Abstract
The effect of chronic exposure to two different levels of cadmium chloride (CdCl2) 30 ppb and 40 ppb in drinking water for 12 weeks on thyroid function of mature male rabbits was studied. Eighteen mature male rabbits were randomly divided into three groups (each of six ) , control group (group I ): were offered ordinary tap water , and treated groups (II and III ) were offered tap water containing 30ppb and 40 ppb respectively for 12 weeks .Serum concentration of thyroxin (T4 ) and triiodothyronine (T3) were measured every six weeks ,as an index of thyroid function , further more , section of thyroid gland were prepared for histological studies. The results showed that chronic exposure of male rabbits to two different levels of CdCl2 caused significant decrease (p<0.05) in serum T3 and T4 in both treated groups in compared with control group, in addition, there were histological changes in thyroid gland of treated groups manifested by hyperplasia with presence of large number of varying size of microfollicels and hypertrophic thyrocytes, small colloid with little secretion .
 Key wards: Cadmium, Thyroid gland, Thyroxin, Triiodothyronin, Thyrocyt
Highlights
The histological structure of thyroid gland of un treated rabbits was shown in figure [1], the thyroid follicles containing colloid of uniform color, oval in shape, lined by cuboidal thyroidal follicular cells, figures 2,3 illustrated the histological changes in thyroid gland of rabbits following 30 and 40 ppb of CdCl2,the figures showed a case of hyperplasia manifested by presence of thyroid microfollicels of varying size lined by high columnar thyroidal follicular cells, small colloid with little secretion in follicular lumen, while the figure 3 showed a large area of irregular and varying size microfollicels with hypertrophic thyrocyte with little colloid secretion
This study showed that exposure of rabbits to cadmium bring the animal to the case of hypothyroidism manifested by significant decrease in serum T3 and T4 concentration associated with biological changes
Considerable body of evidence how exist attesting the involvement at heavy metals including cadmium in the toxicity of a number of endocrine glands including thyroid gland [8,9]
Summary
Cadmium is modern toxic metals (discovered in 1817). Hazardous waste disposal sites are large source of Cd concentration found in soil and water. Tobacco smoke is the main reason for cadmium accumulation in our body [2],on other hand , the major route of cadmium intake ( for non smoker ) is ingestion , this is largely due to the presence of Cd ( 2-40 ppb ) in food staff of natural origin e.g. cereals beans , carrots , beverage, coffee and tea [3] ,or by the ingestion of contaminated food especially fish [4, 5]. Wealth of evidence suggested that heavy metals including cadmium exert profound toxic effects on the activities of a number of endocrine gland including thyroid gland [7,8]
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