NMU-induced mammary carcinogenesis in female rats is influenced by repeated psychoemotional stress

Epidemiological and experimental studies indicate psychoemotional stress as an important factor in carcinogenesis. The aim of this study was to evaluate the effect of restraint stress on N-nitroso-N-methylurea (NMU)-induced mammary carcinogenesis. Female Sprague-Dawley rats were injected with two intraperitoneal NMU doses each per 50 mg/kg b.w. between 39-49 postnatal days. Three experimental groups were created: 1. NMU (without restraint--control group, 12 animals), 2. NMU+1IMS (group with single restraint, IMS--immobilization stress, 12 animals), 3. NMU+7IMS (group restrained 7 times during a week, 12 animals). Animals were immobilized daily in special boxes for 120 minutes or 7 x 120 minutes, respectively from third day after carcinogen administration. The observation lasted for 20 weeks. The incidence, frequency, latency and volume of mammary tumors were evaluated. In repeatedly immobilized group NMU+7IMS increase in tumor incidence by 57% (p<0.05), marked increase in frequency per group by 153% (p<0.01), increase in frequency per animal by 61% and shortened latency period by 7 days were recorded. The effect of single restraint was not seen. In this experiment repeated immobilization carried out early after carcinogen administration had a remarkable stimulatory effect on chemically-induced mammary carcinogenesis in female rats.