OBJECTIVETo study the effect of melatonin on the gastrointestinal motility and plasma levels of the stress hormone in overtraining rats.

METHODThirty adult SD rats were randomly divided into three groups (n = 10): control group, over-training group, melatonin intervention group. 30 min before each training, rats in the control and over-training groups were fed with normal saline (15 mg/kg) once a day and 5 times per week, while rats in the melatonin intervention group were administrated with melatonin, perfusion in the intervention group (15 mg/kg). Excessive training group and melatonin intervention group rats were subjected to excessive training at 5 times a week for 6 weeks. After 6 weeks, the gastric emptying rate, small intestinal propulsion ratio and levels of plasma motilin (MTL) and calcitonin gene-related peptide (CGRP), cortisol (CORT) and catecholamines (CA) were observed in all groups.

RESULTSCompared with the control group, the gastric emptying rate, small intestinal propulsion ratio and levels of plasma MTL, CORT and CA were increased significantly (P < 0.01) while the content of CGRP was reduced (P < 0.01) in over-training group. After treated with melatonin, this trend was reversed, that was, the gastric emptying rate, small intestinal propulsion ratio and levels of plasma MTL, CORT and CA were surpressed significantly (P < 0.01) while the content of CGRP was improved obviously (P < 0.01) in over-training group.

CONCLUSIONMelatonin plays an important role in protecting gastrointestinal tract from dysfunction, in which MTL, CGRP, CORT and CA are all involved.