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USE OF MOLECULAR BIOLOGICAL TECHNIQUES TO EVALUATE EFFECT OF ENDOGENOUS HORMONES AND A XENOBIOTIC PESTICIDE ON GROWTH OF SHEEPSHEAD MINNOW
Knoebl, I., L. D. Gillis, AND L C. Folmar. USE OF MOLECULAR BIOLOGICAL TECHNIQUES TO EVALUATE EFFECT OF ENDOGENOUS HORMONES AND A XENOBIOTIC PESTICIDE ON GROWTH OF SHEEPSHEAD MINNOW. Presented at SETAC 22 Annual Meeting, Baltimore MD, Nov. 11-15, 2001.
We have developed a teleost model to screen physiological effects of endocrine disrupting chemicals (EDCs) on somatic growth. Growth is largely controlled by the endocrine system via the growth-hormone releasing hormone (GRF) - growth hormone (GH) - insulin-like growth factor (IGF) axis. We used two approaches to study this axis. First, we examined the effects endogenous hormones known to affect growth (GH, estradiol (E2), thyroid hormone (T3) and insulin) on the levels of hepatic IGF-I and IGF-II mRNA. Sheepshead minnows (Cypinodon variegatus) were injected with the hormones and then sampled over several hours. Secondly, we conducted an 18-week aquatic exposure of newly hatched sheepshead minnows to E2 (which has been attributed to both enhance and inhibit growth) and chlorpyrifos (an organophosphate insecticide known to inhibit growth in fish). The fish were exposed to two concentrations of E2 (20 and 100ng/L) and to three concentrations (12.5, 25 and 50 ug/L) of chlorpyrifos. While E2 did not affect growth, fish exposed to the highest dose of chlorpyrifos had significantly reduced growth rates (P<0.05) compared to controls. Hepatic IGF-I and IGF-II mRNA levels were measured using quantitative real-time PCR (TaqMan) technology. We also performed differential display analysis to establish patterns of gene up- or down-regulation in relation to endogenous hormones and to the xenobiotic chlorpyrifos.