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Background: Caffeine is known to produce various effects on the gastrointestinal tract. Few studies have, however, investigated the effects of caffeine on gastrointestinal myoelectric activity under physiologic conditions. The aims of this study were to investigate the effects of caffeine on colonic motility (spike activity) and gastric and jejunal slow waves in conscious dogs. Methods: The study was performed in eight healthy female hound dogs (15-20 kg) in which one pair of electrodes was implanted on the serosa of the stomach, one pair on the proximal jejunum, and another pair on the ascending colon. The protocol consisted of a 60-min recording as base line and a 90-min recording after intravenous injection of saline, a low dose of caffeine (125 mg), or a high dose of caffeine (250 mg). Results: In the colon there was a significant increase in the number of spike bursts per minute after the injection of both the low (6.69 ± 1.27 versus 8.22 ± 1.31, P < 0.05) and the high dose (4.38 ± 1.23 versus 6.92 ± 0.98, P < 0.05) of caffeine. The increase in the total energy of spikes per minute after the injection of the high dose of caffeine was significantly higher than that after the low dose of caffeine (41.2 ± 14.6 versus 133.4 ± 39.2, P < 0.05). The characteristics of the gastric and jejunal slow waves were, however, not affected by caffeine. Conclusion: Caffeine increases spike activity in the colon, and its effect may be dose-dependent. Gastric and jejunal slow waves are not affected by caffeine. [ABSTRACT FROM AUTHOR]