UPTAKE AND METABOLISM OF ¹⁴C‐LABELLED TRIGLYCERIDE BY RETICULO‐ENDOTHELIAL CELLS

Abstract

The uptake and metabolism of "4C-labelled triglyceride by R.E. cells in rat lymph nodes has been investigated. After the intraperitoneal injection of a corn oil emulsion containing glyceryl tripalmitate-1-14C uptake of labelled triglyceride by the R.E. cells in the nodes occurs. The uptake is accompanied by hydrolysis of the triglyceride and reincorporation of the liberated fatty acid mainly into phospholipid. Where cholesterol suspension is injected together with the triglyceride emulsion the 14C-labelled fatty acid is also incorporated into cholesterol ester in the nodes. Investigation by gas-liquid chromatography of the labelled fatty acid in each of the lipid moieties in the nodes showed that some chain elongation of the 14C-labelled palmitic acid occurred, but that the stearic acid formed appeared only in the phospholipid fraction.

Metabolism of Cholesterol Ester by Reticulo‐endothelial Cells

“…The ready and relatively rapid incorporation into phospholipid fits in with previous observations in which phospholipid has been shown to accumulate in reticulo-endothelial cells following the uptake of cholesterol and cholesterol ester [Day, 1960 a]. In macrophages in vitro cholesterol ingestion has also been shown to stimulate the synthesis of phospholipid from labelled acetate [Day and Fidge, 1964] and from 32P-labelled phosphate [Day and Fidge, 1965] and after incubation with 14C-labelled palmitate macrophages incorporated the fatty acid into phospholipid [Day and Fidge, 1962]. In experiments similar to those described in the present paper triglyceride fatty acid was also found to be incorporated into phospholipid by RE cells in rat lymph nodes .…”

“…Nevertheless, the uptake of esterified cholesterol does evoke a metabolic response from RE cells, for the cholesterol ester becomes partially hydrolyzed [Day and French, 1959; and its uptake also results in the accumulation of phospholipid within the cells [Day, 1960 a]. The cells not only hydrolyze esterified cholesterol but also esterify the free form [Day and French, 1959;Day and Gould-Hurst, 1961] and synthesize phospholipid in response to free cholesterol uptake [Day, 1962;Day and Fidge, 1965]. Reticulo-endothelial cells are not able to oxidize the side chain of cholesterol [Day, 1961] but they appear to facilitate the incorporation of cholesterol into lipoprotein which probably assists in its suspension and dispersion [Day et al, 1964 b].…”