The research on factors influencing on cholesterol synthesis in chickens and egg cholesterol contents

鸡蛋的胆固醇含量相对较高。对于鸡蛋生产商来说，能够提供低胆固醇鸡蛋在经济上是有利的，许多研究工作都是朝着这个目标进行的。肝脏是蛋鸡胆固醇生物合成的主要部位。然而，肠粘膜已被证明是仅次于肝脏的内源性合成胆固醇的来源。本试验旨在研究不同类型饲粮脂肪通过肠道黏膜和肝脏中HMG-CoA还原酶活性对生长雏鸡胆固醇生物合成的影响（试验1和试验2）。此外，还比较了产蛋母鸡和非产蛋母鸡的酶活性（试验3）。在试验1中，肝脏HMG-CoA还原酶活性在饲粮中表现为最高。饲粮中添加红花油或椰子油的雏鸡肠道HMG-CoA还原酶活性显著低于饲粮中添加橄榄油的雏鸡。试验2中，饲喂脱脂和三硬脂苷组的肝脏HMG-CoA还原酶活性显著高于饲喂其他甘油三酯组的肝脏HMG-CoA还原酶活性，以饲喂三硬脂苷组最低。饲喂三叶草苷时，空肠和回肠中HMG-CoA还原酶活性显著或倾向于高于饲喂其他甘油三酯时的活性。除了饲喂三叶草苷外，饲料中饱和脂肪的存在对肠道HMG-CoA还原酶活性没有显著影响，这与在饲料中添加高度不饱和脂肪时所显示的效果不同。肝脏和肠道的HMG-CoA还原酶活性与肠上皮细胞的胆固醇含量无显著相关。试验3中，蛋鸡肝脏中HMG-CoA还原酶活性显著高于对照组

Egg contains a relatively high cholesterol content. It would be economically advantageous for egg producer to be able to provide a low cholesterol egg and many research efforts have been directed toward this goal. The liver is the primary sites of cholesterol biosynthesis in laying hens. However, intestinal mucosa has been demonstrated to be second only to liver as a source of endogenously synthesized cholesterol. The present investigation was designed to study the effect of different type of dietary fats on cholesterol biosynthesis through HMG-CoA reductase activity in the intestinal mucosa, as well as the liver of growing chicks (Experiment 1 and 2). Furthermore, this enzyme activity was compared laying with non-laying hens (Experiment 3). In experment 1, the hepatic HMG-CoA reductase activity showed the highest value in chicks fed the tallow-containing diet. Chicks fed diets containing safflower or coconut oil resulted in a significantly lower intestinal HMG-CoA reductase activity in comparison with those fed the olive oil-containing diet. In experiment 2, the hepatic HMG-CoA reductase activity was significantly higher when fat-free and trilaurin were fed than when any other triglycerides were fed. This activity showed the lowest value in the chicks fed the diet containing tristearin. The HMG-CoA reductase activities in the jejunum and ileum were significantly or tended to be higher when trilaurin was fed than when any other triglycerides were fed. Except when trilaurin was fed, the presence of saturated fat in the diet did not have a significant effect on the intestinal HMG-CoA reductase activity, unlike the effect shown when a highly unsaturated fat was added to the diet. There was no significant correlation between the HMG-CoA reductase activities of the liver and intestine, and this enzyme activity and cholesterol content of intestinal epithelial cells. In Experiment 3, the hepatic HMG-CoA reductase activity in laying hens was significantly higher than those