Incorporation of 14C-labelled fatty acids into the mammary-gland lipids of the lactating rabbit.

1. [1-(14)C]Stearic acid, [9-(14)C]stearic acid, [9-(14)C]palmitic acid and [9-(14)C]decanoic acid were fed to lactating rabbits, and the fatty acids of the mammary gland were separated and partially degraded. 2. Most of the (14)C recovered was located in the acids fed. Stearic acid was least efficiently absorbed; decanoic acid was the most extensively metabolized. 3. Resynthesis after degradation to C(2) units led to uniform alternate labelling in the C(2)-C(10) acids, whereas C(12)-C(18) acids had excess of (14)C at the carboxyl end. 4. Acids formed by beta-oxidation down to C(12), but not below, were also present in the mammary-gland lipids. Desaturation of the administered acids was a very minor reaction.