GH1 and insomnia: Other possible shared mechanisms for pain and insomnia and possibly mediating factors that are discussed include affect and mood, catastrophizing, endogenous pain modulation including activated hyperalgesic systems, mesolimbic dopaminergic pathways and serotonergic pathways, low-grade inflammatory substances and other endogenous substances [e.g., growth hormone (GH) and prolactin], alterations in autonomic balance, and a cyclic alternating pattern (6, 7, 37–39).