' volume status on acidification (1)(2)(3)(4)(5)(6)(7)(8). In these studies, however, as plasma bicarbonate concentration or ECF volume were altered, there were simultaneous changes in luminal bicarbonate concentration and/or flow rate.…”

High sodium chloride intake exacerbates immobilization-induced bone resorption and protein losses

“…But still other possible mechanisms may be involved, as previously mentioned (25). Enforced activity of cellular Na ϩ /H ϩ exchangers (18,36) as well as Na ϩ /H ϩ ion exchanges on the extracellular glycosaminoglycans (19) and/or a Na-induced expansion of extracellular volume, resulting in a decrease in HCO 3 Ϫ reabsorption (3,38,52,58), can contribute to mediation of the effect of NaCl on acid-base balance. Summarizing, with high NaCl intake, renal loss of bicarbonate but also excess acid production could be reasonably expected to affect acid-base status.…”

Acidosis tubular renal: Presentación de 2 casos clínicos

“…El mecanismo de accion no estd bien claro y probablemente este relacionado con el efecto clo~ ruretico y de contraction del espacio extracelular (22) que mejora la absorcion proximal de bicarbonato. Ademas es bien conocido el efecto de la hidroclorotiazida que dismimiye la excretion de calcio urinario.…”