The teleost melanin-concentrating hormone—A pituitary hormone of hypothalamic origin

Abstract

A simple bioassay method for the teleost melanin-concentrating hormone (MCH) is described. Using this assay and also the Anolis bioassay for melanocyte-stimulating hormone (MSH) the work compares the relative concentrations of MSH and MCH in the pituitary of various teleost species and their pattern of distribution after polyacrylamide gel electrophoresis. Neurointermediate lobes from trout were cultured and various factors [cold, cycloheximide, ethyleneglycol bis(β-aminoethyl ether) N,N′-tetraacetic acid) (EGTA), and high K ion concentration] were examined for their effect on MSH and MCH secretion. EGTA and high K + both inhibited MSH release; cold and cycloheximide appeared to reduce MSH synthesis. Whereas these effects on MSH were predictable and consistent, the response of MCH was erratic and unpredictable. In contrast to MSH, there was no evidence for MCH synthesis in vitro. The hypothalamus of the trout contains as much MCH as the pituitary, and the concentration of MCH in the hypothalamus varies with the background colour on which the fish is kept. The evidence as a whole suggests that MCH is an hypothalamic secretion which is stored and released by the neurohypophysis.