FASTING DURING PROMOTION, BUT NOT DURING INITIATION, ENHANCES THE GROWTH OF METHYLNITROSOUREA-INDUCED MAMMARY-TUMORS

The purpose of this work was to investigate the effect of fasting on t he induction and growth of chemically-induced mammary carcinogenesis, Female Sprague-Dawley rats were given methylnitrosourea (MNU) i,p, (50 mg/kg) at 50 days of age; a group of rats were exposed to 4 day fasti ng followed by 1 day of refeeding before the administration of the car cinogen, while another group was exposed to three cycles of 3 days fas ting in 10 days, beginning 1 week after MNU injection, Fasting enhance d the development of mammary tumours only in rats fasted after carcino gen damage, while it did not affect the induction of tumours in rats f asted before MNU, if compared with full-fed controls, The enhanced gro wth of mammary tumours sustained by fasting during promotion was obser ved in the cervical-thoracic region, In addition, exposure to fasting made rats susceptible to the development of MNU-induced extra-mammary cancers, Different from the preventive effect of caloric restriction o n tumor development, these data demonstrate that fasting affects the p romotion phase of carcinogenesis by enhancing the growth of MNU-induce d mammary tumours.