Coronary flow and cardiac responses to adenosine in beta-1 adrenergic knockout mice

Both adenosine and beta adrenergic receptors play prominent roles in cardiovascular function. There are reports in the literature that cross-talk exists between adenosine receptors and beta adrenergic receptors. Of the 3 major beta adrenergic receptors, beta-1 (B-1) is the predominant subtype in the heart. Using in vivo ultrasound techniques and ex vivo isolated heart experiments, we measured coronary flow (CF) and cardiac responses to isoproterenol (non-specific beta-1 and beta-2 agonist) and adenosine in beta-1 adrenergic knockout (KO) mice and their wild type (WT). Based upon ultrasound experiments, baseline CF (by measuring left coronary artery, 0.36± 0.13 in WT vs 0.31±0.11 in KO, mL/min), stroke volume (SV, 30.25±6.57 in WT vs 28.86±7.63, μL), and ejection fraction (EF, 54.68±5.18 in WT vs 55.86±7.07 in KO, %) were not different between WT (n=10) and KO (n=8). But heart rate (HR, 501±54 in WT vs 432±38 in KO, BPM) and cardiac output (CO, 15.23±4.03 in WT vs 12.31±2.83 in KO, mL/min) were lower in KO...