Seasonal rhythm of the plasma level of alpha-melanocyte stimulating hormone.

The present results indicate the presence of a seasonal rhythm of immunoreactive alpha-melanocyte stimulating hormone (alpha-MSH) in 20- to 40-year-old subjects of skin type I (light color of skin and eyes, red hair, no tanning after sun exposure) and skin type II (light color of skin, eyes, and hair, rare tanning) with raised levels of alpha-MSH in summer and low levels in winter. With increasing age of the investigated subjects, the seasonal rhythm seems to be lost. In subjects with skin type III (light skin, brown eyes and black hair, strong pigmentation after sun exposure) alpha-MSH shows only insignificant variations over the whole year. A seasonal rhythm of ACTH could not be demonstrated. A diurnal rhythm could be seen for ACTH, but not for alpha-MSH. To summarize, one can suppose that the seasonal rhythm of alpha-MSH is controlled by a varying UV exposure of the integument which is different over the whole year.