血管攣縮の分子機構

抄録

Coronary spasm plays an important role in the pathogenesis of coronaty artery disease. Augmented vasoconstrictor response to the stimuli may be due to both hyperreactivity of vascular smooth muscles to specific agonists and reduced endothelium-dependent vasodilatation. To clarify the mechanisms of impaired endothelium-dependent relaxation (EDR) in atherosclerotic arteries, we investigated the effect of Ox-LDL on EDR. Ox-LDL but not native LDL inhibited EDR. Approximately 40% of phosphatidylcholine (PC) was converted to lysophosphatidylcholine (LPC) during oxidative modification of LDL. Fractionation of individual lipids revealed that LPC derived from ox-LDL inhibited EDR. Ox-LDL or LPC inhibited accumulation of IP₃ followed by the increase of intracellular Ca²⁺ concentration induced by agonists including bradykinin. We clarified that low concentration of ox-LDL (10μg protein/mL) or LPC (5μg/mL) upregulated cNOS mRNA and protein levels by using RNase protection assay and immunoblotting. This action of LPC was abolished with cycloheximide but not with staurosporine. Furthermore, in situ hybridization and immunohistochemistry revealed that the cNOS mRNA and protein expression was normally observed in the endothelial cells overlying aortic fatty streaks in WHHL rabbits. These findings suggest that loss of EDRF activity associated with atherosclerotis is not due to an alteration of endothelial cNOS expression. Atherosclerotic arteries exhibit a marked increase increase of contractile response to 5-HT. We measured simultaneously both isometric tension and intracellular Ca²⁺ concentration ([Ca²⁺]_i) in fura 2-loaded aortic smooth muscle strips. Athrosclerotic arteries from WHHL rabbit exhibited increased contraction associated with increase of [Ca²⁺]_i in response to 5-HT. Ketanserin, 5-HT₂ receptor antagonist, failed to inhibit supersensitivity to 5-HT in WHHL rabbit aortas. Moreover, WHHL rabbit aortas exhibited an augmented response to 5-carboxamide tryptamine, a 5-HT₁ like receptor agonist. We clarified 5-HT_1D and 5-HT₂ receptors were present in human coronary arteries using RT-PCR method. From these results, 5-HT_1D receptor-mediated signaling pathway may be involved in the supersensitivity to 5-HT in atherosclerotic arteries. Therefore, endothelial dysfunction by ox-LDL and LPC, and augmented contactile response caused by abnormal 5-HT signaling pathways in smooth muscle cells may play an important role in the abnormal regulation of the vasomotor tone in atherosclerotic arteries.