Circadian rhythm of gastric inhibitory polypeptide (GIP) in man

The diurnal variations of serum gastric inhibitory polypeptide (GIP), serum insulin, plasma glucagon, plasma glucose and serum triglycerides were studied for 24 hr in 6 healthy young men, consuming three meals and performing their usual physical activities. Serum GIP levels peaked after each meal and stayed significantly elevated from the peak after lunch till late night. Glucose and insulin showed early and short-lasting postprandial peaks, declining thereafter to basal values within a short time. Plasma glucagon was inhibited by the meal ingestion and fluctuated around the basal levels in the interdigestive periods. On the other hand, serum triglycerides tended to parallel GIP changes for most of the day, being significantly elevated starting from lunch consumption to late night. The present results suggest that GIP may have effects other than the insulinogenic one, being probably involved in the control of lipid metabolism.