Characterization of O,P′-DDT-Stimulated Contraction Frequency in Rat Uterus in Vitro. JUBERG, D. R., WEBB, R. C., AND LOCH-CARUSO, R. (1991). Fundam. Appl. Toxicol. 17, 543-549. Exposure to organochlorine pesticides, including DDT, has previously been associated with premature birth. Using an improved protocol to characterize dose and time dependent responses, the present report extends a preliminary finding by this laboratory that O,P′-DDT directly stimulates uterine contractility. Contraction frequency was determined in longitudinal uterine strips from pregnant rats under isometric force conditions. Following equilibration, the uterine strips were monitored for a 1-hr baseline period, then treated with O,P′-DDT or ethanol (solvent control) for 3 hr, followed by 3 hr without test substance. During exposure to 100 μM O,P′-DDT, the frequency of contraction significantly increased by 66% relative to matched controls. After removal of O,P′-DDT from the medium, the frequency of contraction continued to increase in uterine strips exposed to 50 and 100 μM O,P′-DDT. A dose effect was clearly observed during the post-treatment period, with 50 and 100 μM O,P′-DDT significantly increasing contraction frequency by 39 and 104% relative to controls. No significant differences in contraction frequency were observed with 10 μM O,P′-DDT during any test period. These data show that O,P′-DDT directly stimulated isometric contractions in rat uterine strips.
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