Influence of dietary calcium on sodium and calcium intake of spontaneously hypertensive rats.

Spontaneously hypertensive rats (SHRs) fed nutritionally complete diets voluntarily ingest more calcium and more NaCl solution than do their normotensive Wistar-Kyoto (WKY) controls. SHRs also have several anomalies in calcium metabolism. Given that calcium availability modulates NaCl intake of other rat strains, we examined whether sodium and calcium intake of the SHR was unusually responsive to manipulations of dietary calcium. In three experiments, groups of SHRs and WKYs ate diets differing in calcium content (0-1,000 mmol/kg) and drank solutions of sodium (50 and 300 mM NaCl or 50 mM sodium lactate) and/or calcium (50 and 110 mM calcium lactate or 50 mM CaCl2). Relative to WKYs, SHRs fed calcium-deficient diet (0 mmol Ca2+/kg) drank the same amount or less calcium solution, drank more NaCl, and increased NaCl intake more rapidly when the diet was first introduced. SHRs fed diets sufficient for normal growth (50-1,000 mmol Ca2+/kg) drank consistently more calcium and sodium solution than did WKYs. However, NaCl intake of SHRs was decreased by high-calcium diets, whereas NaCl intake of WKYs was not. Taken together, these results suggest that a mechanism dependent on the availability of calcium is at least partially responsible for the high salt intake of the SHR.