BONE STRENGTH IN MATURE RATS FED HIGH SALT DIETS AFTER EXPOSURE TO HINDLIMB SUSPENSION:

1861 High salt (HNa) diets promote calcium (Ca) loss in patients with osteoporosis but whether this augments bone loss in unloaded skeletal sites is not known. The purpose of this study was to examine the effect of HNa diets on the ultimate strength and bone mineral content of femurs (FBMC) after exposure to 4 wk of hindlimb suspension. Six mo old (n=30) mature male Sprague-Dawley rats, body weight (Wt) = 491 ± 13.9 g, were fed either normal salt, 0.26% (NNa), or HNa, 8% diets with 0.1% Ca and 0.3% phosphorus. Animals were divided into the following 4 groups: 1) control rats (C) fed NNa (CNNa, n=7) or 2) HNa (CHNa, n=7), and 3) suspension rats (S) fed NNa (SNNa, n=8), or 4) HNa (SHNa, n=8). The C and S rats were pair fed. FBMC was determined from ash weight and ultimate femoral strength was determined using a torsional strength test machine with 1 o/sec internal rotation until failure. After 4 wk of hindlimb suspension Wt of the S groups were lower (p < .05) than C. ANOVA (adjusted for Wt) results showed that ultimate strength in the femurs of SNNa (424.6 ± 89 Nmm) was lower (p < 0.05) than in all other groups: CNNa = 551.3 ± 45, CHNa = 576 ± 19 and SHNa = 533.5 ± 90 Nmm. The correlation coefficient between ultimate femoral strength and FBMC of the S groups (n=15) was .54 (p < .001). We conclude that ultimate strength of mature femurs: 1) is weakened after exposure to hindlimb suspension in rats fed normal but not high salt diets, and 2) is related to the BMC of the femurs. Supported by NASA-Stanford-ASEE Fellowship/NASA Grant 199-26-12-02