The production and release of GH is regulated by numerous feedback mechanisms, converging at the level of the hypothalamus and anterior pituitary gland. Within this extensive network, stimulatory Growth Hormone Releasing Hormone (GHRH)- and inhibitory somatostatin-expressing neurons are thought to predominantly modulate the characteristic patterned release of GH. This pattern of GH release (referred to as pulsatile GH release) is conserved across all species characterised to date. Modulation of GH release via these mechanisms ensures that the release of GH closely matches physiological requirements that are central to optimal growth, metabolic and reproductive needs.
While mechanisms that control GH patterning are seemingly well-defined, our understanding of the mechanisms that converge between the control of GH release, appetite and reproduction are poorly understood. Using the mouse as a model, we are currently assessing the integrative role of neuronal and peripheral regulators of food-intake and reproductive function in modulating the patterned release of GH. I will highlight key interactions between orexigenic Neuropeptide-Y (NPY) expressing neurons and hypothalamic neurons central in the control of GH release. While emphasizing the fundamental role of NPY-expressing neurons in regulating GH release relative to meal-provision, recent observations demonstrate key physiological adaptations that may override this interaction. Indeed, compelling unpublished evidence from the lactating mouse suggests specific maternal adaptations whereby enhanced GH release coincides with increased orexigenic actions of NPY neurons. While still under investigation, it is thought that this maternal adaptation occurs in response to an elevation in prolactin release that is central to lactation. This maternal adaptation is thought to ensure enhanced GH release to meet maternal metabolic requirements central to lactation, while sustaining optimal milk production to meet the metabolic requirements of the developing offspring. Discoveries highlight novel interactions within the GH axis, incorporating key mechanisms that regulate appetite and reproduction.