In vitro steroidogenesis by granulosa cells from equine pre-ovulatory follicles.

The research article presents a study on the steroid production by granulosa cells in pre-ovulatory follicles of mares. The researchers found that the pattern of steroid secretion by these cells changes as the follicle matures.

Sampling and Grouping

• The researchers collected 23 follicles from 14 mares and grouped these based on stages of the estrous cycle. Group 1 contained follicles from early estrus, Group 2 had follicles from mid-estrus, and Group 3 included those from late estrus.

In vitro Culturing of Granulosa Cells

• Granulosa cell (GC), responsible for steroid production, from each follicle were isolated and cultured.
• The researchers cultivated GC in various mediums, including Eagle’s Minimum Essential Medium (MEM), eLH, eFSH, and combinations of these, to examine if these environments influence steroid production.
• They also tested these cultivation conditions in the presence and absence of testosterone as an additional variable.

Assay and Findings

• The cultures were terminated after 48 hours, and the media were assayed for various hormones – estradiol-17 beta (E2), progesterone (P4), androstenedione (A), and testosterone (T) – using radioimmunoassay (RIA).
• The researchers did not find any significant impact of the added hormones (gonadotrophins) on steroid production by GC, hence the data from these test conditions were pooled together.
• The primary steroid produced without added testosterone was progesterone, which showed increasing levels from Group 1 to Group 3, leading the researchers to conclude that its secretion by GC increases as follicular maturation progresses.
• Androstenedione was the major androgen produced, but its levels did not change significantly across the different groups.
• The amounts of estradiol and testosterone were similar in Group 1, but estradiol concentration increased in Group 2 and testosterone concentration increased in Group 3.

Presence of Testosterone

• In the presence of exogenous (external) testosterone, estradiol production increased in all the groups. The increase was most significant in Group 2.
• By the 48-hour mark, progesterone remained the primary steroid secreted by Group 3 granulosa cells.
• Though levels of progesterone weren’t affected by the addition of testosterone, androstenedione increased in the Group 3 medium. Levels of estradiol and testosterone remained unchanged.

Conclusion

• The researchers concluded that steroid secretion patterns by equine granulosa cells change in line with follicular development. The exact implications of these findings for horse breeding or veterinary medicine are not discussed in the abstract.