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The wall of the uterus is composed of three layers : the perimetrium, the myometrium, and the endometrium. The myometrium is the bulky middle layer of the uterus, composed of interlacing bundles of smooth muscle. The myometrium plays an active role during childbirth when it contracts rhythmically to force the baby out of the mother´s body. But, the mechanism of myometrium contraction has not been known in detail. So, this sutdy has explored effects of Ca2+ channel blocker and K+ channel modulator on the contraction in myometrium isolated from pregnant(21, 15, 7 days after gestation) and non-pregnant rats. The summary of the results is shown below. Verapamil(1 nM, 10 mM) decreased the contraction induced by high KCI in both pregnant and non-pregnant rats, myometrium. However, the decreases did not differ significantly between them. Also, the contraction induced by high KC1 was inhibited by cromakalim(100 nM, 1 mM). But, TEA and apamin did not change the tension in resting non-pregnant rats, myometrium. Sodium nitroprusside, a membrane permeable guanylate cyclase activator, also did not change the contraction induced by high KCI and carbachol. From the facts it should be suggested that K+ channel modulator and cGMP pathway play a role in contraction of rats, uterine smooth muscle, but the effects were inconsiderable.
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