Increase in liver pigmentation during natural hibernation in some amphibians

The amount/distribution of liver melanin in 3 amphibian species (Rana escul enta, Triturus a. apuanus, Triturus carnifex) was studied during 2 periods of the annual cycle (summer activity-winter hibernation) by light and elect ron microscopy, image analysis and microspectrofluorometry. The increase in liver pigmentation (melanin content) during winter appeared to be correlat ed with morphological and functional modifications in the hepatocytes, whic h at this period were characterised by a decrease in metabolic activity. Th ese findings were interpreted according to the functional role (e.g. phagoc ytosis, cytotoxic substance inactivation) played by the pigment cell compon ent in the general physiology of the heterothermic vertebrate liver and, in particular, in relation to a compensatory engagement of these cells agains t hepatocellular hypoactivity during the winter period.