Abstract
1) To delineate the role of central ${\alpha}_2-adrenoceptors$ in the pressor response to raised intracranial pressure(ICP), the influence of yohimbine, an ${alpha}_2-adrenoceptor$ antagonist, on the pressor response to raised ICP was investigated in urethane-anesthetized rabbits. 2) The ICP was raised by infusing saline into a balloon placed in the epidural space. The rise of ICP was slow in the beginning of the infusion but it became sharp as the infusion proceeded. 3) In response to raised ICP, blood pressure(BP) tended to decrease slightly in the beginning and then increased sharply. BP, however, fell abruptly and markedly if ICP was raised further. The maximal pressor response to raised ICP was the increase of $49{\pm}2.4%$ of the original $BP(mean{\pm}SE\;in\;32\;experiments)$, and at this point the volume of saline infused into the balloon was $1.22{\pm}0.15\;ml$, and the ICP $165{\pm}6.4\;mmHg$. 4) Intraventricular yohimbine $(50{\mu}g)$ by itself did not affect BP. After the administration of this dose of yohimbine the increase of both ICP and BP was observed after the infusion of much smaller volume of saline than in the control animals, i.e., after the infusion of $0.83{\pm}0.02\;ml$ of saline the maximal increase of preesor response$(57{\pm}4.5%\;in\;6\;experiments)$ appeared and at this state the ICP was $164{\pm}9.6\;mmHg$. 5) Intraventricular $clonidine(30{\mu}g)$ markedly decreased BP by itself, and in the clonidine-treated rabbits the increase of ICP induced by the infusion was much less than in the control group and the pressor response to raised ICP was hardly seen. 6) The hypotensive effect of intraventricular clonidine was reversed by a susequent intraventricular $yohimbine(500\;{\mu}g)$. At this state the pressor response to raised ICP appeared as in the control animals. 7) These results show that the pressor response to raised ICP was facilitated when ${\alpha}_2-adrenoceptors$ in the rabbit brain was blocked by yohimbine and that yohimbine antagonized the inhibitory effect of clonidine on the pressor response to raised ICP.
1) Urethane 마취가토(痲醉家兎)에서 경뇌막외강내(硬腦膜外腔內)에 삽입(揷入)한 balloon을 통(通)한 가압(加壓) 및 두개내압기종방법(頭蓋內壓記種方法)에 의하여 내압(內壓)을 상승(上昇)시키고, 이 내압상승(內壓上昇)에 따른 혈압상승(血壓上昇)에 미치는 ${\alpha}_2-adrenoceptor$ antagonist인 yohimbine의 영향(影響)을 관찰(觀察)하였다. 2) 내압(內壓)은 가압(加壓)balloon 내(內) 식염수주입(食鹽水注入)으로 주입초기(注入初期) 에는 완만(緩慢)하게 그 후 점차(漸次) 급격(急激)하게 상승(上昇)하였다. 이에 따라 혈압(血壓)은 처음에 경미(輕微)한 하강경향(下降傾向)을 보인 후 급격(急激)하게 상승(上昇)하였고, 더욱 내압(內壓)을 상승(上昇)시키면 혈압(血壓)은 심(甚)한 하강(下降)을 보였다. 최고혈압상승정도(最高血壓上昇程度)는 원혈압(元血壓)의 $49{\pm}2.4%$(32예(例) 평균(平均)${\pm}SE)$의 증가(增加)였으며, 이때에 가압(加壓)balloon 내(內)로 주입(注入)된 식염수양(食鹽水量)은 $1.22{\pm}0.15\;ml$, 내압(內壓)은 $165{\pm}6.4\;mmHg$였다. 3) 측뇌실내(側腦室內) yohimbine$(50{\mu}g)$은 혈압자체(血壓自體) 영향(影響)을 미치지 못하였으나, 본양(本量)의 yohimbine 투여후(投與後)에는 가압(加壓)balloon내(內)에 대조동물(對照動物)에서보다 훨씬 적은 양(量)의 식염수주입(食鹽水注入)으로 내압(內壓) 및 혈압(血壓)이 상승(上昇)하였다. 즉(卽) 최고혈압상승(最高血壓上昇) (6예평균(例平均, $57{\pm}4.5%)$이 나타날 때의 가압(加壓)balloon 내(內)에 주입된 식염수양(食鹽水量)은 $0.83{\pm}0.02\;ml$, 내압(內壓)은 $164{\pm}9.6\;mmHg$였다. 4) $Clonidine(30\;{\mu}g)$의 측뇌실내(側腦室內) 주입후(注入後) 혈압자체(血壓自體)는 하강(下降)되었고 이때 가압(加壓)balloon 내 식염수주입(食鹽水注入)에 의한 내압상승(內壓上昇)은 대조군(對照郡)보다 순화(純化)되었으며 혈압상승(血壓上昇)은 거의 볼 수 없었다. 5) $Clonidine(30\;{\mu}g)$투여(投與)로 하강(下降)된 혈압(血壓)은 $yohimbine(500\;{\mu}g)$투여(投與)로 거의 원혈압(原血壓)으로 회복(回復)되었고, 이때 내압(內壓)을 상승(上昇)시키면 대조군(對照郡)에서와 같은 내압상승(內壓上昇)에 따른 혈압상승(血壓上昇)이 나타났다. 6) 본실험(本實驗) 성적(成績)은 가토(家兎)에서 ${\alpha}_2-adrenoceptor$ antagonist가 뇌(腦)에 존재(存在)할 때는 두개뇌압상승(頭蓋腦壓上昇)에 따른 혈압상승(血壓上昇)이 촉진(促進)되고 또한 ${\alpha}_2-adrenoceptor\;agonist$에 의한 두개뇌압상승(頭蓋腦壓上昇)에 따른 혈압상승(血壓上昇)의 억제(抑制)가 나타나지 않음을 가리키고 있다.