No abstract

In animals, the coat-darkening effects of alpha-melanocyte stimulating hormone (alpha-MSH) are opposed by agouti protein. Although agouti protein has been shown to be a competitive antagonist of the melanocyte-associated MC-1 melanocortin receptor, the possibility that agouti protein can affect melanogenesis independently of its ability to antagonise melanocortin activity cannot be excluded. This study demonstrates that murine agouti protein causes both a time- and concentration-dependent suppression of melanogenesis in B16 F1 murine melanoma cells. In addition, human agouti protein decreases melanogenesis in cultured human epidermal melanocytes. However, agouti protein has little effect on the ability of alpha-MSH to stimulate melanogenesis. These observations raise fundamental questions about the mode of action of agouti protein in regulating melanogenesis.

No abstract

The long-term effect of hypothalamic lesions onplasma and pituitary levels of melanocyte-stimulating hormone (MSH) was examined in male rats. Lesions of the paraventricular nuclei (PVN) produced a large increase in both plasma and pituitary MSH levels, whereas lesions of the supra-optic nuclei had little effect. These results support the idea that MSH secretion is under an inhibitory control by the hypothalamus and suggest that the PVN are involved. The PVN may be involved in the release or production of an MSH release inhibiting factor (MIF), although the present results do not exclude the possibility that the PVN control MSH secretion through a direct innervation of the pars intermedia.

No abstract