Abstract

1. The effects of various concentrations of ephedrine and eserine on the actions of adrenaline and acetylcholine respectively were examined in the following preparations under similar conditions: perfused frog heart, cat blood pressure, cat limb volume, perfused rabbit ear, isolated rabbit gut, and cat nictitating membrane.

2. In the first four of these preparations the effects of the two drugs showed a close similarity. Low concentrations of either drug up to about 10^–9 were without effect, while concentrations from about 1O^–9 to 10^–7 produced potentiation, i.e. an increase in the action of the corresponding hormone. At a concentration in the range from 10^–7 to 10^–6, a transition occurred, the effect being reversed from potentiation to depression, and at higher concentrations the degree of depression became greater, until at about 10^–3 the action was completely abolished. These concentration levels were practically identical for the two drugs. The experimental results on isolated rabbit gut and cat nictitating membrane were inconclusive, but as far as they went were in general agreement with the statement above.

3. The action of ephedrine is discussed, and it is concluded that while the close parallelism which exists between the effects of ephedrine and eserine affords some support for the theory that ephedrine acts, in part at least, by inhibiting the enzyme which is responsible for the inactivation of adrenaline, the development of this theory must await further evidence as to the nature and properties of the enzyme.