Alpha-MSH and coat color changes in the mouse

The effect of alpha-MSH on coat color was examined in viable yellow mice (C3H/He-A*vy). These mice normally grow a coat of darkly pigmented hair at puberty. This darkening effect was also evident in hair that grew in a region that had been plucked at 13 days of age. Administration of alpha-MSH increased the darkness of this hair and the hair which grew naturally in an unplucked area. However, the natural coat darkening that occurred at puberty was not associated with an increase in plasma immunoreactive alpha-MSH levels. Moreover, although bromocryptine, a dopamine agonist that inhibits alpha-MSH release from the pituitary reduced the darkness of the coat that grew after plucking the reduction in coat darkening was unrelated to changes in plasma alpha-MSH. Nevertheless, this effect of bromocryptine was reversed when alpha-MSH was administered together with the drug. Apomorphine had no effect on coat darkening and produced only a slight decrease in plasma alpha-MSH. Melatonin reduced coat darkening slightly but, like apomorphine, had little effect on plasma alpha-MSH concentrations. Although alpha-MSH may have a physiological role in coat darkening in the C3H/He-A*vy mouse at puberty the response seems to be unrelated to an increase in circulating alpha-MSH. Thus, other factors, such as changes in melanocyte sensitivity to alpha-MSH or inhibitory mechanisms that prevent coat darkening during prepubertal and adult life may be involved in regulation of coat color in the viable yellow mouse.