Gastric emptying is achieved by co-operation between gastric and duodenal motor activity. Therefore, evaluation of gastric emptying and its associated mechanisms would benefit clinical therapy as well as medical research. Healthy volunteers underwent rapid magnetic resonance imaging (MRI) of the abdomen along the coronal plane after ingestion of a liquid meal. The gastric fundal and duodenal areas were quantified semi-automatically by self-developed segment software. The average gastric fundal area determined by the serosal end in 40 sequential images was reduced to ∼81% 30 min after and to ∼70% 60 min after ingestion of a liquid meal. The average duodenal area also decreased to ∼86% after 30 min and to 83% after 60 min. In contrast, changes in the centre of gravity increased to about fivefold after 30 min and to about threefold after 60 min. The mean velocity of the duodenal wall mimicked changes in the centre of gravity. The application of metoclopramide, a dopamine D 2 receptor antagonist, accelerated gastric emptying, presumably due to facilitated duodenal activity even immediately after liquid meal ingestion. The ingestion of water caused fast gastric emptying in 30 min, accompanied by high duodenal motility, but it ceased after 60 min, presumably reflecting complete gastric emptying. A rapid MRI scan visualized the association between gastric emptying and duodenal motility that could be modified by calories and dopaminergic neurotransmission. Changes in the centre of gravity and mean velocity of the duodenal wall appear to quantify the motility obtained from cine MRI accurately.

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Glutamate is thought to serve as a special signal for gut functions. We investigated the effects of monosodium l‐glutamate (MSG) on gastric emptying and duodenal motility. Ten healthy male volunteers underwent rapid magnetic resonance imaging (MRI) of the abdomen. Coronal images were successively acquired after ingestion of liquid meal (200 kcal in 200 mL: 9 g protein, 28.4 g carbohydrate, 5.6 g fat, 370 mg Na+) with and without 0.5% MSG. During the acquisition of MRI, participants breathed freely. In all participants, the gastric residual volume gradually decreased to 80.1 ± 14.2% without MSG and to 75.9 ± 14.3% with MSG after 60 min (P = 0.45 between the groups, n = 10). In two of 10 participants, gastric emptying slowed down significantly, whereas in the remaining eight participants, gastric residual volume decreased to 84.0 ± 13.1% without MSG, and to 73.0 ± 14.6% with MSG after 60 min (P = 0.015, n = 8). There was no difference in the shape of the stomach between groups. In four of the eight participants responding positively to MSG, the duodenum wall was sufficiently identified to quantify the motions. The inclusion of MSG enhanced duodenal motility, judging from changes in (1) the magnitude of the duodenal area, (2) the center of gravity, and (3) the mean velocity of the wall motions. The third parameter most significantly indicated the excitatory effect of l‐glutamate on duodenum motility (~ three‐ to sevenfold increase during 60 min, P < 0.05, n = 4). These results suggest that MSG accelerates gastric emptying by facilitating duodenal motility, at least in subjects with positive responses to MSG.