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

Ovarian granulosa cells produce a variety of biologically active compounds in addition to steroid hormones that include numerous families of growth factors, cytokines and adipokines. Many of these function as endocrine, paracrine and autocrine hormones to regulate ovarian activity. The goal of this review is to provide an update on the evidence in domestic animals on how FSH, insulin and IGF1 regulate the function of granulosa cells with a focus on ovarian steroidogenesis and cell proliferation with comparisons across six domestic animals: pigs, cattle, horses, water buffalo, goats and sheep. In most species, FSH was not a mitogenic stimulus to granulosa cells whereas insulin and IGF1 were stimulatory to cell proliferation in the species it was evaluated. FSH, insulin and IGF1 were all stimulatory to granulosa cell steroidogenesis in the species it was studied. More research is needed to evaluate the role of insulin in the regulation of cell proliferation and steroidogenesis in water buffalo and goats. The role of IGF1 in regulating granulosa cell function in horses also needs further study. Most granulosa-cell secreted factors have direct effects (either positive or negative) on FSH-, insulin- and IGF1-induced steroid production in ovarian cells, but how they all work together to create a cumulative effect to regulate fertility will require further research.