子宮筋収縮系と弛緩系による二重制御機構からみた分娩発来機序の解析(1子宮収縮機構とその制御)

概要

論文の詳細を見る
The aim of this study is to analyze the mechanism of the maintenance of pregnancy as well as the initiation of parturition from the view point of regulation of myometrial contraction and relaxation, and of uterine cervical ripening. As for the regulation of myometrial relaxation, we investigated the expression of nitric oxide synthase (NOS) as well as activities of its target enyzme, soluble guanylate cyclase (sGC) that produces cGMP, in the human pregnant myometrium. The protein expression of endothelial nitric oxide synthase (eNOS) was detected mainly in endothelial cells and myometrial smooth muscle cells, which increased significantly in the first trimester of pregnancy and decreased at term before labor onset. Moreover, the enzymatic activities of sGC as well as the cGMP content in the myometrium decreased 12% and 40% at term even before the onset of labor, respectively. Therefore, it is plausible that both synthesis of nitric oxide and cGMP production in the myometrium are down-regulated just before the onset of labor, approximately at 37 weeks of gestation. Regarding the regulation of myometrial contraction, we measured prostaglandin E_2 (PGE_2) concentrations in the amniotic fluids at various gestational weeks before the onset of labor. The amniotic fluid PGE_2 levels slightly increased roughly at 37 weeks of gestation, suggesting the possibility that PGE_2 production from amnion may be slightly activated before the onset of labor. After the onset of labor, the expression of cyclooxigenase-2 (COX-2) as well as cytosolic phospholipase A_2 (cPLA_2), the key enzymes of PG synthesis, dramatically increased in amnion and decidua especially near the dilated cervical canal, suggesting that PGE_2 and PGF_<2α> may be secreted mostly from amnion and decidua near the dilated cervical canal in labor. In other words, uterine cervical ripening and dilatation, during the early phase of parturition, may contribute to the augmentation of myometrial contraction by accelerating local PG synthesis in the fetal membrane near the cervix. To clarify the possible contribution of uterine contraction to cervical ripening, we developed cultured human uterine cervical fibroblast cells (CxF cells) and investigated the regulation of production of matrix metalloproteinase-1 (MMP-1), one of key enzymes degrading collagen type I and type III, in the process of cervical ripening, from CxF cells. The stimulation with cyclic mechanical stretch by using Flexercell Strain Unit FX-3000 (Flexcell International Co.), and the treatment with PGF_<2α>, a potent stimulant of myometrial contraction, increased the secretion of MMP-1 from CxF cells, suggesting that uterine contraction as well as PGF_<2α> from decidua may augment cervical ripening by increasing MMP-1 production in the course of parturition. In consideration of the present findings that uterine cervical ripening & dilatation may facilitate the myometrial contraction and also that myometrial contraction may augment uterine cervical ripening, it is specious that myometrial contraction and cervical ripening may amplify each other during active labor. In conclusion, these data leads us to an interesting possibility of serial changes of myometrial tonus throughout the pregnancy ; 1) the augmented myometrial relaxation by nitric oxide and the low activity of myometrial contraction by PG may contribute to the maintenance of pregnancy before parturition, 2) the myometrial relaxation by nitric oxide may be down-regulated and myometrial contraction by PGE_2 production from amnion may be slightly activated just before the onset of labor, as if pregnant uterus prepares for the start of active uterine contraction, and 3) after the onset of labor, myometrial contraction and uterine cervical dilatation may accelerate each other and finally result in giving birth to the neonate.
社団法人日本産科婦人科学会の論文
2000-08-01

子宮筋収縮系と弛緩系による二重制御機構からみた分娩発来機序の解析(1子宮収縮機構とその制御)

スポンサーリンク

概要

著者

関連論文

スポンサーリンク