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[The pattern of spontaneous contraction and the effects of Mg++ and terbutaline on pregnant human myometrium].

The isometric spontaneous contraction and K-contracture of pregnant human myometrium were recorded in order to study the effects of external Mg++ and the correlation between Mg++ and terbutaline. Electrical activities were also recorded with a single sucrose-gap method. Maximum tension, frequency and half duration of spontaneous contractions were not significantly different among all specimens. Maximum tension of the spontaneous contraction was lower than the longitudinal muscle of pregnant rat and higher than the circular one. The frequency was lower and the duration was longer than rat myometrium. Mg++ exhibited the inhibition of the spontaneous contraction and decreased the gradient of pacemaker potential and duration of action potentials. Phasic contraction of K-contracture was also inhibited by the pre-incubation with Mg++. Mg++ rich medium shifted the dose-response curve of terbutaline to the left and the pre-incubation with Mg++ increased the inhibitory effect of terbutaline on the tonic part of K-contracture. The results indicated that human myometrium might be constructed of plural muscle bundles with different characteristics, and Mg++ inhibited the spontaneous contraction by affecting the membrane activities and enhanced the terbutaline effect by penetrating into the membrane.