Stimulating effect of hydrocortisone on the catabolism of endogenous fatty acyl groups by fatty acid-supplemented mouse L fibroblasts.

Hydrocortisone stimulated the catabolism of prelabeled fatty acyls in mouse L fibroblasts supplemented with exogenous fatty acid. Both oxidation to 14CO2 and release as free fatty acid from prelabeled lipids increased up to 20-fold under the described experimental conditions. The stimulating effect of hydrocortisone was observed even at concentrations as low as 1 microgram/ml. Neither the hormone nor exogenous fatty acid alone had a significant effect on endogenous fatty acyl catabolism. The activity of a cellular pH 6.5 lipase was unaffected by exogenous fatty acid, slightly increased by hydrocortisone, but increased 2-fold when both supplements were present. It is suggested that since exogenous fatty acids shunt phospholipid acyls to triglycerides, the latter induce the formation of more pH 6.5 lipase. Hydrocortisone is either needed for this induction to occur, or activates the newly formed enzyme. The lipase acts on the triglycerides to liberate free fatty acids that are then oxidized to 14CO2 or lost into the medium.