Differential transcription of steroidogenic enzymes in the equine primary corpus luteum during diestrus and early pregnancy.

This research investigates how the hormone eCG stimulates the production of different sex hormones in pregnant horses, focusing on their transcriptional regulation at different stages of the reproductive cycle. It reveals specific fluctuations in the production of these hormones and offers insights into the biological mechanisms underpinning them.

Objective and Methodology

• The study’s objective was investigating how eCG—a hormone prominent during horse pregnancies—regulates the production of sex hormones, including androgens and estrogens. This was executed by scrutinizing mRNA expression of certain steroidogenic enzymes linked to their synthesis.
• A technique called Northern blot analyses was used for examining the nucleotide identities of these enzymes in equine primary corpora lutea, an essential part of the horse reproductive system. The enzymes studied were 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD), cytochrome P450 17 alpha-hydroxylase/17,20-lyase (P450 17 alpha), and cytochrome P450 aromatase (P450arom).
• Luteal tissue samples collected at various times during the reproductive cycle: diestrus (Days 8-10), early pregnancy before eCG secretion (Days 29-35), and early pregnancy after eCG secretion (Days 42-45) were used for the analysis.

Results and Findings

• In terms of genetic sequence, steady-state levels of P450(17) alpha mRNA were similar during diestrus and early pregnancy before the prominence of eCG, but surged after eCG began to be secreted.
• Conversely, cytochrome P450arom mRNA levels significantly fell post the eCG secretion onset. Luteal tissue collected during pregnancy before eCG secretion showed the highest levels of P450arom mRNA, followed by the diestrus stage.
• 3 beta-HSD cDNA demonstrated similar nucleotide identity percentages when compared with human, bovine, and rat sequences, indicating that this enzyme’s expression did not vary significantly through different stages of the reproductive cycle.

Conclusion

• Significant fluctuation noticed in the transcription of P450(17) alpha and P450arom, alongside eCG secretion, suggests that eCG influences luteal estrogen synthesis via transcriptional up-regulation of P450(17) alpha expression.
• These insights indicate that availability of aromatizable androgens, produced with the help of these enzymes, could play a crucial role in luteal estrogen synthesis before eCG secretion begins. This could be a rate-limiting step in early pregnancy.