Promoting effects of 3-amino-1,2,4-triazole on the development of thyroid tumors in rats treated with N-bis(2-hydroxypropyl)nitrosamine.

3-Amino-1,2,4-triazole (AT) promoted the development of thyroid tumors in rats treated with a subeffective dose of N-bis(2-hydroxypropyl)nitrosamine (DHPN) for thyroid tumorigenesis. The incidences of thyroid tumors at the end of the 20-week experiment were 91% in rats injected s.c. once a week for four weeks with 70 mg DHPN per 100 g body weight and then given diet containing 2000 p.p.m. AT for 12 weeks, 100% in rats injected s.c. once a week for eight weeks with 70 mg DHPN per 100 g body weight and then given diet containing 2000 p.p.m. AT for 12 weeks, and 58% in rats injected s.c. once a week for 8 weeks with 70 mg DHPN per 100 g body weight. Rats only injected s.c. once a week for four weeks with DHPN or only given diet containing AT for 12 weeks had no thyroid tumors at the end of the experiment.