OXIDATION OF ¹⁴C-LABELLED CHYLOMICRON FAT AND ¹⁴C-LABELLED UNESTERIFIED FATTY ACIDS BY MACROPHAGES IN VITRO AND THE EFFECT OF CLEARING FACTOR

¹ Sir William Dunn School of Pathology, University of Oxford; Department of Human Physiology and Pharmacology, University of Adelaide, South Australia

The oxidation by macrophages of ¹⁴C-labelled chylomicron fat and of ¹⁴C-labelled sodium palmitate was investigated by incubating these substances with rabbit macrophages in vitro and collecting the ¹⁴CO₂ produced. Partial oxidation of both ¹⁴C-labelled chylomicron fat and ¹⁴C-labelled sodium palmitate occurred. The amount of fatty acid oxidized was approximately the same whether it was presented as chylomicron fat or as sodium palmitate.

Clearing factor, added to the medium as post-heparin plasma, inhibited the oxidation of ¹⁴C-labelled chylomicron fat by macrophages. This inhibition was not influenced by the replacement of the calcium ions removed by the unesterified fatty acids formed during clearing. Clearing factor inhibited the oxidation of ¹⁴C-labelled sodium palmitate only if chyle was added to the incubation medium. An excess of sodium palmitate or the addition of glycerol did not reduce the oxidation of sodium palmitate by macrophages.

Thus macrophages can oxidize both chylomicron esterified fatty acids and unesterified fatty acids to CO₂. There were substances produced during the clearing of chyle by post-heparin plasma, which inhibited the oxidation of fatty acids by macrophages.

Note:

I am indebted to Professor Sir Howard Florey for his interest in this work, to Drs. J. E. French and D. S. Robinson for advice and encouragement and to Mr. G. J. Wren for technical assistance. The work was carried out with the aid of a personal grant from the Medical Research Council.