Desaturation of endogenous and exogenous palmitate in lung tissue in vitro

lung slices from rats fed a fat-free diet supplemented with safflower oil (control) or tripalmitoylglycerol (essential fatty acid [EFA]-deficient) were incubated with [14C]acetate, [14C]palmitate, or [14C]stearate. Of the 14C recovered in phospholipids after incubation with [14C]acetate, more than 87% was in 16-carbon fatty acids. Desaturation, as assayed by the percentage of radioactivity in monoenoates in phospholipid fatty acids, was generally double in EFA-deficient slices compared to control slices, regardless of substrate. Desaturation was significantly greater in slices incubated with with acetate or octanoate compared to palmitate, indicating that endogenously synthesized palmitate was desaturated more actively than that derived from an exogenous source.