Submitted to: General and Comparative Endocrinology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/15/2005
Publication Date: 1/15/2006
Citation: Elango, A., Shepherd, B.S., Chen, T.T. 2006. Effects of endocrine disrupters on the expression of growth hormone and prolactin mrna in the rainbow trout pituitary. General and Comparative Endocrinology. 145(2):116-127. Interpretive Summary: Water sources, including those used in aquaculture, can have pollutants from agriculture, industrial and municipal sources that alter, or mimic, the effects the sex steroid hormone, estrogen. Such pollutants are termed "Endocrine Disrupters (EDs)". Another source of estrogen-like EDs are plant sources, such as soybean sterols (e.g., genestein), that are increasingly being used to manufacture aquaculture diets. Exposure to EDs can result in behavioral, metabolic and reproductive problems, but the mechanisms by which EDs exert these effects are poorly understood. We have conducted studies in the rainbow trout that show that two persistent organic compounds, DDT and Dioxin, stimulate pituitary growth hormone (GH) and prolactin (PRL) gene expression via differing mechanisms. Because these two pituitary hormones control important physiological processes (production traits), such as reproduction, growth and salt and water balance, it is conceivable that ED exposure can have negative impacts on production traits in important aquaculture finfish species. An understanding of the mechanisms by which EDs alter vertebrate endocrinology can provide predictive capabilities to determine, for example, whether the use of particular plant-based protein sources, in aquaculture diets, will have adverse affects on production traits.
Technical Abstract: It is now widely accepted that chemical pollutants in the environment can interfere with the endocrine system of animals, thus affecting development and reproduction. Some of these endocrine disrupters (EDs) can have estrogenic or antiestrogenic effects. Most studies to date have focused on the effects of EDs on the reproductive system and sex hormones and only limited information exists on how EDs may affect pituitary gland function. In this study, a rainbow trout (Oncorhynchus mykiss) pituitary gland culture system was used for studying the effects of EDs on growth hormone (GH) and prolactin (PRL) gene expression. We determined that the pituitary glands actively synthesized and secreted GH and PRL over the experimental time-course. In addition, we found that treatment with 17 beta-estradiol (positive control) increased levels of GH and PRL mRNA, in a dose-dependent manner. Treatment of pituitary glands in culture with 1µM of a xenoestrogen, o',p'-DDT (o',p'-dichlorodiphenyltrichloroethane), resulted in a 20-fold increase of PRL mRNA and a 3-fold increase of GH mRNA over controls. Co-incubation of pituitary glands with ICI 182 780 (a selective estrogen receptor antagonist) resulted in inhibition of PRL mRNA level induced by o',p'-DDT, but this inhibitory effect was not observed with GH mRNA. These results suggest that binding of o',p'-DDT to the estrogen receptor (ER) in the pituitary gland may be required for the induction of PRL mRNA but not for GH mRNA. TCDD (2,3,7,8-Tetrachlorodibenzo-p-dioxin), which is known to exert antiestrogenic effects, had an estrogenic effect and resulted in a dose-dependant increase in the levels of GH and PRL mRNA. Alphanapthoflavone (ANF) is an inhibitor of the Aryl hydrocarbon receptor (AhR) and co incubation with ANF caused an inhibition of TCDD-induced PRL mRNA at the higher and lower concentrations, but to a lesser extent on GH mRNA. These results suggest that the effects of TCDD on the rainbow trout pituitary is modulated through the AhR. Combined, our findings indicate that EDs affect pituitary function by altering the expression of GH and PRL genes via ER and non-ER mediated pathways in an ecologically- and economically-important salmonid species, rainbow trout.