Lower-body negative pressure (LBNP) was used to stimulate sympathetic reflexes in anaesthetized cats. At -50 mmHg for 10 min it caused transient reduction in central venous pressure and systemic arterial blood pressure. Arterial blood pressure was then restored within 30 s and there was a tachycardia. Central venous pressure showed only partial recovery. The resting level of plasma renin activity (PRA; 2.9-3.2 ng h-1 ml-1) did not change until approximately 5 min into the manoeuvre. 2. When converting-enzyme inhibitor (CEI) was given 75 s after the onset of suction it caused a greater and more sustained fall in arterial blood pressure than when administered alone. The angiotensin II (ANG II) antagonist [Sar1,Ala8] ANG II produced similar effects after a short-lived pressor response. 3. This prolonged fall in arterial blood pressure produced by CEI was not associated with reduced sympathetic efferent nerve activity. This indicates that the inhibitor affects one of the peripheral actions of angiotensin and in so doing produces vasodilatation of neurogenic origin. 4. These findings suggest that angiotensin, at a level which does not exert a direct vasoconstrictor action, interacts with the sympathetic nervous system to maintain arterial blood pressure when homeostatic reflexes are activated. A reduction in the efficiency of these reflexes by CEI may contribute to its hypotensive effect.
摘要
采用下体负压（LBNP）刺激麻醉猫的交感反射。在-50 mmHg 下持续 10 分钟，可导致中心静脉压和全身动脉血压短暂降低。动脉血压随后在 30 秒内恢复，且出现心动过速。中心静脉压仅部分恢复。血浆肾素活性（PRA；2.9 - 3.2 ng h-1 ml-1）的静息水平在操作开始约 5 分钟内未发生变化。2. 在抽吸开始 75 秒后给予转换酶抑制剂（CEI），与单独给药相比，其导致动脉血压下降幅度更大且更持久。血管紧张素 II（ANG II）拮抗剂[Sar1,Ala8]ANG II 在短暂的升压反应后产生类似效果。3. CEI 导致的动脉血压这种持续性下降与交感传出神经活动降低无关。这表明该抑制剂影响血管紧张素的外周作用之一，从而产生神经源性血管舒张。4. 这些发现表明，在不产生直接血管收缩作用的水平下，血管紧张素在稳态反射激活时与交感神经系统相互作用以维持动脉血压。CEI 使这些反射效率降低可能是其降压作用的原因之一。
