Effect of ketamine, an NMDA-receptor antagonist, on gastric myoelectric activity in experimental pigs

Summary: Introduction: Preclinical studies in experimental pigs are carried out mostly under general anaesthesia. Ketamine is commonly used for induction of anaesthesia. However, there are concerns that ketamine, an NMDA-receptor antagonist, may influence gastric motor function. The aim of this study was to investigate porcine gastric myoelectric activity by means of electrogastrography (EGG). Methods: Seventeen female animals (mean weight 36.2±3.8 kg) were enrolled. Drugs used for induction of anaesthesia were: Group A (n=5): medetomidine 0.1 mg/kg i. m.; butorphanol 0.3 mg/kg i. m.; midazolam 0.3 mg/kg i. m.; Group B (n=6): azaperon 2.2 mg/kg i. m.; Group C (n=6): ketamine 20 mg/kg i. m.; azaperon 2.2 mg/kg i. m., followed in all groups by i.v. 1% propofol (repeated one-mL boluses, 10–12 mL in total). EGG recording started 15 min. after the induction administration and lasted 30 min. Results were evaluated as the dominant frequency of gastric slow waves (DF) and EGG power (areas of amplitudes). Results: In total, 510 one-minute EGG intervals were assessed. DFs were (mean ± standard deviation): 1.4±0.4 (Group A), 1.3±0.3 (Group B) and 0.2±0.1 cycles per min. (Group C). The differences between group C and groups A and B were statistically significant (p<0.001). Median power (IQR) was 0.13 (0.02–0.44; Group A), 0.13 (0.03–0.54; Group B) and 0.30 V2 (0.07–1.44; Group C). The difference between groups A and C was of borderline significance (p=0.066; type 2 error beta 0.295). Conclusions: Ketamine, administered even in a single intramuscular dose, affected myoelectric function of the porcine stomach. Therefore, it should be avoided in gastrointestinal motility studies in experimental pigs. Key words: ketamine – NMDA (N-methyl-D-aspartate) -receptor antagonist – electrogastrography – myoelectrical activity – experimental pigs