Increased Kidney, Liver, and Testicular Cell Death After Chronic Exposure to 17alpha-ethinylestradiol in Medaka (Oryzias Latipes)

Sublethal effects observed in fish exposed to environmental estrogens may be mediated via stimulation of cell death. To investigate whether cell death is induced in fish after chronic exposure to estrogenic chemicals, Japanese medaka (Oryzias latipes) were exposed from hatch until sexual maturity to 10 ng/L 17alpha-ethinylestradiol (EE2) or acetone solvent (control). Cell death was evaluated in blinded histological sections of whole medaka using terminal dideoxynucleotidyl-mediated dUTP nick end-labeling (TUNEL), which labels nuclei of cells containing apoptotic or necrotic (fragmented) DNA. The major impact of EE2 exposure in both male and female medaka was to significantly increase the number of TUNEL-positive hepatocytes and kidney tubule cells compared to control. Cell morphology was consistent with apoptosis in the liver and cloudy swelling or necrosis in the tubule cells. The number of TUNEL-positive interstitial (hematopoietic) and glomerular cells was significantly greater in the kidneys of EE2-exposed male, but not female, medaka. The EE2 exposure also significantly increased the number of TUNEL-positive testicular cells in medaka compared to corresponding controls, namely Leydig cells, Sertoli cells, spermatocytes, and spermatids. In medaka with gonadal intersex, areas of fibrosis and areas containing female gonadal cells were relatively unstained with TUNEL. No effect of EE2 exposure on the number of TUNEL-positive ovarian somatic cells or on the rate of female ovarian follicle atresia was found. These results suggest that chronic exposure to EE2 in medaka is hepatotoxic and nephrotoxic in both sexes, whereas gonadal toxicity is specific to males.