Department of Population Health and ReproductionSchool of Veterinary Medicine, University of California, Davis California, USA.
Gluck Equine Research CenterDepartment of Veterinary Science, University of Kentucky, Lexington Kentucky, USA.
Reproduction. 2017 Oct;154(4):445-454. doi: 10.1530/REP-17-0239.
Equine fetuses have substantial circulating pregnenolone concentrations and thus have been postulated to provide significant substrate for placental 5α-reduced pregnane production, but the fetal site of pregnenolone synthesis remains unclear. The current studies investigated steroid concentrations in blood, adrenal glands, gonads and placenta from fetuses (4, 6, 9 and 10 months of gestational age (GA)), as well as tissue steroidogenic enzyme transcript levels. Pregnenolone and dehydroepiandrosterone (DHEA) were the most abundant steroids in fetal blood, pregnenolone was consistently higher but decreased progressively with GA. Tissue steroid concentrations generally paralleled those in serum with time. Adrenal and gonadal tissue pregnenolone concentrations were similar and 100-fold higher than those in allantochorion. DHEA was far higher in gonads than adrenals and progesterone was higher in adrenals than gonads. Androstenedione decreased with GA in adrenals but not in gonads. Transcript analysis generally supported these data. was higher in fetal gonads than adrenals or allantochorion, and was higher in fetal adrenals and allantochorion than gonads. transcript was also significantly higher in adrenals and gonads than allantochorion and and SRD5A1 transcripts were higher in allantochorion than either fetal adrenals or gonads. Given these data, and their much greater size, the fetal gonads are the source of DHEA and likely contribute more than fetal adrenal glands to circulating fetal pregnenolone concentrations. Low but high and transcript abundance in allantochorion, and low tissue pregnenolone, suggests that endogenous placental pregnenolone synthesis is low and likely contributes little to equine placental 5α-reduced pregnane secretion.
马胎儿具有大量循环的孕烯醇酮浓度，因此被认为是胎盘 5α-还原孕烷产生的重要底物，但胎儿孕烯醇酮合成的部位仍不清楚。本研究调查了来自胎儿（4、6、9 和 10 个月的胎龄（GA））的血液、肾上腺、性腺和胎盘的类固醇浓度，以及组织类固醇生成酶转录水平。孕烯醇酮和脱氢表雄酮（DHEA）是胎儿血液中最丰富的类固醇，孕烯醇酮始终较高，但随着 GA 逐渐降低。组织类固醇浓度通常随时间与血清相似。肾上腺和性腺组织孕烯醇酮浓度相似，比所有胎盘高 100 倍。DHEA 在性腺中的含量远高于肾上腺，而孕酮在肾上腺中的含量高于性腺。雄烯二酮在肾上腺中随 GA 降低，但在性腺中则不然。转录分析普遍支持这些数据。在胎儿性腺中，高于肾上腺或所有胎盘，在胎儿肾上腺和所有胎盘中高于性腺。 转录物在肾上腺和性腺中也明显高于所有胎盘，而 SRD5A1 转录物在所有胎盘中的含量高于胎儿肾上腺或性腺。考虑到这些数据及其更大的体积，胎儿性腺是 DHEA 的来源，并且比胎儿肾上腺更可能对循环胎儿孕烯醇酮浓度做出贡献。所有胎盘中的 含量低，但 和 转录物丰度高，组织孕烯醇酮低，表明内源性胎盘孕烯醇酮合成水平低，对马胎盘 5α-还原孕烷分泌的贡献可能很小。
