Abstract: OBJECTIVE: To assess the potential developmental toxicity of lanthanum nitrate at the middle and advanced stage of gestation in post-implantation whole embryo culture and micromass test. METHODS: Rat embryos were randomly divided into 5 groups and cultured in immediately centrifuged serum,and were exposed to different doses of lanthanum nitrate (0,0.12,0.23,0.46 and 1 mmol/L). After 48 hours culture,yolk sac diameter (YSD),crown-rump length (CRL) and head length (HL) were measured, somites were counted, and the total morphological score (TMS) was calculated according to the Brown's Method to evaluated growth and functional development of embryos. Cytotoxicity in BALB/c 3T3 cells was tested by MTT. Toxicity of lanthanum nitrate in the early embryonic stage was evaluated using the prediction models of ECVAM. In addition,limb bud cells of embryos were isolated from matured SD rats and cultured in micro-mass culture for 5 days. These cultures were exposed to 0.03, 0.06, 0.13, 0.25, 0.5, 1, 2 and 3 mmol/L lanthanum nitrate. The 50% inhibition of cell viability and growth (IC₅₀) of limb bud cells was determined by neutral red staining, and the 50% inhibition of cells differentiation (ID₅₀) was measured by alcian blue staining. Toxicity of lanthanum nitrate in the middle and advanced stages of embryos was evaluated with the prediction model of ECVAM. RESULTS: The no observed adverse effect level (NOAEL) of lanthanum nitrate on embryo growth was 0.12 mmol/L. At the concentration of 0.46 mmol/L,lanthanum nitrate decreased the YSD,CRL and HL of embryos (P < 0.05),which showed that lanthanum nitrate significantly retarded growth of embryos. Besides, 0.46 mmol/L lanthanum nitrate induced developmental malformations and reduced the number of somites (P < 0.05). The NOAEL of lanthanum nitrate on the proliferation of limb bud was 1 mmol/L, the NOAEL on chondrocyte differentiation from limb bud cells was 0.25 mmol/L,the IC₅₀ and ID₅₀ for limb bud cells were 1.57 mmol/L (510.25 μg/mL) and 0.99 mmol/L (321.75 μg/mL),respectively. CONCLUSION: Lanthanum nitrate was evaluated as a weak embryotoxic chemical by whole embryo culture and as a nonembryotoxic chemical by micromass test.

Key words: lanthanum nitrate, whole embryo culture, micromass test, developmental toxicity