Immunocytochemical Evidence for the Presence of γ1-MSH-Like Immunoreactivity in Pituitary Corticotrophs and ACTH-Producing Tumours

Abstract

The presence of γi-MSH has been demonstrated in bovine neuro-intermediate lobe by biochemical methods, thus suggesting that this peptide is cleaved from the cryptic region of pro-opiocortin. In this study we report the localisation of γi-MSH-like immunoreactivity in the adenohypophysis of man, ox, pig, dog and guinea-pig using immunocytochemical procedures at both light and electron microscope levels. Antisera recognising the C-terminal Arg-Pheamide and the C-terminal penta-peptide-amide of γi-MSH have been used throughout this study. The immunostaining was found in all endocrine cells of the pars intermedia (where present) and in scattered cells of the pars distalis identified as corticotrophs. No γi-MSH immunoreactivity was detected in rat adenohypophysis. In addition, 7 ACTH-producing tumours (1 pituitary adenoma and 6 ectopic) were investigated and shown to contain γi-MSH immunoreactive cells.