Reid J J, Stitzel R E, Head R J
Naunyn Schmiedebergs Arch Pharmacol. 1986 Sep;334(1):17-28. doi: 10.1007/BF00498735.
In the present study we investigated the O-methylation of catechol oestrogens by intact rabbit thoracic aorta and subcellular fractions thereof. The O-methylation of 2-hydroxyoestradiol (2OHE2) and 2-hydroxyoestriol (2OHE3) displayed saturation kinetics in the intact tissue. The apparent Km and Vmax values for the O-methylation of 2OHE2 were determined to be 0.91 mumol/l and 104 pmol g-1 min-1, respectively, when 2OHE2 was used as substrate; and 1.14 mumol/l and 188 pmol g-1 min-1 when 2OHE3 was used as substrate. The inhibitors of the extraneuronal uptake process (viz; phenoxybenzamine 33 mumol/l; normetanephrine, 46 mumol/l; and deoxycorticosterone acetate 27 mumol/l) failed to inhibit the O-methylation of either 2OHE2 (3.4 mumol/l) or 2OHE3 (3.4 mumol/l) in intact segments of the rabbit thoracic aorta. (-)-Isoprenaline (40 mumol/l) abolished the O-methylation of 2OHE2 (3.4 mumol/l) and markedly reduced that of 2OHE3 (3.4 mumol/l). Pretreatment of tissues with phenoxybenzamine (33 mumol/l) partially restored the O-methylation of 2OHE2 and 2OHE3 in the presence of (-)-isoprenaline (40 mumol/l). The O-methylation of 2OHE2 (5 mumol/l) was significantly reduced in segments of aorta in which the endothelium was removed. The latter reduction could not be attributed to damage to components of the vessel media. The O-methylation of 2OHE2 and (-)-isoprenaline by subcellular fractions of the rabbit aorta also was examined. Both the microsomal and cytosolic fractions were shown to O-methylate 2OHE2 and (-)-isoprenaline, providing evidence for the existence of membrane-bound and soluble forms of COMT in the rabbit aorta. The O-methylation of 2OHE2 by cytosolic and microsomal fractions of the aorta was determined and compared to that of (-)-isoprenaline. The kinetic constants for the O-methylation of 2OHE2 by cytosolic (Km: 0.27 mumol/l; V max: 112 pmol g-1 min-1) and microsomal (Km: 0.15 mumol/l; Vmax: 161 pmol g-1 min-1) fractions were similar. In contrast, the kinetic constants for the O-methylation of isoprenaline by cytosolic (Km: 121 mumol/l; Vmax: 174 pmol g-1 min-1) and membranal (Km: 0.91 mumol/l; Vmax: 105 pmol g-1 min-1) fractions were very different. It is concluded that catechol oestrogens are excellent substrates for catechol-O-methyltransferase (COMT) in the rabbit aorta. Their O-methylation can occur in endothelial structures as well as in the smooth muscle-containing medial sections of the vessel.(ABSTRACT TRUNCATED AT 400 WORDS)
在本研究中，我们研究了完整兔胸主动脉及其亚细胞组分对儿茶酚雌激素的O-甲基化作用。2-羟雌二醇（2OHE2）和2-羟雌三醇（2OHE3）的O-甲基化在完整组织中呈现饱和动力学。当以2OHE2为底物时，2OHE2 O-甲基化的表观Km和Vmax值分别测定为0.91μmol/L和104 pmol g-1 min-1；当以2OHE3为底物时，分别为1.14μmol/L和188 pmol g-1 min-1。神经外摄取过程的抑制剂（即：酚苄明33μmol/L；去甲变肾上腺素46μmol/L；醋酸脱氧皮质酮27μmol/L）未能抑制兔胸主动脉完整节段中2OHE2（3.4μmol/L）或2OHE3（3.4μmol/L）的O-甲基化。（-）-异丙肾上腺素（40μmol/L）消除了2OHE2（3.4μmol/L）的O-甲基化，并显著降低了2OHE3（3.4μmol/L）的O-甲基化。用酚苄明（33μmol/L）预处理组织可在（-）-异丙肾上腺素（40μmol/L）存在的情况下部分恢复2OHE2和2OHE3的O-甲基化。在内皮被去除的主动脉节段中，2OHE2（5μmol/L）的O-甲基化显著降低。后一种降低不能归因于血管中膜成分的损伤。还检测了兔主动脉亚细胞组分对2OHE2和（-）-异丙肾上腺素的O-甲基化作用。微粒体和胞质组分均显示能对2OHE2和（-）-异丙肾上腺素进行O-甲基化，这为兔主动脉中存在膜结合型和可溶性儿茶酚-O-甲基转移酶（COMT）提供了证据。测定了主动脉胞质和微粒体组分对2OHE2的O-甲基化，并与（-）-异丙肾上腺素的进行比较。胞质组分（Km：0.27μmol/L；Vmax：112 pmol g-1 min-1）和微粒体组分（Km：0.15μmol/L；Vmax：161 pmol g-1 min-1）对2OHE2 O-甲基化的动力学常数相似。相比之下，胞质组分（Km：121μmol/L；Vmax：174 pmol g-1 min-1）和膜组分（Km：0.91μmol/L；Vmax：105 pmol g-1 min-1）对异丙肾上腺素O-甲基化的动力学常数差异很大。结论是，儿茶酚雌激素是兔主动脉中儿茶酚-O-甲基转移酶（COMT）的优良底物。它们的O-甲基化可发生在内皮结构以及血管含平滑肌的中膜部分。（摘要截取自400字）
