Short-term regulation of fatty acid synthesis in isolated alveolar type II cells from adult rat lung. Effects of free fatty acids and hormones.

We measured the total rate of fatty acid synthesis in alveolar type II cells freshly isolated from the lungs of adult rats. The rate of incorporation of 3H from 3H2O into cellular fatty acids was linear during 3-hr incubations and was very brisk [18 ng-atoms 3H/10(6) cells/hr +/- 2 (mean +/- SD, n = 23)]. When the nutrient medium (Minimum Essential Medium) was supplemented with various hormones or free fatty acids, the long-chain fatty acids (C14-C20) caused a decrease in the rate of 3H incorporation to a variable degree depending on the species of fatty acid. Stearate (10(-4) M) and palmitate (10(-4) M) caused the greatest inhibition of de novo cellular fatty acid synthesis, followed by myristate, arachidonate, and oleate. Insulin (10(-7) M), glucagon (10(-8) M), terbutaline (10(-5) M), 8-bromo-cyclic AMP (10(-3) M), the essential fatty acid linoleate (10(-4) M), and the medium-chain-free fatty acids laurate and octanoate (10(-4) M) did not alter the rate of fatty acid synthesis in type II cells. We demonstrated that the alveolar type II cell is a major lipogenic cell type in the rat. We also demonstrated that the availability of preformed fatty acids in the extracellular milieu is one factor regulating the rate of fatty acid synthesis in these cells.