The responses of melanophores in isolated scales of Oryzias latipes to five sympathomimetic amines with an OH group on the phenyl ring, including octopamine, sympatol, phenylephrine, tyramine and hordenine,were quantitatively investigated under a microscope. All of the compounds, except hordenine, strongly induced concentration of the pigment within innervated melanophores. Relative activities for causing pigment concentration were found to be closely similar to each other between octopamine and tyramine and between sympatol and phenylephrine. In these two groups, the former was slightly strong in the concentrating activity. The concentrating action of hordenine on innervated melanophores was extremely weak, and increase in concentration of the drug caused no marked increase in the response. In its high concentrations, the pigment showed a redispersion after a transitory concentration.
Chronically denervated melanophores were less sensitive to all amines tested as conrpared with innervated ones. The reduction in the sensibility after denervation was small in octopainine, sympatol and phenylephrine, but very large in tyramine. From these results the following conclusions were made.
1) These amines have both direct and indirect actions on the melanophore concentrating system. 2) For sensitized response of denervated melanophores, the phenolic hydroxyl groups on the phenyl ring are of greater importance than are presence of the alcoholic hydroxyl group on the beta carbon atom of the side chain, the presence or absence of the latter being of less significant than are assumed hitherto in smooth muscles. 3) The concentrating activity of an amine is made to reduce by N-dimethylation of the terminal amino group.