MEASUREMENT OF THE TIME BETWEEN BIOSYNTHESIS AND SURFACE EXCRETION OF SEBACEOUS LIPIDS IN THE HORSE

The time between the biosynthesis and excretion of sebum to the skin surface of the horse was examined by in vivo intradermal injection of [1-14C]acetate followed by periodic surface lipid collections. The radiolabeling of the major neutral lipid classes, equolides (giant ring .omega.-lactones, C32-C36) and cholesteryl esters, was evaluated by TLC and autoradiography. The distribution of radioactivity within the monounsaturated equolides was examined by oxidative fragmentation and evaluation of the products. A peak of radioactivity in the equolides and cholesteryl esters occurred 15-21 days and 10-16 days, respectively, after injection. The time-courses of specific radioactivity of the 2 types of equolide oxidation fragments were also found to be dissimilar. Apparently, in the biosynthesis of a large proportion of the equolides, de novo fatty acid synthesis was not followed immediately by fatty acid chain elongation. The phospholipids of the sebaceous cells are proposed as the long-term intermediate in which fatty acids reside between these 2 biosynthetic processes.