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EFFECTS OF CADMIUM ON THE HYPOTHALAMUS-PITUITARY-GONADAL AXIS IN JAPANESE MEDAKA (ORYZIAS LATIPES): CONSEQUENCES FOR REPRODUCTION AND DEVELOPMENT
Citation:
Thompson, S. C., C M. Foran, AND W H. Benson. EFFECTS OF CADMIUM ON THE HYPOTHALAMUS-PITUITARY-GONADAL AXIS IN JAPANESE MEDAKA (ORYZIAS LATIPES): CONSEQUENCES FOR REPRODUCTION AND DEVELOPMENT. Presented at 21st Annual Meeting of the Society of Environmental Toxicology and Chemistry, Nashville, TN, 12-16 November 2000.
Description:
Cadmium (Cd) is an important inorganic pollutant that exists from both natural and anthropogenic emission. Concentrations measured in the aquatic environment vary considerably from 0.05 to 1,000 ppb depending on contamination, but even range in drinking water from 1 to 10 ppb. Cd has been previously found to bioaccumulate in reproductive organs of fish and also to disrupt important endocrine processes, especially those involved in the synthesis, release and metabolism of hormones. Clearly, there is potential for reproductive effects in fish populations exposed to Cd, however few studies have investigated the non-lethal consequences of Cd in fish. To this extent, male and female Japanese medaka were exposed to 0, 1, 5 and 10 ppb Cd for 7 weeks. Reproductive endpoints were monitored during weeks 6 and 7 of exposrue and compared to physiological responses along the hypothalamus-pituitary-gonadal (HPG) axis, including plasma vitellogenin (VTG), hepatic estrogen receptor (ER), plasma steroids, gonadal-somatic indices (GSI), gonadal steroidogenesis and pituitary function. Fecundity and spawning frequency were initially elevated in exposed organisms during week 6, but significantly decreased during week 7 at 10 ppb Cd. Cd did not have an effect on egg fertilization, embryo development or offspring sex ratios. While there were also no observed effects on the hepatic biomarkers, VTG and ER, all other physiological responses were significantly altered at concentrations lower than 10 ppb Cd and might be explained by Cd's mode of action. Overall, however, the HPG axis was more sensitive to Cd exposure than the reproductive and developmental endpoints indicating that higher level impairment in fish might be relatively protected.
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