title: Regulation of the rainbow trout (Oncorhynchus mykiss) hepatic beta2-adrenoceptor by adrenergic agonists.
abstract: The characteristics of hepatic beta(2)-adrenoceptors (AR) were examined in rainbow trout (Oncorhynchus mykiss) chased once per day to exhaustion for up to 7 days or fed the repartitioning agents clenbuterol (CLEN) or ractopamine (RACT) that function in mammals as beta-agonists. A one-day chase and feeding the CLEN for 37 days resulted in a significant 27% and 33% decrease, respectively, in the number of CGP-binding sites (B(max)) with no significant change in affinity (Kd) of hepatic beta(2)-ARs. Despite the significant decrease in beta(2)-AR numbers with CLEN feeding, no significant differences were found for either beta(2)-AR mRNA levels or adenylyl cyclase (ACase) activities. In addition, CLEN displayed only partial agonist activities as it was found to be more effective at blocking isoproterenol-stimulated cAMP production in isolated hepatocytes than stimulating cAMP production. The small affects of RACT may be related to its low active stereoisomer content and low affinity for the trout beta(2)-AR. Agonist regulation of the trout hepatic beta(2)-ARs may involve down-regulation of the receptors without affecting responsiveness.
authors.affiliation: Department of Biology, University of Ottawa, 150 Louis Pasteur, Ottawa, ON, Canada K1N 6N5.
authors.forename: Stephen G
authors.initials: SG
authors.lastname: Dugan
authors.forename: Michel B
authors.initials: MB
authors.lastname: Lortie
authors.forename: James G
authors.initials: JG
authors.lastname: Nickerson
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Moon
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000322:Adrenergic Agonists / Q000008:administration & dosage / Q000494:pharmacology*; D000821:Animal Feed; D000818:Animals; D001665:Binding Sites; D002976:Clenbuterol / Q000008:administration & dosage / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004032:Diet; D005260:Female; D008099:Liver / Q000187:drug effects* / Q000378:metabolism*; D017686:Oncorhynchus mykiss / Q000097:blood / Q000378:metabolism; D010627:Phenethylamines / Q000008:administration & dosage / Q000494:pharmacology; D011943:Receptors, Adrenergic, beta / Q000235:genetics / Q000378:metabolism*; D013312:Stress, Physiological / Q000503:physiopathology; D013997:Time Factors
chemical_list: D000322:Adrenergic Agonists; D010627:Phenethylamines; D011943:Receptors, Adrenergic, beta; C060897:ractopamine; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D002976:Clenbuterol