Lu R, Kanai N, Bao Y, Wolkoff A W, Schuster V L
Department of Medicine, Liver Research Center, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Am J Physiol. 1996 Feb;270(2 Pt 2):F332-7. doi: 10.1152/ajprenal.1996.270.2.F332.
A recently cloned cDNA encodes the so-called "organic anion-transporting polypeptide" (i.e., oatp), which is expressed in rat liver and in the kidney S3 proximal tubule. functional characterization of the cloned transporter indicates that estradiol 17 beta-D-glucuronide is a major substrate. Because the urinary excretion of glucuronidated steroids differs between males and females, we hypothesized that renal oatp expression may be under sex hormone control. Total RNA was isolated from male or female kidneys and probed with a digoxigenin-labeled oatp antisense riboprobe. Expression of oatp mRNA expression was quantitated by densitometry from Northern blots. Male kidneys expressed at least six distinct oatp transcripts (approximately 4.0, 3.2, 2.9, 2.6, 1.7, and 1.2 kb). Of these, the 3.2-kb band was consistently the strongest. In female rats, renal oatp mRNA expression was markedly less, such that only the 3.2-kb band was consistently detectable. Administering testosterone to female rats increased, and administering estradiol (E2) to male rats decreased, the steady-state levels of renal oatp mRNA. Gonadectomized male and female rats, as well as adrenalectomized male rats, were given pharmacological hormone replacement (testosterone, E2, or dexamethasone, respectively) by subcutaneous osmotic minipump. Castration of male rats produced a dramatic drop in the steady-state level of all six renal oatp transcripts. These were returned to normal by testosterone replacement. In contrast, there was no regulation of hepatic oatp mRNA expression by testosterone. Renal oatp mRNA expression in female rats was mildly increased by oophorectomy. Administration of E2 to oophorectomized females moderately suppressed renal oatp mRNA expression. Adrenalectomy produced a small decrease in oatp expression, but dexamethasone replacement failed to return expression to normal. We conclude that renal oatp mRNA expression is under strong (stimulatory) testosterone control and perhaps weaker (inhibitory) estrogen control. We speculate that this regulation of renal oatp expression is important in modulating the renal tubular secretion of conjugated E2.
最近克隆的一个cDNA编码所谓的“有机阴离子转运多肽”（即oatp），它在大鼠肝脏和肾近曲小管S3段表达。对克隆的转运体进行功能特性分析表明，17β-D-葡萄糖醛酸雌二醇是其主要底物。由于结合型类固醇的尿排泄在雄性和雌性之间存在差异，我们推测肾脏oatp的表达可能受性激素控制。从雄性或雌性大鼠肾脏中分离出总RNA，并用地高辛标记的oatp反义核糖探针进行检测。通过对Northern杂交结果进行光密度分析来定量oatp mRNA的表达。雄性大鼠肾脏表达至少六种不同的oatp转录本（约4.0、3.2、2.9、2.6、1.7和1.2 kb）。其中，3.2 kb的条带始终是最强的。在雌性大鼠中，肾脏oatp mRNA的表达明显较少，以至于只能持续检测到3.2 kb的条带。给雌性大鼠注射睾酮会增加肾脏oatp mRNA的稳态水平，而给雄性大鼠注射雌二醇（E2）则会降低该水平。通过皮下渗透微型泵给去性腺的雄性和雌性大鼠以及肾上腺切除的雄性大鼠分别给予药理剂量的激素替代物（分别为睾酮、E2或地塞米松）。雄性大鼠去势导致所有六种肾脏oatp转录本的稳态水平急剧下降。通过睾酮替代可使其恢复正常。相比之下，睾酮对肝脏oatp mRNA的表达没有调节作用。雌性大鼠卵巢切除后，肾脏oatp mRNA的表达略有增加。给卵巢切除的雌性大鼠注射E2可适度抑制肾脏oatp mRNA的表达。肾上腺切除导致oatp表达略有下降，但地塞米松替代未能使表达恢复正常。我们得出结论，肾脏oatp mRNA的表达受睾酮的强烈（刺激）控制，可能还受雌激素较弱的（抑制）控制。我们推测这种对肾脏oatp表达的调节对于调节结合型E2的肾小管分泌很重要。
