Modification of Endothelium on Contractile Response of Brain Vessels to Contracting Agents

혈관 수축제의 뇌혈관 수축반응에 대한 혈관근 내피세포의 역할

To delineate the mechanisms of vasoconstriction and vasodilation in cerebral arteries the effects of some vasoconstrictors and calcium antagonists on the basilar artery (BA) and arterial circle of Willis (WC) were examined and also the role of endothelium in the action of these drugs was investigated in pigs, cats and rabbits. In pig cerebral arteries, dose-dependent contractile responses were elicited by KCI, histamine, 5-hydroxytryptamine (5-HT) and angiotensin, but norepinephrine (NE), phenylephrine (PE) and epinephrine (EP) elicited dose-dependent contractions only under pretreatment with propranolol 10-6 M. The magnitudes of maximal contractile effects of these drugs were different from each other, and 5-H~ was the largest and angiotensin the smallest. Some calcium antagonists dose-dependently inhibited KCI (35 mM)-induced contraction and the order of potency in inhibiting the contraction was nifedipine > > diltiazem > flunarizine > oxybutynin > isosorbide dinitrate (ISDN) > glyceryl trinitrate. 5-HT (10-6 M)-induced contraction was dosedependently inhibited by nifedipine but slightly inhibited by diltiazem and ISDN. In rings with intact endothelium, KCI (35 mM)-induced contraction was not affected by acetylcholine (ACh) but $PGF_{2{\alpha}}$ (lO-SM)-induced contraction was dose-dependently relaxed by ACh and adenosine. This endothelium-dependent relaxation was not affected by nifedipine (l0-6M)-pretreatment but markedly inhibited by methylene blue (50,uM)-pretreatment. In the porcine arterial rings without endothelium, ACh had no effect or even contracted the $PGF_{2{\alpha}}-induced$ contraction. However, the dosedependent relaxing effect of ACh appeared when the deendothelized porcine ring and rabbit thoracic aorta with intact endotheli urn were simultaneously suspended into a bath and this relaxing effect was also inhibited by methylene blue-pretreatment. In cat cerebral arteries, 5-HT and NE elicited dose-dependent contractile responses and ACh also produced dose-dependent contraction regardless of the existence of endothelium. ACh-induced contraction was most prominent. 5-HT (IO-SM)induced contraction was not relaxed but contracted additionally by ACh even in the intact endothelial ring. In rabbit cerebral arteries, 5-HT and NE elicited dose-dependent contractile responses and 5-HT-induced contraction was more prominent. In the intact endothelial preparations, 5-HT (lO-s M)-induced contraction was markedly relaxed by the addition of ACh( IO-SM) and this endothelium-dependent relaxing effect was inhibited by atropine (l0-7M)-pretreatment but notaffected by diltiazem (l0-6M)-pretreatment. These results suggest that ACh elicits endotheliumdependent relaxing effect mediated by muscarinic receptors in cerebral arteries of pig and rabbit, and that ACh acts as vasoconstrictor in cat cerebral artery.

돼지, 가표 및 가토의 뇌동맥에서 기저동맥 (basilar artery, BA)과 circle of willis동맥 (WC)의 동맥환을 만들어 혈관수축제와 calcium 길항제의 효과 그리고 내피세포의 역할은 검토하였다. 돼지 BA와 WC에 서 norepinephrine (NE), phenylephrine (PE)및 epinephrine (EP)은 propranolol $10^{-6}M$ 전처리하에서 그리고 KCI, histamine, 5-hydroxytryptamine (5-HT) 및 angiotensin은 모두 용량의존성 수축반응을 일으켰다. 그 최대수축력은 angiotensin에서 가장 적었고, 5-HT에서 가장 강력하였다. KCI 35 mM수축반응은 calcium 길항제로 용량의존성으로 억제되었고, 그 효력은 nifedipine > > diltiazem > flunarizine > oxybutynin > isosorbide dinitrate (ISDN) > glycerl trinitrate의 순서였다. 5-HT $10^{-5}M$의 수축반응은 nifedipine으로는 용량의존성으로 억제 되었으나 diltiazem과 ISDN으로는 경미한 억제만을 일으켰다. 내피세포동맥환에서 KCI 35 mM의 수축반응은 acetylcholine (ACh)으로 거의 영향받지 않았으나 $PGF_{2{\alpha}}\;10^{-5}M$의 수축반응은 ACh과 adenosine으로 용량의존성으로 억제되었고, 이 내피세포 의존성억제는 nifedipine $10^{-6}M$로는 영향받지 않으나 methylene blue $50\;{\mu}M$로는 현저히 억제되었다. 네피제거동맥환에의 $PGF_{2{\alpha}}$의 수축반응은 ACh의 영향이 없거나 더욱 수축되었다. 내피세포를 제거하지 않은 가토흉부대동맥편을 bath에 함께 넣어주면 ACh의 용량의존성 이완반응이 나타났고 이 이완반응도methylene blue로 억제되었다. 가묘 BA와 WC에서 5-HT와 NE는 용량의존성 수축반응을 일으켰고 ACh도 내피세포 존재유무와 관계없이 강력한 용량의존성 수축반응을 일으켰으며 그 최대수축력은 ACh에서 가장 강력하였다. 내피세포동맥환에서 5-HT $10^{-5}M$의 수축반응은 ACh에 의하여 이완반응없이 더욱 수측되었다. 가토 BA에서 5-HT와 NE는 응량의존성 수축반응을 일으졌고5-HT의 수축반응이 더욱 현저하였다. 내피세포동맥환에서 5-HT $10^{-5}M$의 수축반응은 ACh $10^{-5}M$로 현저하게 이완되있고 이 내피세포의존성 이완반응은 atropine $10^{-7}M$로는 억제되었으나 diltiazem $10^{-6}M$로는 거의 억제되지 않았다. 이상의 실험성적은 돼지와 가토의 뇌동맥에서 ACh은 내피세포-의존성 이완반응을 일으키며그 이완반응은 muscarinic receptor를 통해 나타났고, 가묘뇌동맥에서 ACh은 혈관수축제의 역할을 갖고 있음을 시사하고 있다.