LACK OF SYNERGY BY MIXTURES OF WEAKLY ESTROGENIC HYDROXYLATED POLYCHLORINATED-BIPHENYLS AND PESTICIDES

We examined the estrogenicity of binary mixtures of the hydroxylated p olychlorinated biphenyls (OHPCBs) 2,4,6-trichloro-4'-biphenylol (2,4,6 -TCB-4'-OH) and 2,3,4,5,-tetrachloro-4'-biphenylol and the pesticides endosulfan and dieldrin. The OHPCBs and pesticides were tested in both the MCF-7 focus assay and a competitive estrogen-receptor binding ass ay. Although the individual OHPCBs were estrogenic in both assays, the re was no synergy when they were combined at various concentrations as equimolar mixtures. Of the pesticides, only endosulfan was estrogenic . Its weak estrogenicity was seen only in the MCF-7 focus assay at the highest concentration tested-10 CIM There was no synergy of the equim olar mixture of pesticides. To determine whether OHPCBs might respond synergistically when combined with the natural estrogen 17 beta-estrad iol (E-2) we tested various concentrations of 2,4,6-TCB-4'-OH in the M CF-7 focus assay in combination with physiologically relevant concentr ations of E-2. There was no synergy between 2,4,6-TCB-4'-OH and E-2. P retreatment for 3 or 7 days with 2,4,6-TCB-4'-OH had no effect on subs equent foci induced by a combination of 2,4,6-TCB-4'-OH and E-2. Altho ugh our results showing no synergy between the pesticides or the OHPCB s are in contrast to a recent report that binary mixtures of these sam e compounds produce synergistic responses in estrogen-sensitive assays , they are in agreement with the results from other assays showing a l ack of synergy. Considering all results, it appears that synergy of th ese weakly estrogenic compounds acting through the estrogen receptor i s unlikely.