Melanin-concentrating hormone gene-related peptide stimulates ACTH, but not alpha-MSH, release from the tilapia pituitary

Tilapia (Oreochromis mossambicus; teleostei) melanin-concentrating hormone gene-related peptide (tMgrp) was tested for tropic actions on adenocorticotropin hormone (ACTH) and alpha-melanocyte stimulating hormone (alpha-MSH) producing cells in the tilapia pituitary gland in vitro. Up to 100 mu M synthetic tilapia Mgrp (tMgrp) had no effect on alpha-MSH release from tilapia neurointermediate lobes in a superfusion set up. However, at concentrations above 1 mu M, tMgrp concentration dependently stimulated ACTH release from tilapia anterior lobes. This is the first evidence that Mgrp modulates ACTH release from teleost corticotropes, and this might implicate the peptide in the regulation of the pituitary-interrenal axis of fish.