Potassium Perchlorate, Potassium Iodide, and Propylthiouracil: Promoting Effect on the Development of Thyroid Tumors in Rats Treated with N-Bis(2-hydroxypropyl)nitrosamine

Abstract

The effect of 1000ppm potassium perchlorate (KClO₄), 1000ppm potassium iodide (KI) or 1000ppm propylthiouracil (PTU) in the diet on the development of thyroid tumors was studied histologically and biochemically in Wistar rats given a single ip injection of 280mg of N-bis (2-ydroxypropyl) nitrosamine (DHPN) per 100g body weight. Basal diet containing 1000ppm KClO₄, 1000ppm KI or 1000ppm PTU was given for 19 weeks from week 2 to week 20. The incidence of thyroid adenomas at the end of week 20 of the experiment was 100% (20/20) in rats treated with DHPN followed by KClO₄, 85% (17/20) in rats given DHPN followed by KI, 95% (19/20) in rats given DHPN followed by PTU, and 5% (1/20) in rats given DHPN alone. The incidence of thyroid cancers was 100% (20/20) in rats treated with DHPN followed by KClO₄, 65% (13/20) in rats treated with DHPN followed by KI and 0% (0/20) in rats treated with DHPN followed by or not followed by PTU. Rats given KClO₄, KI or PTU alone and untreated rats had no thyroid tumors. The mean values of TSH in serum were 2.94±0.79ng/ml in rats treated with DHPN followed by KClO₄, 9.40±16.0ng/ml in rats treated with DHPN followed by KI and 60.94±20.60ng/ml in rats treated with DHPN followed by PTU. It was confirmed that (1) KClO₄, PTU and KI promote the development of thyroid tumor in rats treated with DHPN, (2) the promoting effect of KClO₄, or KI is stronger than that of PTU and (3) the value of TSH in serum is not parallel to the promoting effect on the development of thyroid tumor.