Characterization of o,p'-DDT-stimulated contraction frequency in rat uterus in vitro.

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 microM 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 microM o,p'-DDT. A dose effect was clearly observed during the post-treatment period, with 50 and 100 microM o,p'-DDT significantly increasing contraction frequency by 39 and 104% relative to controls. No significant differences in contraction frequency were observed with 10 microM o,p'-DDT during any test period. These data show that o,p'-DDT directly stimulated isometric contractions in rat uterine strips.