CIRCADIAN CONTROL OF INSULIN-SECRETION IS INDEPENDENT OF THE TEMPORALDISTRIBUTION OF FEEDING

To investigate whether there is a circadian regulation of insulin secr etion, rats were adapted to a feeding regimen of six meals equally dis tributed over 24 h. Under these conditions basal glucose and insulin l evels increased during the light phase and decreased during the dark p hase. Maximal blood glucose responses were fairly similar during the s ix different meals, but glucose increments were clearly delayed during the last two meals consumed during the light period. Insulin incremen ts were highest during the dark phase and clearly diminished during th e second half of the light phase. This situation was reversed when the scheduled meals were replaced by i.v. glucose infusions, i.e., no sig nificant differences were detected between insulin responses, whereas glucose increments were reduced during the dark period. These results show that there is a circadian regulation of basal blood glucose and f eeding-induced insulin responses, which is independent of the temporal distribution of feeding activity. (C) 1998 Elsevier Science Inc.