RETINOIDS IN LUNG DEVELOPMENT

The ''retinoid revolution'' has had considerable impact on research ac tivity in the field of lung development, Postnatal lungs are very sens itive to dietary retinol (R) deprivation. The trachea and the bronchop ulmonary tree in R-deficient animals show a striking change in morphol ogy. The columnar epithelium undergoes keratinizing metaplasia, which is reversed when R is supplied. The fetal lung develops postnatally to become one of the most complex organs, characterized by 40 different cell types, The fetal lungs can accumulate retinyl esters, Before birt h an unknown signal causes the lowering of these esters, which may be the source of retinoic acid (RA). The administration of glucocorticoid s speeds up this process, which in turn is followed by acceleration of lung maturation, ending postnatally. It is not clear what role, if an y, the cellular retinoid binding proteins play in this phenomenon, Fet al lung branching leading to the development of the alveolar tree is a ccelerated by RA, and so is the expression of some fetal genes coding for surfactant proteins and the enzymes that produce their lipid compo nents, It is not clear whether RA influences the development of pulmon ary epithelium by interacting directly with the epithelial cells or wh ether its effects require interaction with other cells like mesenchyma l cells, Nuclear RA receptors are intimately involved in lung developm ent, Despite the wealth of evidence on the effect of retinoids on lung development, the application of vitamin A to clinical work has been L imited to prematurely delivered infants who have immature lungs. Here attempts are made, by improving their R status, to aid in the developm ent and healing of lungs injured by oxygen therapy.