REGULATION OF BRIGHT-COLORED PIGMENTATION OF AMPHIBIANS

Bright integumental pigmentation of amphibians is imparted by the action of reflecting pigment cells (iridophores), yellow pigment cells (xanthophores), or red pigment cells (erythrophores). Iridophores are sensitive to intermedin and respond by concentrating their pigment. Common features of the intermedin molcule are involved in the stimulation of both iridophores and melanophores. The purines, guanine, hypoxanthine, and adenine are the primary iridophore pigments and are found in discrete organelles, the reflecting platelets. Intermedin markedly affects the form of reflecting platelets as well as the amounts of purine they contain. Xanthophores and erythrophores contain pteridine and carotenoid pigments. Pteridines are found within an organelle, the pterinosome, a spheroid approximately 500 mμ in diameter, formed by a series of concentric lamellae. Carotenoids appear to be contained in droplets interspersed between the pterinosomes. Migration of pigment within xanthophores is not generally controlled by intermedin although such may be the case in adult Hyla arenicolor. The carotenoid content of skin is higher in normal larvae than in hypophysioprivic larvae. Pteridine content of xanthophores is much higher in normal larvae than in hypophysioprivic larvae. Pteridine content of xanthophores is much higher in normal larvae than in hypophysioprivic animals. In the latter, administration of intermedin elevates pteridine levels. Profound changes in pteridine content occur at metamorphosis under the direct control of thyroxine. Adult amphibians which can change their colors rapidly, do so by means of a group of dermal chromatophores constituting the dermal chromatophore unit". Cytological and endocrinological relationships of the unit are discussed in terms of color change mechanisms. © 1969."