Insulin-like growth factor-II and insulin-like growth factor-binding proteins in bovine cystic ovarian disease

Cystic ovarian disease (COD) is one of the most common reproductive disorders of cattle and is considered to have multifactorial aetiology. An accepted hypothesis involves neuroendocrinological dysfunction of the hypothalamic-pituitary-gonadal axis; however, the role of growth factors in COD has not been extensively investigated. The present study examines the potential role of members of the insulin-like growth factor (IGF) family in COD. Expression of genes encoding IGF-II and insulin-like growth factor-binding proteins (IGFBPs) was examined and the distribution of IGF-II within the follicular wall was assessed immunohistochemically. Finally, the concentration of IGF-II protein was determined in follicular fluid. There was increased IGF-II mRNA in the wall of cystic follicles, mainly associated with granulosa cells. Additionally, there was significantly more IGF-II protein in granulosa and theca cells in cystic follicles, but no change in the concentration of IGF-II in follicular fluid. Total IGFBPs, assessed by western blotting, were similar in different structures. However, by discriminating each IGFBP a decrease was detected in IGFBP-2 expression in cystic follicles that may be related to the observed higher expression of IGF-II. In summary, the present study provides evidence to suggest that COD in cattle is associated with modifications in the IGF-II system.