Fixed feeding potentiates interdigestive gastric motor activity in rats: importance of eating habits for maintaining interdigestive MMC

Abstract

Ariga H, Imai K, Chen C, Mantyh C, Pappas TN, Takahashi T. Fixed feeding potentiates interdigestive gastric motor activity in rats: importance of eating habits for maintaining interdigestive MMC. Am J Physiol Gastrointest Liver Physiol 294: G655-G659, 2008. First published January 3, 2007 doi:10.1152/ajpgi.00484.2007.-Endogenous ghrelin regulates the occurrence of interdigestive gastric phase III-like contractions in rats. However, the fasted motor pattern is not as regular and potent in humans and dogs. We hypothesize that eating habits play an important role in maintaining a regular interdigestive gastric contractions. We studied the effect of fixed-feeding regimen on interdigestive gastric contractions and plasma acyl ghrelin levels. The fixed-fed rats were trained to the assigned meal feeding regimen, once daily at 12:00 PM to 4:00 PM for 14 days. Free-fed rats were maintained with free access to food. As ghrelin regulates gastric emptying as well, solid gastric emptying was also studied in fixed-fed rats and free-fed rats. In free-fed rats, two of six rats did not show interdigestive gastric phase III-like contractions. In contrast, phase III-like contractions were observed in all rats 14 days after starting the fixed-feeding regimen. The maximal amplitude of phase III-like contractions significantly increased from 8.4 Ϯ 0.6 to 16.3 Ϯ 1.8 g (n ϭ 6, P Ͻ 0.05) 14 days after the start of the fixed feeding. Fasted and postprandial plasma ghrelin levels were significantly increased after 14 days of fixed feeding. Solid gastric emptying was significantly accelerated in fixed-fed rats (72.1 Ϯ 4.2%) compared with that of free-fed rats (58.7 Ϯ 2.7%, n ϭ 6, P Ͻ 0.05). Our present findings suggest that fixed feeding increases plasma ghrelin levels, potent interdigestive contractions, and acceleration of gastric emptying. migrating motor complex; ghrelin; scheduled feeding DURING THE INTERDIGESTIVE state, the stomach and small intestine show a remarkable motor pattern, known as the migrating motor complex (MMC) in dogs (20) and humans (22). MMC consists of three phases: phase I (period of motor quiescence), phase II (period of irregular low-amplitude contractions), and phase III (period of regular high-amplitude contractions). The pulsatile flow immediately ahead of phase III of the MMC implied physiological importance for clearance of secretions, debris, and microbes during fasting and let the stomach be ready to receive a next meal (22).The characteristic feature of gastric MMC is different among species. In humans and dogs, MMC is usually observed every 90 -120 min in the interdigestive state. In contrast, in rats, the MMC cycle is short (less than 20 min) and not as regular as that of humans and dogs (2,7,21). It is rather difficult to distinguish three phases, especially phase III(-like) contractions. Furthermore, sometimes phase III-like contractions are not clearly observed even after a 24-h fasting in rats. These may be explained by the difference of the peptides that regulate MMC. In dogs and humans, gastric ...

Endogenous ghrelin and 5-HT regulate interdigestive gastrointestinal contractions in conscious rats

“…Rats were trained to the assigned meal-feeding regimen once daily at 12:00 -4:00 PM. We demonstrated that fixed feeding augments interdigestive gastric contractions (2). We also showed that the plasma ghrelin levels of fasted state are higher than that of fed state in rats (3).…”

“…In humans and dogs, MMC is usually observed every 90 -120 min the interdigestive state. In contrast, MMC cycle is short (less than 20 min) in rats and not so regular as that of humans and dogs (2,18,53). Since it is rather difficult to distinguish three phases in rats, these phases are called as phase I-like contractions and phase III-like contractions in rats (3,18,53).…”

Effects of ghrelin on interdigestive contractions of the rat gastrointestinal tract

“…In humans and dogs, MMC is usually observed every 90-120 min in the interdigestive state. In contrast, in rats, MMC cycle is less than 20 min and not so regular, compared to humans and dogs [2,3] . Exogenously administered motilin does not induce phase Ⅲ-like contractions in rats.…”

“…The wires from transducer were exteriorized through abdominal wall, ran under skin toward the back. Intravenous catheter was inserted into right jugular vein, and similarly exteriorized to the back, as previously reported [2,9] . The catheter was filled with heparinized saline (100 U/mL) to prevent coagulation.…”

“…After the implantation of transducers, rats were given food once daily at 12:00 pm-16:00 pm, as previously reported [2] . Experiments of GI motility recording were started at 9:00 am every day.…”