Malee M P, Mellon S H
Department of Obstetrics, Gynecology and Reproductive Sciences, University of California, San Francisco 94143-0556.
Proc Natl Acad Sci U S A. 1991 Jun 1;88(11):4731-5. doi: 10.1073/pnas.88.11.4731.
Adrenal mitochondria possess two steroidogenic cytochrome P450s. P450c11 converts deoxycorticosterone to corticosterone and aldosterone, and P450scc converts cholesterol to pregnenolone. These P450s receive electrons from NADPH via adrenodoxin reductase and adrenodoxin. A single bovine P450c11 protein has 11-hydroxylase, 18-hydroxylase, and 18-oxidase activities, but this series of enzymatic steps may be mediated by more than one enzyme in rats. Enzymatic assays of purified rat mitochondrial proteins have suggested that one enzyme found in all zones of the adrenal cortex has both 11- and 18-hydroxylase activities, whereas another enzyme, found exclusively in the zona glomerulosa, catalyzes 18-hydroxylation and 18-oxidation of corticosterone. We studied the number and zonal distribution of P450c11 mRNA species in the rat adrenal and how these mRNAs are regulated in the adrenals of normal and pregnant rats. Rats synthesize two similar, but distinct, P450c11 mRNAs. One, P450c11A, is found in both the zona glomerulosa and fasciculata/reticularis, whereas the second, P450c11B, is found only in the zona glomerulosa. The abundance of neither P450c11A mRNA nor P450c11B mRNA is affected by a high-salt diet. However, when rats receive a low-salt diet, P450c11A mRNA decreases and P450c11B mRNA increases. Dexamethasone decreases the amount of P450c11A mRNA without affecting P450c11B mRNA. The combination of a high-salt diet and dexamethasone decreases the amount of both mRNAs further to almost undetectable amounts. Rats given a low-salt diet and dexamethasone have a dramatic increase in the abundance of P450c11B mRNA. Thus both forms of P450c11 mRNA are regulated independently in the rat adrenal cortex. In situ hybridization studies show that only the P450c11 found in the zona glomerulosa is regulated by salt treatment in vivo, whereas glucocorticoid treatment in vivo regulates P450c11 in all zones. In the adrenals of pregnant rats, P450c11B is regulated in a similar fashion to its regulation in the nonpregnant rat adrenal, despite major differences in sodium retention and intravascular volume in pregnant and nonpregnant rats. In the pregnant rat, a low-salt diet increases the abundance of P450c11B to a greater degree than in the nonpregnant rat. By contrast, dexamethasone does not diminish the abundance of P450c11A mRNA in the pregnant rat but reduces it to an almost undetectable amount in the nonpregnant rat. Thus, the regulation of glucocorticoid and mineralocorticoid production in the pregnant and nonpregnant rat occurs by different mechanisms.
肾上腺线粒体含有两种类固醇生成细胞色素P450。P450c11将脱氧皮质酮转化为皮质酮和醛固酮，而P450scc将胆固醇转化为孕烯醇酮。这些P450通过肾上腺皮质铁氧还蛋白还原酶和肾上腺皮质铁氧还蛋白从NADPH获取电子。单个牛P450c11蛋白具有11-羟化酶、18-羟化酶和18-氧化酶活性，但在大鼠中，这一系列酶促步骤可能由不止一种酶介导。对纯化的大鼠线粒体蛋白进行的酶活性测定表明：在肾上腺皮质所有区域发现的一种酶同时具有11-和18-羟化酶活性，而另一种仅在球状带发现的酶催化皮质酮的18-羟化和18-氧化。我们研究了大鼠肾上腺中P450c11 mRNA种类的数量和区域分布，以及这些mRNA在正常和妊娠大鼠肾上腺中的调控方式。大鼠合成两种相似但不同的P450c11 mRNA。一种是P450c11A，存在于球状带和束状带/网状带；另一种是P450c11B，仅存在于球状带。高盐饮食对P450c11A mRNA和P450c11B mRNA的丰度均无影响。然而，当大鼠摄入低盐饮食时，P450c11A mRNA减少，P450c11B mRNA增加。地塞米松可减少P450c11A mRNA的量，但不影响P450c11B mRNA。高盐饮食和地塞米松联合使用可使两种mRNA的量进一步减少至几乎检测不到的水平。给予低盐饮食和地塞米松的大鼠，P450c11B mRNA的丰度显著增加。因此，两种形式的P450c11 mRNA在大鼠肾上腺皮质中是独立调控的。原位杂交研究表明，体内盐处理仅调节球状带中的P450c11，而体内糖皮质激素处理则调节所有区域的P450c11。在妊娠大鼠的肾上腺中，P450c11B的调控方式与其在未妊娠大鼠肾上腺中的调控方式相似，尽管妊娠和未妊娠大鼠在钠潴留和血容量方面存在重大差异。在妊娠大鼠中，低盐饮食比在未妊娠大鼠中更能增加P450c11B的丰度。相比之下，地塞米松不会降低妊娠大鼠中P450c11A mRNA的丰度，但会将未妊娠大鼠中的P450c11A mRNA降低至几乎检测不到的水平。因此，妊娠和未妊娠大鼠中糖皮质激素和盐皮质激素产生的调控机制不同。
