Effects of the pineal gland on the growth processes of Guerin epithelioma in male Wistar rats.

The effects of pinealectomy (PX) and melatonin (Mel) administration on the growth processes of Guerin epithelioma, a malignant tumour derived from spontaneous cancer in Wistar rat uterus, was investigated in five groups of male rats. The mean life span of the rats bearing Guerin tumours (GT) and subjected to PX was shorter than in animals with an intact pineal gland. Mel did not affect the lifespan in rats with intact pineals or in those subjected to PX. Mel decreased the mitotic activity of GT cells in rats with and without the pineal gland. Pathomorphological examination revealed high malignancy of the primary tumour but no metastases. The results confirmed the important role of the pineal gland in 'oncostasis'.