Comparative biochemical study on glucocorticoid metabolism in mammary gland and kidney

11 β -羟类固醇脱氢酶（11 β - hsd）的两种同工酶现已被识别：11 β - hsd -1是nadp依赖性酶，Km在微摩尔范围内。11 β - hsd -2是nadd依赖性酶，Km在纳摩尔范围内。在肝脏中，11 β - hsd -1占主导地位，并将11-脱氢皮质酮转化为皮质酮。另一方面，在肾脏中，nad依赖性的11 β - hsd -2氧化失活皮质酮，使非选择性矿化皮质激素受体被矿化皮质激素占据。本研究旨在证明11 β - hsd -2存在于其他钠转运上皮中，如哺乳动物乳腺上皮和产蛋鸟生殖道上皮。用日本鹌鹑肾脏和输卵管各部位的匀浆制备微粒体，在存在或不存在1 mM NAD的情况下，与皮质酮在40℃下孵育1小时。停止反应，用乙酸乙酯提取类固醇。甾体化合物的分离采用氯仿-甲醇（95:5）体系的薄层色谱法。通过测定皮质酮向11-脱氢皮质酮的转化率来测定11- β - hsd -2的活性。在研究的许多组织中，输卵管的壳腺和蛋白分泌区显示出11 β - hsd -2的高活性。在这些组织中，放射性皮质酮完全代谢为11-脱氢皮质酮。另一方面，输卵管、峡部和阴道的活性较低，表明这些部位可能不是矿化皮质激素的靶点。尽管目前还不知道蛋白的分泌和蛋壳的形成过程是由矿糖皮质激素介导的，但我们的研究结果表明，这些组织可能是矿糖皮质激素的靶点。

Corticosteroid action is modulated by the enzyme 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) Two isozymes of 11 beta-HSD are now recognized : 11 beta-HSD-1 is NADP-dependent enzyme with a Km in the micromolar range. 11 beta-HSD-2 is NAD-dependent enzyme with a Km in the nanomolar range. In the liver, 11 beta-HSD-1 is predominant and converts 11-dehydrocorticosterone to corticosterone. On the other hand, in the kidney, the NAD-dependent 11 beta-HSD-2 oxidatively inactivates corticosterone, allowing the nonselective mineralocorticoid receptor to be occupied by mineralocorticoids. The present study was conducted to show that 11 beta-HSD-2 is present in other sodium-transporting epithelia such as those in the mammary gland of mammals and in the reproductive tract of egg-laying birds.The microsome fraction was prepared from homogenates of kidney and various parts of oviduct of Japanese quail, and incubated with traitiated corticosterone for 1 hr at 40 C in the presence or absence of 1 mM NAD.The reaction was stopped, and the steroid was extracted by ethyl acetate. Separation of steroids was performed using a thin-layr chromatography developed in a chloroform-methanol (95 : 5) system. Activity of 11 beta-HSD-2 was determined by measuring the conversion rate of corticosterone to 11-dehydrocorticosterone.Among a number of tissues studied, the shell gland and albumen secreting region of the oviduct showed high activity of 11 beta-HSD-2. In these tissue, radioactive corticosterone was exclusively metabolized to 11-dehydrocorticosterone. On the other hands, infundibulum and isthmus of the oviduct and the vagina contain low activity, indicationg that these parts might not be a target of the mineralocorticoids. Although the process of secretion of albumen and the formation of egg shell is not known to be mediated by mineralocorticoids, our findings indicate that these tissues might be a target of the mineralocorticoids.