Ws. Baldwin et Ga. Leblanc, IN-VIVO BIOTRANSFORMATION OF TESTOSTERONE BY PHASE-I AND PHASE-II DETOXICATION ENZYMES AND THEIR MODULATION BY 20-HYDROXYECDYSONE IN DAPHNIA-MAGNA, Aquatic toxicology, 29(1-2), 1994, pp. 103-117
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.