Background & aims: Morphine increases residual lower esophageal sphincter (LES) pressure during swallow-induced LES relaxation to levels shown experimentally to prevent reflux. The hypothesis that morphine reduces reflux by increasing residual LES pressure during transient LES relaxation was tested in 8 healthy subjects and 8 patients with reflux disease.
Methods: Esophageal pH, LES, and esophageal pressures were recorded simultaneously during three sequential 30-minute periods, basal, after morphine, and after naloxone, while the stomach was distended by constant infusion of 10% dextrose.
Results: Morphine decreased the number of reflux episodes and the time at pH < 4 in the patients (3.0 +/- 0.5 vs. 6.2 +/- 1.0 [P < 0.02] and 44% +/- 7% vs. 64% +/- 7% [P < 0.05], respectively) but not in the healthy subjects (P = NS). Transient LES relaxation was the major mechanism of reflux, and although morphine did not affect residual LES pressure during transient LES relaxations, it decreased their number markedly in the patients (3.0 +/- 0.5 vs. 6.6 +/- 1.7 [P < 0.05]) and marginally in the healthy subjects (2.1 +/- 0.4 vs. 2.6 +/- 0.4; P = NS). Naloxone completely reversed the effects of morphine.
Conclusions: Morphine reduces reflux in patients with reflux disease by decreasing the number of transient LES relaxations.