Amino acid analysis of human fetal lung elastin was undertaken in 49 instances of live born neonates, ranging from 380 g to full term, and in 3 abortuses of 12-14 wk gestation. The data suggest that formation of the crosslinking agents, desmosine and isodesmosine, occurs early, between 14 and 22 wk. The ratio of neutral to charged amino acids remains low until the 36th wk when it attains adult levels. The composition of elastin was independent of sex and duration of survival. In 3 neonatal pulmonary diseases (respiratory distress syndrome, atelectasis, and hemorrhage) ratios were significantly lower than those found in nondiseased lungs. This may be a reflection of immaturity or may be a predisposing factor in neonatal lung disease. The latter hypothesis is attractive and receives indirect support from the association of a more polar elastin with other diseases, including adult emphysema and atheromatous aortic change. The finding of relatively high polarity in elastin from human fetal lung is consistent with previous observations in a variety of fetal organs of other species.
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