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VITELLOGENIN MRNA REGULATION AND PLASMA CLEARANCE IN MALE SHEEPSHEAD MINNOWS, CYPRINODON VARIEGATUS AFTER CESSATION OF EXPOSURE TO 17B-ESTRADIOL AND P-NONYLPHENOL
Citation:
Hemmer, M J., C. J. Bowman, R L. Hemmer, S D. Friedman, D T. Marcovich, K. J. Kroll, AND N D. Denslow. VITELLOGENIN MRNA REGULATION AND PLASMA CLEARANCE IN MALE SHEEPSHEAD MINNOWS, CYPRINODON VARIEGATUS AFTER CESSATION OF EXPOSURE TO 17B-ESTRADIOL AND P-NONYLPHENOL. AQUATIC TOXICOLOGY 58(1-2):99-112, (2002).
Description:
Research was conducted to determine the kinetics of hepatic vitellogenin (VTG) mRNA regulation and plasma VTG accumulation and clearance in male sheepshead minnows (Cyprinodon variegatus) during and after cessation of exposure to either 17b-estradiol (E2) or para-nonylphenol (NP). Adult fish were continuously exposed to aqueous measured concentrations of 0.089 and 0.71 ?g E2/L, and 5.6 and 59.6 ?g NP/L for 16 days using an intermittent flow-through dosing apparatus. Fish were sampled on days 8 and 16 of exposure followed by sampling at discrete intervals for up to 96 days post-exposure. At each interval five fish were randomly sampled from each concentration and hepatic VTG mRNA and serum VTG levels for individual fish determined by slot blot and direct enzyme-linked immunosorbent assay (ELISA) respectively. Exposure to E2 and NP resulted in a dose dependent increase in hepatic VTG mRNA and plasma VTG over the course of the 16 day exposure period. Mean plasma VTG levels at day 16 were >100 mg/ml for both high doses of E2 and NP, and >20 mg/ml for the low exposure treatments. Within 8 days post-exposure, hepatic VTG mRNA levels returned to baseline in both high and low E2 treatments but remained elevated 2-4 fold in the NP treatments. Because of a shortened sampling period, a clearance rate for plasma VTG in the 5.6 ?g NP/L treatment could not be determined. In the 0.089 ?g E2/L, 0.71 ?g E2/L, and 59.6 ?g NP/L treatments, VTG levels began decreasing within 4 days after exposure cessation and exhibited an exponential rate of elimination from plasma. Clearance rates for 0.71 ?g E2/L and 59.6 ?g NP/L were not significantly different (p=0.47), however, both demonstrated significantly higher rates of clearance (p<0.02) than observed in the 0.089 ?g E2/L treatment. Our results indicated that hepatic VTG mRNA rapidly diminishes after cessation of estrogenic exposure in sheepshead minnows, but plasma VTG clearance is concentration and time dependent and may be detected at measurable levels for months after initial exposure to an estrogenic compound.