Influence of exercise and age on myocardial β-adrenergic receptor properties

Abstract

The bradycardia following physical training may be mediated by an alteration in β-adrenergic receptor number or agonist affinity. We characterized the interaction between age and exercise on myocardial β-adrenergic receptor number and agonist affinity in 4- and 24-month-old F344 rats to test the hypothesis that the effects of training should be blunted in older rats. β-adrenergic receptor density was unchanged with age or training. The total number of receptors per heart increased with age due to increased ventricle weight. With training, in the senescent rats the total number of receptors decreased due to a reduced amount of homogenate protein recovered from the ventricle, the significance of which is unknown. The receptor agonist dissociation constant for isoproterenol was determined in both the absence and presence of β, γ-imidoguanosine 5′-triphosphate [Gpp(NH)p] and did not change with age or training. Neither training nor age influenced β-adrenergic receptor characteristics, suggesting that training bradycardia is not mediated by an alteration in β-adrenergic receptors.