Miettinen T A, Proia A, McNamara D J
J Lipid Res. 1981 Mar;22(3):485-95.
The origins of rat fecal neutral steroids were studied in male and female animals fed a sterol-free diet and maintained in an isotopic steady state. The specific activity of fecal cholesterol was found to be consistently lower than that of plasma cholesterol and of the fecal bile acids, indicating that a considerable portion of the fecal neutral steroids was derived from cholesterol not in equilibrium with the rapidly exchangeable pool of body cholesterol. This non-exchanging fraction of neutral steroids was larger in male than in female rats; it appeared to have at least two origins: skin surface lipids licked off fur, and sterols newly synthesized by the intestinal mucosa and secreted into the gut lumen. When the ingestion of skin sterols rich in cholesterol precursors was minimized, the proportion of the non-exchanging fraction of fecal neutral sterols fell somewhat, but the output of cholesterol precursors dropped markedly. This suggests that a significant portion of the non-exchanging fecal cholesterol fraction originated in the intestinal wall by secretion. It can be concluded that the fecal neutral steroids of rats originate primarily from three sources: 1) de novo cholesterol synthesis by the intestinal mucosa, 2) ingested dietary, skin, and fecal sterols, and 3) a rapidly exchangeable cholesterol pool excreted through bile, the intestinal wall, or both.
在以无甾醇饮食喂养并维持同位素稳态的雄性和雌性动物中，对大鼠粪便中性类固醇的来源进行了研究。发现粪便胆固醇的比活性始终低于血浆胆固醇和粪便胆汁酸的比活性，这表明粪便中性类固醇的相当一部分源自与体内快速交换的胆固醇池不平衡的胆固醇。中性类固醇的这种非交换部分在雄性大鼠中比雌性大鼠中更大；它似乎至少有两个来源：从皮毛上舔下的皮肤表面脂质，以及由肠粘膜新合成并分泌到肠腔中的甾醇。当富含胆固醇前体的皮肤甾醇摄入量减至最低时，粪便中性甾醇非交换部分的比例略有下降，但胆固醇前体的输出量明显下降。这表明非交换性粪便胆固醇部分的很大一部分起源于肠壁的分泌。可以得出结论，大鼠粪便中性类固醇主要来源于三个来源：1）肠粘膜从头合成胆固醇，2）摄入的膳食、皮肤和粪便甾醇，3）通过胆汁、肠壁或两者排泄的快速交换胆固醇池。
