Dietary Magnesium, Not Calcium, Regulates Renal Thiazide Receptor

Abstract

Abstract. This study reports for the first time a relationship between dietary Mg and the renal thiazide-sensitive Na-Cl cotransporter (TZR, measured by saturation binding with 3H-metolazone). Ion-selective electrodes measured plasma ionized magnesium (PMg+ +), calcium (PCa + +), and potassium (PK +). Restricting dietary Mg for 1 wk decreased PMg + + 18%, TZR 25%, and renal excretion of magnesium (UMg) and calcium (UCa) more than 50% without changing PCa + +, PK +, or plasma aldosterone. A low Mg diet for 1 d significantly decreased PMg + +, TZR, UMg and UCa. Return of dietary Mg after 5 d of Mg restriction restored PMg + + and TZR toward normal. In the control, Mg-deficient, and Mg-repleting animals, TZR correlated with PMg + + (r = 0.86) and with UMg (r = 0.87) but not UCa (r = 0.09). Increasing oral intake of Mg for 1 wk increased PMg + + 14%, TZR 32%, UMg 74%, and UCa more than fourfold without changing PCa + + or PK +. In contrast, increasing dietary Ca content from 0.02% to 1.91% did not change TZR, but increased UCa fivefold without changing PCa + +. Hormonal mediators (if any) involved in the relationship between dietary Mg and TZR remain to be elucidated, as does the relationship between TZR and tubular reabsorption of Mg.