Dietary conjugated linoleic acids alter serum IGF-I and IGF binding protein concentrations and reduce bone formation in rats fed (n-6) or (n-3) fattyacids

A study was designed to examine the effects of dietary conjugated linoleic acid (CLA) on serum concentrations of insulin-like growth factor-I (IGF-I) and IGF binding proteins (IGFBP) and the relationship of these factors to b one metabolism, Weanling male rats were fed AIN-93G diet containing 70 g/kg of added fat for 42 days. Treatments included ii g/kg or 10 g/kg of CLA an d soybean oil (SBO) or menhaden oil + safflower oh (MSO) following a 2 x 2 factorial design. Serum IGFBP was influenced by dietary polyunsaturated fat ty acid (PUFA) type ((n-6) and (n-3)) and CLA (p = 0.01 for 38-43 kDa bands corresponding to IGFBP-3). CLA increased IGFBP level in rats fed SBO (p = 0.05) but reduced it in those fed MSO (p = 0.01). Rats fed MSO had the high est serum IGFBP-3 level. Both (n-3) fatty acids and CLA lowered ex vivo pro staglandin E-2 production in bone organ culture. In tibia, rats given CLA h ad reduced mineral apposition rate (3.69 w. 2.79 mu m/day) and bone formati on rate (BFR) (0.96 vs, 0.65 mu m(3)/mu m(2)/day); however, the BFR tended to be higher with MSO. Dietary lipid treatments did not affect serum intact osteocalcin or bone mineral content. These results showed that dietary PUF A type and CLA modulate local factors that regulate bone metabolism.