Effect of Opiate and Adrenergic Blockers on the Gut Motor Response to Centrally Acting Stimuli

Labyrinthine stimulation and cold pain inhibit feeding antral pressure activity, delay gastric emptying, and increase blood concentrations of β-endorphin and norepinephrine. Further, labyrinthine stimulation induces, in approximately one-third of healthy individuals, a migrating burst of motor activity in the proximal intestine that interrupts the normal fed pattern. Our hypothesis was that endogenous opiates and catecholamines act as mediators of such disruptive effects of centrally acting stressful stimuli on gut motility. Thus, we studied feeding gastrointestinal pressure activity in healthy volunteers who were exposed to labyrinthine stimulation or cold pressure test, or both (both stimuli being either in their active or in their control forms), while receiving an intravenous infusion of either placebo (saline), or an opioid blocker (naloxone), or a combination of α- and β-adrenergic blockers (phentolamine and propranolol), or all the drugs together. Neither opioid nor adrenergic blockers affected motility during control stimulations. Active stressful stimuli (labyrinthine stimulation, cold pain, or both) significantly inhibited antral feeding activity (p < 0.05), but these effects were prevented by concomitant infusion of naloxone (p < 0.05). Adrenergic blockade also prevented the antral motor inhibition caused by stress (p < 0.05), but it was more effective for cold pain than for labyrinthine stimulation, and, when performed concomitantly with opiate blockode, the preventive effects disappeared. Furthermore, during adrenergic blockade labyrinthine stimulation invariably induced the appearance of a migrating duodenal burst of motor activity. Neither opioid nor adrenergic blockers modified the stress-induced rise of plasma β-endorphin and norepinephrine. Our results suggest that opioids and catecholamines are involved in the mediation of the disruptive effects induced by centrally acting stressful stimuli on postprandial motor activity in the proximal human gut.