Nycthemeral variations of cholecystokinin action on intestinal motility inrats: 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 t he melatonin treatment and the melatonin receptors blockade on CCK action. The peripheral administration of CCK-8s (5 mug/kg iv) during the fasted sta te induces an irregular spiking activity corresponding to an excitation of intestinal motility on the duodenum, the jejunum and the ileum. The duratio n of this excitomotor effect is shorter in the dark phase only on the duode num (-60%) and the jejunum (-40) compared to the light phase. During the li ght phase, melatonin (1 mg/kg iv) administered, 10 min prior to CCK-8s, red uces the duration of CCK-8s excitomotor effect only on the duodenum (-42%) and the jejunum (-52%). On the opposite, during the dark phase, the blockad e of melatonin receptors by S 20928 (1 mg/kg sc), 60 min prior CCK-8s, rest ores the excitomotor effect of CCK-8s to its diurnal values. In conclusion, the action of the neurohormone CCK on intestinal motility follows a biolog ical rhythm related to the light-dark cycle. Melatonin, released by the pin eal gland at night, seems to be physiologically involved in this modulation . (C) 2000 Harcourt Publishers Ltd.