Ramsay B, Sooranna S R, Johnson M R
Academic Department of Obstetrics and Gynaecology, Chelsea and Westminister Hospital, London, United Kingdom.
Obstet Gynecol. 1996 Feb;87(2):249-53. doi: 10.1016/0029-7844(95)00391-6.
To study the changes in nitric oxide synthase activities in human myometrium and trophoblast throughout pregnancy and around delivery.
Samples of villous trophoblast were collected from women undergoing elective cesarean delivery at term (n = 12) or voluntary termination of pregnancy in the first (n = 27) or second (n = 11) trimesters of pregnancy. Myometrial samples were obtained from nonpregnant women undergoing hysterectomy (n = 5) and pregnant women both before (n = 7) and after (n = 7) the onset of spontaneous labor at term. Nitric oxide synthase activity was quantified for homogenized samples using the L-citrulline assay in the presence and absence of calcium.
The highest levels of nitric oxide synthase activity were found in first-trimester villi (range 2-29 nmol L-citrulline/minute/g protein), with a significant fall in activity in the third trimester (range 2-10 nmol L-citrulline/minute/g protein; P < .001 for both calcium-dependent and calcium-independent activity). Myometrial activities were relatively low compared with those in the trophoblast (0-2 nmol L-citrulline/minute/g protein), with no significant differences in calcium-dependent activities between subgroups. Myometrial calcium-independent activities were lower in pregnant than in nonpregnant women (P = .007), with those in labor having levels higher than those not in labor (P = .048).
Levels of nitric oxide synthase activity are relatively high in villous trophoblast, particularly during the first trimester. Although the contribution to total nitric oxide production in the uterus by myometrial nitric oxide synthase appears to be relatively small, nitric oxide produced by the trophoblast may play a role in maintaining uterine quiescence by a paracrine effect. Further work is needed to test this hypothesis and explore other possible roles for trophoblast-derived nitric oxide in early pregnancy.
研究妊娠全过程及分娩前后人子宫肌层和滋养层中一氧化氮合酶活性的变化。
从足月择期剖宫产的妇女（n = 12）、妊娠早期（n = 27）或中期（n = 11）自愿终止妊娠的妇女中采集绒毛滋养层样本。子宫肌层样本取自接受子宫切除术的非妊娠妇女（n = 5）以及足月自然临产前后的妊娠妇女（n = 7）。在有钙和无钙的情况下，使用L - 瓜氨酸测定法对匀浆样本中的一氧化氮合酶活性进行定量。
在妊娠早期绒毛中发现一氧化氮合酶活性最高（范围为2 - 29 nmol L - 瓜氨酸/分钟/克蛋白质），在妊娠晚期活性显著下降（范围为2 - 10 nmol L - 瓜氨酸/分钟/克蛋白质；钙依赖性和非钙依赖性活性均P <.001）。与滋养层相比，子宫肌层的活性相对较低（0 - 2 nmol L - 瓜氨酸/分钟/克蛋白质），各亚组之间钙依赖性活性无显著差异。妊娠妇女子宫肌层非钙依赖性活性低于非妊娠妇女（P =.007），临产妇女的该活性水平高于未临产妇女（P =.048）。
绒毛滋养层中一氧化氮合酶活性水平相对较高，尤其是在妊娠早期。尽管子宫肌层一氧化氮合酶对子宫总一氧化氮产生的贡献似乎相对较小，但滋养层产生的一氧化氮可能通过旁分泌作用在维持子宫静息中发挥作用。需要进一步开展工作来验证这一假设，并探索滋养层来源的一氧化氮在早期妊娠中的其他可能作用。
