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

Abstract

ABSTRACT. We studied P-adrenergic receptors and responses in human fetal lung (15-25 wk gestation) maintained in explant culture with and without added dexamethasone. To determine P-adrenergic receptor concentration, we performed radioligand binding assays with [lZ5I]-iodocyanopindolol. We also examined the ability of isoproterenol to stimulate cAMP generation as a measure of response to P-adrenergic receptor occupancy. In control cultures, P-receptor concentration increased significantly from d 0 to 3 of culture and thereafter remained stable. The kd (-24 pM) of [1251]-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 ,f3-receptor concentration and decreased both cAMP content and generation (basal and stimulated) in a dose-dependent manner (median effective concentration -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 P-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 P-adrenergic receptor concentration and inhibits P-adrenergic responses. (Pediatr Res 28: 190-195,1990) Abbreviations ICYP, [1251]-iodocyanopindololThere is increasing clinical and experimental evidence that /Iadrenergic responses play a key role in the adaptation of the fetal lung to extrauterine life (I). In vivo and in vitro, P-adrenergic agonists and cAMP analogues stimulate surfactant release and the synthesis of surfactant apoprotein and lipid. P-adrenergic receptors have been identified in human fetal lung during early gestation (2, 3) and the receptor concentration has been shown to increase between 15 and 23 wk gestation (3). In addition, lung P-adrenergic receptors are functionally linked to adenylate cy- Although the effects of explant culture and glucocorticoids on the P-adrenergic response cascade in human fetal lung have not been previously studied, several groups have demonstrated enhancement of morphologic maturation and increased surfactant synthesis in fetal lung of different species in vivo and in explant culture after glucocorticoid treatment (4). Maternal dexamethasone treatment increases the concentration of pulmonary Padrenergic receptors in fetal rabbit (5, 6). In explant cultures of fetal rabbit (7-9) and rat (10) lung and in a cell line derived from adult human lung (1 I), glucocorticoids increase the concentration of P-adrenergic receptors. Additionally, maternal glucocorticoid treatment increased high affinity agonist P-receptor complexes in fetal rabbit lung (7), a functional alteration found previously in some adult tissues (12). In this study, we measured the concentration...

Combined Effects of Fetal Beta Agonist Stimulation and Glucocorticoids on Lung Function of Preterm Lambs

“…By 7 days, surfactant lipids in the lung and airspaces increase and contribute to the phys iological responses. The beta: receptor in creases in lung tissue with advancing gesta tional age, and glucocorticoid exposure can increase the number of beta receptors in rat fetal lung explants [23], although receptors decreased in human fetal lung explants after exposure to glucocorticoid [24], Glucocorti coid exposure also augments postreceptor re sponses in the postnatal preterm lamb with out increasing beta receptors in the heart [25]. A component of the respiratory diseases asso ciated with prematurity is the inability to clear fluid from the airspaces, and epineph rine is the endogenous catecholamine that ac tivates sodium-dependent fluid clearance from the fetal lung in anticipation of delivery [7], Catecholamine-dependent fluid clearance is not demonstrable in preterm fetal sheep, but it can be induced procociously by fetal infusions of the combination of glucocorti coids and T3 [8], Chapman et al [26] demon strated that the beta: agonists terbutaline and aminophylline can enhance fetal lung fluid clearance in lambs.…”

Alveolar liquid clearance in the anesthetized ventilated guinea pig

“…Lungs from three guinea pigs were perfused blood free with 0.9% NaCl via the pulmonary artery and were used for the determination of intracellular cAMP under basal and stimulated conditions. Duplicate samples of blood-free distal lung tissue (25-30 mg) were incubated in 0.25 ml of 5 mM tris(hydroxymethyl)aminomethane (Merck, Darmstadt, Germany) in 0.9% NaCl (pH 7.4), 1 mM 3-isobutyl-1-methylxanthine (a phosphodiesterase inhibitor; Sigma), 0.1 mM ascorbic acid (Merck), and 0.1 mM HCl (Merck), as done earlier (9). Basal cAMP content was determined after incubation at 4°C for 10 min, and basal production of cAMP was studied after a 10-min incubation at 37°C.…”

Modulations of the epithelial phenotype and functional activity of cultured bovine tracheal gland cells: dependence on the culture medium and passage number

“…The difference in response to stimulation by isoproterenol may be due to a decrease of ~-adrenergic receptor concentration under these culture conditions or to the inhibitory factors conrained in Ultroser G or in FCS. Recently, it has been shown [12] that dexamethasone, which is present at a high concentration in Uitroser G, decreases ~-adrenergic receptor concentration and inhibits ~-adrenergic responses during explant culture of human fetal lung.…”