Antonaccio M J, Kerwin L
Arch Int Pharmacodyn Ther. 1977 Mar;226(1):56-68.
L-Dopa (5 mg/kg i.v.) decreased blood pressure and heart rate after extracerebral decarboxylase inhibition with MK-486 (25 mg/kg i.v.) in anesthetize MAO-inhibited dogs. In addition, reflex bradycardia caused by injected norepinephrine was significantly enhanced by L-dopa, DL-Threo-dihydroxyphenylserine had no effect on blood pressure, heart rate or reflex responses to norepinephrine. FLA-63, a dopamine-beta-oxidase inhibitor, did not have any effect on the hypotension, bradycardia or reflex-enhancing effect of L-dopa. Pimozide did not affect the actions of L-dopa on blood pressure and heart rate but completely blocked the enhancement of reflexes. Removal of the carotid sinuses caused an elevation blood pressure and heart rate and abolished the negative chronotropic effect of norepinephrine. However, L-dopa restored the bradycardia caused by norepinephrine in addition to decreasing blood pressure and heart rate. 5-HTP (5 mg/kg i.v.) decreased blood pressure and heart rate and decreased the reflex bradycardia to norepinephrine. It is concluded that L-dopa enhances reflex bradycardia through central alpha-receptor stimulation. Furthermore, the effects are mediated through dopamine rather than norepinephrine and do not require the carotid sinus baroreceptors.
在麻醉的单胺氧化酶抑制犬中，静脉注射MK - 486（25毫克/千克）抑制脑外脱羧酶后，左旋多巴（5毫克/千克静脉注射）可降低血压和心率。此外，左旋多巴可显著增强注射去甲肾上腺素引起的反射性心动过缓，DL - 苏式 - 二羟基苯丝氨酸对血压、心率或对去甲肾上腺素的反射反应均无影响。多巴胺β氧化酶抑制剂FLA - 63对左旋多巴的低血压、心动过缓或反射增强作用均无影响。匹莫齐特不影响左旋多巴对血压和心率的作用，但完全阻断反射增强作用。切除颈动脉窦可导致血压和心率升高，并消除去甲肾上腺素的负性变时作用。然而，左旋多巴除降低血压和心率外，还可恢复去甲肾上腺素引起的心动过缓。5 - 羟色氨酸（5毫克/千克静脉注射）可降低血压和心率，并减少对去甲肾上腺素的反射性心动过缓。结论是，左旋多巴通过中枢α受体刺激增强反射性心动过缓。此外，其作用是通过多巴胺而非去甲肾上腺素介导的，且不需要颈动脉窦压力感受器。
