Circulation to Female Reproductive Organs

Role of the placenta in developmental programming: Observations from models using large animals

Developmental programming, which proposes that "insults" or "stressors" during intrauterine or postnatal development can have not only immediate but also long-term consequences for healthy and productivity, has emerged as a major biological principle, and based on studies in many animal species also seems to be a universal phenomenon. In eutherians, the placenta appears to be programmed during its development, which has consequences for fetal growth and development throughout pregnancy, and likewise has long-term consequences for postnatal development, leading to programming of organ function of the offspring even into adulthood. This review summarizes our current understanding of the placenta's role in developmental programming, the mechanisms involved, and the challenges remaining.

Preeclampsia link to gestational hypoxia

Complications of pregnancy remain key drivers of morbidity and mortality, affecting the health of both the mother and her offspring in the short and long term. There is lack of detailed understanding of the pathways involved in the pathology and pathogenesis of compromised pregnancy, as well as a shortfall of effective prognostic, diagnostic and treatment options. In many complications of pregnancy, such as in preeclampsia, there is an increase in uteroplacental vascular resistance. However, the cause and effect relationship between placental dysfunction and adverse outcomes in the mother and her offspring remains uncertain. In this review, we aim to highlight the value of gestational hypoxia-induced complications of pregnancy in elucidating underlying molecular pathways and in assessing candidate therapeutic options for these complex disorders. Chronic maternal hypoxia not only mimics the placental pathology associated with obstetric syndromes like gestational hypertension at morphological, molecular and functional levels, but also recapitulates key symptoms that occur as maternal and fetal clinical manifestations of these pregnancy disorders. We propose that gestational hypoxia provides a useful model to study the inter-relationship between placental dysfunction and adverse outcomes in the mother and her offspring in a wide array of examples of complicated pregnancy, such as in preeclampsia.

Effects of maternal nutrient restriction followed by realimentation during midgestation on uterine blood flow in beef cows

The objective was to examine the effect of maternal nutrient restriction followed by realimentation during midgestation on uterine blood flow (BF). On Day 30 of pregnancy, lactating, multiparous Simmental beef cows were assigned randomly to treatments: control (CON; 100% National Research Council; n = 6) and nutrient restriction (RES; 60% of CON; n = 4) from Day 30 to 140 (period 1), and thereafter, realimented to CON until Day 198 of gestation (period 2). Uterine BF, pulsatility index (PI), and resistance index (RI) were obtained from both the ipsilateral and contralateral uterine arteries via Doppler ultrasonography. Generalized least square analysis was performed. Ipsilateral uterine BF in both groups increased quadratically (P < 0.01) during period 1 and linearly (P < 0.01) during period 2. There was a treatment (P = 0.05) effect during period 2; where RES cows had greater ipsilateral BF versus CON. Ipsilateral uterine PI and RI decreased linearly (P ≤ 0.01) during period 1 across treatments. Contralateral uterine BF in CON cows tended (P < 0.09) to be greater versus RES in both periods. Contralateral PI in both groups increased linearly (P ≤ 0.01) during period 1. Contralateral uterine RI was increased (P ≤ 0.05) in RES cows versus CON in both periods. There was no interaction or treatment effect (P ≥ 0.24) for total BF during either period. Nutrient restriction does not alter total uterine BF, but it may increase vascular resistance. However, up on realimentation, local conceptus-derived vasoactive factors appear to influence ipsilateral uterine BF.

Decreased function of voltage-gated potassium channels contributes to augmented myogenic tone of uterine arteries in late pregnancy

Increased pressure-induced (myogenic) tone in small uteroplacental arteries from late pregnant (LP) rats has been previously observed. In this study, we hypothesized that this response may result from a diminished activity of vascular smooth muscle cell (SMC) voltage-gated delayed-rectifier K+(Kv) channels, leading to membrane depolarization, augmented Ca2+influx, and vasoconstriction (tone). Elevation of intraluminal pressure from 10 to 60 and 100 mmHg resulted in a marked, diltiazem-sensitive rise in SMC cytosolic Ca2+concentration ([Ca2+]i) associated with a vasoconstriction of uteroplacental arteries of LP rats. In contrast, these changes were significantly diminished in uterine arteries from nonpregnant (NP) rats. Gestational augmentation of pressure-induced Ca2+influx through L-type Ca2+channels was associated with an enhanced SMC depolarization, the appearance of electrical and [Ca2+]ioscillatory activities, and vasomotion. Exposure of vessels from NP animals to 4-aminopyridine, which inhibits the activity of Kvchannels, mimicked the effects of pregnancy by increasing pressure-induced depolarization, elevation of [Ca2+]i, and development of myogenic tone. Furthermore, currents through Kvchannels were significantly reduced in myocytes dissociated from arteries of LP rats compared with those of NP controls. Based on these results, we conclude that decreased Kvchannel activity contributes importantly to enhanced pressure-induced depolarization, Ca2+entry, and increase in myogenic tone present in uteroplacental arteries from LP rats.

Upregulation of endothelial cell Ca2+ signaling contributes to pregnancy-enhanced vasodilation of rat uteroplacental arteries

Normal pregnancy is characterized by an increased uterine blood flow due to growth and remodeling of the maternal uterine vasculature and enhanced vasodilation of the uterine arteries. The objective of the present study was to examine the role of endothelial cell Ca2+ signaling in augmented endothelium-mediated vasodilation of uteroplacental arteries in late pregnancy. We performed fura-2-based measurements of the intracellular Ca2+ concentration ([Ca2+]i) in the cytoplasm of endothelial cells simultaneously with diameter in pressurized uterine arteries from nonpregnant (NP) and late-pregnant (LP) rats. Basal levels of endothelial cell [Ca2+]i were higher in arteries from LP rats compared with NP controls. Withdrawal of extracellular Ca2+ resulted in a decrease in the level of basal [Ca2+]i that was significantly larger in arteries of LP than NP rats. The rate of Mn2+ -induced quenching of fura-2 fluorescence was significantly elevated in late pregnancy, implicating augmented Ca2+ influx as a cause of increased basal levels of [Ca2+]i in endothelial cells. Elevation of intraluminal pressure resulted in a transient increase in endothelial [Ca2+]i that was markedly potentiated in late gestation. ACh-induced [Ca2+]i and vasodilator responses were significantly augmented in arteries of LP compared with NP rats and were abolished by BAPTA treatment, demonstrating a critical role of [Ca2+]i elevation in the production of endothelium-derived vasodilators. Together, these results indicate that late pregnancy is a state of enhanced basal and stimulated Ca2+ signaling in endothelial cells of uterine vessels, which may represent an important underlying mechanism for augmented vasodilation in the maternal uterine circulation.

Effect of chronic hypoxia on adrenoceptor responses of ovine foetal umbilical vessels

1. The effects of chronic hypoxia on alpha1-adrenoceptor-mediated contractions were investigated in foetal umbilical vessels obtained from near-term (approximately 140 day gestation) pregnant sheep maintained near sea level ( 300 m) and at high altitude (3820 m) from 30 day gestation. 2. Chronic hypoxia significantly decreased contractile sensitivity of the umbilical vein to noradrenaline (pD2: 6.22+/-0.19 vs 5.67+/-0.09) and reduced the maximum response by 43%. Noradrenaline-induced contraction of the umbilical artery was abolished. In contrast, contractions to KCI were not affected by chronic hypoxia. 3. In umbilical vein, the apparent dissociation constant (KA) of noradrenaline to alpha1-adrenoceptors was increased from 0.54+/-0.06 microM in control animals to 1.35+/-0.14 microM in chronically hypoxic animals. In accordance, radioligand binding of agonist showed high and low affinity binding sites for noradrenaline in both normoxic and chronically hypoxic tissues. Addition of GTPgammaS (100 microM) abolished apparent high affinity binding sites. Whereas proportional binding sites were not changed by chronic hypoxia, the apparent high affinity of noradrenaline was significantly decreased (pKi: 7.80+/-0.17 vs 7.20+/-0.16). 4. Chronic hypoxia significantly decreased alpha1-adrenoceptor density (fmol mg protein(-1)) in umbilical vein (24.6+/-3.2 vs 12.3+/-3.1) and the artery (7.1+/-0.4 vs 3.1+/-0.9) with no change in [3H]-prazosin binding affinity. There was a linear correlation of the maximum contractions to noradrenaline and alpha1-adrenoceptor density. 5. We conclude that chronically hypoxic-induced depression in contractions of ovine foetal umbilical vessels to noradrenaline is mediated predominantly by decreases in alpha1-adrenoceptor density and the agonist binding affinity.