Growth hormone regulation of follicular growth

Abstract

The somatotropic axis-consisting of growth hormone (GH), the insulin-like growth factors 1 and 2 (IGF1 and IGF2), GH binding protein (GHBP), IGF binding proteins (IGFBPs) 1 to 6, and the cell-surface receptors for GH and the IGFs-has major effects on growth, lactation and reproduction. The primary target tissues for GH are involved in growth and metabolism. The functionality of the somatotropic axis depends in part on the expression of liver GH receptor (GHR), which determines the amount of IGF1 released from the liver in response to GH. The IGF1 acts as a pleiotropic growth factor and also serves as the endocrine negative feedback signal controlling pituitary GH secretion. Growth hormone and IGF1 undergo dynamic changes throughout the life cycle, particularly when animals are either growing, early post partum or lactating. Cells within the reproductive tract can respond directly to GH but to a lesser degree than the primary target tissues. The major impact that GH has on reproduction, therefore, may be secondary to its systemic effects on metabolism (including insulin sensitivity) or secondary to the capacity for GH to control IGF1 secretion. Insulin-like growth factor 1 and IGFBP are also synthesised within the ovary and this local synthesis is a component of the collective IGF1 action on the follicle. Future studies of GH should focus on its direct effects on the follicle as well as its indirect effects mediated by shifts in nutrient metabolism, insulin sensitivity, IGF1 and IGFBP.

The Distribution of Stroma and Antral Follicles Differs between Insulin-Resistance and Hyperandrogenism-Related Polycystic Ovarian Syndrome

“…Normally, insulin, by way of the classic mechanism of “spill-over,” binds insulin growth factor-1 (IGF-1) receptor thereby exerting mitogenic effects on the granulosa and theca. IGF-2 plays a pivotal role in the FSH-mediated proliferation of the granulosa and is hence important for the growth and development of follicles (15). If the proliferation of antral follicles is not finely regulated, the mechanisms governing the selection of the dominant follicle could be deranged thereby fostering follicle atresia.…”

Integrative Control of Energy Balance and Reproduction in Females

“…GH as well as systemic and locally produced IGF can exert stimulatory, synergistic, or permissive effects at each level of the HPG axis, in the reproductive tract, external genitalia, and mammary gland [62]. This group of hormones has major effects on growth, lactation, and reproduction [63] and has a clear link with the metabolic status of the animals. Indeed, actions of GH and adequate levels of IGF-I in peripheral circulation are required to reach puberty and full reproductive potential [64].…”

Changes in granulosa cells' gene expression associated with increased oocyte competence in bovine

“…3) is associated with cell survival and IGF2 has been linked to developmental competence and validated by QPCR. In our study, IGF2 has a developmental competence expression profile and would probably act differently from IGF1, which is associated with FSH response in bovine folliculogenesis (Lucy 2011). In fishes, IGF2 stimulates follicles and oocyte maturation (Reinecke 2010) but the mouse KO shows no infertility (Chandrashekar et al 2004).…”