Vein size in intact and hysterectomized mice during the estrous cycle and pregnancy

Origin and flow-mediated remodeling of the murine and human extraembryonic circulation systems

The transduction of mechanical stimuli produced by blood flow is an important regulator of vascular development. The vitelline and umbilico-placental circulations are extraembryonic vascular systems that are required for proper embryonic development in mammalian embryos. The morphogenesis of the extraembryonic vasculature and the cardiovascular system of the embryo are hemodynamically and molecularly connected. Here we provide an overview of the establishment of the murine and human vitelline and umbilico-placental vascular systems and how blood flow influences various steps in their development. A deeper comprehension of extraembryonic vessel development may aid the establishment of stem-cell based embryo models and provide novel insights to understanding pregnancy complications related to the umbilical cord and placenta.

Mechanotransduction and Uterine Blood Flow in Preeclampsia: The Role of Mechanosensing Piezo 1 Ion Channels

There is a large increase in uterine arterial blood flow during normal pregnancy. Structural and cellular adjustments occur in the uterine vasculature during pregnancy to accommodate this increased blood flow through a complex adaptive process that is dependent on multiple coordinated and interactive influences and this process is known as "vascular remodeling." The etiology of preeclampsia involves aberrant placentation and vascular remodeling leading to reduced uteroplacental perfusion. The placental ischemia leads to development of hypertension and proteinuria in the mother, intrauterine growth restriction, and perinatal death in the fetus. However, the underlying source of the deficient vascular remodeling and the subsequent development of preeclampsia remain to be fully understood. Mechanoreceptors in the vascular system convert mechanical force (shear stress) to biochemical signals and feedback mechanisms. This review focuses on the Piezo 1 channel, a mechanosensitive channel that is sensitive to shear stress in the endothelium; it induces Ca2+ entry which is linked to endothelial nitric oxide synthase (eNOS) activation as the mechanoreceptor responsible for uterine vascular dilatation during pregnancy. Here we describe the downstream signaling pathways involved in this process and the possibility of a deficiency in expression of Piezo 1 in preeclampsia leading to the abnormal vascular dysfunction responsible for the pathophysiology of the disease. The Piezo 1 ion channel is expressed in the endothelium and vascular smooth muscle cells (VSMCs) of small-diameter arteries. It plays a role in the structural remodeling of arteries and is involved in mechanotransduction of hemodynamic shear stress by endothelial cells (ECs).

Hemodynamic, vascular, and reproductive impact of FMS-like tyrosine kinase 1 (FLT1) blockade on the uteroplacental circulation during normal mouse pregnancy

To investigate the role of FMS-like tyrosine kinase 1 (FLT1, also known as VEGFR1) signaling during pregnancy, mice were injected with anti-FLT1 neutralizing antibody (Ab) beginning on Gestational Day 8 or 12 and every other day thereafter until Day 18; vehicle-only injected mice served as controls. Uterine artery blood flow was measured with ultrasound on Days 13 and 18, and morphometric measurements of the uterine arcade were carried out on Day 19 to provide a measure of gestational vascular remodeling; reproductive performance was evaluated by determining litter size, resorption rates, and pup and placental weights. Ab injections beginning on Day 8 or Day 12 resulted in significant reductions of uterine artery peak systolic and diastolic flows at Days 13 and 18. In addition, normal reproductive function was compromised, as evidenced by a significant reduction in average number of viable pups along with enhanced resorption rates. Reproductive performance was also significantly compromised in this group, although less severely. There was no evidence of a reduction in main uterine artery diameters, though arterial distensibility was reduced, and the diameter of the main uterine vein was significantly smaller in the Ab-injected mice. Significant reductions in main uterine artery and segmental artery length were also noted. Placental and pup weights were similar in all the groups. FLT1 inhibition during murine pregnancy impaired blood flow to the fetal-placental unit, compromised several indices of vascular remodeling, reduced fecundity, and increased fetal reabsorptions. The effects of FLT1 inhibition are most pronounced when targeted during early pregnancy.

Maternal uterine vascular remodeling during pregnancy

Sufficient uteroplacental blood flow is essential for normal pregnancy outcome and is accomplished by the coordinated growth and remodeling of the entire uterine circulation, as well as the creation of a new fetal vascular organ: the placenta. The process of remodeling involves a number of cellular processes, including hyperplasia and hypertrophy, rearrangement of existing elements, and changes in extracellular matrix. In this review, we provide information on uterine blood flow increases during pregnancy, the influence of placentation type on the distribution of uterine vascular resistance, consideration of the patterns, nature, and extent of maternal uterine vascular remodeling during pregnancy, and what is known about the underlying cellular mechanisms.

Predominance of local over systemic factors in uterine arterial remodeling during pregnancy

This study used a rat model in which pregnancy was surgically restricted to one uterine horn to differentiate between local (fetoplacental) and systemic (endocrine) influences on uterine vascular remodeling during pregnancy. Sprague-Dawley rats with single-horn pregnancies were studied on day 20/22 of gestation and compared to age-matched nonpregnant and late-pregnant controls. The morphology (axial length, lumen diameter, wall thickness) of the main uterine artery and of smaller arcuate vessels showed that vascular growth was dramatically increased in the pregnant versus nonpregnant horn, (P < .05). Arcuate artery wall thickness increased in the nonpregnant horn (compared to nonpregnant controls, P < .05), suggesting a limited role for systemic hormonal influences on vascular remodeling. Notably, animals with only one functional horn compensated by increasing the average number of implantation sites per horn from 7.6 to 12.9, thereby maintaining essentially normal litter size without any reduction in fetal or placental weights. These results demonstrate unequivocally that local rather than systemic influences play the dominant role in uterine vascular gestational remodeling of both large and small uterine arteries, and reveal a significant adaptive process that maintains relatively normal fecundity in spite of surgical restriction of normal bilateral pregnancy.

Specific response of ovarian and uterine veins of mice to sex hormones

Pellets of glass (control), progesterone (P), testosterone (T), and estradiol-17beta (E) were placed on the mesentery or subcutaneously in the flank in ovariectomized (O) and ovariectomized-hysterectomized (OH) mice, insuring that all or most of the hormone would pass through the superior mesinteric or circumflex iliac veins. After 21 days the diameters of these and of the ovarian, uterine, and femoral veins and inferior vena cava were measured at autopsy. T and E caused significant enlargement of the uteri; E was also responsible for bladder distention. The ovarian and uterine veins enlarged significantly in mice treated with T and E as compared to the controls. All other veins failed to respond to P, T, and E. The evidence demonstrates a specific response of ovarian and uterine veins in O and OH mice to T and E.