Insecticide-induced changes in secretory activity of the thyroid gland in rats.

The present study was conducted to examine the effect of organochlorine (Heptachlor, Benzene hexachloride (BHC)), organophosphorus (Malathion, Monitor) and pyrethroid (Karate, Talstar) insecticides on the thyroid secretory function in rats. Heptachlor (0.5 mg per rat), BHC (0.66 mg per rat) Malathion (0.06 mg per rat), Monitor (0.2 mg per rat), Karate (0.2 mg per rat), Talstar (0.5 mg per rat) were orally administered to young adult rats for 21 days. Serum concentrations of triiodothyronine (T3), thyroxine (T4) and thyrotrophin (TSH) were determined by using specific radioimmunoassays. Body weight was not affected by treatment with any insecticide except Talstar (P < 0.01). Among organochlorine and organophosphorus insecticides, treatment with BHC and Malathion, respectively, led to a significant decrease (P < 0.01) in serum concentration of T3 and T4. Administration of BHC and Malathion also increased (P < 0.01) TSH secretion. Treatment with both of the pyrethroid insecticides similarly induced significant suppression (P < 0.01) of serum T3 and T4 levels, and concomitant stimulation (P < 0.01) of TSH concentrations. The T4/T3 ratio was decreased (P < 0.05) in rats treated with Karate but not with any other insecticide. These data indicate that immense care is warranted in the use of insecticides, because they not only affect the liver, kidney and other organs but also may alter the activity of the endocrine glands.