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Wax Esters in Fish. Metabolism of Dietary Palmityl Palmitate in the Gourami (Trichogaster cosby)¹

The Hormel Institute, University of Minnesota, Austin, Minnesota 55912

Dual labeled wax ester, [1-¹⁴C]palmityl [9,10-³H]palmitate, was fed to female gouramis (Trichogaster cosby) to study its metabolism and incorporation into wax esters of the roe. When 0.25 mg test compound was fed with 1 or 30 mg natural roe wax esters as carrier lipid, 60 to 75% of each radioactivity was incorporated into the lipids of the fish. Three hours after feeding, nearly all radioactivity was still in the intestinal tissue, but the dual labeled test compound had undergone extensive hydrolysis. Part of the alcohol was reesterified to form C₃₄ wax esters but most of it was oxidized to acid which then behaved as dietary acid. The amount of carrier wax esters influenced the extent of reesterification and oxidation. Analyses of the blood wax esters, after the same period of 3 hours, verified these observations and proved, in addition, that some of the test wax ester was absorbed without hydrolysis. Direct absorption as C₃₂ wax ester was more obvious at low feed level whereas hydrolysis and recombination to C₃₄ wax ester became more prominent at high feed level. Analysis of the roe wax esters after 24 hours showed that ¹⁴C and ³H were mainly in the alcohol moiety of C₃₄ species. Nearly 50% of the ¹⁴C alcohol absorbed was found as such in roe wax esters, but most of it had been oxidized and reduced again. Somewhat more than 4% had not undergone intermediary oxidation and only 1.5% of the ingested palmityl palmitate was in the original labeled form. In contrast to the wax esters in intestines and blood, the distribution of radioactivities in roe wax esters is not markedly affected by the amount of carrier wax esters fed. The metabolism of the alcohol moiety of dietary wax esters is very similar to that of dietary free fatty alcohol.

KEY WORDS: • gourami • lipid absorption in fish • palmityl palmitate • roe wax esters

¹ This investigation was supported by U. S. Public Health Service Research Grant AM 13424 from the National Institutes of Health: U. S. Public Health Service Research Grant HL 08214 from the Program Project Branch, Extramural Programs, National Heart and Lung Institute; and by The Hormel Foundation.

Manuscript received 22 March 1973.