Evaluation of the toxicity of eugenol at anesthetic doses in African clawed frogs (Xenopus laevis).

Eugenol has been shown to induce anesthesia in African clawed frogs (Xenopus laevis). The toxicity of eugenol, administered at anesthetic doses, was evaluated in Xenopus frogs with an average body weight of 28.2 ± 13.7 g. Frogs were immersed in 250 mL of an aqueous solution containing 350 µl/L of eugenol for ten minutes and received a single administration (group 1, twelve animals) or three consecutive daily administrations (group 2, twelve animals). In each group, six frogs were scheduled to be euthanized the following day (subgroup A) and the other six were scheduled to be euthanized after a one-week recovery period (subgroup B). Morphologic changes consistent with renal tubular apoptosis affecting distal tubules in the medulla were observed in all subgroup A animals, ranging from mild to moderate in group 1, and from mild to severe in group 2. In subgroup B, renal tubular regeneration was present in all but one animal examined. These findings suggest that eugenol toxicity in amphibians is first manifested by renal tubular apoptosis. Other eugenol-related lesions were massive hepatic necrosis in group 2 (n = 6), hyaline membranes in the lung (n = 5), and adipose tissue hemorrhages in group/subgroup 2B (n = 4).