Estudos sobre a Morfogénese, Histogénese e Histofisiologia do Pulmão (Contribuição Experimental).Coimbra, ed. autor, 1986, 526 p.

Abstract

The present publication is a collection of studies developed with the aim of attaining a better understanding of the histomorphology, histogenesis and histophysiology of the prenatal and postnatal lung, using the mouse as the laboratory animal. Following the definition and presentation of the main objectives and topics, a historical perspective of the histological studies developed ever since is presented. In this historical sinopsis a great deal of emphasis is devoted to the controversy that existed concerning the continuity, descontinuity and origin of the alveolar lining cells. In order to embody the studies on a biological perspective of development, the problems concerning the morphogenesis of the lung are analysed, based on the general mechanisms of induction, differentiation and morphogenetic interactions. On this general overview, the cellular interactions mediated by diffusion,cellular contact, effects of the extracellular matrix and the influence of hormones and other cellular stimulating factors conditioning morphogenesis and growth, are presented. The methodologies for the collection, fixing, processing and stabilization of the lung are described, considering the better preservation of the pneumocytes type II multilamellar bodies. A methodology fulfilling the best compromise between the stabilization of the various biochemical components of the lung cells is also described. The methods involved in the biochemical determination, ultracentrifugal characterization, ultrastructural cytochemistry and microfluorimetric analysis of the glycogen are presented and their pitfalls discussed. The microfluorimetric and ultrastructural detection of vitamin A is also analysed. The problems concerned with the characterization and identification of vitamin A and the difficulties encountered with the methodologies and their limitations in order to avoid errors in the cytochemical and histological interpretations are discussed. The results are divided in different headings : histomorphology of postnatal maturation of mousse lung from 4 to 6 hours after birth to 24 days; histomorphologic aspects of the «lung elastic system» thouroughout the postnatal development; ponderal aspects during the postonatal maturation considering the total body weight, the biochemical parameters of the nucleic acids, cytofluorimetry the DNA, not only of animals inhalating normal atmospheric air but also of animais inhalating air with 90% O2. As a first conclusion a model of the postnatal alveolization process is described base on a connective-vasculo-epithelial process supported by a meccano-expansive mechanism. In contradiction to other studies, the alveoli are developed by the appearance of slits and channels in the walls of the primitive saccules, with the progressive expansion of theses spaces. In that interpretation the alveoli results from an evagination process leading to the appearance of the secondary septa. The process generates the observed transient appearance of bulbs and of a dinamic valvular mechanism operated by the walls of the slits and of the channels. This model is justified not only by the histomorphologic appearance but also by the topographic localization of the elastic fibers and the lipid storage in the interstitical connective tissue cells. Under subsequent headings the interstitial connective tissue cells of the lung of adult and postnatal animals storing lipids and vitamin A are characterized by ultrastructural cytochemistry and biophsical methods. By the administration of an excess of vitamin A to adult animals, postnatal histological aspects of the lung undergoing maturation were induced. Linking that storage to the postnatal storage of lipids and the detection in these lipids of vitamin A, during the weaning period vitamin A appears to modulate the postnatal alveolization process and the lung maturation, justifying the of alveolization, described above. In another group of studies the abundance of glycogen on perinatal lung is characterized. The type of glycogen particles and its correlation and closed association with the appearance of the first myelin figures and multilamellar bodies inside glycogen pools in the cytoplasm of the pneumocytes type II are demonstrated. Concerned with the perinatal studies of glycogen the cellular differentation and interaction of different types of bronchiolar and alveolar epithelial cells are presented. An interpretation of liotropic and thermotropic mesomorphism of the phospholipids of the multilamellar bodies is presented, based on blocking the phase transitions of the chemical species of the multilamellar bodies with a greater ultrastructural stability at + 37ºC. Considering the studies developed by various investigators and those obtained in the present work a macromolecular interpretation of the prenatal and postnatal genesis and structuration of the multilamellar bodies and its transformarion into the alveolar surfactant material is discussed and presented. This general prenatal and postnatal interpretation considers: the prenatal organization of the first multilamellar bodies in relation to glycogen; the presence of multivesicular bodies; the function of the phospholipids transfer proteins; the phosoholipids phase transitions; a phospholipid shuttle between the pneumocyte type II and the alveolar lining surfactant and the phase transitions generated inside of the multilamellar bodies as a biophysical process of normal occurrence. The interpretation justifies the different ultrastructural configurations of the multilamellar bodies as the consequence of L, P and H phases and the different arrays commonly observed. A general survey of the studies related to the biophysical interactions of simple model systems of lipid-water, lipid-lipid and lipid-protein are also presented in order to support the mentioned general macromolecular and ultrastructural interpretation of the multilamellar bodies behaviour in the pneumocytes type II and their transformation into the alveolar surfactant.