Effect of propylthiouracil on the thyroid tumorigenesis induced by N-bis(2-hydroxypropyl)nitrosamine in rats.

The effect of 0.15% propylthiouracil (PTU) on thyroid tumorigenesis was studied in male Wistar rats given a single i.p. injection of 280 mg of N-bis(-2-hydroxypropyl)nitrosamine (DHPN) per 100 g body weight. The mean weights of the thyroid of rats treated with DHPN followed by PTU and with PTU alone were significantly higher than those of rats treated with DHPN only and control rats. The incidences of follicular adenoma at the end of week 20 of the experiment were 100% (21/21) in rats treated with DHPN followed by PTU, and 19% (4/21) in rats given DHPN alone. Papillary adenoma was observed in one rat treated with DHPN followed by PTU. The incidence of follicular carcinomas with invasive growth into the capsule, adipose tissues or blood vessels was 52% (11/21) in rats given DHPN and then PTU. No papillary carcinomas or solid tumors were found in any rats. Rats given PTU alone and untreated rats had no thyroid tumors. The serum concentration of T4 in rats treated with PTU alone was significantly lower than that in the control group. The serum concentration of T4 in rats treated with DHPN followed by PTU was slightly, but not significantly, lower than that in control rats. The serum concentrations of T3 in rats treated with DHPN followed by PTU, DHPN alone and PTU alone were also slightly, but not significantly, lower than that in controls.