SURFACTANT SECRETION BY TYPE-II PNEUMOCYTES IS INHIBITED BY HIGH GLUCOSE-CONCENTRATIONS

Delayed fetal lung maturation is observed in poorly controlled diabeti c pregnancies. To investigate whether elevated glucose levels inhibit basal surfactant secretion and synthesis in type II cells and whether inhibitory effects on secretion can be reversed by secretagogues, type II cells isolated from 20-day fetal rat lung explants were initially cultured in [H-3] choline containing media with glucose concentrations of 5.5, 10, 25, 50, and 100 mM, or in equiosmolar mannitol controls. Further incubation in nonradioactive media containing matched glucose levels with and without 1 x 10(-5) M terbutaline or 1 x 10(-6) M and 1 x 10(-8) M 12-O-tetradecanoylphorbol 13-acetate (TPA) allowed assessm ent of incorporation of choline into phosphatidylcholine (PC) and its subsequent secretion. PC secretion was inhibited by culture in high gl ucose conditions, resulting in an similar to 30% ro reduction in secre tion under 50 and 100 mM glucose conditions compared to culture at 5.5 or 10 mM glucose (p <.01); this decrease could not be explained by ch anges in osmolarity or in cell viability after culture in high glucose . Insulin (I unit/mL) had no significant impact on secretion (92 +/- 7 % of control). Terbutaline-stimulated cells grown under 50 and 100 mM glucose conditions had significantly lower secretion rates than did te rbutaline-stimulated cells cultured in 5.5 mM glucose (p <.05). Exposu re to TPA resulted in significant increases in surfactant secretion by cells grown in both 5.5 and 100 mM glucose; however, the percentage i ncrease (39.5 +/- 6.8% and 94.8 +/- 8.0% with 10(-8) M and 10(-6) M TP A, respectively) was significantly lower than in controls (87.8 +/- 8. 0% and 152.1 +/- 18.8%, respectively) (p <.001). Choline incorporation into PC was also decreased by 100 mM glucose to 77 +/- 9% of control (p <.01). These data indicate that high glucose levels inhibit both su rfactant synthesis and baseline and secretagogue-stimulated surfactant secretion by type II cells. This inhibitory effect on surfactant secr etion may further exacerbate the decrease in surfactant synthesis and the pulmonary maturational delay seen in infants of diabetic pregnanci es.