Modification of the synergism acetylcholine-eserine induced by morphine in amphibian muscle.

The modification of the synergism acetylcholine-eserine induced by two different concentrations of morphine (0.2 and 8 microgram/ml) was studied on the frog rectus abdominis muscle. Morphine increases the Ach-potentiating action of low concentrations of eserine (from 3 to 40 ng/ml). On the contrary at higher eserine concentrations (from 0.1 to 1.0 microgram/ml), morphine reduces the potentiation of Ach effects caused by eserine. It is concluded that in amphibian muscle eserine and morphine potentiate the effects of exogenous Ach by acting on the same population of receptors.