A comparison of the utilization of medium and long-chain fatty acids for oxidation and ketogenesis in the suckling rat: In vivo and in vitro studies

Abstract

Fatty acid metabolism was studied both in vivo and in perfused liver of suckling rats. In vivo studies showed that [ 14C]decanoate was oxidized to 14CO 2 at a faster rate than was [ 14C]palmitate. This difference was due in part to the different modes of absorption of medium- and long-chain fatty acids. [1- 14C]- and [16- 14C]palmitate were oxidized at similar rates indicating complete oxidation of the fatty acid. Analysis of plasma acetoacetate and β-hydroxybutyrate showed that ketone body production was three times as great from labeled decanoate as from palmitate. Perfusion of livers from suckling rats with physiological concentration of fatty acid showed that ketone bodies were generated from decanoate at three times the rate observed with palmitate. The apparent K m for ketogenesis from decanoate was 0.4 m m while that from palmitate was 2.9 m m. The V for palmitate was 2.9 μmol/min/g liver while that for decanoate was 1.5 μmol/min/g liver. Compared to decanoate, palmitate was preferentially converted to triglycerides and phospholipids both in vivo and in vitro. These data suggest that medium-chain fatty acid oxidation in the neonatal rat spares long-chain fatty acids for utilization in complex lipid synthesis. Although medium-chain fatty acid catabolism appears similar to that in the adult rat, it is physiologically relevant during the neonatal period since rat milk, the major source of food, is rich in triglycerides which contain about 35% medium-chain fatty acids.