Metabolism of Ethyl Esters of Fatty Acids

It has been demonstrated 1 that the conversion of caproic, butyric, and beta-hydroxy butyric acids to acetone bodies in fasting rats by beta oxidation is quantitative, whereas greater amounts of ketone bodies originate after sodium caprylate than after isomolecular quantities of sodium acetoacetate are fed. The latter phenomenon suggests that delta oxidation occurs in the latter case. No ketone bodies are formed when the sodium salts of the fatty acids with an odd carbon chain, as propionic, valeric, heptoic or nonylic acids were fed. It was later demonstrated 2 that the conversion of the odd chain fatty acids into glycogen must represent an approximately quantitative transformation by beta oxidation into propionic acid. The fatty acids with an even number of carbon atoms were entirely ineffective as glycogen formers. However, it was impossible to feed the soaps of the fatty acids having a greater number of carbon atoms than 9 in an equimolecular dose to that found effective with the shorter chain fatty acids because of the relatively large quantities of solution which must be administered.

In the present experiments, by administering the fatty acids as their ethyl esters it has been possible to feed isomolecular quantities of all of the fatty acids up to stearic acid in similar doses to those employed in the earlier work—namely, 15 gm. per square meter of body surface per day, calculated as acetone.

The average excretion of acetone bodies in fasting male rats, second to fourth days, calculated as acetone in grams per square meter of body surface per day after feeding the ethyl esters was as follows: acetoacetate, 2.01 (57)∗; butyrate, 1.37 (27); caproate, 1.95 (31); caprylate, 7.29 (12); caprate, 6.74 (16); laurate, 6.75 (17); myristate, 5.21 (9); palmitate, 2.94 (10); stearate, 2.40 (11); oleate, 5.07 (11). This indicates that the excretion of acetone bodies after the caproate and butyrate is an approximately quantitative one, whereas the acetonuria after the administration of the ethyl esters of the fatty acids with 8 or more carbon atoms is greater than that of the acetoacetate controls. This would indicate that more than one acetoacetate residue originates from the oxidation of one molecule of fatty acid having 8 or more carbon atoms.