AUTONOMIC REGURATION AND CARDIAC FUNCTION IN MITRAL REGURGITATION.

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Cardiac fibrosis is major problem in dogs with mitral regurgitation (MR). Cardiac fibrosis is induced by activation of sympathetic tone, reducing of coronary flow, activation of renin-angiotensin-aldosteron axis. The objective of this study was to clarify autonomic regulation and cardiac function in dogs with mitral regurgitation. 1. Blood catecholamines ; epinephrine, norepinephrine were increased in MR dogs comparing with healthy dogs in right lateral and standing position. After 3 minutes running, epinephrine was not changed, but norepinephrine increased in both group. 2. Dobutamine was administered for 5 minutes, improvement of hemodynamic and cardiac function was observed. Response to dobutamine with left ventricular fractional shortening and ejection fraction and cardiac output was attenuated in MR dogs comparing with healthy dogs. These results suggest that cardiac contractility response to endo- and exogenous catecholamines are reducing in MR dogs. 3. Propranolol was administered 0.001〜0.1 mg/kg with isoproterenol 0.025 μg/kg/min infusion in healthy and MR dogs. This propranolol study suggested that β_2 receptor in sinus node was dominant in regulation of heart rate, and regulation of left ventricular contractile function was β_1 dominant in dogs. These results suggest that to accomplish reducing heart rate to minimize oxygen consumption without reducing ventricular contractility in failing heart, nonselective β-clocker may benefit for MR dogs.