Abstract

The potassium-depolarized rat uterus is highly sensitive to calcium. It responds to calcium by contraction and to calcium-chelating agents by relaxation. Magnesium antagonizes or potentiates the contractile effect of calcium in different concentrations.

Isoproterenol produces relaxation which is antagonized competitively by DCI and nonspecifically by chelating agents. The relaxant effect of isoproterenol in potassium-Ringer deteriorates in time but can be restored by temporary immersion in sodium-Ringer. A hypothesis is discussed according to which relaxation is due to a decrease of free intracellular calcium.