DIETARY NACL-RESTRICTION PREVENTS THE CALCIURIA OF KCL-DEPRIVATION AND BLUNTS THE CALCIURIA OF KHCO3-DEPRIVATION IN HEALTHY-ADULTS

Previous studies have demonstrated that dietary potassium deprivation in healthy human subjects eating diets otherwise containing normal qua ntities of NaCl is accompanied by an increase in urinary calcium excre tion. This increase in urinary Ca excretion occurs in association with reductions in urinary Na and Cl excretion together with trends for we ight gain and is delayed for several days after the initiation of K-de privation, suggesting that it is mediated by NaCl retention and expans ion of the extra-cellular volume. The present studies were thus undert aken to determine whether dietary NaCl restriction prevents the calciu ric effect of subsequent K-deprivation. When dietary NaCl intake was l imited to 5 +/- 3 mmol/day among 10 healthy adults, subsequent depriva tion of KCl (-67 mmol/day) in 5 subjects or deprivation of KHCO3 (-64 mmol/day) in 5 subjects prevented any significant increase in daily ur inary Ca excretion during five days of K-deprivation. There was, howev er, a small but significant cumulative increase above control in urina ry Ca excretion at the end of KHCO3-deprivation, averaging +1.9 +/- 0. 6 mmol; P < 0.05. When KCl was restored to the diets urinary Ca excret ion increased while restoration of KHCO3 to the diets caused urinary C a to fall to rates below control. We conclude that the calciuria of K- deprivation when NaCl is present in the diet is largely dependent upon NaCl retention by the kidneys and subsequent ECF-volume expansion. In addition, HCO3 is anti-calciuric.