The purpose of this study was to investigate the hydrolysis of saturated and unsaturated triglycerides by lung lipoprotein lipase and to measure the incorporation of triglyceride fatty acids into lung tissue lipids. Lipolytic activity was studied in the isolated ventilated rat lung, perfused for 100 rain in a recycling system with Krebs Ringer bicarbonate containing bovine serum albumin, 5.6 mM glucose, and 1.5 or 10 mM triglyceride. Saturated triglycerides were hydrolyzed at significantly (p<0.05) lower rates than unsaturated triglycerides; tricaprylin, trimyristin and tripahnitin were hydrolyzed at 8.1 + 1.8, 5.4 + 1.5 and 9.5 + 1.8/~mol free fatty acids/g dry wt/100 min, respectively, whereas triolein and trilinolein were hydrolyzed at 20.2 + 1.8 and 20.6 + 0.3 ~mol free fatty acids/g dry wt/100 min, respectively. The polyunsaturated triglycerides, tdlinolein and triarachidonin were hydrolyzed at even higher rates (44.3 + 3.0 and 50.9 + 5.4 #mol free fatty acids/g dry wt/100 min, respectively). Intralipid infused at a conoentration of 10 mM triglyceride was hydrolyzed at a significantly higher rate than at 1.5 mM triglyceride (58 + 6.3 #mol free fatty adds/g dry wt/100 min vs 16.6 + 1.7/~mol free fatty aeids/g dry wt/100 min, respectively). Labeled unsaturated triglycerides were broken down at significantly higher rates than labeled saturated triglycerides. Incorporation of triglyceride-fatty acid into lung lipid was greater into neutral lipids than into phospholipids. The data su~ggest that (a) the factors that appear to affect lung lipoprotein iipase activity are composition and concentration of circulating triglyceride, (b) uptake of fatty acids into the tissue was proportional to the rate of hydrolysis of the emulsion, and (c) triglyceride-fatty acids could therefore be used by the lung for metabolic needs.

We investigated the relative contribution cf the two pathways of phosphatidylcholine (PC) synthesis in lungs from chick embryos of 12 to 20 days of incubation as well as from hatched chicks and adult chickens. Lung "blocks" were incubated for 60 min in vitro in the presence of IgHlmethionine and [14Clcholine. P C was s e p arated by thin-layer chromatography, and the amount of labeled product was determined by liquid scintillation counting. P C synthesis (expressed as pmoles P C per mg protein per 60 min) by the choline pathway declined from the 12-day value of 40 to a minimum of 8 at day 16 and then rose gradually to a peak of 74 on day 1 posthatching. P C synthesis via the phosphatidylethanolamine pathway also declined from day 12 (9) to day 16 (13) but peaked on day 19 (65) and again on day 1 posthatching (9). Synthetic activities of the two pathways differed significantly (P 5 0.05) only on days 14, 18, and 19 of incubation. Unlike the mammalian lung, neither pathway seems to predominate throughout incubation or after hatching. The increase in P C synthesis towards the end of incubation correlates with the time of appearance of lamellar bodies in the lung epithelial cells and of surfactant in the airways.

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SummaryWe investigated the relative contribution cf the two pathways of phosphatidylcholine (PC) synthesis in lungs from chick embryos of 12 to 20 days of incubation as well as from hatched chicks and adult chickens. Lung "blocks" were incubated for 60 min in vitro in the presence of IgHlmethionine and [14Clcholine. P C was s e p arated by thin-layer chromatography, and the amount of labeled product was determined by liquid scintillation counting. P C synthesis (expressed as pmoles P C per mg protein per 60 min) by the choline pathway declined from the 12-day value of 40 to a minimum of 8 at day 16 and then rose gradually to a peak of 74 on day 1 posthatching. P C synthesis via the phosphatidylethanolamine pathway also declined from day 12 (9) to day 16 (13) but peaked on day 19 (65) and again on day 1 posthatching (9). Synthetic activities of the two pathways differed significantly (P 5 0.05) only on days 14, 18, and 19 of incubation. Unlike the mammalian lung, neither pathway seems to predominate throughout incubation or after hatching. The increase in P C synthesis towards the end of incubation correlates with the time of appearance of lamellar bodies in the lung epithelial cells and of surfactant in the airways. SpeculationBecause normal morphologic and biochemical development of the chick lung resembles that occurring in the mammalian lung in many respects, conclusions drawn from the study of avian lungs may well be germane to an appreciation of mammalian lung differentiation in general. Information concerning regulation of the biosynthetic pathways for phosphatidylcholine in the avian embryo may provide some clues for improved clinical treatment of certain pulmonary disorders, including respiratory distress syndrome of the newborn.Until recently, the question of whether or not the avian lung possessed surfactant was a matter of controversy (17). Now this material has been demonstrated lining the parabronchial, atrial, and air capillary membranes in the lungs of several avian species (18. 19). Cells resembling mammalian types I and I1 pneumocytes have been described by several investigators in the adult and embryonic chick lung (14, 21).The major component of avian pulmonary surfactant is phosphatidylcholine (PC) (16,21). Two pathways are involved in the de novo synthesis of PC: the choline incorporation pathway (I) and the phosphatidylethanolamine (PE) methylation pathway (11). Fetal and adult lungs of all mammalian species examined to date have been shown to possess the enzymes necessary for each pathway (1,6,7). ~h e ' c h o l i n e incorpdration has been identified as the maior route for PC svnthesis in the adult and late fetal mammalian l A g (5). No studieg have been published on the pathways for PC synthesis in the embryonic, newly hatched, or adult chicken lung.We investigated the production of PC in blocks of lungs from chicks of different ages. The blocks were incubated in the presence of radioactive precursors specific to the two pathways for PC synthesis. This provided us with a measure of the r...