MSH; α-melanocyte-stimulating hormone; alpha-MSH; α-MSH; alpha-melanotropin; alpha-melanocortin; alpha-intermedin; melanophore-stimulating hormone
Melanocyte-stimulating hormone is a collective name for a group of peptide hormones produced by the skin, pituitary gland and hypothalamus in response to ultraviolet (UV) radiation. It plays a key role in producing coloured pigmentation found in the skin, hair and eyes. It does this by inducing specialised skin cells called melanocytes to produce a pigment called melanin; melanin protects cells from DNA damage, which can lead to skin cancer (melanoma).
Melanocyte-stimulating hormone is produced from the same precursor molecule as adrenocorticotropic hormone called pro-opiomelanocortin (POMC).
Although known for its stimulatory effect on pigment cells, studies have shown that melanocyte-stimulating hormone can also suppress appetite by acting on receptors in the hypothalamus in the brain. This effect is enhanced by leptin, a hormone released from fat cells.
Melanocyte-stimulating hormone is also thought to affect a range of other processes in the body; it has anti-inflammatory effects, can influence the release of the hormone aldosterone, which controls salt and water balance in the body, and is also thought to have an effect on energy homeostasis and sexual behaviour. However, further research is needed to clarify the exact role of melanocyte-stimulating hormone in these processes.
Melanocyte-stimulating hormone production is increased by exposure to UV light. Due to the many other functions of melanocyte-stimulating hormone besides melanin production, there are likely to be a number of other factors that regulate its production. This means that, unlike most hormones, melanocyte-stimulating hormone release is not thought to be controlled by a direct feedback mechanism.
A direct consequence of high levels of melanocyte-stimulating hormone is increased production of melanin. This can occur as a result of prolonged exposure to the sun or skin tanning. However, people with a high blood level of melanocyte-stimulating hormone do not necessarily tan very well or have even skin pigmentation. Very fair-skinned people tend to produce less melanin due to variations in their melanocyte-stimulating hormone receptors, which means they do not respond to melanocyte-stimulating hormone levels in the blood.
Hyperpigmentation or abnormal darkening of the skin is found in patients with primary adrenal insufficiency (Addison's disease). In Addison's disease, the adrenal glands do not produce enough hormones (including cortisol). This leads to a positive feedback loop where the hypothalamus stimulates the pituitary gland to release more adrenocorticotropic hormone to try and stimulate the adrenal glands to produce more cortisol. Adrenocorticotropic hormone can be broken down to produce melanocyte-stimulating hormone, leading to hyperpigmentation of the skin.
Melanocyte-stimulating hormone levels are also raised during pregnancy and in women using birth control pills, which can cause hyperpigmentation of the skin. Cushing's syndrome, due to an excess production of adrenocorticotropic hormone, can also lead to hyperpigmentation.
A deficiency in melanocyte-stimulating hormone results in a lack of skin pigmentation and subsequent loss of natural protection from UV rays of the sun. In secondary adrenal insufficiency, damage to the pituitary gland prevents release of adrenocorticotropic hormone and melanocyte-stimulating hormone and there is reduced pigmentation of the skin. Melanocyte-stimulating hormone deficiency can cause increased inflammation, pain, and sleeping problems, as well as a reduction in the levels of anti-diuretic hormone, which causes thirst and frequent urination. Melanocyte-stimulating hormone deficiency may also result in increased food intake and obesity.
Last reviewed: Mar 2015