The stimulant action of acetylcholine and catecholamines on the uterus

Abstract

The α action of catecholamines on oestrogen dominated guinea-pig uterus is stimulant. The cell membrane is depolarized, membrane conductance is increased, spike discharge is accelerated and tension develops. This action resembles that of acetylcholine though catecholamines are less potent, and, in equiactive concentrations, catecholamines have a longer latency and a longer duration of action. Evidence, obtained by modifications of the ionic environment, indicates that the depolarization by acetylcholine is due to an increase in sodium and calcium permeability and that acetylcholine can release calcium from intracellular stores. The depolarization by catecholamines is due to an increase in chloride permeability and, in addition, sodium is required for the ensuing increase of spike discharge. Catecholamines produce an increase in the force of contraction, long outlasting their immediate stimulation. Moreover, their effect on membrane potential and membrane conductance persists in the presence of lanthanum. These results suggest that Ca release from intracellular stores may be the primary effect produced by the α action of catecholamines and that the increase in the cytoplasmic Ca ²⁺ concentration may cause the changes at the cell membrane.