Lung phospholipids in the embryonic and immature chicken: Changes in lipid composition and biosynthesis during maturation of the surfactant system

Abstract

Total phospholipid and its components were measured in lungs of the embryonic chick, and in tissue, lamellar bodies, and lavage fluid after hatching. Phosphatidylcholine (PC), the major phospholipid in surfactant, was fractionated and the amount and fatty acid composition of its disaturated (DSPC) component was determined. The synthetic rates of PC, DSPC, and other choline phospholipids were determined on days 14 and 19 of incubation from incorporation of 14C-choline. Choline pool size was also estimated at these times. Phospholipid content of the lung increased most rapidly after day 18 of incubation with the greatest increase in PC. The PC synthesized just prior to breathing was enriched in DSPC, which constituted 45% of PC on day 19 and only 30% on day 14. DSPC content was even lower in embryonic liver and yolk. Incorporation of 14C-choline in vitro into pulmonary PC, Sphingomyelin (Sphingo), and DSPC was greater in birds before breathing (day 19) than in the younger embryos. Choline pool size decreased between days 14 and 19 of incubation, but the synthetic rate of DSPC doubled in this interval. Increased accumulation and biosynthesis of pulmonary PC, Sphingo, and DSPC in lung tissue of the embryo paralleled appearance of lamellar bodies. In 5-6-week-old chickens the major pulmonary phospholipid was also DSPC. In lavage, 70% of PC was DSPC, predominantly dipalmitoyl PC. As in the mammalian lung, PC, especially its DSPC component, forms the major phospholipid of avian surfactant, and the synthesis of DSPC is specifically stimulated prior to breathing.

Microscopic and submicroscopic anatomy of the parabronchi, air sacs, and respiratory space of the budgerigar (Melopsittacus undulatus)

“…Other workers, however, have demonstrated in essence the same findings (ie., the continuous osmiophilic layer and the atrial cells with laminated myelinoid inclusions in fetal and newborn chicks as well as adult chickens, sparrows, and pigeons) but have come to the conclusion that the material was produced by squamous pneumocytes and phagacytosed by cells lining the parabronchi and atria (Petrik and Riedel, 1968a,b). Additionally, this myelinoid material has been postulated to be the surfactant material in turkeys (Fugiwara et al, 1970) and in chickens (Pattle and Hopkinson, 1963;Hylka and Doneen, 1982). Carlson and Beggs (1973) described similar cells lining the abdominal air sacs of chickens.…”

An electron microscopic study of the parabronchial epithelium in the mature lung of four bird species

“…Both cell types exhibit an intense proteosynthetic secretory activity. This trilaminar substance, like the lamellated bodies, has been postulated to be a surfactant material in turkeys (Fujiwara et al, 1970) and in chickens (Pattle and Hopkinson, 1963;Hylka and Doneen, 1982).…”

Pulmonary Vascular Endothelial Growth Factor Expression and Disaturated Phospholipid Content in a Chicken Model of Hypoxia-Induced Fetal Growth Restriction

“…Despite these differences, the phospholipid composition and the fetal developmental pattern of surfactant in the chicken are very similar to those of mammals and other vertebrates [21,22,34] . Type II cells develop within the atrial walls of the parabronchi between the 14th and 15th day of incubation [37] , and lamellar bodies appear on day 16 and increase in number to a maximum at day 18 [38] . Concomitantly, the amount of total phospholipids and DSPL increases in the final stages of incubation, and the DSPL:total phospholipid ratio becomes maximal at days 19-20 [39] .…”

“…The molecular mechanisms that regulate lung development differ to some extent between species, including humans and chickens [38,41] . On the other hand, important similarities are present, such as the stimulatory effect of corticosteroids on surfactant production [22,41] .…”