Sex dependence of hypothyroidism on malignant tumor growth.

Abstract

e23558 Background: Experimental data showed proliferative and anti-apoptotic effects of thyroxine (T4) and triiodothyronine (T3) on cancer cells which regulate gene expression and stimulate estrogen-like effects. The purpose of the study was to analyze effects of hypothyroidism on the development of malignant tumors in male and female rats. Methods: Female (n = 15) and male (n = 15) white outbred rats weighing 150 g and more received mercazolil (2.5 mg/100 g of weight) daily for 30 days (total dose of 75 mg/100 g of weight). Blood levels of T3, T4 and TSH were measured in all animals. When persistent hypothyroidism was observed, Guerin's carcinoma (GC, group 1) and sarcoma 45 (S45, group 2) were inoculated at a dose of 2 million cells in 0.5 ml of saline under the skin of the back to animals of both genders. The control group included rats of both genders with subcutaneous inoculation of Guerin's carcinoma and sarcoma-45 in the same dosage and volume but without preliminary reproduction of the hypothyroidism model. Results: Average tumor volumes in females with GC and hypothyroidism were less than in animals of the control group: after 4 days by 1.3 times (p < 0.05), after 7 and 10 days by 1.4 times (p < 0.05), after 14 days by 1.5 times (p < 0.05), after 18 days by 1.3 times (p < 0.05), and after 21 days by 1.4 times (p < 0.05). The survival of female rats in the main group was 1.6 times higher (p < 0.05) than in rats of the control group. Average tumor volumes in females with S45 and hypothyroidism were less than in animals of the control group: after 4 days by 1.4 times (p < 0.05), after 7 and 10 days by 1.6 and 3.2 times (p < 0.05), after 14 days by 3.9 times, and after 18 days by 4.8 times. The survival of female rats in the main group was 1.8 times higher (p < 0.05) than in rats of the control group. Average tumor volumes in males of the main group with GC and hypothyroidism after 18 and 21 days were similar to the values in animals of the control group. Their survival did not differ from the survival of control males. Average tumor volumes in males of the main group with S45 and hypothyroidism after 10 and 21 days were similar to the values in animals of the control group. Their survival did not differ from the survival of control males. Conclusions: Hypothyroidism in female rats with GC and S45 inhibited the growth of malignant tumors and improved the survival of animals, while in males no such inhibiting effect was observed.