Growth hormone, insulin-like growth factors, and the ovary

This chapter focuses on the actions of growth hormone (GH) and insulin-like growth factors (IGFs) at the level of the ovary. GH, also known as somatotropin, is best known for its role in postnatal somatic growth. GH is released from the anterior pituitary into the circulation and stimulates the synthesis and release of IGF-1 from the liver and some local tissues, with GH-stimulated IGF-1. IGFs appear to be important regulators of ovarian follicular growth and selection and luteal steroidogenesis in the rat and mouse. The IGF-1 receptor is highly expressed in the oocyte, in granulosa cells of follicles at all stages, from small primary to mature preovulatory follicles and corpus luteum (CL) in both rat and mouse. IGF-1 expression is more selective, however, being limited to the granulosa of healthy, growing, and selected follicles. Ovarian IGF-1 expression is selectively localized in follicle-stimulating hormone (FSH) receptor-expressing follicles but does not appear to be regulated by gonadotropin or GH, whereas IGF-1 receptor expression is dramatically increased by gonadotropin, as determined by in vivo observations in hypophysectomized animals.