Diurnal profile of plasma motilin concentrations during fasting and feeding in man.

Oscillations in basal plasma levels of the pancreatic hormones; insulin, glucagon and pancreatic polypeptide have been reported previously. We now report on oscillations in circulating motilin-like immunoreactivity (MLI) in fasted and fed man. Six healthy subjects were studied during two 36-hour test periods, one while fasting and another with the regular ingestion of equicaloric meals at 0800, 1200 and 1800 hours. Blood was sampled every 30 min. from 0800 to 2400 and every 60 min. from 2400 to 0800 the next morning. In the fasting state the mean +/- S.E. concentrations in plasma for the 6 subjects were: MLI, 180 +/- 19.4 pg/ml, insulin 4.4 +/- 1.1 microU/ml, pancreatic polypeptide (hpp), 119 +/- 25.0 pg/ml, and glucose 82 +/- 6.4 mg/dl. Large oscillations in plasma MLI were detected with 1/2 amplitude of 23.2 +/- 4.7% of mean, and a period of 159 min. which varied according to each subject. Plasma hpp levels fluctuated similarly, and a good correlation was found between MLI and hPP indicating a rhythmic secretion of these peptides by the gut and pancreas. MLI fluctuations were independent of insulin which revealed a significant oscillation with a period of 320 min. The ingestion of meals caused the expected increase in circulating levels of insulin, hPP, and glucose. In contrast a decrease in the concentration of MLI was observed. An inverse correlation was found between MLI and glucose and between MLI and insulin. Thus, fasting is associated with large oscillations of motilin, the gut motility hormone, which are suppressed by feeding. The increase in glucose and/or insulin may be important in suppressing motilin secretion during feeding.