Effects of hypothyroidism on development of nitrosomethylurea-induced tumors of the mammary gland, thyroid gland, and other tissues.

Abstract

AbstractFemale rats were injected with the mammary gland carcinogen N-nitrosomethylurea (NMU) and were made hypothyroid by treatment with either propylthiouracil (PTU) or 131I. NMU (25–100 mg/kg) itself caused a dose-related increase in serum thyroxine levels. PTU (1.0–3.0 mg/100 ml of drinking water) caused a decrease in serum thyroxine and triiodothyronine levels in NMU-treated rats. At 28–31 weeks after injection of NMU alone, 9/43 rats (21%) had malignant mammary tumors. This incidence was increased to 11/30 (37% P > 0.1) and 13/30 (43% P P > 0.05) and caused a 33% decrease in final body weight. Treatment with 10 μCi of 131I gave a small decrease in serum thyroxine levels in NMU-treated rats and increased the incidence of malignant mammary tumors to 11/26 rats (42%, 0.1 > P > 0.05). In addition, PTU (0.3 mg/100 ml) plus NMU induced ...