Nycthemeral variations of cholecystokinin action on intestinal motility in rats: effects of melatonin and S 20928, a melatonin receptor antagonist.

The aim of the present work was to investigate the impact of the light-dark cycle on CCK intestinal motor effect and to evaluate the consequence of the melatonin treatment and the melatonin receptors blockade on CCK action. The peripheral administration of CCK-8s (5 microg/kg iv) during the fasted state induces an irregular spiking activity corresponding to an excitation of intestinal motility on the duodenum, the jejunum and the ileum. The duration of this excitomotor effect is shorter in the dark phase only on the duodenum (-60%) and the jejunum (-40) compared to the light phase. During the light phase, melatonin (1 mg/kg iv) administered, 10 min prior to CCK-8s, reduces the duration of CCK-8s excitomotor effect only on the duodenum (-42%) and the jejunum (-52%). On the opposite, during the dark phase, the blockade of melatonin receptors by S 20928 (1 mg/kg sc), 60 min prior CCK-8s, restores the excitomotor effect of CCK-8s to its diurnal values. In conclusion, the action of the neurohormone CCK on intestinal motility follows a biological rhythm related to the light-dark cycle. Melatonin, released by the pineal gland at night, seems to be physiologically involved in this modulation.