1999 Progress Report: Reproductive and endocrine effects of o,p'-DDT, an environmental estrogen, and p,p'-DDE, an antiandrogen in male and female Atlantic croaker during critical periods of their reproductive life history cyclesEPA Grant Number: R826125
Title: Reproductive and endocrine effects of o,p'-DDT, an environmental estrogen, and p,p'-DDE, an antiandrogen in male and female Atlantic croaker during critical periods of their reproductive life history cycles
Investigators: Thomas, Peter
Institution: The University of Texas at Austin
EPA Project Officer: Carleton, James N
Project Period: October 1, 1997 through September 30, 2000
Project Period Covered by this Report: October 1, 1998 through September 30, 1999
Project Amount: $430,010
RFA: Endocrine Disruptors (1997) RFA Text | Recipients Lists
Research Category: Endocrine Disruptors , Economics and Decision Sciences , Health , Safer Chemicals
Objective:Specific objectives are to determine: (1) which stages of the croaker reproductive life history cycle are disrupted by o,p'DDT and p,p'DDE; (2) what endocrine and reproductive effects of o,p'DDT and o,p'DDE are related to their estrogenicity and antiandrogenicity, respectively; (3) the sites of o,p'DDT and p,p'DDE action on the HPGL axis; (4) the role of the ER in mediating the actions of p,p'DDE; and (5) whether there are sex differences in the susceptibility to o,p'DDT and p,p'DDE.
1. In vitro exposure to antiandrogens. Croaker at the beginning of ovarian recrudescence (N=470) were divided among 10 tanks (3 control; 3 low dose p,p'DDE - 0.01mg/100g bw/day; 3 high dose p,p'DDE - 0.05mg/100g bw/day, and one fed cyproterone acetate 0.1 mg/100g bw/day). Fish was sampled at a midpoint in gonadal recrudescence and towards the end of the reproductive cycle (14 weeks exposure) when gonadal growth was advanced (24 week exposure). The highest dose of p,p'DDE caused a significant reduction in gonadal growth in females by the second sampling time, which was accompanied by a significant decline in circulating estradiol levels. Similarly, in males decreases in gonadal growth and plasma levels of 11-ketotestostorone were observed after 26 weeks treatment with the highest dose of p,p'DDE; however, these declines in circulatory steroid levels were not accompanied by decreases in steroidogenesis in either sex. The mechanisms by which p,p'DDE disrupts the gonadal physiology of both males and females is currently being explored in in vitro bioassays and steroid receptor competition studies, including androgen and estrogen membrane receptors that mediate nongenomic steroid actions and have recently been characterized in croaker tissues (see below). Unfortunately, a power outage in early fall of 1999 caused by Hurricane Bret caused loss of the remaining samples from the experiment (for receptor analysis) and experimental animals for the 1999 experiments. These aspects of the study will be repeated during the 2000 fall reproductive season of Atlantic Croaker.
2. In vitro effects of androgens and estrogens on gonadal steroid steroidogenesis. In vitro steroidogenesis bioassays were developed to investigate how androgens, estrogens, and xenobiotic estrogens and antiandrogens could influence gonadal physiology and possibly account for the endocrine alterations observed in the in vitro studies. Recently, two distinct androgen receptors have been characterized in croaker, one of which is present in high concentrations in the ovary (Sperry and Thomas Endocrinology 1999;140:1602-1611). In addition, an estrogen receptor has been characterized in croaker testes (Loomis and Thomas, 1999). Moreover, we showed that both testes and ovaries synthesize androgen and estrogens (Loomis and Thomas, 1999). These results clearly demonstrate for the first time that the sex steroid action is not sex specific in fishes. A study of estrogen action in croaker testes showed that estradiol inhibited androgen synthesis and that several xenoestrogens (o'p'DDE, Kepone, nonylphenol, and 2,2'5'-PCB-4-OH) mimicked the action of estradiol causing a decline in androgen synthesis (Loomis and Thomas, in press). Interestingly, it was found that the action of estradiol was rapid, cell-surface mediated, and nongenomic, characteristics typical of steroid membrane receptors. In addition, an estradiol binding moiety was characterized on croaker testicular membranes that satisfied all the criteria for its designation as an estrogen membrane receptor (Loomis and Thomas, in press). An assay also is being developed to investigate the effects of androgens on ovarian estrogen production. Nonaromatizable androgens cause down regulation of gonadatropin-simulated estradiol synthesis and preliminary evidence indicates that this action too is nongenomic and mediated at the cell surface. An androgen binding moiety has been identified on ovarian membranes that is incompletely characterized, but appears to represent a novel androgen membrane receptor. It is concluded from these studies that estrogens can modulate testicular androgen production, and conversely, androgens can downregulate ovarian estrogen production. Both classic nuclear and membrane receptors for estrogens and androgens have been identified in testicular and ovarian tissues, respectively. Thus, xenobiotics chemicals potentially can interfere with a variety of mechanisms of steroid action in gonadal tissues to interfere with gonadal physiology.
3. Cloning of three estrogen receptors cDNAs from the Atlantic Croaker. cDNAs encoding of three distinct estrogen receptors have been identified in Atlantic Croaker, ER alpha, ER beta, and ER gamma. This is the first evidence for three ER subtypes in any vertebrate species. The three ERs are genetically distinct, differentially distributed in croaker tissues, and ER beta and gamma proteins can bind estradiol. The presence of three forms of the estrogen receptor in a teleost fish shows that ER multiplicity occurred early in the vertebrate lineage. This suggests that the presence of different nuclear steroid receptor subtypes is a fundamental aspect of steroid hormone regulation and function throughout vertebrates. The multiplicity of estrogen receptors and their binding affinities for xenoestrogens should be taken into consideration when predicting the toxicological consequences of exposure to these compounds at different target tissues.
Future Activities:The proposed research is proceeding as planned.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
|Other project views:||All 18 publications||5 publications in selected types||All 5 journal articles|
||Loomis AK, Thomas P. Effects of estrogens and xenoestrogens on androgen production by Atlantic croaker testes in vitro: Evidence for a nongenomic action mediated by an estrogen membrane receptor. Biology of Reproduction 2000;62(4):995-1004.||
||Thomas P. Chemical interference with genomic and nongenomic actions of steroids in fishes: role of receptor binding. Marine Environmental Research 2000;50(1-5):127-134.||