title: Selective attenuation of norepinephrine release and stress-induced heart rate increase by partial adenosine A1 agonism.
abstract: The release of the neurotransmitter norepinephrine (NE) is modulated by presynaptic adenosine receptors. In the present study we investigated the effect of a partial activation of this feedback mechanism. We hypothesized that partial agonism would have differential effects on NE release in isolated hearts as well as on heart rate in vivo depending on the genetic background and baseline sympathetic activity. In isolated perfused hearts of Wistar and Spontaneously Hypertensive Rats (SHR), NE release was induced by electrical stimulation under control conditions (S1), and with capadenoson 6 · 10(-8) M (30 µg/l), 6 · 10(-7) M (300 µg/l) or 2-chloro-N(6)-cyclopentyladenosine (CCPA) 10(-6) M (S2). Under control conditions (S1), NE release was significantly higher in SHR hearts compared to Wistar (766+/-87 pmol/g vs. 173+/-18 pmol/g, p<0.01). Capadenoson led to a concentration-dependent decrease of the stimulation-induced NE release in SHR (S2/S1  =  0.90 ± 0.08 with capadenoson 6 · 10(-8) M, 0.54 ± 0.02 with 6 · 10(-7) M), but not in Wistar hearts (S2/S1  =  1.05 ± 0.12 with 6 · 10(-8) M, 1.03 ± 0.09 with 6 · 10(-7) M). CCPA reduced NE release to a similar degree in hearts from both strains. In vivo capadenoson did not alter resting heart rate in Wistar rats or SHR. Restraint stress induced a significantly greater increase of heart rate in SHR than in Wistar rats. Capadenoson blunted this stress-induced tachycardia by 45% in SHR, but not in Wistar rats. Using a [(35)S]GTPγS assay we demonstrated that capadenoson is a partial agonist compared to the full agonist CCPA (74+/-2% A(1)-receptor stimulation). These results suggest that partial adenosine A(1)-agonism dampens stress-induced tachycardia selectively in rats susceptible to strong increases in sympathetic activity, most likely due to a presynaptic attenuation of NE release.
authors.affiliation: Medizinische Klinik, Klinikum rechts der Isar and Deutsches Herzzentrum München, Technische Universität, München, Germany.
authors.forename: Lorenz
authors.initials: L
authors.lastname: Bott-Flügel
authors.forename: Alexandra
authors.initials: A
authors.lastname: Bernshausen
authors.forename: Heike
authors.initials: H
authors.lastname: Schneider
authors.forename: Peter
authors.initials: P
authors.lastname: Luppa
authors.forename: Katja
authors.initials: K
authors.lastname: Zimmermann
authors.forename: Barbara
authors.initials: B
authors.lastname: Albrecht-Küpper
authors.forename: Raimund
authors.initials: R
authors.lastname: Kast
authors.forename: Karl-Ludwig
authors.initials: KL
authors.lastname: Laugwitz
authors.forename: Heimo
authors.initials: H
authors.lastname: Ehmke
authors.forename: Andreas
authors.initials: A
authors.lastname: Knorr
authors.forename: Melchior
authors.initials: M
authors.lastname: Seyfarth
mesh_terms: D058907:Adenosine A1 Receptor Agonists / Q000494:pharmacology*; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D005260:Female; D006339:Heart Rate / Q000187:drug effects*; D066298:In Vitro Techniques; D009638:Norepinephrine / Q000378:metabolism*; D051381:Rats; D011918:Rats, Inbred SHR; D017208:Rats, Wistar; D043682:Receptor, Adenosine A1 / Q000378:metabolism*; D012149:Restraint, Physical; D013312:Stress, Physiological / Q000187:drug effects*
chemical_list: D058907:Adenosine A1 Receptor Agonists; D043682:Receptor, Adenosine A1; D009638:Norepinephrine