The distribution of some proopiomelanocortin-related peptides in the pituitary gland of the rainbow trout, Salmo gairdneri.

Acid extracts of neurointermediate lobe (NIL) and pars distalis (PD) of the pituitary gland of the rainbow trout were radioimmunoassayed for alpha-melanocyte-stimulating hormone (alpha-MSH), beta-melanocyte-stimulating hormone (beta-MSH), adrenocorticotrophin (ACTH), and endorphin. The majority of the alpha-MSH, beta-MSH, and endorphin was present in the NIL; the small amount of these peptides present in the PD may be native to this lobe, or may be due to slight contamination with NIL material--it is not possible to distinguish between these possibilities at present. All the ACTH was present in the PD. These results support the hypothesis that throughout the vertebrates proopiomelanocortin is cleaved to smaller peptides in the NIL than it is in the PD.