Age-related changes in melatonin release in the murine distal colon

Constipation and fecal impaction are conditions of the bowel whose prevalence increases with age. Limited information is known about how these conditions manifest, however functional deficits are likely to be due to changes in signalling within the bowel. This study investigated the effects of age on colonic mucosal melatonin (MEL) release and the consequences this had on colonic motility. Electrochemical measurements of MEL overflow demonstrated that both basal and mechanically stimulated MEL release decreased with age. The MEL:serotonin also decreased with increasing age and the trend was similar to that of MEL overflow, suggestive that age-related changes were primarily due to a reduction in MEL levels. Levels of N-acetylserotonin and the N-acetylserotonin:serotonin ratio were reduced with age providing an explanation for the reduction in MEL release. Decreases in colonic motility were observed between 3 and 24 month old animals. Exogenous application of MEL could reverse this deficit in aged colon. In summary, we propose that the age-related decline in MEL release may be due to either decreases or alterations in mechanosensory channels and/or a loss in levels/activity of the N-acetyltransferase enzyme responsible for the synthesis of N-acetylserotonin. Decreases in MEL release may explain the decreases in colonic motility observed in 24 month old animals and could offer a new potential therapeutic treatment for age-related constipation.