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SUPPRESSION OF THE LUTEINIZING HORMONE SURGE BY CHLORDIMEFORM IN OVARIECTOMIZED, STEROID-PRIMED FEMALE RATS
Citation:
Goldman, J., R. Cooper, T. Edwards, G. Rehnberg, W. McElroy, AND J. Hein. SUPPRESSION OF THE LUTEINIZING HORMONE SURGE BY CHLORDIMEFORM IN OVARIECTOMIZED, STEROID-PRIMED FEMALE RATS. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-91/096 (NTIS PB91200303), 1991.
Description:
The midcycle surge of luteinizing hormone (LH) from the pituitary provides the physiological trigger in the mammalian female for the process of ovulation. ccordingly, any agent that compromises the LH surge could function as a reproductive toxicant. ince ovariectomized (OVX) rats implanted with estradiol capsules will exhibit daily afternoon surges, such animals can serve as a useful model for the investigation of toxicant-induced alterations in this functional hormonal event. he acaricide chlordimeform (CDF) has previously been found to decrease serum IN, probably by altering the hypothalamic noradrenergic transmitter control of LH secretion. onsequently, the present study focused on the effect of acute CDF administration on the appearance of the induced LH surge. ingle intraperitoneal injections of CDF (0, 10, 25, 50 mg/kg) in OVX, estradiol-implanted female Long-Evans rats approximately 5 hrs prior to the expected surge caused a complete suppression at 25 and 50 mg/kg. en mg/kg had no effect on surge amplitude, but advanced the LH peak by 2 hrs. he observed suppression did not persist beyond the day of CDF administration. arlier dosing at 11 or 18 hrs prior to the surge was without effect. ince CDF has been found to elevate serum corticosterone (CORT), 10 mg CORT/rat were given at different times prior to the surge. ollowing 20 hrs of CORT exposure, only a partial lowering was seen; 5 hrs exposure were ineffective, indicating an indirect adrenal effect was not the principal route, but may accompany an action of CDF on the hypothalamic mechanisms regulating the surge.