Equine fetal adrenal, gonadal and placental steroidogenesis.

The research article examines where pregnenolone, a hormone that contributes to the creation of other steroid hormones, is produced in equine fetuses. The study proposes that it may be the fetal gonads (sex organs), not the adrenal glands or placenta, that contribute significantly to circulating fetal pregnenolone concentrations.

Fetal Pregnenolone Production

• The research focuses on the origination of pregnenolone in equine fetuses as it wasn’t previously clear where this hormone was synthesized.
• Through investigations involving steroid concentrations in the blood, adrenal glands, gonads, and placenta of fetuses at different gestational ages (4, 6, 9 and 10 months), it was noted that pregnenolone and dehydroepiandrosterone (DHEA) are the most abundant steroids in fetal blood.
• Pregnenolone levels were found to be consistently higher, although they decreased as gestational age advanced.

Steroid Concentrations in Tissues

• Upon examining tissue steroid concentrations at different gestational ages, it was found that they generally paralleled those in the serum.
• Interestingly, adrenal and gonadal tissue pregnenolone concentrations were similar and 100-fold higher than those in the allantochorion, a part of the placenta.
• DHEA levels were observed to be much higher in the gonads than in the adrenal glands. In contrast, progesterone was found to be higher in the adrenal glands than the gonads.
• Transcript analysis, which underpins these data, reveals that the steroidogenic enzyme transcript levels to be higher in fetal gonads than in adrenals or allantochorion.

Role of Gonads and Adrenal Glands

• The research suggests that because of their much larger size, the gonads are likely the source of DHEA and contribute more significantly to circulating fetal pregnenolone concentrations than the adrenal glands.
• In terms of androstenedione, another steroid hormone, its level decreased with gestational age in adrenals but remained the same in the gonads.

Low Contribution from Placenta

• Contrary to previous postulates, the research suggests the placenta may contribute little to equine placental 5α-reduced pregnane secretion, as indicated by low placental tissue pregnenolone and high transcript abundance in the allantochorion.

In conclusion, the research sheds light on the complex process of steroidogenesis (production of steroid hormones) in equine fetuses, especially focusing on the significant role likely played by the gonads in circulating fetal pregnenolone concentrations. Also, it challenges the previous belief about the major role of the placenta in this process.