Reduced Cardiac Beta 1 Receptor Expression and Function in a Mouse Model of Hypertrophic Cardiomyopathy
Authors: Disser Jenna , Marchese Haley , Larson Robert 
Published: May 2024

Hypertrophic cardiomyopathy (HCM) is the most common genetic heart disorder. HCMis characterized by cardiac hypertrophy, fibrosis, and an increased risk of fatalarrhythmias and sudden cardiac death. Previous studies in humans with HCM havedemonstrated increased cardiac norepinephrine spillover and reduced beta-1 receptor(B1R) expression in the left ventricle (LV). We have previously demonstrated thatcardiac sympathetic tone is elevated in an alpha-tropomyosin mutant mouse model ofHCM. We hypothesized that HCM mice would demonstrate reduced B1R expression inthe LV and attenuated heart rate (HR) and dP/dt max responses to ramped infusion of theB1R agonist, dobutamine. First, we utilized western blot to measure B1R proteinexpression in LV tissue from HCM and littermate wild-type (WT) mice (n=4 male micein each group). B1R expression was significantly reduced in the LV of HCM micecompared to WT littermate controls (HCM 60±1% vs. WT 100±4%; paired t-test, p<0.05). Next, we recorded left ventricular pressure in male and female HCM andlittermate WT control (n=5 male mice, each group; n=6 female mice, each group) miceanesthetized with isoflurane (2% in O2). Data were analyzed by 2-way ANOVA withgenotype and sex as factors. Baseline HR and dP/dt max were significantly lower inHCM compared to WT mice (genotype p<0.05), however, there were no sex differencesin either variable (sex p>0.05). Next, in order to assess cardiac B1R function, we firstinfused the ganglionic blocker chlorisondamine (6ug/g) to eliminate autonomic reflexfunction in HCM and littermate WT mice (n=4 mice, each group). Then, we performed adobutamine stress test via ramped infusion of dobutamine starting at 2ng/g/min andincreasing the dose in 2ng/g/min increments every 2 minutes up to 12ng/g/min via aprogrammable syringe pump. Data were analyzed by 2-way ANOVA with dose andgenotype as factors. Contrary to our hypothesis, ramped infusion of dobutamine resultedin a similar, significant (dose p<0.05) increase in HR in both HCM and WT mice(genotype p>0.05). Peak increases in HR occurred during the highest dose ofdobutamine (12ng/g/min; ΔHR HCM 58±19 vs. WT 70±20 beats/min) in both groups.Consistent with our hypothesis, increases in dP/dt max were significantly blunted inHCM mice compared to littermate WT controls (dose x genotype p<0.05). Peakincreases in dP/dt max occurred at a lower dose of dobutamine for HCM (4ng/g/min;ΔdP/dt max 1129±767 mmHg/s) compared to WT (8ng/g/min; ΔdP/dt max 4882±499mmHg/s). In summary, LV B1R expression is reduced in HCM mice. Increases in HR inresponse to ramped infusion of dobutamine were similar between HCM and WT micewhereas increases in dP/dt max were attenuated in HCM mice. We speculate that thedifferential inotropic and chronotropic responses to dobutamine could be due to regionaldifferences in B1R expression or contractile dysfunction in HCM mice. Michigan Technological University Startup. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.