Characterization of immunoreactive alpha-melanocyte stimulating hormone (alpha-MSHi) in human brain tissue

Adult human hypothalamic tissue was analyzed for the presence of products generated by post-cleavage processing of ACTH 1-13. The displacement curve generated by immunoreactive alpha-melanocyte stimulating hormone (alpha-MSHi) in extracts (5 M acetic acid or acidified ethanol) of adult human hypothalamic tissue was parallel to the alpha-MSH radioimmunoassay standard curve, and alpha-MSHi eluted as a single peak on Sephadex G-10, G-25, and G-50 columns in a manner identical to that of synthetic alpha-MSH. The alpha-MSHi was clearly distinguishable in its mobility on Sephadex G-50 columns from such peptides as beta-MSH, luteinizing hormone releasing hormone, and ACTH. After high performance liquid chromatography of extracts of hypothalamic tissue from young as well as aged men and women, we found that the major peak of alpha-MSHi (75-95% of total alpha-MSHi) coeluted with desacetyl alpha-MSH (ACTH 1-13 amide) rather than alpha-MSH. We suggest that desacetyl alpha-MSH, rather than alpha-MSH, is the predominant alpha-MSHi in adult human brain tissue.