Abstract:
It has been suggested that the productive success of amphibians might be depressed by increasing amounts of estrogenic chemicals released into the environment. In order to explore this possibility, thirty male plains leopard frogs were injected with 0.1 ug 17 B-estradioI/g body weight, 0.5 ug 17 B-estradioI/g body weight, Qr a control solution of corn oil twice weekly for a period of 6 weeks. These treatments simulated the effects of Iong-term, Iowlevel exposure to estrogenic chemicals on the reproductive physioIogy and endocrinology of the frogs. The yolk protein vitellogenin, used by Others as an indicator Qf estrogen influence, comprised nearly half of the plasma proteins in the estrogen-treated frogs and significantly increased the total plasma protein concentration in the 0.1 ug E2 group (P<0.05). Vitellogenin was completely absent in the centrals. Estrogen treatment dramatically depressed the plasma androgen levels, decreasing androgen levels by 53% in the 0.1 ug E2 group (P<0.001) and 73% in the 0.5 ug E2 group (P<0.001). The depressed androgen levels were probably
related to a significant decrease in testis weights (P<0.05) at the highest estrogen dose. Sperm motility and spermatogenesis were not different among groups. A significant decrease in liver weights and a 30% mortality rate of frogs in the 0.5 ~g E2 group suggested that continuous, low-level exposure to estrogen might be harmful to the frogs. This study showed that vitellogenin synthesis stimulated by continuous, low levels of estrogen could be linked to depressed androgen levels and other possibly detrimental effects on the reproductive system of the plains leopard frog.
