EFFECT OF MORPHINE ON GASTROESOPHAGEAL REFLUX AND TRANSIENT LOWER ESOPHAGEAL SPHINCTER RELAXATION

Background & Aims: Morphine increases residual lower esophageal sphinc ter (LES) pressure during swallow-induced LES relaxation to levels sho wn experimentally to prevent reflux. The hypothesis that morphine redu ces reflux by increasing residual LES pressure during transient LES re laxation was tested in 8 healthy subjects and 8 patients with reflux d isease. Methods: Esophageal pH, LES, and esophageal pressures were rec orded simultaneously during three sequential 30-minute periods, basal, after morphine, and after naloxone, while the stomach was distended b y constant infusion of 10% dextrose. Results: Morphine decreased the n umber 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). Transien t LES relaxation was the major mechanism of reflux, and although morph ine did not affect residual LES pressure during transient LES relaxati ons, it decreased their number markedly in the patients (3.0 +/- 0.5 v s. 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 ef fects of morphine. Conclusions: Morphine reduces reflux in patients wi th reflux disease by decreasing the number of transient LES relaxation s.