THE EFFECT OF DIFFERENT N-6 N-3 ESSENTIAL FATTY-ACID RATIOS ON CALCIUM BALANCE AND BONE IN RATS

Prostaglandins (PGs) are known to have various effects on bone metabol ism. The supplementation of essential fatty acids (EFAs), the precurso rs of PGs, leads to increased intestinal calcium absorption and calciu m balance. It is, however, not known whether increased calcium absorpt ion and calcium balance will enhance the calcium content in bone. Male Sprague-Dawley rats (n = 40) aged 5-12 weeks were supplemented with E FAs. The main dietary EFAs, linoleic acid (LA) and alpha-linolenic aci d (ALA) were administered in a ratio of 3:1 as a control group. The co nversion of LA to ALA to the PG precursors is slow, with the first ste p, delta-6-desaturation being rate limiting. Fatty acids beyond this r ate-limiting step, gamma-linolenic acid (GLA, n-6) and eicoapentaenioc acid (EPA, n-3), were administered to different groups in the ratios 3:1, 1:1 and 1:3 to explore the impact of different ratios of n-6 and n-3 EFAs. Intestinal calcium absorption (mg/24 h) increased by 41.5% i n the 3:1 supplemented group, compared with the control group. The dec rease in urinary calcium (mg/24 h) correlated with the increase in n-3 level. The calcium balance (mg/24 h) and bone calcium (mg/g bone ash) increased significantly in the 3:1 (41.5% and 24.7%) group, compared with the control. The increase in bone calcium might be attributed to an EFA-induced increase in circulating PGs. An increased synthesis of PGs acting on target bone cells, as well as changes in membrane fluidi ty, may underlie these observations.