Application of the balance method to determining accumulation, metabolism, and apparent oxidation of linoleic and alpha-linolenic acids in the pregnant rat.

Pregnancy-induced changes in whole-body partitioning of linoleic acid (18:2n-6) and alpha-linolenic acid (18:3n-3) between accumulation, conversion to longer-chain polyunsaturates (LCP), and disappearance (apparent oxidation) were determined over a 13-day balance period. 18:2n-6, 18:3n-3 and n-6 and n-3 LCP levels were measured in food, feces, organs, and carcass. Accumulation was estimated on the basis of paired difference values between one group killed at the beginning and one at the end of the balance period. Actual whole-body accumulation of 18:2n-6 and 18:3n-3 (mg per rat) was similar in pregnant and nonpregnant rats, but when expressed as milligrams per gram weight gain, it was greater in nonpregnant rats. Net accumulation of n-6 and n-3 LCP was significantly greater in pregnant rats whether expressed as milligrams per rat or as milligrams per gram body weight gain. Apparent oxidation of 18:2n-6 and 18:3n-3 expressed as a percentage of intake was similar in both groups, but when expressed as milligrams per gram weight gained, it was significantly greater in the nonpregnant group. We conclude that the balance method provides a useful index of whole-body and organ partitioning of 18:2n-6 and 18:3n-3. This method demonstrates that despite the higher accumulation of LCP during pregnancy, significantly more 18:2n-6 and 18:3n-3 is apparently oxidized than is converted to their respective LCP.