Ethinyl Estradiol

Heightened concern over endocrine-disrupting chemicals is driven by the hypothesis that they could reduce reproductive success and affect wildlife populations, but there is little evidence for this expectation. The pharmaceutical ethynylestradiol (EE2) is a potent endocrine modulator and is present in the aquatic environment at biologically active concentrations. To investigate impacts on reproductive success and mechanisms of disruption, we exposed breeding populations (n = 12) of zebrafish (Danio rerio) over multiple generations to environmentally relevant concentrations of EE2. Life-long exposure to 5 ng/L EE2 in the F1 generation caused a 56% reduction in fecundity and complete population failure with no fertilization. Conversely, the same level of exposure for up to 40 days in mature adults in the parental F0 generation had no impact on reproductive success. Infertility in the F1 generation after life-long exposure to 5 ng/L EE2 was due to disturbed sexual differentiation, with males having no functional testes and either undifferentiated or intersex gonads. These F1 males also showed a reduced vitellogenic response when compared with F0 males, indicating an acclimation to EE2 exposure. Depuration studies found only a partial recovery in reproductive capacity after 5 months. Significantly, even though the F1 males lacked functional testes, they showed male-pattern reproductive behavior, inducing the spawning act and competing with healthy males to disrupt fertilization. Endocrine disruption is therefore likely to affect breeding dynamics and reproductive success in group-spawning fish. Our findings raise major concerns about the population-level impacts for wildlife of long-term exposure to low concentrations of estrogenic endocrine disruptors.

Existing environmental risk assessment procedures are limited in their ability to evaluate the combined effects of chemical mixtures. We investigated the implications of this by analyzing the combined effects of a multicomponent mixture of five estrogenic chemicals using vitellogenin induction in male fathead minnows as an end point. The mixture consisted of estradiol, ethynylestradiol, nonylphenol, octylphenol, and bisphenol A. We determined concentration-response curves for each of the chemicals individually. The chemicals were then combined at equipotent concentrations and the mixture tested using fixed-ratio design. The effects of the mixture were compared with those predicted by the model of concentration addition using biomathematical methods, which revealed that there was no deviation between the observed and predicted effects of the mixture. These findings demonstrate that estrogenic chemicals have the capacity to act together in an additive manner and that their combined effects can be accurately predicted by concentration addition. We also explored the potential for mixture effects at low concentrations by exposing the fish to each chemical at one-fifth of its median effective concentration (EC50). Individually, the chemicals did not induce a significant response, although their combined effects were consistent with the predictions of concentration addition. This demonstrates the potential for estrogenic chemicals to act additively at environmentally relevant concentrations. These findings highlight the potential for existing environmental risk assessment procedures to underestimate the hazard posed by mixtures of chemicals that act via a similar mode of action, thereby leading to erroneous conclusions of absence of risk.

The transgenerational consequences of environmental contaminant exposures of aquatic vertebrates have the potential for broad ecological impacts, yet are largely uninvestigated. Bisphenol A (BPA) and 17α-ethinylestradiol (EE2) are two ubiquitous estrogenic chemicals present in aquatic environments throughout the United States and many other countries. Aquatic organisms, including fish, are exposed to varying concentrations of these chemicals at various stages of their life history. Here, we tested the ability of embryonic exposure to BPA or EE2 to cause adverse health outcomes at later life stages and transgenerational abnormalities in medaka fish. Exposures of F0 medaka to either BPA (100 μg/L) or EE2 (0.05 μg/L) during the first 7 days of embryonic development, when germ cells are differentiating, did not cause any apparent phenotypic abnormalities in F0 or F1 generations, but led to a significant reduction in the fertilization rate in offspring two generations later (F2) as well as a reduction of embryo survival in offspring three generations later (F3). Our present observations suggest that BPA or EE2 exposure during development induces transgenerational phenotypes of reproductive impairment and compromised embryonic survival in fish of subsequent generations. These adverse outcomes may have negative impacts on populations of fish inhabiting contaminated aquatic environments.

Oral contraceptives containing ethinyl estradiol (EE) with levonorgestrel (LNG) are common in hormonal contraceptives. EE+LNG suppresses weight gain in rodents, but the mechanisms for this remain unclear. Further, metabolic demands in adolescence are increased relative to adulthood. We tested the metabolic effect of a low dose of EE + LNG in adolescents and adult female Long-Evans rats. Rats were given EE (10 µg/kg) + LNG (20 µg/kg) or vehicle subcutaneous injections daily for 16 days. Body mass, food intake, whole-body oxygen consumption, respiratory exchange ratio, and energy expenditure were measured in Promethion phenotyping cages. Dual-energy X-ray absorptiometry (DXA), glucose tolerance, serum metabolic hormone levels, depot-specific adipose and reproductive tissues were collected. EE+LNG limited body-mass gain in both age groups by combining hypophagia with a marked elevation in total energy expenditure and no change in locomotion, implicating potential thermogenic pathways. Dual-energy X-ray absorptiometry scans showed curtailed fat accrual and the preservation of lean mass in EE + LNG-treated rats. White-adipose depots were smaller in all hormone-treated rats, whereas brown adipose tissue mass was reduced only in adults. EE+LNG-treated adults had lower leptin and C-peptide levels with enhanced glucose clearance, whereas adolescents had reductions in GLP-1, glucagon, and PYY levels without altered glucose clearance. Thus low-dose EE + LNG reduced caloric intake, increased energy expenditure, and limited white-adipose deposition irrespective of age. Age-specific effects on metabolic hormones and adipose depot UCP1 content were noted. Together, these results delineate an age-sensitive metabolic and endocrine profile of EE + LNG.