Ghosh D K, Peegel H, Dunham W R, Sands R H, Menon K M
Department of Obstetrics/Gynecology, University of Michigan, Ann Arbor 48109.
Endocrinology. 1988 Jul;123(1):514-22. doi: 10.1210/endo-123-1-514.
Down-regulation of hCG receptors and a steroidogenic lesion in progesterone production were observed in isolated luteal cells after 24-h treatment of pseudopregnant rats with 50 IU hCG. The luteal cells from hCG-desensitized rats exhibited a complete loss of steroidogenic response to lipoproteins in both the absence and presence of hCG. This loss of response was not overcome by the addition of 25-hydroxycholesterol. To examine if the loss of steroidogenic response is due to a transient loss of steroidogenic enzymes or inadequate delivery of substrate cholesterol, cholesterol side-chain cleavage enzyme (P450scc) activity was measured in the isolated mitochondria. No differences appeared in enzyme activity between control and hCG-treated groups. Furthermore, electron paramagnetic resonance spectra of mitochondrial cytochrome P450scc from control and hCG-treated groups exhibited no appreciable differences in low spin electron paramagnetic resonance signal (g = 1.9, 2.2, and 2.4) or high spin EPR signal (g = 8.2), suggesting that the binding of the substrate to P450scc was not impaired. Additionally, the iron sulfur protein signal (g = 1.95 and 2.03) of the reduced mitochondria remained unchanged in the desensitized group. These data were supported by immunoblotting analysis which revealed no difference in the relative amounts of iron sulfur protein or cytochrome P450scc between the two groups. Moreover, the inner mitochondrial membranes, the locus of cytochrome P450scc, showed an identical cholesterol content in control and desensitized mitochondria, indicating that the availability of cholesterol substrate is not impaired during desensitization. These results suggest that the intramitochondrial transfer of cholesterol and cholesterol side-chain cleavage enzyme activity are unaffected in the desensitized state, but an inhibitory substance might be responsible for the lack of steroidogenic response.
用50国际单位人绒毛膜促性腺激素（hCG）对假孕大鼠进行24小时处理后，在分离的黄体细胞中观察到hCG受体下调以及孕酮生成中的类固醇生成损伤。来自hCG脱敏大鼠的黄体细胞在不存在和存在hCG的情况下均对脂蛋白表现出类固醇生成反应完全丧失。添加25-羟基胆固醇并不能克服这种反应丧失。为了检查类固醇生成反应丧失是否是由于类固醇生成酶的短暂丧失或底物胆固醇的供应不足，在分离的线粒体中测量了胆固醇侧链裂解酶（P450scc）的活性。对照组和hCG处理组之间的酶活性没有差异。此外，对照组和hCG处理组线粒体细胞色素P450scc的电子顺磁共振光谱在低自旋电子顺磁共振信号（g = 1.9、2.2和2.4）或高自旋电子顺磁共振信号（g = 8.2）方面没有明显差异，表明底物与P450scc的结合没有受损。此外，脱敏组中还原型线粒体的铁硫蛋白信号（g = 1.95和2.03）保持不变。这些数据得到免疫印迹分析的支持，该分析显示两组之间铁硫蛋白或细胞色素P450scc的相对量没有差异。此外，细胞色素P450scc所在的线粒体内膜在对照线粒体和脱敏线粒体中的胆固醇含量相同，表明脱敏过程中胆固醇底物的可用性没有受损。这些结果表明，脱敏状态下胆固醇的线粒体内转运和胆固醇侧链裂解酶活性不受影响，但一种抑制物质可能是类固醇生成反应缺乏的原因。
