Toxicity of cadmium, endosulfan, and atrazine in adrenal steroidogenic cells of two amphibian species, Xenopus laevis and Rana catesbeiana.

The effects of cadmium, endosulfan, and atrazine on corticosterone secretion and viability of adrenal cells of African clawed frog (Xenopus laevis) and bullfrog (Rana catesbeiana) were assessed in vitro using a new bioassay. The bioassay relies on stimulation with adrenocorticotropic hormone (ACTH), the endogenous secretagogue for corticosterone secretion, and with dibutyryl cyclic adenosine monophosphate (dbcAMP), an analogue of cAMP, to pinpoint the site of action of the xenobiotics within the steroidogenic cell. To compare the test toxicants according to their endocrine-disrupting potential, the lethal concentration needed to kill 50% of the cells:effective concentration of 50% (LC50:EC50) ratio was calculated, with LC50 as the concentration that kills 50% of the steroidogenic cells and the EC50 as the concentration that impairs corticosterone secretion by 50%. The higher the ratio, the higher the potential for endocrine disruption. Atrazine had no affect on cell viability and on corticosterone secretion in X. laevis, but its endocrine-disrupting potential was high in R. catesbeiana. The LC50:EC50 ratio for cadmium and endosulfan in X. laevis was 26.07 and 1.23, respectively, and for atrazine, cadmium, and endosulfan in R. catesbeiana it was 909, 41, and 3, respectively. The dbcAMP did not restore corticosterone secretion in the cells exposed to the test toxicants in both species. Our study suggests that the secretory capacity of adrenal cells of amphibians can be impaired by environmental chemicals, especially atrazine in the bullfrog, and that these adrenotoxicants disrupt the enzymatic pathways leading to corticosterone secretion downstream from the step-generating cAMP.