Lipopolysaccharides induce changes in the visceral pigmentation of Eupemphix nattereri (Anura: Leiuperidae).

Amphibians have an extracutaneous pigmentary system composed of melanin-containing cells in various tissues and organs. The functional role of these pigment cells in visceral organs has not yet been determined, although several hypotheses have been proposed. Our aim was to describe the visceral pigmentation in the frog Eupemphix nattereri under conditions of endotoxemia induced experimentally with lipopolysaccharides (LPS) from Escherichia coli and to analyze the pigmentation on the organs' surface. We used 60 adult males of E. nattereri and analyzed the visceral pigmentation 2 (LPS 2h), 6 (LPS 6h), 12 (LPS 12h), 24 (LPS 24h) or 48 h (LPS 48 h) after the LPS inoculation. We observed pigmentation on the surface of several abdominal organs. The highest degree of pigmentation was found only on the testes of the animals in the LPS 2h, LPS 6h and LPS 12h groups. The pigmentation decreased in the animals of the LPS 24h and LPS 48 h groups. The LPS administration produced no changes in the pigmentation of the cardio-respiratory and digestive systems. Thus, the cells appear to have responded to LPS intoxication, producing a rapid increase of pigmentation on the surface of the testes and a subsequent decrease in the pigmentation. These changes are most likely related to the bactericidal role of melanin, which neutralizes the effects of LPS.