Gebhard R L, Cooper A D
J Biol Chem. 1978 Apr 25;253(8):2790-6.
The regulation of intestinal cholesterol synthesis was studied utilizing canine ileal mucosa maintained in organ culture for 6 h. Viability was monitored by light and electron microscopy, measurement of cellular enzymes, and the ability to actively transport a glucose analogue. The activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase (EC 1.1.4.3.4), the rate-limiting enzyme of cholesterol synthesis, increased 4-fold during a 6-h culture. A parallel increase occurred in the rate of acetate incorporation into digitonin-precipitable sterols during this period. This increase could be prevented by the addition of cycloheximide to the culture. Pure cholesterol, 7-ketocholesterol, and 25-hydroxycholesterol, when present during the last 4 h of culture, also caused significant suppression of the rise in HMG-CoA reductase activity (final HMG-CoA reductase with the three sterols was 77 +/- 4%, 68 +/- 5%, and 58 +/- 3% of control postculture value). Bile salts at low, nontoxic concentrations also inhibited the increase of enzyme activity (2 mM taurocholate = 63 +/- 3% of control, 0.5 mM taurochenodeoxycholate = 76 +/- 6% of control). In contrast, dog lipoproteins separated by ultracentrifugation failed to significantly affect intestinal cholesterol synthesis in these short term organ cultures.
利用在器官培养中维持6小时的犬回肠黏膜研究肠道胆固醇合成的调节。通过光学和电子显微镜、细胞酶的测量以及主动转运葡萄糖类似物的能力来监测活力。胆固醇合成的限速酶3-羟基-3-甲基戊二酰辅酶A（HMG-CoA）还原酶（EC 1.1.4.3.4）的活性在6小时培养期间增加了4倍。在此期间，乙酸掺入可被洋地黄皂苷沉淀的固醇的速率也出现了平行增加。这种增加可通过向培养物中添加环己酰亚胺来阻止。在培养的最后4小时存在时，纯胆固醇、7-酮胆固醇和25-羟基胆固醇也显著抑制了HMG-CoA还原酶活性的升高（三种固醇存在时最终的HMG-CoA还原酶活性分别为培养后对照值的77±4%、68±5%和58±3%）。低浓度、无毒的胆汁盐也抑制了酶活性的增加（2 mM牛磺胆酸盐为对照值的63±3%，0.5 mM牛磺鹅去氧胆酸盐为对照值的76±6%）。相比之下，通过超速离心分离的犬脂蛋白在这些短期器官培养中未能显著影响肠道胆固醇合成。
