Objective: To observe the role of leptin on the regulation of inter-digestive migrating motor complex (MMC) and gastric motility of postprandial period, as well as the serum leptin level and its relationship with motilin during different fast and postprandial periods.
Methods: Strain gauges were implanted on the serosa of corpus, antrum and pylorus in 50 conscious Wistar rats to record the gastric motility activities. Canula was inserted in the external jugular vein for drug perfusion and blood sampling. The rats were randomly divided into 5 groups: (1) Group 1 to observe the relationship between the postprandial fasting MMC and MMC after feeding. MMC on the empty stomach was recorded, soon afterwards test meal was fed, then the gastric motility was recorded for 60 minutes. Blood samples were collected during the phases I, II, III, and IV, 3 minutes after feeding and then every 5 minutes to test the serum leptin and motilin. (2) Leptin group. After the recording of the first MMC, leptin was perfused during the second MMC to observe its effect on the stomach motility. (3) Anti-leptin serum group. During the second MMC, 5 minutes before feeding and 60 minutes after feeding, anti-leptin serum was perfused to observe its effect on the postprandial stomach motility. (4) Leptin + atropine group. During the first MMC perfusion of atropine was followed by perfusion of leptin. and (5) leptin + cholecystokinin (CCK)-A receptor blocker group. Perfusion of CCK-A receptor blocker was followed by perfusion of leptin. Serum leptin and motilin levels were measured by radioimmunoassay.
Results: Typical MMC with phase I, II, III, and IV was recorded in the fasting rats. The phase III of antral MMC could migrate to the pylorus. During the postprandial period, the gastric motility patterns were persistent rhythmic peristaltic contractions. When the stomach was empty, the mean concentration of serum leptin was (5.6 +/- 1.0) microg/L, (11.4 +/- 2.1) microg/L, and (2.1 +/- 0.7) microg/L during the phase I, II and III respectively, being the highest in the phase II, significantly higher than those in the phase I and III (both P < 0.01). During digestive period, the serum concentration of leptin began to increase 3 minutes after the meal and reached its peak of (28.1 +/- 4.4) microg/L 10 minutes after the meal. The serum concentration of leptin remained on a high level till 30 minutes later (compared with that in the inter-digestive period, P < 0.01). On the contrary, the serum concentration of motilin was the highest in the phase III of MMC and the lowest in the digestive period. Intravenous infusion of leptin (2.5 microg x kg(-1) x 10 min) turned the inter-digestive pattern of gastric motility to digestive period pattern with corpus distension and contraction of antrum and pylorus. The effects of leptin on gastric motility were blocked by anti-leptin serum, atropine, and CCK-A receptor blocker loxiglumide.
Conclusion: Leptin is a hormone to promote the inter-digestive MMC phase II and postprandial digestive motility activities of stomach, the concentration fluctuation of which will cause satiety related delay of gastric emptying. The effect of leptin on gastric motility is mediated by cholinergic nerve and CCK-A receptors.