Leptin is a protein hormone that derives its name from the Greek word leptos, which means thin. The hormone affects your body weight, metabolism, reproductive and immune systems. The hypothalus region of your brain has an abundance of leptin receptors, which have long-term effects that regulate your eating behavior, body temperature and energy expenditure. Leptin receptors also line the interior surface of your blood vessels and affect the development of specific immune cells.
Appetite
Leptin affects areas of your brain that control appetite. Cells in your gut and the hypothalamus portion of your brain secret neuropeptide Y, which stimulates hunger. Leptin counteracts the effects of neuropeptide Y. Leptin also counteracts the effects of anandamide, a cannabinoid substance derived from omega-6 fatty acids. Anandamide is a neurotransmitter that induces hunger and binds to the same receptors as tetrahydrocannabinol, which is the active ingredient that stimulates hunger in marijuana. Leptin also promotes the production of alpha melanocyte-stimulating hormone, which suppresses appetite.
Sexual Physiology
Gonadotropin-releasing hormone triggers sexual development during puberty, and maintains normal sexual physiology for the rest of your life. Leptin acts on centers of your brain that control gonadotropin-releasing hormone secretions. A February 2009 "Journal of Sexual Medicine" study led by Annamaria Morelli, Ph.D., at the University of Florence found that leptin increased GnRH secretions in human neuroblasts. The researchers determined that the combination of leptin and male hormones might positively affect GnRH secretions, which regulate sexual reproductive systems. Women that develop abnormal menstrual cycles due to strenuous physical training or nutritional deficiencies may regain normal menstruation with recombinant human leptin treatments.
Bone Formation and Breakdown
Leptin acts on neurons that stimulate your sympathetic nervous system and regulate the balance between osteoblast and osteoclast activity. Osteoblasts are responsible for bone formation and form a sheet of cells that cover the surface of your bones. Osteoclasts are cells located in small depressions on the surface of your bones. Osteoclastic activity dissolves bone in response to structural stress or to help meet your body's need for calcium. An April 2002 "Journal of Clinical Biochemistry" study led by Jan O. Gordeladze, Ph.D., at the University of Oslo reports that continuously exposing cultured human iliac crest osteoblasts to leptin promotes collagen production, cell differentiation and mineralization.
Inflammation
Leptin enhances the production of Th1 cells, which produce inflammatory responses. Th1 cells are responsible for killing parasites inside of cells and carrying out autoimmune responses. Excessive inflammatory responses can lead to uncontrolled tissue damage. Th1 cells are known as T-helper cells because they assist cytotoxic T cells that destroy other target cells. Target cells might include virus-infected cells, cells infested with parasites, transplanted organ cells or cancer cells. Mice without leptin are protected from autoimmune diseases.
References
- "British Medical Journal": Th1 and Th2 Responses - What are they?; Abi Berger; August 2000
- Kimball's Biology Pages: Leptin
- Merriam-Webster: Anandamide
- "Journal of Sexual Medicine"; Dihydrotestosterone and Leptin regulate GnRH Expression and Secretion; Annamaria Morelli Ph.D.; February 2009
- Encyclopedia Brittanica: Osteoblast
- Encyclopedia Brittanica: Osteoclast
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