title: Exogenous and endogenous adenosine inhibits fetal calf serum-induced growth of rat cardiac fibroblasts: role of A2B receptors.
abstract: BACKGROUND
  Because proliferation of cardiac fibroblasts participates in cardiac hypertrophy/remodeling associated with hypertension and myocardial infarction, it is important to elucidate factors regulating cardiac fibroblast proliferation. Adenosine, a nucleoside abundantly produced by cardiac cells, is antimitogenic vis-à-vis vascular smooth muscle cells; however, the effect of adenosine on cardiac fibroblast proliferation is unknown. The objective of this study was to characterize the effects of exogenous and endogenous (cardiac fibroblast-derived) adenosine on cardiac fibroblast proliferation.
  
  
  RESULTS
  Growth-arrested cardiac fibroblasts were stimulated with 2.5% FCS in the presence and absence of adenosine, 2-chloroadenosine (stable adenosine analogue), or modulators of adenosine levels, including (1) erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA; adenosine deaminase inhibitor); (2) dipyridamole (adenosine transport blocker); and (3) iodotubericidin (adenosine kinase inhibitor). All of these agents inhibited, in a concentration-dependent manner, FCS-induced cardiac fibroblast proliferation as assessed by DNA synthesis ([3H]thymidine incorporation) and cell counting. EHNA, dipyridamole, and iodotubericidin increased extracellular levels of adenosine by 2.3- to 5.6-fold when added separately to cardiac fibroblasts, and EHNA+iodotubericidin or EHNA+iodotubericidin+dipyridamole increased extracellular adenosine levels by >690-fold. Both KF17837 (selective A2 antagonist) and DPSPX (nonselective A2 antagonist) but not DPCPX (selective A1 antagonist) blocked the antimitogenic effects of 2-chloroadenosine, EHNA, and dipyridamole on DNA synthesis, suggesting the involvement of A2A and/or A2B but excluding the participation of A1 receptors. The lack of effect of CGS21680 (selective A2A agonist) excluded involvement of A2A receptors and suggested a major role for A2B receptors. This conclusion was confirmed by the rank order potencies of four adenosine analogues.
  
  
  CONCLUSIONS
  Cardiac fibroblasts synthesize adenosine, and exogenous and cardiac fibroblast-derived adenosine inhibits cardiac fibroblast proliferation via activation of A2B receptors. Cardiac fibroblast-derived adenosine may regulate cardiac hypertrophy and/or remodeling by modulating cardiac fibroblast proliferation.
authors.affiliation: Center for Clinical Pharmacology, Department of Medicine, University of Pittsburgh Medical Center, Pa 15213-2582, USA. dubey@med1.dept-med.pitt.edu
authors.forename: R K
authors.initials: RK
authors.lastname: Dubey
authors.forename: D G
authors.initials: DG
authors.lastname: Gillespie
authors.forename: Z
authors.initials: Z
authors.lastname: Mi
authors.forename: E K
authors.initials: EK
authors.lastname: Jackson
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives / Q000494:pharmacology; D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology / Q000502:physiology*; D058892:Adenosine Deaminase Inhibitors; D000248:Adenosine Kinase / Q000037:antagonists & inhibitors; D019830:Adenosine-5'-(N-ethylcarboxamide) / Q000494:pharmacology; D058647:Adrenergic alpha-2 Receptor Agonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D000818:Animals; D002417:Cattle; D002455:Cell Division / Q000187:drug effects; D003470:Culture Media; D004261:DNA Replication / Q000187:drug effects; D004176:Dipyridamole / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects*; D006321:Heart / Q000187:drug effects*; D008297:Male; D009206:Myocardium / Q000166:cytology*; D010627:Phenethylamines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism*; D014372:Tubercidin / Q000031:analogs & derivatives / Q000494:pharmacology; D014970:Xanthines / Q000494:pharmacology
chemical_list: D058892:Adenosine Deaminase Inhibitors; C547773:Adra2b protein, rat; D058647:Adrenergic alpha-2 Receptor Agonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D003470:Culture Media; D004791:Enzyme Inhibitors; D010627:Phenethylamines; D018341:Receptors, Adrenergic, alpha-2; D014970:Xanthines; C061282:2-(4-(2-carboxyethyl)phenethylamino)-5'-N-ethylcarboxamidoadenosine; C081198:KF 17837; C034214:5-iodotubercidin; C046756:5'-N-methylcarboxamideadenosine; D019830:Adenosine-5'-(N-ethylcarboxamide); C048599:N(6)-cyclopentyladenosine; C010192:9-(2-hydroxy-3-nonyl)adenine; D004176:Dipyridamole; C053896:1,3-dipropyl-8-(4-sulfophenyl)xanthine; D000248:Adenosine Kinase; D000225:Adenine; D000241:Adenosine; D014372:Tubercidin