Submitted to: General and Comparative Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/6/2005
Publication Date: 9/26/2005
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. 145:116-127. Interpretive Summary: It is well known that the aquatic environment is heavily contaminated by pollutants that have endocrine disrupting properties. These compounds are known to disrupt development, growth, and reproduction of fish populations. A sensitive method for detecting the presence of these compounds in the aquatic environment would be essential to management. Although many studies on endocrine disrupters have focused on their effects on the reproductive system and/or synthesis of sex hormones in animals, only limited studies exist on how these compounds may affect the pituitary gland function. A rainbow trout pituitary gland culture system was used to characterize the effects of endocrine disrupters on growth bt determining the expression of growth hormone and prolactin genes. We found that endocrine disrupters such as o,p-DDT (o,p-dichlorodiphenyltrichloroethane)and TCDD (2,3,7,8-tetrachlorodibenzo-pdioxin) caused significant increases in the expression of growth hormone and prolactin genes. These results clearly suggest that the rainbow trout pituitary gland culture system could be used to assess the presence of environmental xenoestrogens in an aquatic environment which can affect the growth, development, and reproduction of fish. This discovery will help agencies of environmental protection and the aquaculture industry to insure that environmental xenoestrogenic compounds can be identified and removed from the aquatic environment.
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. A rainbow trout (Oncorhynchus mykiss) pituitary gland culture system was used for studying the effects of EDs on growth hormone (GH) and prolactin (PRL) mRNA 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 concentration-dependent manner. Treatment of pituitary glands with 500 and 1000 nM of a xenoestrogen, o,p-DDT (o,p-dichlorodiphenyltrichloroethane), resulted in a significant induction of GH and PRL mRNA, with a 20-fold increase for PRL and 3-fold increase for GH following treatment with 1000 nM o,p-DDT. Co-incubation of pituitary glands with ICI 182 780 (a selective estrogen receptor antagonist) and o,p-DDT resulted in inhibition of PRL mRNA levels; however, the stimulatory eVect of DDT on GH mRNA was not seen in this experiment, nor was the inhibitory eVect of ICI 182 780 observed with GH mRNA. To the contrary, ICI 182 780 (2.5nM) had a stimulatory eVect on GH mRNA levels. TCDD (2,3,7,8-tetrachlorodibenzo-pdioxin), which is known to exert antiestrogenic effects, had an estrogenic-like effect that resulted in a concentration-dependant increase in the levels of GH and PRL mRNA. Co-incubation of pituitaries with TCDD and alpha-napthoXavone (ANF), which is an inhibitor of the aryl hydrocarbon receptor (AhR), caused an inhibition of TCDD-induced PRL mRNA at the higher and lower concentrations, but these effects were less consistent on GH mRNA levels. However, the responses of PRL and GH mRNA to co-incubation with TCDD and ANF, at the various concentrations, were bi-phasic wherein stimulation was seen at the low concentrations and inhibition at the high concentrations. Combined, these results suggest that o,p-DDT and TCDD are xenoestrogens and that their effects on the expression of GH and PRL genes in the rainbow trout pituitary are modulated, in part, through the ER and AhR, respectively.