Relationships between PCBs and thyroid hormones and retinol in female and male polar bears

We studied the relationships between polychlorinated biphenyls (PCBs) and thyroid hormones (THs) and retinol within two groups of female polar bears (Ursus maritimus), females with cubs of the year (FWCOY) and females without cubs of the year (FWOCOY), and within a group of males. Concentrations of five of the six quantified PCB congeners, i.e., PCB-99, PCB-153, PCB-156, PCB-180, PCB-194 (sigma PCB5), correlated with each other, whereas the concentrations of PCB-118 did not correlate with the other congeners. sigma PCB5 and PCB-118 did not differ between the three different groups of polar bears, and the plasma levels ranged from 16.7 to 203.2 ng/g wet weight (ww) for sigma PCB5 and from 0.09 to 0.93 ng/g ww for PCB-118. PCBs did not affect the retinol status in any of the three groups. In FWCOY, we found negative correlations between sigma PCB5 and the three TH variables free thyroxin (FT4) (r2 = 0.35), free triiodothyronine (FT3) (r2 = 0.30), and the total T4:total T3 ratio (TT4:TT3) (r2 = 0.92). In FWOCOY, sigma PCB5 was negatively correlated to TT4 (r2 = 0.14) and positively correlated to TT3:FT3 (r2 = 0.31), whereas PCB-118 was positively correlated to FT3 (r2 = 0.21) and negatively correlated to TT3:FT3 (r2 = 0.26). In males, sigma PCB5 was negatively correlated to FT3 (r2 = 0.56) and positively correlated to FT4:FT3 (r2 = 0.78), whereas PCB-118 was negatively correlated to FT4:FT3 (r2 = 0.53). Thus, PCBs affected five TH variables in the female polar bears (TT4, FT4, FT3, TT3:FT3, TT4:TT3), but PCBs affected only two TH variables in males (FT3, FT4:FT3). Female polar bears could be more susceptible to TH-related effects of PCBs than are males. PCBs also affected T3 to a larger degree than T4.