Down regulation of hepatic flavin-containing monooxygenase activity by 17 beta-estradiol in rainbow trout (Oncorhynchus mykiss).
Expression of flavin-containing monooxygenase (FMO) activity has been shown to be directly correlated with salinity in euryhaline fish. Sex steroids play a significant role in osmoregulation in euryhaline fish. The effects of 17 beta-estradiol and testosterone on hepatic FMO activity (N,N-dimethylaniline N-oxygenase; thiourea S-oxygenase) and expression was examined in 6-month-old and 1-year-old rainbow trout (Oncorhynchus mykiss). Fish were treated with 3 mg/kg of each compound on days 1, 4, 7, 10, 13, and 15 with euthanasia on day 19. Treatment of 6-month-old and 1-year-old female rainbow trout with testosterone or estradiol significantly reduced FMO-catalyzed DMA N-oxygenase activity in liver. However, testosterone treatment failed to significantly alter thiourea S-oxidase in 1-year-old males, although 17 beta-estradiol significantly reduced FMO activity. These results parallel those of studies showing repressive effects of sex steroids on branchial chloride cells and Na+K+ATPase of salmonids and provide further evidence of a role for FMO in teleost osmoregulation.
Schlenk
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D
Department of Pharmacology and Environmental Toxicology Program, School of Pharmacy, University of Mississippi, University 38677, USA. dschlenk@olemiss.edu
El-Alfy
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A
Buhler
D R
DR
D000818:Animals; D015536:Down-Regulation; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D017686:Oncorhynchus mykiss / Q000254:growth & development; D010105:Oxygenases / Q000096:biosynthesis*; D013739:Testosterone / Q000494:pharmacology
D013739:Testosterone; D004958:Estradiol; D010105:Oxygenases; C020066:dimethylaniline monooxygenase (N-oxide forming)