title: Postreceptor defects in alveolar epithelial beta-adrenergic signaling after prolonged isoproterenol infusion.
abstract: We previously found that prolonged isoproterenol (Iso) infusion in rats impaired the ability of beta-adrenoceptor (beta-AR) agonists to increase alveolar liquid clearance (ALC). Here, we determined if postreceptor defects in beta-AR signaling contribute to this impairment. Iso was infused using subcutaneous miniosmotic pumps (4, 40, or 400 microg. kg-1. h-1) in rats for 48 h. At this time, forskolin-stimulated ALC was measured by mass balance. Forskolin-stimulated ALC [33.4 +/- 2.1%/h (mean +/- SE) in vehicle-infused rats] was reduced by 25 and 38%, respectively, after the 40 and 400 microg. kg-1. h-1 Iso infusions. The ability of forskolin to increase cAMP was reduced by 70% in alveolar type II (ATII) cells isolated from rats infused with 400 microg. kg-1. h-1 Iso. Additionally, the ability of the stable cAMP analog 8-bromoadenosine-3',5'-cyclic monophosphorothioate, Sp-isomer, to increase ALC (48.7 +/- 3.0% in vehicle-infused rats) was reduced by 25 and 51%, respectively, after the 40 and 400 microg. kg-1. h-1 infusions. Finally, the ability of cAMP to increase protein kinase A activity was eliminated in ATII cells isolated from rats infused with Iso at 400 microg. kg-1. h-1. These data demonstrate that prolonged beta-AR agonist exposure can impair alveolar epithelial beta-AR signaling downstream of the beta-AR.
authors.affiliation: Dept. of Physiology, Northeastern Ohio Universities, College of Medicine, 4209 State Route 44, P. O. Box 95, Rootstown, OH 44272-0095, USA.
authors.forename: Eric E
authors.initials: EE
authors.lastname: Morgan
authors.forename: Sonya M
authors.initials: SM
authors.lastname: Stader
authors.forename: Cheryl M
authors.initials: CM
authors.lastname: Hodnichak
authors.forename: Kate E
authors.initials: KE
authors.lastname: Mavrich
authors.forename: Hans G
authors.initials: HG
authors.lastname: Folkesson
authors.forename: Michael B
authors.initials: MB
authors.lastname: Maron
mesh_terms: D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000262:Adenylyl Cyclases / Q000378:metabolism; D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D054746:Cyclic AMP-Dependent Protein Kinase Type II; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D015633:Extravascular Lung Water / Q000378:metabolism; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male; D011650:Pulmonary Alveoli / Q000187:drug effects* / Q000378:metabolism*; D011654:Pulmonary Edema / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D020545:Respiratory Mucosa / Q000187:drug effects / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D000318:Adrenergic beta-Agonists; D011943:Receptors, Adrenergic, beta; D005576:Colforsin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D000242:Cyclic AMP; D054746:Cyclic AMP-Dependent Protein Kinase Type II; D017868:Cyclic AMP-Dependent Protein Kinases; D000262:Adenylyl Cyclases; D007545:Isoproterenol