Effects of dietary protein source and isoflavones on bone quality in Dahl salt‐sensitive and salt‐resistant rats

Abstract

13C molar % excess of plasma and intracellular fatty acids in human skeletal muscle This study tested effects of protein source and soy isoflavones (IF) supplementation on bone mass and microarchitecture in hypertensive rats. Weanling male Dahl salt-sensitive (DS) and Dahl salt-resistant rats (DR) were fed one of six experimental diets for 12 wk and given drinking water with 10 g NaCl / L to induce earlier hypertension. Sixty DS and 60 DR rats (10/group) were randomly assigned to one of the following: casein control, casein +100 mg isoflavones/kg diet, casein + 200 mg isoflavones/kg, soy protein isolate (SPI) which was alcohol washed to be devoid of isoflavones SPI + 100 mg isoflavones/kg or SPI + 200 mg isoflavones/kg. At necropsy, a hind limb was stored at −20oC. Femurs were isolated later. Mortality was high among DS rats supplemented with IF, but surviving DS rats were significantly heavier than DR rats. With dual-energy X-ray absorptiometry (DEXA), bone mineral area and bone mineral content were higher in DS rats than in DR. To assess microarchitecture, the distal femur was scanned at 16.5 μ intervals and 100 slices were contoured. Bone volume fraction (BV/TV) was significantly lowered by IF in DS but not in DR rats; this reduction was seen with both casein and SPI. In the DS rats, significant decreases in connectivity density and increases in trabecular separation supported the BV/TV results. Cortical thickness at the femur midshaft was also significantly reduced by IF in DS rats but not in DR. In this study addition of IF to the diet significantly impaired bone quality in DS rats and had little effect in DR rats.