Differential fractionation of hydrogen isotopes in liver and mammary gland

Publisher Website
Google Scholar
Abstract
A theory is presented which predicts that biological fractionation of H isotopes during the reversible incorporation of water H into any metabolite will be observed only under conditions of net synthesis, not under conditions of turnover. As net synthesis and turnover are probably the dominant processes in the fatty acid metabolism of mammary gland and liver, incorporation into fatty acids of H from water labeled with deuterium and tritium was studied. Rats at term were placed on doubly labeled water for 11-14 days and the isotopic abundances were determined in blood water and in the fatty acids extracted from mammary gland, liver, perinephric fat, and pup carcass fat. Calculating the tritium/deuterium ratio in the drinking water as 1, the ratios in blood water were 1, in maternal mammary gland 0.775, and in maternal liver 0.87. This indicates that there was more net synthesis of fatty acids in the mammary gland than in the liver and that differential fractionation of H isotopes occurred. Since the incorporation of tritium was 25% less than that of deuterium, the difference between deuterium and protium may be as great. The isotopic abundance in the pup carcass fatty acids varied considerably, but was the same as that of the fatty acids from the gland from which they were feeding. No water H was incorporated into the maternal depot fatty acids, in constrast to the earlier findings of Schoenheimer and Rittenberg. The isotope level in the blood water was 50 to 70% of that in the drinking water.