[The pattern of spontaneous contraction and the effects of catecholamines on pregnant human isthmic myometrium]

The spontaneous isometric contraction of human isthmic myometrium was recorded with regard to the stage of pregnancy, the run of muscle bundles and the resected part of the muscles. Then, the effects of noradrenaline or terbutaline and the relationship between beta-inhibition and Mg2+ were also studied. 1. The frequency of spontaneous contraction was lower than that of rat myometrium, and the amplitude was smaller than the longitudinal muscle of rat under the same conditions. 2. The pattern of the spontaneous contractions was almost the same in different muscle bundles resected from the serosal or endometrial side, and also at different stages of pregnancy. 3. The effect of noradrenaline (10(-12)-10(-6) g/ml) always exhibited alpha-excitatory action and terbutaline (10(-8)-10(-6) g/ml) induced beta-inhibition in every strip. These actions depended on the concentration of the drug. 4. The frequency of spontaneous contractions was gradually decreased and the beta-inhibition of terbutaline (10(-7) g/ml) was progressively potentiated with the increase in external Mg concentration. These results show the fundamental difference in the pattern of spontaneous contractions due to the difference in the arrangement of muscle bundles or species between human and rat, and also suggest that the human myometrium possesses both alpha- and beta-receptors of catecholamine, and the combined therapy using MgSO4 and beta 2-stimulants for premature labor is available, although the physiological role of adrenergic innervation is still unknown.