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Morphometric changes in the prepubertal rat thyroid gland following acute exposure to PCBs

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Title: Morphometric changes in the prepubertal rat thyroid gland following acute exposure to PCBs
Author(s): Saeed, Anwer
Doctoral Committee Chair(s): G.Hansen, Larry
Department / Program: Comparative Biosciences
Discipline: Comparative Biosciences
Degree Granting Institution: University of Illinois at Urbana-Champaign
Degree: Ph.D.
Genre: Dissertation
Subject(s): Health Sciences, Toxicology Biology, Animal Physiology Biology, Veterinary Science
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.
Issue Date: 1996
Type: Text
Language: English
URI: http://hdl.handle.net/2142/22150
ISBN: 9780591200225
Rights Information: Copyright 1996 Saeed, Anwer
Date Available in IDEALS: 2011-05-07
Identifier in Online Catalog: AAI9712425
OCLC Identifier: (UMI)AAI9712425
 

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