Impact of cadmium on liver pigmentary system of the frog Rana ridibunda.

The liver pigmentary system of the frog Rana ridibunda was investigated after exposure to CdCl2. There was a time-dependent alteration in the area occupied by pigment cells. Most pigment was melanin, but lipofuscin and ferritin were also detected, being similarly increased with time. There was a time-dependent increase in the dimensions of pigment cells as a result of forming a cluster of more than two pigment cells, the so-called melanomacrophage aggregates (MMC). A thin capsule of connective tissue with fibroblast-like cells surrounds some MMCs. The various possible roles of MMCs are discussed, for instance, those of scavengers of foreign substances, for lowering of metabolic activities to survive in an anoxic environment probably caused by cadmium, or as scavenger of cadmium, thus playing a protective role against this metal.