Dorn G W, Becker M W, Davis M G
Department of Medicine/Cardiology, University of Cincinnati College of Medicine, Ohio 45267.
J Biol Chem. 1992 Dec 5;267(34):24897-905.
To more clearly define the physiologic roles of thromboxane (TX)A2 and primary prostaglandins (PG) in vascular tissue we examined vascular contractility, cell signaling, and growth responses. The growth-promoting effects of (15S)-hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5Z,13E-dienoic acid (U46619; TXA2 agonist), PGF2 alpha, and PGE2 consisted of protein synthesis and proto-oncogene expression, but not DNA synthesis or cell proliferation. U46619 contracted rat aortas and increased cultured rat aortic vascular smooth muscle cell intracellular free calcium concentration [Ca2+]i, [3H]inositol monophosphate (IP) accumulation, myosin light chain phosphorylation, and protein synthesis ([3H]leucine incorporation) with EC50 values ranging from 10 to 50 nM. Each of these responses was inhibitable with the TXA2 receptor antagonist [1S]1 alpha,2 beta(5Z),3 beta,4 alpha-7-(3-[2- [(phenylamino)carbonyl]hydrazino]methyl)-7-oxabicyclo[2.2.1]hept-2- yl-5-heptenoic acid (SQ29548). In contrast, PGF2 alpha increased [Ca2+]i, [3H]IP, and protein synthesis with EC50 values of 30-230 nM but contracted rat aortas with an EC50 of 4800 nM. PGE2 increased [Ca2+]i, [3H]IP accumulation, protein synthesis, and contracted rat aortas with EC50 values of 2.5-3.5 microM. TXA2 receptor blockade prevented PGF2 alpha- and PGE2-induced aortic contraction and cell myosin light chain phosphorylation, but not cell signaling or protein synthesis. Binding studies to vascular smooth muscle TXA2 receptors using 1S-[1 alpha,2 beta(5Z),3 alpha(1E,3S),4 alpha]-7-(3-[3-hydroxy-4-(p- [125I]iodophenoxy)-1-butenyl]7-oxabicyclo[2.2.1]hept-2-yl)-5-hepte noic acid ([125I]BOP) showed U46619, SQ29548, PGF2 alpha, and PGE2 competition for TXA2 receptor binding at concentrations similar to their EC50 values for aortic contraction, while binding competition with [3H]PGF2 alpha and [3H]PGE2 demonstrated the specificity of [125I]BOP and SQ29548 for TXA2 receptors. The results suggest that 1) PGF2 alpha- and E2-stimulated vessel contraction is due to cross-agonism at vascular TXA2 receptors; 2) PGF2 alpha stimulates TXA2 receptor-independent vascular smooth muscle protein synthesis at nanomolar concentrations, consistent with an interaction at its primary receptor; and 3) TXA2 is a potent stimulus for vascular smooth muscle contraction and protein synthesis. We suggest that the main physiologic effect of PGF2 alpha may be as a stimulus for vascular smooth muscle cell hypertrophy, not as a contractile agonist.
为了更清晰地界定血栓素（TX）A2和主要前列腺素（PG）在血管组织中的生理作用，我们研究了血管收缩性、细胞信号传导及生长反应。（15S）-羟基-11α,9α-（环氧亚甲基）前列腺-5Z,13E-二烯酸（U46619；TX A2激动剂）、前列腺素F2α（PGF2α）和前列腺素E2（PGE2）的促生长作用包括蛋白质合成和原癌基因表达，但不包括DNA合成或细胞增殖。U46619使大鼠主动脉收缩，并增加培养的大鼠主动脉血管平滑肌细胞内游离钙浓度[Ca2+]i、[3H]肌醇一磷酸（IP）积累、肌球蛋白轻链磷酸化及蛋白质合成（[3H]亮氨酸掺入），其半数有效浓度（EC50）值范围为10至50 nM。这些反应中的每一种都可被TX A2受体拮抗剂[1S]1α,2β(5Z),3β,4α-7-(3-[2-[(苯氨基)羰基]肼基]甲基)-7-氧杂双环[2.2.1]庚-2-基-5-庚烯酸（SQ29548）抑制。相比之下，PGF2α使[Ca2+]i、[3H]IP及蛋白质合成增加，其EC50值为30 - 230 nM，但使大鼠主动脉收缩的EC50为4800 nM。PGE2使[Ca2+]i、[3H]IP积累、蛋白质合成增加，并使大鼠主动脉收缩，其EC50值为2.5 - 3.5 μM。TX A2受体阻断可防止PGF2α和PGE2诱导的主动脉收缩及细胞肌球蛋白轻链磷酸化，但不能防止细胞信号传导或蛋白质合成。使用1S-[1α,2β(5Z),3α(1E,3S),4α]-7-(3-[3-羟基-4-(对-[125I]碘苯氧基)-1-丁烯基]7-氧杂双环[2.2.1]庚-2-基)-5-庚烯酸（[125I]BOP）对血管平滑肌TX A2受体进行的结合研究表明，U46619、SQ29548、PGF2α和PGE2在与其使主动脉收缩的EC50值相似的浓度下竞争TX A2受体结合，而与[3H]PGF2α和[3H]PGE2的结合竞争证明了[125I]BOP和SQ29548对TX A2受体的特异性。结果表明：1）PGF2α和E2刺激的血管收缩是由于对血管TX A2受体的交叉激动作用；2）PGF2α在纳摩尔浓度下刺激TX A2受体非依赖性血管平滑肌蛋白质合成，这与其在主要受体上的相互作用一致；3）TX A2是血管平滑肌收缩和蛋白质合成的有效刺激物。我们认为，PGF2α的主要生理作用可能是作为血管平滑肌细胞肥大的刺激物，而非收缩激动剂。
