Characterization of glycoconjugates in developing rat respiratory system by means of conventional and lectin histochemistry.

The glycoconjugates of the respiratory system of rats from 15 days of gestation through the adult period have been characterized by means of both conventional and lectin histochemistry. The main changes occurred at 20-21 days of gestation immediately before birth. An increase of acidic groups in the glycoproteins of the lung and airway epithelium was observed by conventional mucin histochemistry. The combined use of neuraminidase digestion and lectin histochemistry demonstrated an increase of sialic acid residues at the terminal position of the glucidic moieties of the glycoproteins. The sialic acid residues were linked alpha (2-3, 6) to D-galactose (beta 1-3)-N-acetylgalactosamine, thus masking the PNA-reactivity detected on the luminal surface of Clara cells and pneumonocytes before birth. In the adult period, alpha-L-fucose residues, detected by UEA-I, were localized in the glycoproteins contained in goblet cells and periciliary layer of the rat airway epithelium. The modifications observed in the lung of developing rats are similar to those previously described in human fetal and neonatal lungs. This suggests that the rat represents a useful model to study the glycoprotein synthesis during lung development.