Progestin exposure impacts oocyte development in adult Xenopus tropicalis frogs
Anna Norder
Number of amphibian species is declining worldwide, a decline that partly might be linked to the high concentration of endocrine disrupting chemicals in the environment.
Amphibians are highly susceptible to waterborne compounds due to their aquatic life history and permeable skin. Levonorgestrel (LNG) is a synthetic progestin that is mainly used in contraceptive pills. It has been found in the environment at ng/L levels. Progestins have been shown to reduce reproduction in adult fathead minnow and Japanese medaka (Oryzias latipes) at environmental concentrations. In frogs LNG causes infertility after developmental exposure. The present study investigates effects on the reproductive system after LNG exposure in adult female frogs, a previously unstudied area. This study will contribute to the development of methods to study reproductive toxicity in adult female frogs. Three experiments were carried out with sexually mature female Xenopus tropicalis exposed for seven days to the LNG concentrations of 0, 0.01, 0.1, or 1 nM (n=2-4/exposure group). The ovaries were analyzed histologically and the oocytes were scored as immature (early meiotic prophase; leptotene until early diplotene), previtellogenic (stage I-II), or late stage mature oocytes (stage III-VI). In experiment two there was a higher proportion of immature oocytes as well as previtellogenic oocytes in the females exposed to 1 nM LNG compared with the controls. This indicates that LNG caused an inhibition of oogenesis in adult Xenopus tropicalis. This could subsequently lead to sterility if the oocytes never reach maturation. These results show that oogenesis is a sensitive endpoint of progestin exposure in frogs.
Degree project in biology, Master of science (2 years), 2011 Examensarbete i biologi 30 hp till masterexamen, 2011
Biology Education Centre and Institutionen för organismbiologi, Uppsala University Supervisors: Cecilia Berg and Moa Säfholm
