Changes in plasma palmitate specific radioactivity during long-term intravenous infusions of tritiated palmitate into lactating goats

Abstract

Vascular injection or infusion of isotopically labelled fatty acids into both ruminant and nonruminant species has been used as a method for determining the entry rate of non-esterified fatty acids (NEFA) into blood (Bickerstaffe, Annison & Linzell, 1974; Vranic, 1975). Results obtained in this way represent the release of fatty acids from several sources, principally adipose tissue. The predominant labelled end-products from [3H]– and [14C]fatty acid metabolism are water and carbon dioxide respectively. Both these metabolites enter extensive body pools and the label is unlikely to be reincorporated into plasma NEFA during the time course of conventional short-term experiments (2–4 h). During isotope dilution experiments, however, some labelled fatty acid could be incorporated into adipose tissue triacyglycerol (TAG) following synthesis of low-density lipoprotein in the liver. In addition, the contribution of NEFA carbon to endogenous acetate production could result in transfer of 14C in any C, or 8H attached to the C8 position in acetate, from the infused fatty acid to fatty acids synthesized by liver and adipose tissue.