Bombesin and Vasoactive Intestinal Polypeptide in the Developing Lung: Marked Changes in Acute Respiratory Distress Syndrome*

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Abstract
The quantitative distribution of bombesin-and vasoactive intestinal polypeptide (VIP)-like immunoreactivities was determined by RIA and immunocytochemistry in regions of trachea, bronchus, and whole lung at various stages of human fetal development and in neonates, children, and adults. In addition, these two immunoreactivities were studied in infants that had died of the acute respiratory distress syndrome. The concentration of bombesin-like immunoreactivity in the whole respiratory tract steadily increased during gestation, reaching a plateau at birth. In the lung, the bombesin concentration remained almost unchanged during childhood, but decreased to one tenth in the adult. In neonates with the acute respiratory distress syndrome, there was a significantly lower bombesin content in all regions of the respiratory tract compared to either normal full-term infants or 24- to 28-week-old fetuses. Immunocytochemistry localized bombesin immunoreactivity within mucosal neuroendocrine cells present in the airway epithelium throughout the respiratory tract and particularly in the intrapulmonary airways. The number of cells increased throughout gestation, reflecting the pattern found by RIA, and were greatly decreased in acute respiratory distress syndrome patients. VIP concentrations were much lower than those of bombesin and did not change significantly with gestational age. In contrast to bombesin, VIP was mainly concentrated in the upper respiratory tract. In infants with the respiratory distress syndrome, the VIP content was not different from normal. These results are compatible with the possibility that bombesin-like peptides may have a role in the normal development of the human lung.