Metabolism of triglyceride fatty acid by the perfused rat heart

Abstract

1. Chyle lipids, labelled with (14)C, are taken up and oxidized by the isolated perfused rat heart. 2. In recirculatory perfusions, when chyle lipids are the sole exogenous energy source, about 24% of the total oxygen uptake is accounted for by their oxidation. This proportion is not changed by starvation of the rats for 48hr. and falls when an external work load is imposed on the left ventricle. 3. With albumin in the perfusion medium, the rate of (14)CO(2) output is reduced by half and there is a rise in the proportion of (14)C-labelled free fatty acids in the medium. 4. Clearing-factor lipase appears in the perfusion medium when chyle lipids are perfused through the heart. In the absence of albumin, the activity of the medium enzyme is low and only a small proportion of the (14)CO(2) output can be accounted for by the oxidation of free fatty acids released by it. In the presence of albumin, the enzyme is more active in the medium. 5. When a substantial proportion of the total clearing-factor lipase is removed from the heart by a prior perfusion with heparin, (14)C-labelled chyle lipid perfused subsequently is oxidized at only half the normal rate.

The role of triacylglycerol in cardiac energy provision

“…Significant cardiac utilisation of d<1.006 lipoprotein-TAG (CM) was also found in isolated rat heart [9] TAG oxidation accounted for 40% of CO 2 production (equivalent to that of NEFA oxidation) [10] (and in broad agreement with earlier studies [11]). Further evidence for a role for…”

Differences in the metabolism of very-low-density lipoproteins by isolated beating-heart cells and the isolated perfused rat heart. Evidence for collagenase-released extracellular lipoprotein lipase

“…This loss was a result of release of the enzyme in perfusion medium. Such a release of lipoprotein lipase in the perfusion medium after heparin perfusion of the heart has been reported by Enser et al (1967) (Table 4) and may be analogous to the hepatic triacylglycerol lipase. It is known that hepatic triacylglycerol lipase is not inhibited by NaCl and also hydrolyses the triacylglycerol-rich lipoproteins, although less efficiently Augustin et al, 1976).…”

“…Studies performed in vivo (Eisenberg & Levy, 1975), in isolated perfused hearts (Delcher et al, 1965;Enser et al, 1967; Fielding & Higgins, 1974;Higgins & Fielding, 1975) and in vitro (Eisenberg & Rachmilewitz, 1975) have all implicated an involvement of lipoprotein lipase (EC 3.1.1.3) in the hydrolysis of the triacylglycerolrich plasma lipoproteins. It has been suggested that this hydrolysis may occur at a site close to the endothelial cells lining the blood capillaries (Robinson, 1963;Blanchette-Mackie & Scow, 1971), where the lipoprotein lipase involved is believed to be located .…”

The metabolism of chylomicron fatty acids by isolated rat heart‐lung preparations

“…[14C]palmitic acid measured in the experiments of Evans et al (1963) and considerably in excess of the rates of uptake and oxidation of chylomicron fatty acid by the isolated saline-perfused rat heart (Crass & Meng, 1966;Kreisberg, 1966;Scheur & Olson, 1967;Enser et al 1967). Thus chylomicron fatty acids could be potentially as important in the energy metabolism of the heart as unesterified fatty acids.…”

“…However, the abnormal capillary permeability in such saline-perfused hearts discussed above casts some doubt on the true physiological significance of the results in relation to the initial removal of chylomicrons from the circulation in vivo. Moreover, these preparations do not tolerate well higher perfusate concentrations of chylomicrons which still fall within the physiological range (Enser et al 1967). …”