Acetylation of melanocyte-stimulating hormone and beta-endorphin in the pars intermedia of the perinatal pituitary gland in the mouse.

This report concerns ontogenetic aspects of the production and in vitro release of NH2-terminally acetylated forms of melanocyte-stimulating hormone (alpha-MSH) and beta-endorphin by the pars intermedia of the pituitary gland of the mouse. In vitro biosynthetic analysis and radioimmunoassay revealed that approximately 12 h before birth most of the MSH in the fetal pars intermedia is present as des-N alpha-acetyl alpha-MSH. The same non-acetylated peptide is at this stage also the major release form of melanotropin. In 1-day-old mice the level of alpha-MSH and diacetylated alpha-MSH had increased considerably, although des-N alpha-acetyl alpha-MSH remained the major form. Five days after birth alpha-MSH and its diacetylated form constitute the major tissue and release form of the peptide, a situation very similar to that in adult mice. Acetylation of beta-endorphin appeared to occur earlier in development, N alpha-acetyl beta-endorphin (1-31) being the major form of endorphin already in the fetal pars intermedia. It is concluded that in the mouse acetylation of melanotropin and acetylation of beta-endorphin are not necessarily concomitant events. It could be established that the ability of the pars intermedia cells for cleaving N alpha-acetyl beta-endorphin (1-31) to yield C-terminally shortened forms of beta-endorphin develops after birth.