Morphological study of the basement membrane of the developing lung in rats

In order to know the significance of the basement membrane in the developing lung, an immunohistochemical study and an electron microscopical study were conducted. Wistar-Imamichi rats, which were 15, 18 and 20 day-old embryos and 5 day-old newborns, were used. The ABC method (labeled antibody method) and immunofluorescence method (FITC-labeled antibody method) were introduced, using antisera against laminin, type IV collagen and fibronectin which are the major components of the basement membrane. The basement membrane of 15 day-old embryos (pseudo-glandular period) showed very wide fine structures: the lamina lucida and lamina densa could not be defined. The width of the basement membrane became narrow in 18 and 20 day-old embryonic lungs, and the fine structural appearance of lamina lucida and lamina densa became visible after birth. There was no difference between laminin and type IV collagen immunostainability. The width of the type IV collagen and laminin immunoreactions gradually became narrow with the fine structural maturation of the basement membrane. Fibronectin immunostaining with the FITC-labeled method presented a diffuse nodular pattern, while that with the peroxidase labeled antibody method displayed a notched linear pattern. In 15 day-old embryos, fibronectin was mainly localized in the basement membrane zone of pseudo-glandular tubules and in the mesenchymal tissue. This immunoreaction in the mesenchymal tissue gradually disappeared.