New Aspects of Immunoregulation by Growth and Lactogenic Hormones

Abstract

Growth hormone and prolactin maintain adaptive immunity, which incudes cell mediated immunity, antibody- and autoimmune reactions, maintain thymus and bone marrow function. Insulin like growth factor-1 participate in the regulatory action of growth hormone and prolactin. The hypothalamus-pituitary-adrenal axis stimulates innate immunity and suppresses adaptive immunity. Dopamine also inhibits adaptive immunity and regulates innate immunity. Catecholamine's and corticosteroids support innate immunity and stimulate suppressor-regulatory T cells, which inhibit adaptive immunity. Adrenalectomy sensitized mice to Lipid A, which was mediated by exaggerated production of tumor necrosis factor-alpha, due to the lack of functional hypothalamic pituitary adrenal axis. Growth and lactogenic hormones share signal transduction pathways with type I (gamma-c) cytokines. This indicates functional overlap. The hypothalamic pituitary adrenal axis produces glucocorticoids, which stimulate innate immunity, and play a primary role during the acute phase response. Vasopressin supports the acute phase response, maintains chronic inflammatory reactions and coordinates heeling. Vasopressin maintains immunocompetence during homeostasis as it stimulates the hypothalamus-pituitary- adrenal axis and also prolactin. Vasopressin stimulates innate immune cytokine production. Oxytocin is immunoregulatory. Thyroidectomy in rats suppresses immune function and thyroxin releases growth hormone and prolactin from transplanted pituitary grafts in rats and also restores immunocompetence. This indicates that thyroxin is an indirect immunoregulator. The growth hormone secretagouge, ghrelin, is immunoregulatory. Dopamine is a neurotransmitter and immunoregulator. Dopamine has a role in normal immune function and in stress, inflammatory diseases, schizophrenia, Parkinson disease, Tourette syndrome, Lupus, Multiple Sclerosis, AIDS, and generalized anxiety syndrome.