Aims: 

The relation between psychoemotional stress and mammary carcinogenesis has not been sufficiently elucidated yet. The present study is focused on the effect of prolonged immobilization stress on development of chemically induced mammary tumours in rats.

Methods: 

Female Sprague-Dawley rats were injected with two intraperitoneal N-nitroso-N-methylurea (NMU) doses each per 50mg.kg^-1 b.w. between 40-50 postnatal days. Five days after injection the rats were immobilized in special boxes three times a week for 120 minutes during 18 weeks (NMU+IMS). Melatonin (4 mg/ml of drinking water) was administered to one experimental group (NMU+IMS+MEL); application was initiated 3 days prior NMU injection and lasted until the end of the experiment. Tumour incidence, latency, frequency, average tumour volume gain and cumulative tumour gain were evaluated.

Results: 

Long-term repeated immobilization of rats decreased tumour frequency per group and animal by 30% when compared to control (NMU) group; tumour volume gain reduced by 16% (p < 0.01). Combination of immobilization and melatonin application decreased tumour frequency per group (by 44%, p < 0.01) and per animal (by 35%); tumour volume gain increased by 35% (p < 0.05) and their cumulative volume markedly decreased by 74% when compared to control.

Conclusion: 

Long-term repeated immobilization stress inhibited NMU-induced mammary tumour development in female rats and this inhibiting effect of psychoemotional stress was enhanced by long-term melatonin administration.