Objective: To assess thyroid disruption induced by sodium pentachlorophenol (PCP) using Organization for Economic Co-operation and Development (OECD) recommended TG 407 method.
Methods: A total of 30 specific pathogen free (SPF) SD adult male and female rats were randomly divided into 3 groups, and treated with water, 0.33 and 30 mg x kg(-1)x d(-1) of PCP-Na by oral gavage for consecutive 28 days, respectively. After final treatment, histological changes of thyroid were observed by hematoxylin-eosin stain, and the levels of thyroid hormones (total thyroxine (TT(4)), free thyroxine (FT(4)), total triiodothyronine (TT(3)), and free triiodothyronine (FT(3))) were determined by radioimmunoassay. The expression levels of thyroid receptors (TRalpha and TRbeta) mRNA and deiodinases (DioI, DioII and DioIII) mRNA in liver were analyzed by RT-PCR.
Results: In high dose group, liver weight coefficient of male and female rats were (4.82 +/- 0.42)% and (4.99 +/- 0.17)%, increased by 36.2% (t = 7.338, P < 0.01) and 41.8% (t = 8.955, P < 0.01), compared to control group ((3.54 +/- 0.14)%, (3.52 +/- 0.19)%), respectively, while the significant changes of kidney or thyroid weight were not observed. In high dose group, the levels of TT(4) and FT(4) in serum of male rats were (64.95 +/- 7.16) nmol/L and (8.16 +/- 2.29) pmol/L, and decreased by 26.6% (t = -3.999, P < 0.01) and 42.3% (t = -4.112, P < 0.01) compared to control group ((88.48 +/- 6.99) nmol/L, (14.13 +/- 1.68) pmol/L). In the same group, FT(4) in serum of female rats was (4.94 +/- 0.89) pmol/L, decreased by 55.5% (t = -3.380, P = 0.012) compared to control group ((11.10 +/- 3.40) pmol/L) and TT(3) and FT(3) in serum of female rats were (1.92 +/- 0.24) nmol/L and (3.05 +/- 0.79) pmol/L, increased by 74.5% (t = 5.263, P < 0.01) and 55.6% (t = 3.495, P < 0.01) compared to control group ((1.10 +/- 0.23) nmol/L, (1.96 +/- 0.32) pmol/L), respectively. PCP-Na didn't affect the expression levels of TRalpha, TRbeta, DioIII mRNA in high dose group, while DioII expression of male rats (0.209 +/- 0.017) down-regulated by 79.2% (t = -5.426, P < 0.01) compared to control group (1.006 +/- 0.137), and DioI expression of female rats (1.844 +/- 0.189) up-regulated by 66.6% (t = 4.359, P < 0.01) compared to control group (1.005 +/- 0.083), indicating DioI and DioII poss different sensitivity to adverse effects induced by PCP-Na between male and female rats. The histopathological results showed that PCP-Na could give rise to hyperplasia of the follicular epithelium cells, and the depletion of colloid. There were no significant changes in serum THs levels and expression of TRalpha, TRbeta, DioI-IIImRNA in low dose group. However, sporadic lymphocytic infiltration, follicles amplification in part and slightly increased in thickness of follicular cells were observed in this group.
Conclusion: PCP is a kind of thyroid disrupting chemical.