Aromatase activity in the mare ovary during estrous cycle. Measurement of endogenous steroids and of their in vitro inhibitory effect.

The research investigates the synthesis of estrogen in the mare ovary and the possible role of certain endogenous steroids in regulating this process.

Research Objective

• The primary aim of the study was to understand the process of estrogen synthesis in the mare ovary. The researchers wanted to identify the levels of endogenous steroids at different phases of the estrous cycle and evaluate their potential inhibitory impact on aromatase activity. Aromatase is an enzyme responsible for the conversion of androgens to estrogens, which is vital for female fertility.

Methods and Measurements

• Steroid contents in the follicular fluid and luteal tissue were evaluated at varied luteal phases. These measurements were conducted through Radioimmunoassays after separating and purifying each hormone using chromatography.
• The researchers also conducted an in vitro examination of the aromatization capability of the cyclic corpus luteum. The cyclic corpus luteum is an essential part of the ovary produced after ovulation and is vital in regulating the estrous cycle.

Discoveries

• The study found high quantities of both conjugated and unconjugated estradiol-17 beta, a form of estrogen, in the follicular fluid of larger follicles. However, these levels of estrogen decreased considerably in luteal tissue, with only low levels present during the luteal phase.
• In terms of endogenous steroids’ impact on aromatase activity, 5 alpha-Dihydrotestosterone emerged as the most competitive inhibitor. On the contrary, the inclusion of a 3-sulfate group made a substantial drop in the inhibitory potency of estrone and dehydroepiandrosterone.

Implications and Conclusion

• The researchers proposed that the observed conjugated steroids might protect aromatase from inhibition. Additionally, the high amounts of progesterone found in the luteal tissue could also play a role in regulating estrogen production, either by suppressing the induction of aromatase synthesis or by inhibiting the activity of the enzyme complex.
• In conclusion, the paper offers insightful findings into the process of estrogen synthesis in the mare ovary and suggests that endogenous steroids might play a significant role in this regulation. However, further studies are needed to fully understand these mechanisms.