Characterization of α-MSH-related peptides released from rat hypothalamic neurons in vitro

Abstract

Reverse-phase high-performance liquid chromatography analysis, coupled with a sensitive radioimmunoassay for α-melanocyte-stimulating hormone (α-MSH), was used to characterize the α-MSH-related peptides stored in the rat hypothalamus or released from perifused hypothalamic slices. Four peaks of α-MSH-like immunoreactivity (α-MSH-LI) co-eluting with synthetic des- Nα-acetyl α-MSH, α-MSH and their respective sulfoxide derivatives were resolved and quantified. In hypothalamic extract, deacetyl α-MSH which was the predominant peptide represented 94.4% of total α-MSH-LI content, while the relative amount of α-MSH was only 5.6%. Analysis of α-MSH-related peptides contained in effluent perifusates showed that deacetyl α-MSH and its oxidized form were the major peptides released from neurons in basal conditions or under KCl-induced depolarization (50 mM KCl for 75 min). However, the proportion of acetylated peptide was 3–4 times higher in the perifusion medium than in hypothalamic extracts. Our data indicate that acetylation of des- Nα-acetyl α-MSH may occur during the process of exocytosis. Since acetylation of α-MSH markedly increases the behavioural potency of the peptide, these results suggest that regulation of the acetyltransferase activity could be a key mechanism to modulate the bioactivity of α-MSH-related peptides in the brain.