Melatonin content in plasma and large intestine of patients with colorectal carcinoma before and after surgery

The distinct melatonin rhythm with higher concentrations during the darktim e was found in plasma of both control patients and patients with colorectal carcinoma. Moderate surgery did not induce any changes in plasma melatonin levels, but a pronounced increase in both the day- and nighttime melatonin concentrations was found after surgical treatment for colon cancer. The me latonin content in the tumor tissue did not differ from that in the proxima l and the distal parts of the resected gut, which were without signs of mal ignant changes. Neither concentrations of serotonin nor 5-hydroxyindole ace tic acid differed among analyzed parts of the gut. Daytime melatonin concen trations in gut tissue (314.7 +/- 87.8 pg/g of wet tissue) were more than t en rimes higher than the daytime levels in circulation. It was hypothesized that increased levels of this hormone in the gastrointestinal tract may pl ay an important protective role against the development of colorectal cance r via stimulation of the immune system, protection against free radicals, a nd interaction with fatty acid uptake and metabolism.