The effect of morphine on the adrenergic nerves of the isolated guinea-pig jejunum.

Nerves accompanying the mesenteric blood-vessels of the isolated guinea-pig jejunum were stimulated and changes in the longitudinal muscle coat were recorded. Stimulation of the nerves led to a rapid relaxation if the intestine was contracted by a previous administration of histamine. The relaxation was inhibited by morphine and partially restored by nalorphine. Bretylium and atropine also inhibited the relaxation and cocaine increased it somewhat. Morphine, atropine, and bretylium had no significant effect on the depressant action of noradrenaline on histamine contractions, whereas cocaine slightly enhanced the action of noradrenaline. Morphine, but not the other drugs, prevented the inhibitory action of dopamine.