Abstracts of Work not Formally Presented

The response of the iris of amphibians to alpha melanocyte stimulating hormone (MSH), caffeine, melatonin, and phenylephrine was studied. Three species of animals were used: Rana pipiens, Rana catesbeiana, and Bufo marinus. In in vivo studies, the iris was observed and photographed through a Zeiss operating microscope at 25x magnification. The appearance of the pigment patterns of each iris was examined following the subcutaneous injection of various drugs and changes were quantitated by measuring the light transmission through selected regions of the photographic transparency of the iris. In in vitro studies reflectance curves were obtained directly from the enucleated eyes. All specimens were subsequently studied histopathologically. In eyes studied in vitro no effect was obtained with concentrations of MSH of 2 ug/ml but occurred with concentrations of 20 ,ug/ml or more. The effect of MSH and caffeine was similar in all the eyes tested, both in vivo and in vitro. The general coloration of the iris darkened, the peripheral iris pigmentation migrated in toward the central iris, and the iris markings increased in length and width. Melatonin and phenylephrine reversed the effects of MSH and caffeine. The iris of the frog consists of an anterior "mesothelial layer" of iridophores, a thin stroma containing blood vessels, connective tissue, and numerous dendritic melanocytes and posteriorly two layers of pigmented epithelial cells associated with pigmented sphincter and dilator muscles. Comparisons of control eyes and eyes treated with MSH and caffeine indicated that the darkening of the iris resulted from changes in the stromal melanocytes. Pseudopodlike processes containing dispersed melanin appeared between and above the surface layer of iridophores. Conversely, the lightening effect appeared due to an aggregation of the pigment granules and contraction of the stromal melanocytes. No change in the appearance of the iridophores or pigment epithelium was observed. Previous studies of the biochemical composition of lipofuscin have focused on its lipid composition. Some preliminary investigations in this laboratory and histochemical studies have suggested that lipofuscin may contain a melaninlike component in addition to lipid. In the present studies we have applied a technique for isolating melanin (similar to Nicolaus, R. A. et al., Tetrahedron 20, 1163, 1964) for the identification and quantification of the brown "age pigment" found in liver and heart tissue. Heart and liver tissues (5-15 g) obtained at autopsy from subjects ranging in age from 5 mo intrauterine to 90 yr were digested with concentrated hydrochloric acid at …