title: Strain-dependent beta-adrenergic receptor function influences myocardial responses to isoproterenol stimulation in mice.
abstract: Recently, we showed that compared with the A/J inbred mouse strain, C57BL/6J (B6) mice have an athlete's cardiac phenotype. We postulated that strain differences would result in greater left ventricular (LV) hypertrophy in response to isoproterenol in B6 than A/J mice and tested the hypothesis that a differential response could be explained partly by differences in beta-adrenergic receptor (beta-AR) density and/or coupling. A/J and B6 mice were randomized to receive daily isoproterenol (100 mg/kg sc) or isovolumic vehicle for 5 days. Animals were studied using echocardiography, tail-cuff blood pressure, histopathology, beta-AR density and percent high-affinity binding, and basal and stimulated adenylyl cyclase activities. One hundred twenty-eight mice (66 A/J and 62 B6) were studied. Isoproterenol-treated A/J mice demonstrated greater percent increases in echocardiographic LV mass/body weight (97 +/- 11 vs. 20 +/- 10%, P = 0.001) and in gravimetric heart mass/body weight versus same-strain controls than B6 mice. Histopathology scores (a composite of myocyte hypertrophy, nuclear changes, fibrosis, and calcification) were greater in isoproterenol-treated A/J vs. B6 mice (2.8 +/- 0.2 vs.1.9 +/- 0.3, P < 0.05), as was quantitation of myocyte damage (22.3 +/- 11.5 vs. 4.3 +/- 3.5%). Interstrain differences in basal beta-AR density, high-affinity binding, and adenylyl cyclase activity were not significant. However, whereas isoproterenol-treated A/J mice showed nonsignificant increases in all beta-AR activity measures, isoproterenol-treated B6 mice had lower beta-AR density (57 +/- 6 vs. 83 +/- 8 fmol/mg, P < 0.05), percent high-affinity binding (15 +/- 2 vs. 26 +/- 3%, P < 0.005), and GTP + isoproterenol-stimulated adenylyl cyclase activity (10 +/- 1.1 vs. 5.8 +/- 1.5 pmol cAMP.mg(-1).min(-1)) compared with controls. High-dose, short-term isoproterenol produces greater macro- and microscopic cardiac hypertrophy and injury in A/J than B6 mice. A/J mice, unlike B6 mice, do not experience beta-AR downregulation or uncoupling in response to isoproterenol. Abnormalities in beta-adrenergic regulation may contribute to strain-related differences in the vulnerability to isoproterenol-induced cardiac changes.
authors.affiliation: Division of Cardiology, Dept. of Medicine, Univ. Hospitals of Cleveland and Case Western Reserve Univ., MS 5038, 11100 Euclid Ave., Cleveland, OH 44106-5038, USA.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Faulx
authors.forename: Paul
authors.initials: P
authors.lastname: Ernsberger
authors.forename: Dorothy
authors.initials: D
authors.lastname: Vatner
authors.forename: Robert D
authors.initials: RD
authors.lastname: Hoffman
authors.forename: William
authors.initials: W
authors.lastname: Lewis
authors.forename: Ryan
authors.initials: R
authors.lastname: Strachan
authors.forename: Brian D
authors.initials: BD
authors.lastname: Hoit
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D006332:Cardiomegaly / Q000139:chemically induced* / Q000000981:diagnostic imaging; D004452:Echocardiography; D006321:Heart / Q000187:drug effects* / Q000503:physiopathology; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D009206:Myocardium / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D009929:Organ Size / Q000187:drug effects; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D013045:Species Specificity
chemical_list: D000318:Adrenergic beta-Agonists; D011943:Receptors, Adrenergic, beta; D000262:Adenylyl Cyclases; D007545:Isoproterenol