β-Adrenergic Receptors and cAMP Response Increase during Explant Culture of Human Fetal Lung: Partial Inhibition by Dexamethasone

Abstract

We studied beta-adrenergic receptors and responses in human fetal lung (15-25 wk gestation) maintained in explant culture with and without added dexamethasone. To determine beta-adrenergic receptor concentration, we performed radioligand binding assays with [125I]-iodocyanopindolol. We also examined the ability of isoproterenol to stimulate cAMP generation as a measure of response to beta-adrenergic receptor occupancy. In control cultures, beta-receptor concentration increased significantly from d 0 to 3 of culture and thereafter remained stable. The kd (approximately 24 pM) of [125I]-iodocyanopindolol did not change with time in culture. The ability of isoproterenol to stimulate cAMP generation over basal levels increased in controls throughout the 5 d in explant culture. Addition of dexamethasone (10 nM) to the culture medium partially blocked the increase in beta-receptor concentration and decreased both cAMP content and generation (basal and stimulated) in a dose-dependent manner (median effective concentration approximately 1 nM). In these same explants, dexamethasone increased the activity of fatty acid synthetase, an enzyme important in surfactant synthesis, more than 2-fold. Our results indicate that beta-adrenergic receptors and isoproterenol stimulation of cAMP generation increase spontaneously in human fetal lung grown in explant culture. Dexamethasone, which accelerates other aspects of human lung development in vitro, decreases beta-adrenergic receptor concentration and inhibits beta-adrenergic responses.