Effect of the preventive-therapeutic administration of melatonin on mammary tumour-bearing animals.

Melatonin has been reported to be involved in the feedback between neuroendocrine and immune functions and to exert oncostatic actions. Likewise, this hormone seems to lengthen life span in healthy animals. As of present, most studies have analysed the therapeutic effect of melatonin on cancer growth, but few have tested the preventive effect of melatonin in reducing the risk of cancer. Thus, the aim of this study was to evaluate the preventive-therapeutic effects of melatonin on rats with DMBA-induced mammary tumours, and to examine the effect of melatonin on the first line of cell defence against cancer (macrophages and NK cells) and on some of the neuroendocrine factors that are involved in the development of tumours (prolactin and catecholamines). Melatonin treatment (5 mg/day/animal) began one month prior to DMBA (9,10-dimethyl-1,2-benzanthracene) administration to females Sprague Dawley rats. It was found that the treatment led to an increase in survival and in latency time in the tumour-bearing rats. Although the melatonin treatment did not influence either the phagocytic capacity of macrophages or the number of peripheral blood NK cells, it did stabilise the levels of prolactin by returning the concentrations of this hormone to those of the healthy animals. We conclude that melatonin can exert an oncostatic action, lengthening the survival time of mammary tumour-bearing animals, and suggest that this effect is due, at least in part, to regulating the neuroendocrine parameters of tumour-bearing animals, bringing them closer to their optimal physiological status.