TERATOGENICITY OF NI2+ IN XENOPUS-LAEVIS, ASSAYED BY THE FETAX PROCEDURE

The teratogenicity of Ni2+ was tested by the FETAX (Frog Embryo Teratogenesis Assay: Xenopus) procedure in the South African frog, Xenopus laevis. In seven assays, beginning at 5 h postfertilization, groups of Xenopus embryos were incubated for 96 h in media that contained Ni2+ (added as NiCl2) at concentrations ranging from 1 X 10(-7) to 3 x 10(-3) mol/L; control groups were incubated in the same medium without added NiCl2. At 101 h postfertilization, surviving embryos were counted, fixed in formalin, and examined by microscopy to determine their developmental stages, malformations, and head-to-tail lengths. In control embryos, survival was greater-than-or-equal-to 95% and malformations were less-than-or-equal-to 7%. Malformations were found in > 95% of embryos exposed to Ni2+ concentrations greater-than-or-equal-to 5.6-mu-mol/L. The most frequent malformations in Ni2+-exposed embryos were ocular, skeletal, and intestinal deformities; less common malformations included facial, cardiac, and integumentary deformities. Other abnormalities, not categorized as malformations, included stunted growth, dermal hypopigmentation, and coelomic effusions or hemorrhages. The median embryolethal concentration (LC50) of Ni2+ was 365 (SE +/- 9) mu-mol/L; the median teratogenic concentration (EC50) was 2.5 (SE +/- 0.l) mu-mol/L; the Teratogenic Index (TI = LC50/EC50) was 147 (SE +/- 5), indicating that Ni2+ is a potent teratogen for Xenopus laevis. Experiments in which Ni2+-exposures were limited to specific 24 h periods showed that Xenopus embryos were most susceptible to Ni2+-induced malformations on the second and third days of life, during the most active period of organogenesis.