1690 EFFECTS OF EXOGENOUS PALMITATE ON DE NOVO FATTY ACID SYNTHESIS IN FETAL LUNG EXPLANTS

Abstract

De novo fatty acid synthesis in fetal lung is probably an important source of the long chain fatty acid constituents of pulmonary surfactant and membrane phospholipids. In some tissues, de novo fatty acid synthesis is regulated, in part, by the availability of exogenous fatty acids. Utilizing fetal rat lung explants, we measured de novo fatty acid synthesis by determining the rate of 3H₂O incorporation in saponifiable lipids. During a 48 hr. incubation in synthetic medium, 3H₂O incorporation in explants from 19 day fetal rat lung increased from 15.1 nmoles/mg protein/hr to 34.2 nmoles/mg protein/hr. Incorporation into glycerides increased from 5.81 nmoles/mg protein/hr to 8.58 nmoles/mg protein/hr. ¹⁴C-glucose incorporation into fatty acids also increased 2 fold during this time. Addition of 2.5mM palmitic acid to the incubation medium for 24 hrs. resulted in a 45% decrease in ³H₂O and ¹⁴C-glucose incorporation into fatty acids. There was,however,a 2.5 fold increase in ³H₂O incorporation into glycerides. After 48 hrs. of culture in palmitate,³H₂O incorporation into fatty acids was not different from the control explants, while incorporation into glycerides by the explants cultured in palmitate continued to be 2.5 fold greater than controls. These data suggest that de novo fatty acid synthesis in fetal lung explants is regulated in the short term by the availability of exogenous fatty acid. In addition, exogenous fatty acid results in an increase in the incorporation at ³H₂O into the glyceride moiety.

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