Development of short-term, whole-embryo assays to evaluate detrimental effects on amphibian limb development and metamorphosis using Xenopus laevis

Short-term static-renewal studies were performed on Xenopus embryos from day 5 (Stage 46) to day 26 (Stage 54) [21-d test] with copper and acetyl hydrazide to evaluate effects on limb development. Studies with pentachlorophenol, nonylphenol, methimazole (anti-triiodothyronine [T-3]), and tamoxifen (anti-estradiol) were also performed from day 50 (Stage 60) to day 64 (Stage 66) [14-d test] to evaluate effects on tail resorption. Both copper and acetyl hydrazide caused abnormal development of the hind limbs at concentrations of greater than or equal to 0.5 mg/L and greater than or equal to 25.0 mg/L, respectively. Malformation of the hind limbs were primarily characterized as reduction deficiencies, but acetyl hydrazide also caused flexure defects. Pentachlorophenol and methimazole decreased the rate of tail resorption significantly in metamorphs, whereas nonylphenol increased the rate of tail resorption. Tamoxifen had no effect on the rate of tail resorption. These results suggested that alteration in the rate of tail resorption during metamorphosis in Xenopus is at least partially under the control of T-3 and/or T-3-like hormones. The stimulatory effects observed with nonylphenol did not appear to be associated with estrogenic activity since tamoxifen did not alter the rate of tail resorption.