A teleost skin bioassay for melanotropic peptides

A teleost (the eel, Synbranchus marmoratus) skin bioassay for melanotropic peptides and other agonists is described. Unlike previous teleost assays that generally monitor or observe individual melanophores, this objective assay utilizes large intact pieces of skin and quantitative photoreflectance methods. Since melanosomes within most teleost melanophores are generally dispersed, the present assay provides a method for measuring the response of integumental melanophores to melanosome-aggregating agents such as MCH, a putative melanin-concentrating hormone. This bioassay is sensitive to MCH at a concentration as low as 10(-12) M. Because of the magnitude of this lightening response, four-point dose-response curves can be obtained. Skins lightened by MCH can then be used for bioassay of melanotropins or other melanosome-dispersing agents, such as beta-adrenoceptor agonists. This bioassay is unique in providing a method for determining the biological activities of melanotropic peptides with opposing actions.