The effect of psychoemotional stress on chemically induced mammary carcinogenesis in female rats

Psychoemotional stress is regarded as a factor promoting tumorigenesis and its spreading. However, experiments proving the above link seem insufficient. The present experiment has assessed the effect of immobilization stress on N-methyl-N-nitrosourea (NMU)-induced mammary carcinogenesis in female Sprague-Dawley rats. NMU was administered intraperitoneally in a dose of 50 mg kg(-1) body weight (b.w.) three days after immobilization. Selected animals were immobilized in special boxes before carcinogen administration as follows: once for 120 minutes and 5 times for 120 minutes. Tumour incidence, latency period, frequency per animal, frequency per group and mean tumour volume were evaluated after 25 weeks in each group. The effect of immobilization stress in the experimental group influenced only once was documented by increased incidence (+17%), increased tumour frequency per group (+30%) and mean tumour volume (+203%) and shortened latency period by 23 days when compared to the control group. Repeated stress in the group having been immobilized 5 times increased tumour incidence by 53%, frequency per animal by 45%, frequency per group by 127%, and tumour volume by 78%. Recorded differences were not significant because of the small number of tumour-bearing animals compared in individual groups. The results of the present experiment point to immobilization stress as a factor promoting oncogenic transformation of mammary gland cells.