No abstract

In the present study, we determined the contribution of myometrial hyperplasia, hypertrophy, and apoptosis to uterine growth during pregnancy. The changes in two endogenous markers of cell replication, proliferating cell nuclear antigen (PCNA) protein expression and bromodeoxyuridine (BrdU) incorporation, were studied. Myocyte hypertrophy was assessed by measuring the protein:DNA ratio. The expression levels of antiapoptotic regulatory proteins (BCL2 and BCL2L1) and enzymes involved in apoptosis (caspases 3, 6, 7, 9, and 10) were assessed by immunoblotting throughout gestation and postpartum. Myometrial cell apoptosis was determined by TUNEL staining and DNA fragmentation assays. Both BrdU incorporation and PCNA labeling were elevated in early pregnant myometrium and decreased dramatically after midgestation, with a simultaneous increase in cellular hypertrophy. Levels of BCL2 were high during early gestation, followed by significantly elevated levels of BCL2L1 at midgestation. The expression of caspase 10 in myometrial samples declined from a high nonpregnant level to a complete loss at early gestation. The cleaved forms of caspases (CC) 3, 6, 7, and 9, as well as poly(ADP-ribose)polymerase-1, were undetectable in the myometrial samples at early or late gestation but were transiently elevated at midgestation. Immunohistochemical staining of CC3 confirmed the activation of the caspase cascade, but TUNEL-positive staining or the increase in DNA fragmentation was not detected. Collectively, two distinct phases of myometrial growth were observed: myocyte hyperplasia associated with an increase in antiapoptotic proteins during the first half of gestation, and cellular hypertrophy during the second part of gestation. The transition between these phases was associated with transient activation of the caspase cascade that triggered the differentiation of uterine smooth muscle.

Abstract-Preeclampsia is associated with impaired uteroplacental adaptations during pregnancy and abnormalities in the endothelial NO synthase (eNOS)-NO pathway, but whether eNOS deficiency plays a causal role is unknown. Thus, the objective of the current study was to determine the role of eNOS in the mother and/or conceptus in uteroplacental changes during pregnancy using eNOS knockout mice. We quantified uterine artery blood flow using microultrasound, visualized the uteroplacental vasculature using vascular corrosion casts, and used pimonidazole and hypoxia-inducible factor 1␣ immunohistochemistry as markers of hypoxia in the placentas of eNOS knockout mice versus the background strain, C57Bl/6J (wild type). We found that increases in uteroplacental blood flow, uterine artery diameter, and spiral artery length were reduced, and markers of placental hypoxia in the junctional zone were elevated in late gestation in eNOS knockout mice. Both maternal and conceptus genotypes contributed to changes in uterine artery diameter and flow. Despite placental hypoxia, placental soluble fms-like tyrosine kinase 1 and tumor necrosis factor-␣ mRNA, and in maternal plasma, soluble fms-like tyrosine kinase 1 were not elevated in eNOS knockout mice. Thus, our results show that both eNOS in the mother and the conceptus contribute to uteroplacental vascular changes and increased uterine arterial blood flow in normal pregnancy. Key Words: preeclampsia/pregnancy Ⅲ blood flow regulation Ⅲ NO Ⅲ hypoxia Ⅲ placenta Ⅲ endothelial NO synthase T he maternal cardiovascular system undergoes structural and functional changes to accommodate the increased circulatory requirements of the growing fetus. Nowhere is this more profound than in the uteroplacental vasculature, where a marked increase in uteroplacental blood flow is achieved by a large reduction in vascular resistance 1,2 and pronounced enlargement and structural reorganization of the uterine and spiral arteries.3 Failure to make or to sustain these changes may result in preeclampsia, one of the most common and serious complications of human pregnancy.The mechanisms mediating uteroplacental changes during pregnancy are not fully understood. However, the L-arginine-NO pathway appears to play a central role in both normal pregnancy and in preeclampsia. 4 In preeclampsia in humans, diverse elements of the l-arginine-NO signaling pathway may be abnormal, including reduced l-arginine substrate or cofactor availability, reduced endothelial NO synthase (eNOS) enzyme activity attributed to gene polymorphisms, or elevated levels of asymmetrical dimethylarginine. 4 In pregnant rats 5 and mice, 6 NO synthase inhibition with N G -nitro-L-arginine methyl ester induces preeclamptic signs.Despite considerable evidence implicating eNOS in preeclampsia, eNOS knockout (KO) mice do not develop the hallmark signs, gestational hypertension 7-9 or proteinuria. 9Indeed, arterial pressure in eNOS KO mice decreases during pregnancy to become similar to that of pregnant wild-type controls. 7-9 Nevertheless, t...