Reguratory mechanism of hypotensive responses to muscarinic cholinergic stimulation through the adrenergic receptor system.

戊巴比妥（30mg/kg，静脉注射）麻醉犬的结果如下：以0.3 ~ 10mug/kg的速率向右头静脉输注苯肾上腺素（Phe），通过刺激血管平滑肌细胞上的α -肾上腺素受体，诱导持续的剂量依赖性升压反应。以上述范围内的速率输注Phe可抑制乙酰胆碱引起的低血压，其方式取决于Phe输注的剂量和时间。以3杯/千克的速度输注苯丙氨酸120分钟后，乙酰胆碱降压反应的剂量-反应曲线右移约80倍。Phe输注对乙酰胆碱性低血压的抑制作用是持久的。例如，在停止以3杯/千克的速率进行120分钟的Phe输注后，至少120分钟内没有观察到抑制恢复。停止Phe输注后，血压立即恢复到基础水平。其他α -肾上腺素受体激动剂，甲氧基胺和去甲肾上腺素，以及非肾上腺素血管收缩剂，血管紧张素II，也以与苯丙氨酸相似的方式抑制乙酰胆碱诱导的低血压，提示血压升高在这种现象中的重要性。5 .苯丙酚输注对组胺、硝普钠、丙二醇和甲基苯丙胺的降压反应影响不大。用胆碱酯酶抑制剂新斯的明治疗犬，可逆转Phe输注对乙酰胆碱酯酶诱导的低血压的抑制作用。此外，即使在以3杯/千克的速度输注苯丙氨酸120分钟后，将乙酰胆碱注入左心室，而不是静脉，也只观察到很小的抑制作用。这些结果表明，肺中乙酰胆碱代谢的加速是乙酰胆碱诱导的乙酰胆碱反应抑制的原因。到目前为止，在包括大鼠、豚鼠和兔子在内的其他动物物种中，Phe输注未能影响乙酰胆碱的降压反应。

The following findings were obtained in pentobarbital (30mg/kg, i.v) -anesthetized dogs.1.Phenylephrine (Phe) infusions into the right cephalic vein at a rate between 0.3 and 10mug/kg induced persistent and dose-dependent pressor responses through stimulation of alpha-adrenoceptors on the vascular smooth muscle cells.2.Infusions of Phe at a rate in the above range suppressed ACh-induced hypotension in a manner that is dependent on the dose and the period of time of Phe infusion.After Phe infusion at a rate of 3 mug/kg for 120 min shifted the dose-response curve for the hypotensive responses to ACh to the right by about 80-times.3.Inhibitory effect of Phe infusions on the ACh-induced hypotension was long-lasting.For instance, no recovery in the inhibition was observed for at last 120 min after cessation of a Phe infusion that was carried out at a rate of 3 mug/kg for 120 min.Blood pressure returned to the basal level immediately after stopping the Phe infusions.4.Other alpha-adrenoceptor agonists, methoxamine and norepinephrice, and a non-adrenerigic vasoconstrictor, angiotensin II,also inhibited ACh-induced hypotension in a similar manner as observed with Phe, suggesting importance of elevation of blood pressure in this phenomenon.5.Phe infusions little affected hypotensive responses to histamine, sodium nitroprusside, carbachol and methacholine.6.The inhibitory effect of Phe infusions on ACh-induced hypotension was reversed by treatment of dogs with a cholinesterase inhibitor, neostigmine.In addition, only small inhibition was observed when ACh was administered into the left ventricle, instead of vein, even after Phe infusions at a rate of 3 mug/kg for 120min.These results suggest that acceleration of ACh metabolism in the lung is responsible for Phe-induced inhibition of ACh responses.In other animal species examined so far, including rats, guinea-pigs and rabbits, Phe infusions failed to affect hypotensive responses to ACh.