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The effect of DDT upon the metabolism of estradiol in coho salmon (Oncorhynchus kisutch) Harvey, Brian John


In the first experiment, sexually immature male and female coho salmon were exposed for 21 days to dietary DDT at a level of 10 or 100 parts per million (ppm), or to methoxychlor at a level of 100 ppm. Exposure to 100 ppm DDT was found to increase the level of liver microsomal Cytochrome P-450 from a control level of 1.32 ± .04 nmoles/1000 mg liver to a level of 1.98 ± .04 nmoles/1000 mg liver, a statistically significant difference (P<.001). None of the treatments were found to affect the hepato-somatic index. In the second experiment, liver slices from sexually maturing male and female coho salmon fed 100 ppm DDT for 21 days or a control diet were incubated with 4-C¹⁴-estradiol-17β in vitro. Metabolites produced were extracted with dichloromethane, separated by thin-layer chromatography and assayed using scintillation counting techniques. Produced in the incubation were estrone, estriol and one other unidentified polar metabolite. DDT treatment was found to significantly increase the amount of estriol and unidentified metabolite produced (P< .001). In the third experiment, sexually maturing male and female coho salmon fed 100 ppm DDT for 21 days or for 7 days or a control diet were injected with 625,500 dpm 4-C¹⁴-estradiol-17β and permitted to metabolize the hormone in vivo. Serial blood samples were extracted, chromatographed and subjected to scintillation counting techniques to obtain values for Metabolic Clearance Rate, Half-life Time and Volumes of Distribution of the injected steroid. It was found that ingestion of DDT had no significant effect upon any of these parameters (P<.001). The pattern of metabolites produced in vivo closely resembled that produced in vitro. The evidence presented in this study suggests that enhancement of the activity of the Mixed Function Oxidase system in coho salmon may occur upon ingestion of an organochlorine insecticide, but that the phenomenon may have little significance in vivo.

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