Effects of calcium channel blockers on the female genital tract.

Contractile activity and vascular resistance in the female genital tract are influenced by several smooth muscle tissues with individual mechanisms for control of mechanical activation. Calcium channel blockers have potent relaxant effects on preparations of human myometrium. The myometrial arteries utilize multiple sources of calcium for contractile activation, and excitation-contraction coupling in isolated vessels from non-pregnant uteri seems comparatively less sensitive to nifedipine than in corresponding myometrial preparations. Contractile activation of myometrial and placental arteries at term is inhibited by nitrendipine and nifedipine. Human oviductal smooth muscle depends on superficially bound calcium for mechanical activation, but only phasic contractions can be abolished by nifedipine, while tonic contractions induced by various agents are more resistant to the calcium channel blocker. Menstrual uterine contractions and pain are effectively counteracted by nifedipine in normal and dysmenorrhoeic women. Such therapy may represent an alternative principle in the treatment of dysmenorrhea. Nifedipine has potent relaxant effects on the mid-term pregnant and the post-partum uterus and calcium channel blockers may prove useful in the treatment of premature labor. Nifedipine and related compounds may further show effective in the treatment of pregnancy-associated hypertension. Whether such treatment in late pregnancy involves maintained or even improved placental perfusion could be assumed from in vitro data but needs further studies.