Stimulation of contraction of pregnant rat uterus in vitro by non-dechlorinated and microbially dechlorinated mixtures of polychlorinated biphenyls

A previous study of six polychlorinated biphenyl (PCB) congeners showed tha t DCBs with four or fewer chlorines and ortho substitution stimulate uterin e contraction frequency in vitro, whereas congeners with a greater number o f chlorines or non-ortho substitution are inactive in vitro. We tested the hypothesis that PCB mixtures stimulate uterine contractions in a manner inv ersely related to the degree of chlorination and the presence of chlorines in the ortho- position of the biphenyl constituents of the mixtures. Uterin e strips From pregnant rats were suspended in standard muscle baths and ana lyzed for changes in isometric contractions in response to in vitro exposur e to commercial PCB mixtures (Aroclors) and their dechlorinated products af ter microbial degradation. The PCB mixtures Aroclor 1242, 1248, and 1254 si gnificantly stimulated uterine contraction frequency, and the least chlorin ated mixture, Aroclor 1242, was the most potent stimulant. Microbes from Hu dson River sediment dechlorinated Aroclor 1242 and Aroclor 1254 under reduc ing conditions to produce mixtures with an increased proportion of ortho-su bstituted congeners with one or two chlorine substitutions. The PCB mixture s that had undergone microbia reductive dechlorination stimulated uterine c ontraction frequency to a significantly greater extent than the parent mixt ures. These results show that increased uterotonic activity was associated with decreased chlorination and increased ortho substitution of the bipheny l constituents of the mixtures.