Changes in equine follicular aromatase activity during transition from winter anoestrus.

The research studied and compared the changes in the activity of a hormone-creating enzyme called aromatase in mares during their transition from winter anoestrus (a period of sexual inactivity) to the breeding season. It emphasized how these changes might affect their overall hormone production and metabolism.

Research Methodology

• The study involved three groups of five pony mares each. The groups were segmented based on their transition period from winter anoestrus to breeding season: early transition (Group ET), late transition (Group LT) and full breeding condition (Group C).
• The granulosa and theca cells, which are an integral part of the ovarian follicle and responsible for the production of sex hormones, were separated and incubated with radioactively labeled androstenedione or progesterone hormones for 3 hours.
• This was followed by analysis of the free oestrogenic products using High Performance Liquid Chromatography (HPLC).

Findings

• The research found highly variable oestrogen production in both cell types in all three groups of mares.
• Only oestrone and oestradiol, two forms of oestrogen, were found in the chromatographs post analysis.
• The conversion of androstenedione to oestrogens was seen to be higher than that of progesterone.
• Detailed observations and comparisons of the enzymatic activity of the two cell types showed that the granulosa cells were more active in converting precursors to oestrogens as compared to the theca cells.
• The research also noted variations in the ratio of oestrone to oestradiol production within the groups. Specifically, Group ET, the early transition group, recorded a lower ratio possibly due to increased oestradiol production.
• Radioactive activity in the samples was observed to vary during early transition and then increased progressively as the transition period progressed. It was significantly higher in granulosa cell incubations with androstenedione.

Conclusions

• The research could not establish absolute conversion rates among the three groups due to individual follicle variations in oestrogen production.
• However, it did establish that changes in the oestrone to oestradiol ratio, along with the changes in water-soluble materials during the transition period, suggest a qualitative change in follicular oestrogen production and perhaps overall steroid metabolism. This indicates an underlying alteration in the hormonal regulatory processes in these animals during their reproductive cycle progression.