title: Negative chronotropic response to adenosine receptor stimulation in rat right atria after run training.
abstract: The aim of the present study was to evaluate the potency and maximal responses (E(max)) to the adenosine receptor agonists N(6)-cyclopentyladenosine (CPA), N-ethylcarboxamidoadenosine (NECA) and N(6)-(3-iodobenzyl)-5'-N-methylcarbaxamidoadenosine (IB-MECA) in right atria from trained rats. We also investigated the interaction between the training bradycardia and the sensitivity of the chronotropic response mediated by adenosine receptor stimulation. Animals were submitted to run training for 60 min, 5 days a week, over a period of 8 weeks. Mean blood pressure and heart rate were measured in conscious animals. Right atria were isolated and concentration-response curves to CPA, NECA and IB-MECA were obtained. A reduction in heart rate was found in trained rats, indicating that the training programme was successful in inducing physical conditioning. The three adenosine receptor agonists induced a concentration-dependent negative chronotropic response. The rank order of potency and E(max) for the three adenosine receptor agonists was CPA > NECA > IB-MECA. Dynamic exercise for 8 weeks did not alter the E(max) for CPA, NECA and IB-MECA. Similarly, the potencies of CPA and NECA were not affected by run training, whereas the potency of IB-MECA was reduced (6.10 +/- 0.09 vs 5.66 +/- 0.10 for sedentary and trained groups, respectively). In conclusion, run training for 8 weeks induced a desensitization of the chronotropic response to IB-MECA without changing the potency of CPA and NECA. These findings exclude the participation of adenosine receptors in the training bradycardia.
authors.affiliation: Department of Physical Education, UNESP, Rio Claro, Brazil.
authors.forename: Fernanda
authors.initials: F
authors.lastname: Priviero
authors.forename: Gilberto
authors.initials: G
authors.lastname: De Nucci
authors.forename: Edson
authors.initials: E
authors.lastname: Antunes
authors.forename: Angelina
authors.initials: A
authors.lastname: Zanesco
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D058907:Adenosine A1 Receptor Agonists; D058909:Adenosine A3 Receptor Agonists; D019830:Adenosine-5'-(N-ethylcarboxamide) / Q000494:pharmacology; D000818:Animals; D003864:Depression, Chemical; D006321:Heart / Q000187:drug effects*; D006325:Heart Atria / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects*; D066298:In Vitro Techniques; D008297:Male; D010805:Physical Conditioning, Animal / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology; D058906:Purinergic P1 Receptor Agonists; D051381:Rats; D017208:Rats, Wistar; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D058907:Adenosine A1 Receptor Agonists; D058909:Adenosine A3 Receptor Agonists; D058906:Purinergic P1 Receptor Agonists; D014665:Vasodilator Agents; C084956:N(6)-(3-iodobenzyl)-5'-N-methylcarboxamidoadenosine; D019830:Adenosine-5'-(N-ethylcarboxamide); C048599:N(6)-cyclopentyladenosine; D000241:Adenosine