Effect of melatonin on gastrointestinal transit in rats induced by noise stress and its mechanism

Abstract

AIM:To study the effects of melatonin on gastrointestinal transit function in rats,and its possible mechanism. METHODS:Forty Sprague-Dawley rats were randomly divided into a blank group,control groups 1 and 2,and experimental groups 1 and 2.Experimental and control groups were treated with 15 mg/kg melatonin by intraperitoneal injection,or the same volume of physiological saline,at 30 min before noise stress.Both groups were stimulated separately by 120 dB(A) im- pulse noise of type 56 submachine guns to set up noise stress models.Rats in control group 1 and experimental group 1 were subjected to 1 d stress;rats in control group 2 and experi- mental group 2 were subjected to 3 d stress.We observed the effects of melatonin on stomach residual rate,small intestine transit time and the plasma levels of cortisol,motilin and calcitonin- gene related peptide (CGRP). RESULTS:Stomach residual rate and small in- testine transit time were significantly increased in control groups 1 and 2 compared with those in the blank group (54.52%±4.53%,63.56%±5.51% vs 41.41%±7.74%,58.42%±8.77%,67.98%±6.63% vs 41.26%±6.08%,P0.05).Stomach residual rate and small intestine transit time in experimen- tal group 1 (44.53%±8.93%,44.18%±4.36%) and experimental group 2 (47.52%±4.98%,46.4%±4.96%) were significantly delayed compared with those in the control group (P0.01).However, there was no difference between the experimen- tal group and the blank group.Levels of cortisol and motilin in blood plasma of control 1 and 2 groups were significantly enhanced compared to the blank group (1.99±0.08,2.59±0.09 vs 0.95±0.10,158.09±10.44,180.09±14.85 vs 124.95±7.83, P0.01);the experimental groups (group 1:1.27±0.14,128.67±10.25;group 2:1.63±0.09,134.29±18.33) were degraded significantly compared to the control group (P0.01),but did not change much in comparison with the blank group (P0.05).Level of calcitonin-gene related peptide in blood plasma of control groups 1 and 2 was lower than that of the blank group (125.24±8.5, 134.29±18.33 vs 195.03±7.70,P0.01),and was higher in the experimental group (191.67±10.13, 190.04±11.43) than in the control group (P0.01), but did not significantly differ from blank group (P0.05). CONCLUSION:Melatonin is effective in pre- venting gastrointestinal transit in rats induced by noise stress.Cortisol,CGRP and motilin play an important role in the pathogenesis.