title: Regulation of fetal cardiac and hepatic beta-adrenoceptors and adenylyl cyclase signaling: terbutaline effects.
abstract: Terbutaline (Ter), a beta(2)-adrenergic agonist used in preterm labor, stimulates fetal beta-adrenoceptors (beta-ARs). We administered Ter to pregnant rats on gestational days 17-20 and examined beta-ARs and adenylyl cyclase (AC) signaling in heart and liver. Ter produced less downregulation of cardiac beta-ARs than in adults, despite a higher proportion of the beta(2)-subtype, and failed to elicit desensitization of the receptor-mediated AC response. AC stimulants acting at different points indicated an offsetting of homologous desensitization at the level of the beta-AR by heterologous sensitization at the level of AC: induction of total AC catalytic activity and a shift in the catalytic profile or AC isoform. In fetal liver, Ter produced downregulation of beta-ARs, in keeping with the predominance of the beta(2)-subtype; hepatic receptor downregulation was equivalent in fetus and adult. Nevertheless, there was still no desensitization of beta-AR-mediated AC responses and again AC was induced. Our results indicate that, unlike in the adult, fetal beta-AR signaling is not desensitized by beta-agonists and, in fact, displays heterologous sensitization, thus sustaining responses during parturition. At the same time, the inability to desensitize beta-AR AC responses may lead to disruption of cardiac, hepatic, or neural cell development as a consequence of tocolytic therapy with beta-agonists.
authors.affiliation: Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710, USA.
authors.forename: J T
authors.initials: JT
authors.lastname: Auman
authors.forename: F J
authors.initials: FJ
authors.lastname: Seidler
authors.forename: T A
authors.initials: TA
authors.lastname: Slotkin
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D015536:Down-Regulation / Q000187:drug effects; D004790:Enzyme Induction / Q000187:drug effects; D005260:Female; D020567:Fetal Weight / Q000187:drug effects; D005333:Fetus / Q000187:drug effects / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D008297:Male; D008431:Maternal-Fetal Exchange / Q000502:physiology; D009206:Myocardium / Q000378:metabolism*; D009929:Organ Size / Q000187:drug effects; D011247:Pregnancy; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013726:Terbutaline / Q000494:pharmacology
chemical_list: D000316:Adrenergic alpha-Agonists; D000318:Adrenergic beta-Agonists; D011943:Receptors, Adrenergic, beta; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D013726:Terbutaline