ADAPTATIONS TO CHLORIDE-DEPLETION ALKALOSIS

The systemic and renal adaptations for the maintenance and correction of metabolic alkalosis generated by chloride depletion (CDA) are the focus of this review. The hypothesis that extracellular fluid (ECF) volume expansion is essential for the correction of CDA is refuted, while the concept that Cl-repletion is necessary and sufficient for correction is developed. Contraction of ECF volume probably can occur as a consequence of CDA. The principal mechanisms by which the kidney corrects CDA appear to reside primarily in the collecting duct, which is endowed with the anion exchange mechanisms and the capacity to effect the necessary changes in body anion composition. Although the remainder of the collecting duct is undoubtedly important in this response, the cortical segment appears to have the paramount role since it can either absorb or secrete HCO3-. Alterations in the delivery of Cl- or HCO3- to the collecting duct may also be important but changes in glomerular filtration rate appear to have a minor role. Major unanswered questions in the pathophysiology of CDA are the manner in which exogenous Cl- repletion is detected and the kidney is signaled to excrete HCO3- and the cellular mechanisms by which this is accomplished in the various nephron segments.