Histological study of the possible toxic effect of selenium on the thyroid follicular cells of albino rats

ABSTRACT

Selenium is a trace element, essential in small amounts, but it can be toxic in larger amounts. Selenium compounds are widely used as a dietary supplement and as a prophylaxis for the prevention of cancer, cardiovascular diseases and viral mutations. However, there is a narrow margin between safe therapeutic and toxic doses of selenium. The goal of the present study was to study the histological effect of the adequate and toxic doses of selenium on the follicular cells of thyroid gland of albino rats. The study was carried out on 30 adult male albino rats weighing 120-150 gm. Animals were divided into 3 equal groups Control group; which received adequate diet but without the addition of selenium. Group I [supplemented group] received sodium selenite in a dose of 75 microgram / kg b.w., and group II [Intoxicated group] received sodium selenite in a dose of 300 microgram /kg bw. Histological examination of the semithin and ultrathin sections of the supplemented group [group I] revealed nearly normal control image in most of the examined thyroid follicles. Few follicles showed some follicular cells with vacuolated cytoplasm and many dense bodies and others showed irregular nuclei. Ultrastructural examination revealed some cells with dilated cisternae of rough endoplasmic reticulum, widened intercellular spaces and the infiltration of the interstitial spaces with some inflammatory cells and excessive collagen deposition. Histological examination of the intoxicated group [group II] revealed hypertrophy and hyperplasia of the thyroid follicles which appeared crowded with minimal interfollicular spaces. Some follicles showed stratification of their lining cells while others showed dome shaped cells with vacuolated cytoplasm and many dense bodies. Numerous basal and lateral cytoplasmic processes, interrupted epithelial lining and exfoliated cells in the lumina were frequently encountered. The present work recommend the intake of natural diet enriched with high content of selenium and warn about daily intake of exceeding doses of selenium supplementations