Morphometric Changes in the Prepubertal Female Rat Thyroid Gland Following Acute Exposure to 2,2',4,4'-Tetrachlorobiphenyl and Aroclor 1242

Endocrine Disruptive Effects of Polychlorinated Biphenyls on the Thyroid Gland in Female Rats

“…Our observation is consistent in part with a recent study that A1254 induced an increased rate of thyroid carcinomas in rats (Vansell et al 2004). A1254 administration brought about an increase in height of the thyroid follicular epithelial cells (Saeed and Hansen 1997). The dose-dependent changes in the histology of thyroid gland after dietary treatment with PCB 28 for 90 days have been shown (Chu et al 1996).…”

Stepping backward to improve assessment of PCB congener toxicities.

“…After acute (2-day) exposures, thyroidstimulating hormone (TSH) levels may increase up to 5-fold (38) and the thyroid follicles show typical responses (32,39) to TSH-stimulated mobilization of T4 (39)(40)(41). The follicular response (increased cell height and decreased colloid area) appears maximal at doses below those at which significant declines in serum T4 are seen (40,41).…”

“…Modestly chlorinated congeners such as CB 47 and mixtures such as Aroclor 1242, as well as labile 2,3,6-substituted CBs, can acutely decrease serum T4 to a greater extent (17,37,38,40,42,43) than more highly chlorinated congeners such as CBs 99 and 153 (43,44). Thus, mechanisms other than UDPGT induction, including direct effects on the thyroid gland (32,33), are also important and this makes additive and/or synergistic effects likely.…”

“…The follicular response (increased cell height and decreased colloid area) appears maximal at doses below those at which significant declines in serum T4 are seen (40,41). Mobilization of stored T4 from the thyroid follicles at doses lower than or times prior to those causing significant UDPGT induction (17,38) can cause elevations in serum T4 (17,42,43); at higher doses, declines in serum T4 are still seen at times prior to maximal UDPGT induction (17,38,42,43).…”

Neonatal-Prepubertal Hypothyroidism on Postnatal Testis Development

“…It is reported that polychlorinated biphenyls disrupt the thyroid gland function in humans (Langer et al, 1998;Cheek et al, 1999;Nagayama et al, 1998) and in many other mammalian species, e.g. the rat (Collins, 1980;Saeed and Hansen 1985;Fig. 9.…”