Morphine responders with unexplained pain after cholecystectomy may have sympathetic overactivity

In patients with unexplained pain after cholecystectomy, morphine often induces pain and may increase plasma aspartate aminotransferase activity because of exaggerated or prolonged rises in pressure within the biliary system. Previous studies have demonstrated that patients showing increases in aspartate aminotransferase have increases in plasma concentrations of noradrenaline and dopamine prior to and soon after induction of pain. The purpose of this study was to assess sympathetic activity under basal conditions in patients with (responders) and without (non-responders) increases in aspartate aminotransferase after challenge with morphine. When compared to non-responders, morphine responders had higher plasma concentrations of noradrenaline (p = 0.0001) and dopamine (p = 0.02) and higher urinary excretion of noradrenaline over 24 h (p = 0.03). Plasma and urinary levels of adrenaline were similar in the two groups. These observations indicate higher basal levels of sympathetic activity in the subgroup of patients showing increases in aspartate aminotransferase after challenge with morphine.