Granulosa cell function in domestic animals: A review on the in vitro effects of FSH, insulin and insulin-like growth factor 1.

Overview

• This research article reviews how follicle-stimulating hormone (FSH), insulin, and insulin-like growth factor 1 (IGF1) influence the function of ovarian granulosa cells in domestic animals.
• The focus is on how these hormones affect granulosa cell steroid hormone production and cell proliferation across six species: pigs, cattle, horses, water buffalo, goats, and sheep.

Background on Granulosa Cells

• Granulosa cells line the ovarian follicles and play essential roles in reproduction by producing steroid hormones (e.g., estrogen and progesterone).
• Besides steroid hormones, they produce growth factors, cytokines, and adipokines—biologically active compounds that influence ovarian function.
• These secreted factors act through endocrine (bloodstream), paracrine (nearby cells), and autocrine (self-signaling) mechanisms.
• The complex interplay of these molecules helps regulate follicle development, ovulation, and fertility.

Hormonal Regulation: FSH, Insulin, and IGF1

• FSH (Follicle stimulating hormone): A key hormone stimulating ovarian follicle growth and estrogen production.
• Insulin: A metabolic hormone that also influences ovarian function by regulating cell growth and steroid synthesis.
• IGF1 (Insulin-like growth factor 1): A growth factor that has important roles in cell proliferation and differentiation, including within ovarian follicles.

Findings on Cell Proliferation

• In most studied species, FSH alone does not stimulate granulosa cell proliferation (i.e., it is not mitogenic).
• In contrast, insulin and IGF1 generally promote granulosa cell proliferation across species where this was assessed.
• This indicates that metabolic and growth factors may be more influential than FSH in driving granulosa cell multiplication.
• Specific data gaps exist, especially regarding insulin’s role in water buffalo and goats.

Findings on Steroidogenesis (Hormone Production)

• All three hormones—FSH, insulin, and IGF1—stimulate steroid hormone production by granulosa cells across species where investigated.
• This suggests cooperative roles in promoting estrogen and other steroid synthesis necessary for follicle maturation and reproductive function.
• Clarification is needed on IGF1’s influence in horses, as current research is limited.

Interactions with Granulosa Cell Secreted Factors

• Granulosa cells secrete many biologically active substances that can modulate the effects of FSH, insulin, and IGF1.
• These secreted factors may enhance or inhibit steroid production induced by the three hormones.
• The combined, cumulative impact of these factors on ovarian function and fertility is complex and not fully understood.
• Further research is needed to unravel how these numerous signals integrate to ultimately regulate female fertility in various domestic species.

Gaps and Future Directions

• More research is needed to better understand insulin’s role in regulating granulosa cell proliferation and steroidogenesis in water buffalo and goats.
• The role of IGF1 in horse granulosa cell function remains underexplored and requires deeper study.
• Investigations into interactions among granulosa cell secreted factors and hormones will be key to fully deciphering ovarian regulation mechanisms.
• Such insights can inform reproductive management and improve fertility in domestic animal species.