The mechanism of formation of alveolar pores (Kohn's pores) in neonatal rabbit

The mechanism of the formation of alveolar pores (Kohn's pores) in neonatal male rabbits was studied by scanning electron microscopy and scanning electron microscopic morphometric analysis. The number of alveolar pores per alveolus was increased after birth. About 80 percent f alveolar pores had Type H alveolar epithelial cells on their edges when the rabbits were I-day old. This percentage decreased thereafter. Circlelike intercellular junctions of Type I cells were frequently observed in or around the alveolar pores and Type II cells frequently attached to these junctions in the early neonatal stage. The alveolar pores with Type II cells which were mainly faced this side of alveolar lumen, and Type II cells which were separated from the pores tended to be found at the points where three or more Type I alveolar epithelial cells gathered in the early neonatal stage. However, alveolar pores with Type H cells which were mainly faced other side of the alveolar lumen, and alveolar pores without Type II cells tended to be found between two Type I cells. At the rims of the pore, crescent-shaped Type II cells located between circle-like intercellular junctions were frequently observed in the early neonatal stage. In conclusion. 1) One of the function of Type H alveolar epithelial cells is to form the alveolar pores. 2) Alveolar pores are formed by Type II cells whichhave penetrated into the alveolar wall and faced both sides of the alveolar lumina. Type II cells combine the Type I alveolar epithelial cells of both sides of the alveolar wall and make pores with circle-like intercellular junctions. 3) Type II cells, attached to circle-like intercellular junctions, move and decrease in number after theformation of alveolar pores.