SummaryThe biological and physiologic maturation of the lung in the primate M a c a c a nemestrina (pigtail monkey) from 1 0 7 days of gestation through term is the subject of this report. Total lung volume increased approximately 1CO% during the last 20% of gestation (Fig. 1). The increase from 30% to 85% of total lung volume a t a deflation pressure of 1 0 cm H,O indicates a marked change in lung stability during the last 30-40 days of gestation (Fig. 2). Lung phospholipid per g dry weight of lung more than doubles during the last 20% of gestation (Fig. 3). This increase in phospholipid is due almost entirely to a n increase in lecithin, and surface active material (SAM) lecithin accounts for the major part of this increase (Figs. 4 and 5). The increases in total lung and SAM lecithin parallel but precede the increase in lecithin in amniotic fluid (Fig. 6). A s lung SAM increases the amniotic fluid lecithin t o sphingomyelin ratio also increases ( Fig. 7 and Table 1). Low ratios of lecithin t o protein in SAM are found before 135 days of gestation. Subsequently, the amount of lecithin increases and, although protein also increases, the ratio increases 4-fold (Fig. 8). The amount of lung required t o reduce surface tension of 1 cm2 t o 1 2 dynes tended to decrease with advancing gestational age ( Fig. 9 and Table 1). Parallel studies of airway generation demonstrate a similarity t o the human fetal lung. Thus, the structural, compositional, and physiologic changes described in our studies strongly support the use of the fetal monkey for studies of developmentally related disorders of the human lung. SpeculationBiochemical and functional maturational changes in the fetal M . nemestrina indicate its suitability for studies of developmentally related pulmonary disorders of the human. Premature delivery by cesarean section between 1 3 0 and 1 4 0 days should provide a satisfactory homolog for hyaline membrane disease.Body and lung growth in the primate M. nemestrina in the last third of gestation has been described in a previous paper (19). The biochemical and physiologic maturation of the lung in this primate from 107 days of gestation through term (168 days) is the subject of this report. Boyden (3) has shown that develop ment of the terminal air sacs and airways in M. nemestrinn closely resembles that of the human. Maturational events in the primate M. nernestrina are presented, demonstrating the suitability of this primate for studies of human fetal lung development and clinically associated abnormalities. MATERIALS AND METHODSThe lungs of 23 fetal and 2 newborn M. gemestrina were obtained as previously described (19). In most cases, either the 1 right upper lobe or the medial basal (rose) lobule was removed for microscopic studies. Static pressure volume curves were obtained from the remaining lung. Deflation volumes after the second inflation were recorded at intervals between 35 and 0 cm H 2 0 transpulmonary pressure (4). Weights of the individual lobes were then obtained and samples were taken for determin...

SummaryDelivery of M. nemestrina at 80% of normal gestation provides a population of neonates at high risk for hyaline membrane disease (HMD). The diagnosis of HMD was made by the presence of reticulogranular densities and air bronchograms on chest radiographs. Patchy atelectasis was seen in the lungs of animals assigned by clinical and radiographic criteria to the HMD group and not in the normal lungs of animals matched for gestational and postnatal age. Total phospholipid and phosphatidylcholine in whole lung, airway lavage fluid, and surface-active materials were lower in animals with HMD. Amniotic fluid L/S ratios were lower in the group that developed HMD. Pressure-volume measurements indicated decreased distensibility and unstable terminal air spaces in the HMD group. Alveolar-arterial oxygen pressure differences were greater in animals with HMD. There were no differences between HMD and normal groups in body weight, lung weight, percent dry lung weight, gestational age, and postnatal age at death. This primate species, subjected to premature delivery, is a suitable animal model of HMD in human neonates. Speculation An animal model of hyaline membrane disease (HMD) in a primate species is of interest to investigators of developmentally related pulmonary disorders. More complete knowledge of abnormalities in pulmonary function in HMD will contribute to development of both preventive and therapeutic measures and affords the opportunity to determine risks and benefits of such treatments to the fetus and newborn.