Inhibition of lung, mammary gland and colon tumors by melatonin John H. Weisburger, Abraham Rivenson, Chang-In Choi, Joel Reinhardt, Brian Pittman, Edith Zang. Institute for Cancer Prevention, Valhalla, NY. The pineal gland secretes the hormone melatonin as a function of exposure to light. In darkness, larger amounts of melatonin are secreted that decrease upon exposure to light. Melatonin is also an antioxidant, effective in eliminating reactive oxygen species, that in turn play a role in physiological systems impinging on carcinogenesis and cancer development. A series of experiments were conducted based on the hypothesis that melatonin might affect carcinogenesis. Female SD rats were given a single dose of 10 mg of DMBA at age 50 days, and groups were injected sc with 0.5 mg melatonin in 10% ethanol solution 5 times per week at 4:30 pm beginning at age 47 days. Controls were handled identically without melatonin. Male F344 rats were injected sc with an aqueous solution of 15 mg/kg azoxymethane on day 50 and day 57, and a group was also given the melatonin solutions, as above. Female A/J mice were injected sc with a single dose of urethane at 49 days of age and injected with 0.1 mg melatonin solution in aqueous ethanol 5 times per week. These groups of animals were kept in light from 4:30 pm to 4:30 am on the basis that the spontaneous melatonin secretion would not interfere with the injected substance. There was a delay in the occurrence of palpable mammary tumors in the melatonin/DMBA group for the first 15 weeks, compared to the rats given DMBA alone, but at a later time during the experiment lasting 21 weeks there was no difference between the melatonin group and the controls. In this experiment, the 10% alcohol control group, also during the first 15 weeks displayed a higher incidence of mammary gland tumors. The rats given AOM were examined for foci of aberrant crypts in the descending colon after 8 weeks on test. In the group receiving AOM and the melatonin injections, there were fewer foci of aberrant crypts in the colon and the average number of crypts was lower as well. The mice given urethane and melatonin displayed insignificantly fewer pulmonary tumors, than the controls on urethane alone, after an 18 week period. Thus, melatonin displayed a moderate inhibition of tumor formation in the mammary gland and the colon. It seems likely that the main action of melatonin occurred during the development of the tumors, affecting their growth. AACR Abstract Number: 5694, 2003 Remember we are NOT Doctors and have NO medical training. This site is like an Encylopedia - there are many pages, many links on many topics. Support our work with any size DONATION - see left side of any page - for how to donate. You can help raise awareness of CAM.