An investigation of the melanophore-aggregating principle of the pituitary of some teleost fishes

Abstract

A brief summary of previous literature on vertebrate chromatic responses is presented. The influence of pituitary preparations on the responses of the melanophores of teleosts and of other chromatic vertebrates is examined and a new classification of teleost melanophore responses proposed.The time relations of melanophore and erythrophore response in Phoxinus and melanophore responses in Ameiurus and Rana to injections of teleost pituitary material have been examined.A method of assay, using Phoxinus as test animal, for the melanophore-aggregating hormone is proposed.The distribution of minnow melanophore-aggregating and erythrophore-dispersing, and frog melanophore-dispersing activity in the minnow pituitary closely mirrors the distribution of the meta-adenohypophyseal cells.Experiments with peptic and tryptic digestion suggest that these factors are polypeptide in nature.The influence of alkaline extraction on these factors has been examined and it is suggested that the results can be interpreted in terms of a single polypeptide hormone.All three factors are substantially soluble in alcohol.Electrophoretic analysis of teleost pituitary material failed to separate the minnow melanophore-aggregating activity from the minnow erythrophore-dispersing and frog melanophore-dispersing factors. Similar results were obtained with paper and column chromatography.The responses of hypophysectomised spinal-sectioned Phoxinus are, qualitatively, the same as those of spinal-sectioned fish with intact pituitarios.The erythrophore response of Phoxinus is stronger in black-adapted than in white-adapted fish.The fbihumoral hypothesis' of Hogben and Slome (1931,1936) has been critically examined. The time relations of colour change provide no evidence in favour of a two-hormone control.It is concluded that the evidence in favour of a bihumoral control of teleost melanophores is insufficient to deny the possibility that these responses are in fact under the control of a single, polypeptide, hormone.