Supplemented gamma-linolenic acid and eicosapentaenoic acid influence bone status in young male rats: effects on free urinary collagen crosslinks, total urinary hydroxyproline, and bone calcium content.

The effect of different ratios of the prostaglandin precursors gamma-linolenic (GLA) and eicosapentaenoic (EPA) acids on bone status in growing rats measured as a function of free urinary pyridinium crosslinks and hydroxyproline levels was investigated. Male Sprague-Dawley rats were weaned onto an essential fatty acid deficient diet and from their fifth week, different groups of rats received a balanced, semisynthetic diet, supplemented with different ratios of GLA:EPA supplied as a mixture of evening primrose oil (EPO) and fish oil (FO). Controls were supplemented with linoleic (LA; sunflower oil) and alpha-linolenic (ALA; linseed oil) acids (3:1) or a commercially available rat chow. Animals were terminated at 84 days and femur length, ash weight, calcium content, free urinary pyridinium crosslinks (Pyd and Dpyd), total hydroxyproline (Hyp), and creatinine levels measured. Free urinary Pyd and Dpyd are good indicators of bone status and they correlated well with Hyp. Pyd and Dpyd excretion were significantly decreased in the higher GLA:EPA dietary groups and correlated well (r = 0.7) with Hyp levels. Concomitantly, bone calcium content increased significantly in the same dietary groups. These results suggest that diet supplementation with relatively high GLA:EPA ratios are more effective in inhibiting bone resorption than LA:ALA.