THE ROLE OF CYCLIC AMP IN LAMELLAR BODY SYNTHESIS & SECRETION

Abstract

To assess the effect of dibutryl cyclic 3′-5′ adenosine monophosphate (DBcAMP) on some aspects of pulmonary Type II cell morphology and biochemistry, adult rats were injected i.p. with 47 mg/kg DBcAMP and sacrificed at intervals. Control rats received saline or 5′ AMP. Lung tissue was prepared for electron microscopy. 5 min. postinjection, Type II cells in treated rats appeared more numerous than in controls and endoplasmic reticulum (ER) dilated. By 10 min. the cells appeared larger, lamellar bodies (LB) were increased per cell and ER remained dilated. Multivesicular bodies (MVB) appeared in increased numbers. By 15 min. the cells were swollen, often with loss of microvilli and MVB's conspicuous. There appeared to be fusion of LB limiting membranes with plasma membranes and extrusion of LB contents into alveoli. By 30 min. macrophages appeared in alveoli and septa. Type II cells were of more normal size and vacuoles appeared in the cytoplasm near the alveolar surface suggestive of endocytosis. By 60 min. Type II cells were not remarkable. Choline kinase (CK) activity was assayed in LB rich cell fractions from pooled lung of 6 DBcAMP treated and 6 control rats sacrificed at 15 min. There was a 5-fold increase in CK activity in the DBcAMP treated rats. These findings suggest that intracellular synthesis and extrusion of LB from Type II cells may be mediated by cAMP.