A NONGLYCOSYLATED FORM OF PULMONARY SURFACTANT PROTEIN A APPEARS IN RAT AMNIOTIC-FLUID

Surfactant protein A (SP-A) is a family of glycoproteins that have a t riplet with 26, 32 and 36 kDa under reducing conditions in rat lung. W e wanted to evaluate the SP-A forms in amniotic fluid of pregnant rats compared to those found in rat lungs. By Western blot analysis, glyco sylated SP-A, was not found in the amniotic fluid in contrast to the p ulmonary surfactant triplet SP-A, which comprises a 26 kDa protein and its glycosylated 32 and 36 kDa forms. The SP-A concentration in amnio tic fluid was barely detectable at 18 days of gestation (20+/-12 ng.ml (-1), and then increased and reached 700+/-333 ng.ml(-1) at the final gestational day 21, as determined by an enzyme-linked immunoabsorbent assay. Immunohistochemically, SPA was found in some epithelial cells o f larger respiratory bronchi, but not, or to a lesser degree, in small er respiratory bronchi at gestational day 18. At 21 days of gestation, SP-A was detected in bronchial and bronchiolar nonciliated epithelial Clara cells, alveolar epithelial type II cells and some alveolar macr ophages. The ratio of the 26, 32 and 36 kDa SP-A forms in bronchoalveo lar, bronchobronchiolar and tracheal lavage fluids prepared from adult rats was 6:29:65, 84:5:11 and 100:0:0, respectively. These findings s how the presence of a non-glycosylated SP-A in rat amniotic fluid. Thi s may reflect the increased ratio of non-glycosylated SP-A to bronchoa lveolar, bronchobronchiolar and tracheal lavage fluids, respectively.