AUTONOMIC REGURATION AND CARDIAC FUNCTION IN MITRAL REGURGITATION.

心脏纤维化是二尖瓣返流（MR）犬的主要问题。心脏纤维化是由交感神经紧张激活，冠脉流量减少，肾素-血管紧张素-醛固酮轴激活引起的。本研究的目的是阐明二尖瓣返流犬的自主调节和心脏功能。1.与健康犬相比，MR犬在右侧卧位和站立位时血中儿茶酚胺、肾上腺素、去甲肾上腺素升高。运动3 min后，两组肾上腺素无变化，去甲肾上腺素升高。2.给予多巴酚丁胺5分钟，观察血流动力学和心功能的改善。多巴酚丁胺对MR犬左室短轴缩短率、射血分数和心输出量的反应均较健康犬减弱。这些结果表明，心肌收缩反应的内源性和外源性儿茶酚胺减少MR狗。3.普萘洛尔0.001 ~ 0.1 mg/kg，异丙肾上腺素0.025 μg/kg/min，分别输注于健康犬和MR犬。提示窦房结β_2受体对心率的调节是优势的，而对左室收缩功能的调节是β_1受体的优势。这些结果表明，为了在不降低心力衰竭心室收缩力的情况下实现降低心率以最大限度地减少耗氧量，非选择性β-受体阻滞剂可能对MR犬有益。

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.