Inhibition of steroid 5 alpha-reductase and its effects on testosterone hydroxylation by rat liver microsomal cytochrome P-450.
Inhibition of steroid 5 alpha-reductase and its effects on testosterone hydroxylation by rat liver microsomal cytochrome P-450.
复制标题
大鼠肝微粒体细胞色素 P-450 对类固醇 5 α 还原酶的抑制及其对睾酮羟化的影响。
DOI：
10.1016/0003-9861(88)90386-4
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发表时间：
1988
影响因子：
3.9
通讯作者：
Parkinson,A
中科院分区：
文献类型：
--
作者：
Sonderfan,AJ;Parkinson,A
先前已表明，雌性大鼠肝微粒体类固醇5α-还原酶活性随年龄增加而增加，但雄性大鼠不增加，这与睾酮向1β-、2α-、2β-、6α-、6β-、7α-、15β-、16α-、16β-和18-羟基睾酮和雄烯二酮的细胞色素P-450依赖性氧化的雌性特异性、年龄依赖性下降相一致。为了确定类固醇5α-还原酶活性的增加是否是睾酮氧化减少的原因，我们研究了类固醇5α-还原酶抑制剂4-MA（17β-N，N-二乙基氨基甲酰基-4-甲基-4-氮杂-5 α-雄甾烷-3-酮）对大鼠肝微粒体催化的睾酮氧化途径的影响。我们还确定了哪些羟基睾酮代谢物是类固醇5α-还原酶的底物。在0.1 ~ 10 μm浓度范围内，4-MA完全抑制类固醇5α-还原酶活性，而不抑制不同年龄和性别大鼠肝微粒体以及苯巴比妥或双烯醇酮-16 α-甲腈诱导大鼠肝微粒体催化的睾酮氧化途径。4-MA（10 μm）对成熟雄性大鼠肝微粒体（具有低类固醇5α-还原酶活性）催化的睾酮氧化作用几乎没有或没有影响。相比之下，在存在4-MA的情况下，成熟雌性大鼠（具有高类固醇5α-还原酶活性）肝微粒体形成的羟基化睾酮代谢物的蓄积程度更高。有证据表明，4-MA通过两种机制增加羟基睾酮的积累。首先，4-MA抑制那些代谢物（如6β-羟基睾酮）的5α-还原，这些代谢物被发现是类固醇5α-还原酶的极好底物。在不存在4-MA的情况下，这些代谢产物最终从含有成熟雌性大鼠肝微粒体的孵育物中消失。第二，4-MA抑制5α-二氢睾酮的形成，否则5α-二氢睾酮与睾酮竞争细胞色素P-450的氧化。这第二种机制解释了为什么4-MA增加了代谢物（如7α-羟基睾酮）的积累，这些代谢物被发现是类固醇5α-还原酶的不良底物。尽管4-MA对羟基化睾酮代谢产物的积累有显著影响，但对雄性或雌性大鼠肝微粒体的初始形成速率没有影响。由此我们得出结论，睾酮羟化的年龄和性别依赖性差异主要是由于肝微粒体中细胞色素P-450同工酶谱的年龄和性别依赖性差异，而不是由于类固醇5α-还原酶活性差异造成的假象。4-MA对成熟雌性大鼠肝微粒体睾酮羟化的初始速率无影响，这也表明大鼠肝微粒体类固醇5α-还原酶和细胞色素P-450不会相互竞争NADPH-细胞色素P-450还原酶的电子。
It has been shown previously that liver microsomal steroid 5α-reductase activity increases with age in female but not male rats, which coincides with a female-specific, age-dependent decline in the cytochromeP-450-dependent oxidation of testosterone to 1β-, 2α-, 2β-, 6α-, 6β-, 7α-, 15β-, 16α-, 16β-, and 18-hydroxytestosterone and androstenedione. To determine whether the increase in steroid 5α-reductase activity is responsible for the decrease in testosterone oxidation, we have examined the effects of the steroid 5α-reductase inhibitor, 4-MA (17β-N,N-diethylcarbamoyl-4-methyl-4-aza-5α-androstan-3-one), on the pathways of testosterone oxidation catalyzed by rat liver microsomes. We have also determined which hydroxytestosterone metabolites are substrates for steroid 5α-reductase. At concentrations of 0.1 to 10 μm, 4-MA completely inhibited steroid 5α-reductase activity without inhibiting the pathways of testosterone oxidation catalyzed by liver microsomes from rats of different age and sex, and from rats induced with phenobarbital or pregnenolone-16α-carbonitrile. 4-MA (10 μm) had little or no effect on the oxidation of testosterone catalyzed by liver microsomes from mature male rats (which have low steroid 5α-reductase activity). In contrast, the hydroxylated testosterone metabolites formed by liver microsomes from mature female rats (which have high steroid 5α-reductase activity) accumulated to a much greater extent in the presence of 4-MA. Evidence is presented that 4-MA increases the accumulation of hydroxytestosterones by two mechanisms. First, 4-MA inhibited the 5α-reduction of those metabolites (such as 6β-hydroxytestosterone) that were found to be excellent substrates for steroid 5α-reductase. In the absence of 4-MA, these metabolites eventually disappeared from incubations containing liver microsomes from mature female rats. Second, 4-MA inhibited the formation of 5α-dihydrotestosterone, which otherwise competed with testosterone for oxidation by cytochromeP-450. This second mechanism explains why 4-MA increased the accumulation of metabolites (such as 7α-hydroxytestosterone) that were found to be poor substrates for steroid 5α-reductase. Despite its marked effect on the accumulation of hydroxylated testosterone metabolites, 4-MA had no effect on their initial rate of formation by liver microsomes from either male or female rats. From this we conclude that age- and sex-dependent differences in testosterone hydroxylation are largely due to age- and sex-dependent differences in the profile of cytochromeP-450 isozymes in liver microsomes, and are not an artifact due to differences in steroid 5α-reductase activity. The lack of effect of 4-MA on the initial rate of testosterone hydroxylation by liver microsomes from mature female rats also suggests that rat liver microsomal steroid 5α-reductase and cytochromeP-450 do not compete with each other for electrons from NADPH-cytochromeP-450 reductase.