title: Receptor-mediated enhancement of beta adrenergic drug activity by ascorbate in vitro and in vivo.
abstract: BACKGROUND
  Previous in vitro research demonstrated that ascorbate enhances potency and duration of activity of agonists binding to alpha 1 adrenergic and histamine receptors.
  
  
  OBJECTIVE
  Extending this work to beta 2 adrenergic systems in vitro and in vivo.
  
  
  METHODS
  Ultraviolet spectroscopy was used to study ascorbate binding to adrenergic receptor preparations and peptides. Force transduction studies on acetylcholine-contracted trachealis preparations from pigs and guinea pigs measured the effect of ascorbate on relaxation due to submaximal doses of beta adrenergic agonists. The effect of inhaled albuterol with and without ascorbate was tested on horses with heaves and sheep with carbachol-induced bronchoconstriction.
  
  
  METHODS
  Binding constants for ascorbate binding to beta adrenergic receptor were derived from concentration-dependent spectral shifts. Dose- dependence curves were obtained for the relaxation of pre-contracted trachealis preparations due to beta agonists in the presence and absence of varied ascorbate. Tachyphylaxis and fade were also measured. Dose response curves were determined for the effect of albuterol plus-and-minus ascorbate on airway resistance in horses and sheep.
  
  
  RESULTS
  Ascorbate binds to the beta 2 adrenergic receptor at physiological concentrations. The receptor recycles dehydroascorbate. Physiological and supra-physiological concentrations of ascorbate enhance submaximal epinephrine and isoproterenol relaxation of trachealis, producing a 3-10-fold increase in sensitivity, preventing tachyphylaxis, and reversing fade. In vivo, ascorbate improves albuterol's effect on heaves and produces a 10-fold enhancement of albuterol activity in "asthmatic" sheep.
  
  
  CONCLUSIONS
  Ascorbate enhances beta-adrenergic activity via a novel receptor-mediated mechanism; increases potency and duration of beta adrenergic agonists effective in asthma and COPD; prevents tachyphylaxis; and reverses fade. These novel effects are probably caused by a novel mechanism involving phosphorylation of aminergic receptors and have clinical and drug-development applications.
authors.affiliation: Department of Physiology, Michigan State University, East Lansing, Michigan, United States of America.
authors.forename: Patrick F
authors.initials: PF
authors.lastname: Dillon
authors.forename: Robert
authors.initials: R
authors.lastname: Root-Bernstein
authors.forename: N Edward
authors.initials: NE
authors.lastname: Robinson
authors.forename: William M
authors.initials: WM
authors.lastname: Abraham
authors.forename: Catherine
authors.initials: C
authors.lastname: Berney
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000420:Albuterol / Q000494:pharmacology; D000818:Animals; D001205:Ascorbic Acid / Q000737:chemistry* / Q000494:pharmacology; D016084:Bronchoconstriction; D002217:Carbachol / Q000737:chemistry / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004837:Epinephrine / Q000737:chemistry; D006168:Guinea Pigs; D006632:Histamine / Q000737:chemistry; D006736:Horses; D066298:In Vitro Techniques; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D012756:Sheep; D013056:Spectrophotometry, Ultraviolet / Q000379:methods; D013552:Swine
chemical_list: D000318:Adrenergic beta-Agonists; D011943:Receptors, Adrenergic, beta; D006632:Histamine; D002217:Carbachol; D001205:Ascorbic Acid; D000420:Albuterol; D004837:Epinephrine