cardiovascular system
• adult male homozygotes exhibit increased sensitivity to beta-adrenergic stimulation, as shown by altered cardiac responses to isoproterenol
• however, no significant differences in life expectancy, blood chemistry, mean resting blood pressure, resting heart rate, left ventricular ejection fraction or immune systems are observed
• basal, isoproterenol-stimulated, and NaF-stimulated adenylyl cyclase activities remain normal in heart membrane preparations
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• in response to increasing concentrations of beta-agonist isoproterenol, homozygotes exhibit a significantly increased left ventricular ejection fraction (i.e. enhanced contractility) at each isoproterenol concentration relative to wild-type mice
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• homozygotes show no differences in the isoproterenol-mediated increase in heart rate relative to wild-type controls except at the highest isoproterenol concentration used (0.2 mg/min/kg)
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muscle
• in response to increasing concentrations of beta-agonist isoproterenol, homozygotes exhibit a significantly increased left ventricular ejection fraction (i.e. enhanced contractility) at each isoproterenol concentration relative to wild-type mice
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