The regulation of renal acid secretion: New observations from studies of distal nephron segments

Abstract

In this review we have attempted to present for the general reader the new information on renal acidification that has emerged from the study of discrete segments of the distal nephron. We have structured our presentation in the context of the cation exchange hypothesis which has strongly influenced modern thinking of acid-base regulation. We have shown that distal nephron acidification is active and can proceed even in the absence of sodium. We have also shown beyond doubt, that pH or the determinants of pH can influence the rate of proton secretion in probably all of the distal nephron segments. We have drawn attention to an exciting new means by which chloride (or its substitution) could alter the rate of net bicarbonate transport. A possible role for bicarbonate secretory activity in the mammalian distal nephron has been discussed as has the influence of mineralocorticoids on acid secretion. We think the following is a concise and balanced view of the regulation of distal nephron acid excretion: 1) hydrogen ion secretion is active and is variably offset by simultaneous bicarbonate secretion; 2) hydrogen ion secretion can proceed in the absence of sodium and can be modulated by mineralocorticoid independent of sodium effects; 3) hydrogen ion secretion is undoubtedly influenced by peritubular pH or bicarbonate concentration; and 4) both luminal and peritubular chloride concentration may play an important role in regulation of net HCO3 transport.