Morphometric changes in the prepubertal rat thyroid gland following acute exposure to PCBs
Saeed, Anwer
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Permalink
https://hdl.handle.net/2142/22150
Description
Title
Morphometric changes in the prepubertal rat thyroid gland following acute exposure to PCBs
Author(s)
Saeed, Anwer
Issue Date
1996
Doctoral Committee Chair(s)
Hansen, Larry
Department of Study
Comparative Biosciences
Discipline
Comparative Biosciences
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Health Sciences, Toxicology
Biology, Animal Physiology
Biology, Veterinary Science
Language
eng
Abstract
Female rats subjected to a short-term immature rodent bioassay, developed to study the effects of polychlorinated biphenyls (PCBs), were further used to examine the effects of PCBs on thyroid glands through examination of serum thyroxine (T$\sb4$) and morphometry.
CB 47 (2,2$\sp\prime,4,4\sp\prime$-tetraCB) administered at 30 mg/kg/day resulted in modest T$\sb4$ depression. Thyroid follicular cell height increased from 9 $\mu$m to 10-12 $\mu$m and the colloid area decreased from 1100 $\rm\mu m\sp2$ to 800-900 $\rm\mu m\sp2$. Aroclor 1242 treatment (120 mg/kg) was divided into 5, 3, or 2 daily doses. Serum T$\sb4$ declined to 50% of control values, with the maximum decline in the 2-day treatment group. Increases in follicular cell height and decreases in colloid area were most prominent in 3- and 5-day treatment groups. Higher doses of Aroclor 1242 (160 mg/kg, 240 mg/kg) were administered for 1-3 days followed by animal terminations at different time intervals. In the 160 mg/kg group, serum T$\sb4$ declined to 54%-58% of controls regardless of time. In the 240 mg/kg group, serum T$\sb4$ was 48% of controls killed at 20 hours and 28%-38% at 44 hours. T$\sb3$ levels were not affected. Thyroid stimulating hormone (TSH) levels increased 4- to 5-fold in both groups at 20 hours. In the 160 mg/kg group, TSH was back to near control levels by 30 and 48 hours. All groups exhibited increases in follicular cell height and shrinkage of colloid area.
Various media from a PCB-contaminated landfill were collected, extracted and refined for dosing. Different doses of soil, dust and air extracts decreased serum T$\sb4$ significantly, but increases in follicular cell heights were not significant. Air extracts decreased colloid area 34-44% in a dose-dependent manner. The soil extract decreased colloid area about 32% at the 2 lowest doses and 40% at the 3 highest doses. The dust extract decreased colloid area 16-40%. In a separate study of the soil extract, follicular cell height increases and colloid area decreases became prominent at doses lower than those causing significant declines in serum T$\sb4$.
Individual PCBs and PCB mixtures resulted in alteration of thyroid hormone status and thyroid follicle morphology. Declines in serum T$\sb4$ were not detectable at low doses due to mobilization of storage forms, which replaced T$\sb4$ losses. This greatly attenuated measured T$\sb4$ loss in these short-term studies, but the morphological changes were detected at early stages of toxicity.
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