Luminal surfaces of fetal rat alveolar type II and Clara lung cells react with antibody to Heymann nephritis antigen.

We have used affinity purified antibody, which reacts with the renal antigen gp600, to examine the immunoreactivity of pulmonary cells in the quick frozen lung tissue of fetal rats. On immunoelectron microscopy, we found that the reaction was specifically localized to the luminal surfaces of Clara cell and, as previously reported, to alveolar type II cell (ATII) membranes. No immunoreaction was seen on or in type I cells, endothelial cells or any other lung or blood cell. These studies suggest that the anti-gp600 immunoselection can be used as a marker to identify and quantify Clara and ATII cells in rat lung tissue.

Definition of an immunologic marker for type II pneumocytes.

Based on our previous finding in lung parenchyma of high concentration of the shared epitopes of gp600, a well characterized kidney glycoprotein, we attempted to identify the anatomic site of these epitopes and characterize them biochemically. Affinity-purified polyclonal anti-gp600 antibody was used as the probe. Immunocytochemically in lung on light and electron microscopy the probe reacted exclusively with type II pneumocytes and no other lung cell. The reaction was also demonstrated on freshly isolated and cultured type II pneumocytes. Both approaches showed the reaction to localize on the cell membrane of type II pneumocytes. Immunoprecipitation of radiolabeled type II pneumocyte cell membranes identified two 270- to 290-kDa polypeptides as the reactive proteins. We conclude that the reactive epitopes for anti-gp600 in lung parenchyma are exclusively localized on type II pneumocytes and have a Mr of approximately 270 to 290 kDa and that anti-gp600 may be used as a specific immunologic marker for the type II pneumocytes. Finally, it is possible that the differences in the molecular forms of the cross-reactive proteins in lung and kidney identified in this report are the reason for the known non-nephritogenicity of rat lung for the induction of Heymann nephritis in rat.

Biochemical and physiological development of fetal rhesus lung.

Study of 17 fetal rhesus monkeys (Macaca mulatta) revealed a sequential rise in lung phosphatidylcholine (PC) concentration due to elevations in both disaturated (DSPC) and unsaturated constituents. The % DSPC in lung tissue clinical abruptly at 145 days of gestation prior to significant increases in PC or DSPC concentration but in association with improved lung deflation stability (% V10). This suggests that the DSPC-to-PC ratio may be a sensitive biochemical indicator of surfactant phospholipid production in lung parenchyma. Phosphatidyl-glycerol content did not increase significantly until after 155 days gestation, which was coincident with maximizing pulmonary distensibility (V max). Declining levels of phosphatidylethanolamine and sphingomyelin in lung tissue at 162 days support the hypothesis that preferential synthesis of PC occurs during late gestation. A serial decline in lung glycogen content with advancing gestation may reflect glycogen utilization as a substrate for lung phospholipid production. Comparison of biochemical and physiological data confirms the impression that discordances occur among lung maturational events. Lastly, a relationship between rising fetal blood cortisol levels and indices of fetal lung development was not demonstrated.

The influence of sex on fetal rabbit lung maturation and on the response to glucocorticoid.

Female premature rabbit fetuses had more stable lungs than male premature rabbit fetuses. In both male and female rabbit fetuses, deflation stability increased to a similar extent after administration of glucocorticoid, but the resultant male lungs were significantly less stable. The lungs of female fetuses treated with steroid had greater histologic maturity than those of male fetuses, with a higher proportion of air space and thinner airspace after completion of pressure-volume studies. These results indicate that sex differences must be considered in studies of lung maturation.

Influence of glucocorticoid administration and inhibition on fetal baboon pulmonary maturity and the amniotic fluid L/S ratio.

The pregnant baboon feto-placental unit responded to intra-amniotic dexamethasone by a rise in the lecithin-sphingomyelin ratio (L/S ratio) and accelerated pulmonary maturity with evidence of increased amounts of pulmonary surfactant. Metyrapone 11 beta-hydroxylase inhibition of corticoid synthesis prevented the expected rise in the L/S ratio without influencing the normal development of pulmonary maturity. The L/S ratio did not accurately reflect pulmonary maturity when metyrapone was administered to the pregnant baboon. Prudently, model systems such as the baboon should be used for more detailed studies of endocrine effects on pulmonary development because of the reported untoward effects of exogenous steroid administration on the human neonatal nervous system.

Response of immature baboon fetal lung to intra-amniotic betamethasone.

Intra-amniotic betamethasone (6 mg.) given to six immature fetal baboons, at four and again at three days prior to delivery by cesarean section, between 147 and 158 days' gestation (term = 180 days), significantly increased the amniotic fluid lecithin/sphingomyelin (L/S) ratio. At delivery, treated animal lungs were more mature in that they had a significantly increased deflation stability and significantly decreased minimum surface tension in minced lung when compared to five control animals. Changes in maximum air distensibility lagged behind changes in deflation stability. The major molecular species of pulmonary phosphatidylcholine were analyzed by gas liquid chromatography as the diacylglycerol derivatives. The proportions of 14:0/16:0, 16:0/16:0, and 16:0/18:0, were significantly increased over control proportions while unsaturated species tended to decrease in animals exposed to intra-amniotic betamethasone. The immature fetal baboon pulmonary system responded to intra-amniotic betamethasone with a synchronous increase in the L/S ratio, improved pulmonary stability, and a more mature pulmonary lecithin composition, but did not demonstrate a synchronous increase in tissue distensibility.

The prevention of hyaline membrane disease: new concepts and approaches to therapy.

New approaches to hyaline membrane disease have emerged in recent years. These developments are principally attributable to advances in our understanding of the following: (1) the pathophysiology and pathogenesis of HMD in relationship to pulmonary surfactant, (2) fundamental aspects of fetal lung development, including the movement of surfactant phospholipids from fetal pulmonary fluid to the amniotic space, (3) mechanisms for accelerating lung maturation, particularly with maternally administered prenatal glucocorticoids, and (4) ventilatory techniques effective in protecting and conserving alveolar surfactant by the continuous application of end expiratory pressure. Prenatal assessment of the risk for developing hyaline membrane disease is now routinely possible by amniocentesis and analysis of the ratio of lecithin to sphingomyelin in amniotic fluid. Such predictability, coupled with the ability to postpone delviery, allows the perinatologist in some instances to provide the fetus with ample opportunity for lung development in utero. Recent clinical trials around the world with pregnant women in premature labor document a significantly lower incidence of hyaline membrane disease after antenatal glucocorticoid treatment. In neonates with the disease weighing more than 1500 gm, it is now established that reduced mortality rates accrue from the use of end expiratory positive pressure. These clinical advances offer great promise in changing the nature of HMD management from procedures that are largely supportive to approaches that are truly preventative.

A new model for neonatal pulmonary hemorrhage research.

Hemorrhagic atelectasis was successfully produced in newborn rabbits by pharmacologically narrowing airways leading to alveoli ventilated with oxygen-enriched gas. Between 48% and 62% of alveoli filled with blood cells. Areas of lung with a tendency to collapse were measured by pressure volume studies. Animals given supplemental oxygen retained 56% of total lung volume compared with 79% in the pilocarpine group, which suggested increased effectiveness of anti-atelectasis factors in the latter. Less total lung gas was present in the pilocarpine group (4.0 plus or minus 0.4 cc/g) compared with oxygen controls (5.1 plus or minus 0.81 cc/g), which indicated more noninflatable lung. Neither surfactant deficiency nor heart failure needed to be present for pulmonary hemorrhage to occur.

The significance of circulating glycerol as a precursor of pulmonary phosphatidylcholine in the developing mammalian lung.

There is scant information regarding the contribution made by circulating precursors to pulmonary phosphatidylcholine synthesis in the developing mammalian lung. In situ pulmonary artery perfusions were performed in term New Zealand newborn rabbits with physiologic buffer containing either 3.6 mM or 10.8 mM glycerol. There was a twofold increase in nanomoles of glycerol-phosphatidylcholine synthesized at 30 min when the higher concentration of glycerol was used. Continuing with the higher concentration, a near three-fold increase was observed between the 30-min and 60-min perfusions. This data indicates that the de novo synthesis of pulmonary phosphatidylcholine is influenced by the concentration of glycerol in the perfusate as well as the duration of perfusion.

Endocrine influences on pulmonary maturation and the lecithin/sphingomyelin ratio in the fetal baboon.

By utilizing the baboon model system, preliminary data indicate that intra-amniotic dexamethasone caused an increase in the L/S ratio. Metopirone 11-betahydroxylase inhibition prevented the expected increase in the L/S ratio without influencing pulmonary distensibility, stability on deflation, or lung mince minimal surface tension. Infants born at term to Metopirone-treated baboons were free of pulmonary distress and survived to adolescence.