Proceedings of The Physiological Society
University of Central Lancashire (2002) J Physiol 543P, S241
Study of how physical activity and/or melatonin treatment affect the survival of female rats with induced mammary tumours
Department of Physiology, Faculty of Science, University of Extremadura, Badajoz, Spain
Physical activity has received little attention as a primary strategy in cancer control, but an increasing number of epidemiological studies have addressed the question of a possible influence of physical activity on the risk of cancer (Pedersen & Hoffman-Goetz, 2000). Also, studies on the relationship between melatonin and neoplastic disease have recently become one of the most fascinating areas of pineal research. The bulk of the experimental evidence indicates the influence of melatonin on the malignant tumour formation and/or growth (Karasek & Pawlikowski, 1999).
Thus the purpose of this study was to determinate how exercise and melatonin administration can affect the survival of rats with induced mammary tumours, and their relationship with the tumours' progression. Female Sprague-Dawley rats (Rattus norvegicus) were administered the carcinogen DMBA (9,10-dimethyl-1,2-benzantracene). Animals were then randomized into four groups (n = 10) as follows: (1) DMBA rats as control group; (2) DMBA rats + exercise (swimming; 30 min/day; 5 days/week); (3) DMBA rats + melatonin (2 X 10-2 M; 5 days/week); (4) DMBA rats + exercise + melatonin. Rats were handled according to the guidelines of the European Community Council Directives 86/6091 EEC.
The results showed that physical activity alone induces a greater tumour growth rate (Fig. 1) but does not significantly affect survival (control group survival: 53 ± 5 days vs. exercise group survival: 45 ± 15 days). Intraperitoneal melatonin administration delays tumour growth and increases survival by approximately 40 % (melatonin group survival 81 ± 20 days; P < 0.05). The melatonin administration also counteracts the increased tumour development induced by exercise, but does not affect survival of the animals of this group (exercise + melatonin group survival: 47 ± 4 days). Student's t test was used for statistical analysis of survival time, and results are expressed as means ± S.D.
In conclusion, these data suggest that melatonin could be of therapeutic help in breast cancer, slowing down the growth rate of the tumours. This is not the case for exercise, or at least in our model of physical activity.
This research was supported in part by a grant from Junta de Extremadura-Consejer
Where applicable, experiments conform with Society ethical requirements