Uptake and metabolism of alpha-monopalmitin by rat lung in vitro

CO2 production from and uptake of alpha-glyceryl mono (palmitate-1-14C) were studied in an in vitro system using minced rat lung. Monoglyceride radioactivity was readily incorporated into lung tissue lipids. In a time course of 5-120 min, ca. 2.9-21.9% of the initial medium 14C-radioactivity was recovered in tissue lipids, including free fatty acid and monoglyceride, per one g of tissue. From 93 to 72% of the initial radioactivity remained in the medium during the same incubation periods. The ratio of tissue neutral lipid to phospholipid radioactivity decreased from 2:1 at 5 min to ca. 1:2.1 at 120 min. Most of the phospholipid-14C was in phosphatidyl choline, and this accounted for 80% of phospholipid-14C. Analysis of the tissue lipid radioactivity pattern revealed that during early periods of incubation (5-15 min) there was a rapid accumulation of 14C in monoglycerides and free fatty acids, which decreased with increasing incubation time concomitant with increase in radioactivity of tissue phospholipids and triglycerides. During the same time course, 6.5-85.3% of medium-14C was in free fatty acid, indicating the presence of an active alpha-monopalmitin-hydrolyzing system. After 2 hr of incubation, only 1.8% of the initial medium-14C had been oxidized to CO2. Under the same experimental conditions, 14C-alpha-monopalmitin and palmitate-1-14C were almost equally utilized and the patterns of lipid incorporated from both substrates were similar. It is suggested that rat lungs can utilize alpha-monopalmitin in a similar manner as palmitate after the former is hydrolyzed.