title: Beta-adrenergic receptor desensitization in man: insight into post-exercise attenuation of cardiac function.
abstract: Desensitization of the beta-adrenoreceptors (beta-AR) may contribute to a post-exercise reduction in left ventricular (LV) function. However, attenuation of the chronotropic and inotropic responses to a beta-AR agonist may depend upon alterations in parasympathetic tone. Furthermore, changes in cardiac output and LV diastolic function in response to a beta-AR agonist, pre- to post-prolonged exercise, remain unclear. Seven trained males (mean+/-s.d., age 27+/-6 years) performed 4 h of ergometer rowing. Peak heart rate (HR) and LV systolic and diastolic functional responses to incremental isoproterenol (isoprenaline) infusion (2, 4 and 6 microg kg min-1) were assessed after vagal blockade (glycopyrrolate, 1.2 mg). LV systolic function was assessed by the pressure/volume ratio (systolic blood pressure/end systolic volume) and , whilst diastolic function was evaluated as peak early and late transmitral filling velocities. Following exercise, the pressure/volume ratio decreased by 25% (P<0.05), whereas was unchanged (P>0.05). The early/late filling ratio was reduced by 36% after exercise, due to an elevation in late LV filling (P<0.01). The increase in HR response to isoproterenol infusion was blunted post-exercise at both 4 and 6 microg kg min-1 (127+/-7 and 132+/-6 beats min-1) compared with pre-exercise (138+/-8 and 141+/-12 beats min-1, P<0.05). Additionally, the pressure/volume ratio and were blunted post-exercise in response to isoproterenol (P<0.05). In contrast, diastolic function was similar before and after exercise during isoproterenol infusion (P>0.05). Desensitization of the beta-AR contributes to an attenuated left ventricular systolic but not diastolic function following prolonged exercise.
authors.affiliation: Centre for Sports Medicine and Human Performance, Brunel University, Uxbridge, Middlesex UB8 3PH, UK, and Copenhagen Muscle Research Centre, Department of Anaesthesia, Rigshospitalet, University of Copenhagen, Denmark.
authors.forename: Emma
authors.initials: E
authors.lastname: Hart
authors.forename: Ellen
authors.initials: E
authors.lastname: Dawson
authors.forename: Peter
authors.initials: P
authors.lastname: Rasmussen
authors.forename: Keith
authors.initials: K
authors.lastname: George
authors.forename: Niels H
authors.initials: NH
authors.lastname: Secher
authors.forename: Greg
authors.initials: G
authors.lastname: Whyte
authors.forename: Rob
authors.initials: R
authors.lastname: Shave
mesh_terms: D000318:Adrenergic beta-Agonists / Q000008:administration & dosage / Q000494:pharmacology*; D000328:Adult; D002320:Cardiovascular Physiological Phenomena / Q000187:drug effects*; D003971:Diastole; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006024:Glycopyrrolate / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects; D011943:Receptors, Adrenergic, beta / Q000187:drug effects* / Q000378:metabolism; D012016:Reference Values; D013599:Systole; D013997:Time Factors; D014630:Vagus Nerve / Q000187:drug effects; D016277:Ventricular Function, Left / Q000187:drug effects*
chemical_list: D000318:Adrenergic beta-Agonists; D018727:Muscarinic Antagonists; D011943:Receptors, Adrenergic, beta; D007545:Isoproterenol; D006024:Glycopyrrolate