| The effect of salinity on aldicarb toxicity was examined in Japanese medaka. Following a 2-week exposure period to 1.5, 12.0, and 20.0‰ salinity, the toxicity of aldicarb was significantly enhanced to both sexually mature male and female medaka. Furthermore, females seemed to be more sensitive to such enhanced toxicity especially at the highest salinity level. The study showed that the mechanism by which salinity enhances aldicarb toxicity in medaka is mediated through the upregulation of flavin monooxygenases (FMOs) which bioactivate aldicarb to the more potent AChE inhibitor, aldicarb sulfoxide. In addition, salinity seems to potentiate the anti-cholinesterase activity of aldicarb through an unknown mechanism. Pretreatment of medaka with 17beta-estradiol (E2) and testosterone (T) showed that both hormones significantly reduced the toxicity of aldicarb in male medaka. In females, estradiol caused a significant increase in mortality while testosterone significantly reduced toxicity. Mortality in each gender directly correlated with the effect of the sex hormones on gill FMO activity. In addition, both hormones counteracted the inhibitory effect of aldicarb on AChE.;The regulation of FMOs by the two osmoregulatory hormones, cortisol (F) and growth hormone (GH) was examined in rainbow trout (Oncorhunchus mykiss). At 500 ng/ml hormone blood levels, F caused a significant increase in FMO activity in gills, kidney and RBC microsomes. FMO activity significantly increased in response to F in gills, kidney, and RBC, respectively. GH treatment failed to significantly alter FMO activity or expression in rainbow trout.;The molecular mechanisms underlaying the modulation of FMO expression and activity in euryhaline fish by steroid hormones and other environmental factors, such as salinity are unknown. In order to examine whether FMO expression is controlled by specific upstream regulatory elements, which may be activated by steroids or other trans activating molecules, it was essential to clone a gene encoding FMO from a euryhaline fish. Using reverse transcription polymerase chain reaction (RT-PCR) technique, an 842 by product was obtained, cloned, and sequenced from rainbow trout liver. The deduced amino acid sequence was 96% identical to rabbit hepatic FMO1, 85% identical to pig FMO1, and only 53% identical to the human FMO3 sequence. |
