Kubo T, Nagura J, Misu Y
J Pharmacol Exp Ther. 1987 Jan;240(1):298-302.
The effects of various alpha adrenoceptor agonists and antagonists injected into the spinal subarachnoid space on blood pressure and heart rate were investigated in pentobarbital-anesthetized male rats. A dose-dependent decrease in blood pressure and heart rate was induced by intrathecal injections of clonidine (0.3-3 micrograms), at the T6-T7 level. Guanabenz (3-30 micrograms) and an azepine derivative B-HT 920 (1-3 micrograms) also reduced blood pressure and heart rate. In contrast, an imidazolidine derivative St 587 (10 micrograms) was ineffective. The clonidine-induced hypotensive effect was antagonized by yohimbine but not by prazosin. Yohimbine (3-10 micrograms) alone caused an increase in blood pressure and heart rate while only a weak hypotenion occurred with prazosin (10 micrograms). Pretreatment with intrathecal 6-hydroxydopamine (50 micrograms X 2) did not impair the hypotensive action of clonidine (1 microgram) whereas the hypertensive effect of yohimbine was reduced markedly by this treatment. When injected i.v. or intrathecally at the C1-C2 level, clonidine (1 microgram) produced only a slight decrease in blood pressure. It is concluded that, in rat spinal cord, alpha-2 adrenoceptors located postsynaptically are involved in blood pressure control. Endogenous catecholamines, especially norepinephrine in the spinal cord seem to activate tonically the alpha-2 adrenoceptors.
在戊巴比妥麻醉的雄性大鼠中，研究了经脊髓蛛网膜下腔注射各种α肾上腺素能受体激动剂和拮抗剂对血压和心率的影响。在T6-T7水平鞘内注射可乐定（0.3-3微克）可引起血压和心率呈剂量依赖性下降。胍那苄（3-30微克）和一种氮杂卓衍生物B-HT 920（1-3微克）也可降低血压和心率。相比之下，一种咪唑烷衍生物St 587（10微克）无效。可乐定诱导的降压作用可被育亨宾拮抗，但不能被哌唑嗪拮抗。单独使用育亨宾（3-10微克）可引起血压和心率升高，而哌唑嗪（10微克）仅引起轻微降压。鞘内注射6-羟基多巴胺（50微克×2）预处理并不损害可乐定（1微克）的降压作用，而这种处理可显著降低育亨宾的升压作用。当在C1-C2水平静脉注射或鞘内注射时，可乐定（1微克）仅引起血压轻微下降。结论是，在大鼠脊髓中，突触后定位的α-2肾上腺素能受体参与血压控制。内源性儿茶酚胺，尤其是脊髓中的去甲肾上腺素似乎持续激活α-2肾上腺素能受体。
