FACTORS INFLUENCING TESTOSTERONE-METABOLISM BY ANURAN LARVAE

The effects of experimental conditions-steroid concentration, temperat ure, treatment duration, tadpole density, and delivery mode-on testost erone (T) metabolic rates were examined in larval anurans. T uptake in to tadpoles was measured by scintillation counting of [H-3]T and metab olism of T was studied by thin layer chromatography in two anuran spec ies, the African clawed frog (Xenopus laevis) and the western toad (Bu fo boreas). T was extensively metabolized by both species, but the eff ects of each experimental condition on T metabolism varied between spe cies. In the study of delivery mode, tadpoles injected with T dissolve d in saline metabolized T faster than animals in groups where the ster oid was added directly to the water. Animals injected with T dissolved in oil metabolized T the slowest, but T was short-lived in all cases. The current study demonstrates that concentration, temperature, treat ment duration, tadpole density, and delivery mode may all affect stero id metabolic rates, but these effects vary between species in unpredic table ways. Since steroid metabolism may either activate or deactivate steroids, these factors are important in understanding the potency of steroids in tadpoles. A review of the literature dealing with steroid effects in anuran larvae illustrates these problems. (C) 1995 Wiley-L iss, Inc.