STUDY OF DISTRIBUTION AND INTERACTION OF ARSENIC AND SELENIUM IN RAT-THYROID

Seventy-eight Wistar weanling rats were pretreated with arsenate (100 mg/L As), selenite (1 mg/L Se), and arsenate (100 mg/L As) plus seleni te (1 mg/L Se) added to the drinking water. After 4 w, all the animals were sacrificed and serum T3 and T4 were determined by double-antibod y radioimmunoassay. Thyroid tissue concentrations of As and Se were de termined in female rats by neutron activation analysis, and tissue spe cimens were examined histopathologically. For both sexes, the measurem ents indicated that T4/T3 was lowest in the Se group, intermediate in the As group, and highest in the controls. Corrected for the mean valu e of the controls, mean As concentration of thyroid tissue was of the same magnitude in the group pretreated with As + Se as the sum of the mean As concentration in the groups pretreated with As or Se alone. Th e outcome was symmetric with regard to the Se concentration: Ln the As + Se pretreated group, the mean Se concentration was of the same magn itude as the sum of the mean Se concentration in the groups pretreated with As or Se alone. Thus, As and Se tended to accumulate in the thyr oid tissue. Postmortem examination showed that the thyroid tissue of r ats pretreated with As alone exhibited obvious, toxic changes, whereas only minor or no changes were found in the tissues of the groups pret reated with Se or As + Se, and in the tissues of the controls. Multiva riate analyses demonstrated that s-T4 and s-T3 were significantly corr elated with sex, that s-T3 was positively correlated (p less than or e qual to 0.001) with Se pretreatment, and that the T4/T3 ratio was nega tively correlated with both As (p less than or equal to 0.012) and Se pretreatment (p less than or equal to 0.001). The results were discuss ed in relation to the cancer preventive effect of Se.