The regulation of reproductive neuroendocrine function by insulin and insulin-like growth factor-1 (IGF-1)

• Kisspeptin neuron, GnRH neuron and pituitary gonadotrophs are targets of insulin and IGF-1 action.
• Insulin action in the pituitary may mediate pathophysiologic effects of obesity.
• IGF-1 in the brain may act at both the kisspeptin and GnRH neurons to regulate puberty.

The mammalian reproductive hormone axis regulates gonadal steroid hormone levels and gonadal function essential for reproduction. The neuroendocrine control of the axis integrates signals from a wide array of inputs. The regulatory pathways important for mediating these inputs have been the subject of numerous studies. One class of proteins that have been shown to mediate metabolic and growth signals to the CNS includes Insulin and IGF-1. These proteins are structurally related and can exert endocrine and growth factor like action via related receptor tyrosine kinases. The role that insulin and IGF-1 play in controlling the hypothalamus and pituitary and their role in regulating puberty and nutritional control of reproduction has been studied extensively. This review summarizes the in vitro and in vivo models that have been used to study these neuroendocrine structures and the influence of these growth factors on neuroendocrine control of reproduction.