IN-VIVO BIOTRANSFORMATION OF TESTOSTERONE BY PHASE-I AND PHASE-II DETOXICATION ENZYMES AND THEIR MODULATION BY 20-HYDROXYECDYSONE IN DAPHNIA-MAGNA

Phase I and phase II chemical detoxication processes were elucidated i n Daphnia magna using in vivo techniques and [C-14]testosterone as a s ubstrate. Testosterone was used because this compound undergoes multip le biotransformations and its metabolites are well characterized in ot her species. In addition, regulation of these processes by the endogen ous steroid hormone, 20-hydroxyecdysone, was investigated. Daphnids pr oduced at least ten polar phase I metabolites and four nonpolar phase I metabolites of testosterone. Six of the ten polar metabolites have b een identified as monohydroxy-products of testosterone. The polar meta bolites were preferentially excreted while the nonpolar metabolites we re preferentially retained by the daphnids. In addition, testosterone and all phase I metabolites were also excreted as glucose conjugates. A polar metabolite designated 'C' was preferentially conjugated with g lucose over the other metabolites. Testosterone and its polar phase I metabolites were also excreted as sulfate conjugates with 2alpha-hydro xytestosterone being the predominant sulfate-conjugated metabolite. In contrast to glucose conjugation, no nonpolar phase I metabolites of t estosterone were sulfate conjugated. Twenty-four hour pre-exposure of daphnids to 4.2 muM 20-hydroxyecdysone did not affect phase I metaboli sm of testosterone, but differentially modulated phase 11 conjugation in a manner suggesting the presence of at least two glucosyltransferas es and two sulfotransferases. Treatment with 20-hydroxyecdysone signif icantly increased the elimination of sulfate conjugates due largely to increased sulfate conjugation of unmetabolized testosterone. These re sults demonstrate that daphnids can convert polycyclic compounds to mu ltiple polar and nonpolar metabolites resulting from both phase I and phase II biotransformations, and that some phase II activities are und er the regulatory control of 20-hydroxyecdysone.