HU, F.; GENTLES, A.; GOLEMAN, W.L.; CARR, J.A.; Texas Tech Univ.; Texas Tech Unvi.; Texas Tech Univ.; Texas Tech Univ.: The Thyroid Disrupting Effects of Ammonium Perchlorate Depend upon Environmental Iodide and Developmental Stage in Larval Xenopus Laevis

Ammonium perchlorate, a military and aerospace industry waste product, disrupts thyroid function and retards metamorphosis in laboratory raised African frogs (Xenopus laevis). In natural frog populations, factors such as the timing of exposure as well as the amount of iodide available in the environment are likely to affect the antimetamorphic effects of perchlorate. In the present study, we investigated the influence of developmental stage and environmental iodide on metamorphosis and thyroid function in the South African clawed frog, Xenopus laevis. In the first experiment, larvae were exposed to 14 mg/L ammonium perchlorate (AP) beginning at Nieuwkoop-Faber-stages 1-10 (< 24 h after fertilization), NF-stage 49 or NF-stage 55 until day 68 post-hatch. Metamorphosis and hind-limb growth were inhibited by perchlorate when exposures began at NF-stage 1-10 and NF-stage 49, but not when exposure began at NF-stage 55. AP exposure produced significant follicle cell hypertrophy and colloid depletion in tadpoles exposed at stage1-10 or 49, but not in tadpoles exposed at stage 55. In the second experiment, X. laevis at NF-stage 1-10 were exposed to AP (14 mg/L) in the presence or absence of sodium iodide (14 mg/L) for 68 d post-hatch. Simultaneous exposure to iodide completely reversed the antimetamorphic and thyroid effects of perchlorate exposure. We conclude that the sensitivity of X. laevis to the antimetamorphic effects of perchlorate is influenced by the stage of exposure and the amount of iodide available to the tadpole. (Supported in part by the U.S. Department of Defense, through SERDP under a Cooperative Agreement with the USAF, Inst. for Environ, Safety, and Occup. Health, Brooks AFB, TX).