Harderian Gland as a Model Organ for Study of Lipid Metabolism

哈德氏腺在某些动物身上发育良好，例如啮齿类动物。它占据了轨道的相当大的一部分，位于轨道的后半部分周围。除了作为润滑剂排泄脂质外，这个腺体还具有多种功能，如视网膜外光感受器、调节昼夜节律及其信息素效应。不同物种的脂类成分不同。这个腺体是一个有趣的模型器官，它与特定的膜成分一起具有特定的功能。测定了豚鼠哈德氏腺排泄物中1-烷基-2，3-二酰甘油和膜脂磷脂酰胆碱和磷脂酰乙醇胺的脂肪酸组成。检测到大量的甲基支链脂肪酸。也注意到了必需脂肪酸的缺失。该腺体的脂肪酸合成酶不同于肝脏的脂肪酸合成酶，前者在甲基丙二酰辅酶A存在下产生许多奇数和甲基分支脂肪酸，而后者被甲基丙二酰辅酶A强烈抑制。本文研究了豚鼠哈德氏腺微粒体3-磷酸甘油酰基转移酶。发现了两种不同类型的酶，其中一种酶与其他研究人员报告的二羟丙酮-P酰基转移酶不同。这些结果表明，哈德氏腺就像一个独立的工厂，执行着与周围环境隔绝的独特的脂肪代谢。甲基支化脂肪酸的天然标记被认为是分析脂代谢的有用工具，它无疑将在不久的将来为阐明这些脂类在哈德氏腺特殊功能中的生理作用提供线索。

The Harderian gland is well developed in certain animals, for example, rodents. It occupies aconsiderable part of the orbit and is located around the posterior half of the orbit. This gland has several functions as an extraretinal photoreceptor, regulation of the circadian rhythm and its pheromonal effect, in addition to the excretion of lipids as lubricants. The constituents of the lipids are different from species to species. This gland is an interesting model organ, which has specific functions together with specific membrane constituents. The fatty acid compositions of excretory lipid, 1-alkyl-2,3-diacylglycerol, and the membrane lipids, phosphatidyl choline and phosphatidyl ethanolamine, of the guinea pig Harderian gland were examined. A large amount of methyl-branched fatty acids was detected. The absence of essential fatty acids was also noticed. The fatty acid synthetase of this gland was different from that of liver; the former enzyme produced many odd-numbered and methyl-branched fatty acids in the presence of methylmalonyl-CoA, but the latter enzyme was strongly inhibited by methylmalonyl-CoA. Microsomal glycerol 3-phosphate acyltransferase from the guinea pig Harderian gland was studied. Two distinct types of enzyme were found, one of which is a different enzyme from dihydroxyacetone-P acyltransferase, as reported by other investigators. These results indicated that the Harderian gland is like an "Independent Factory" performing a unique lipid metabolism isolated from surroundings. The natural labeling of fatty acids with methyl-branching is thought to be a useful tool to analyze the lipid metabolism, and it will undoubtedly offer a clue in the near future to elucidate the physiological roles of these lipids in the special functions of Harderian gland.