Cortisol-mediated potentiation of uterine artery contractility: effect of pregnancy

During pregnancy, maternal plasma cortisol concentrations approximately double. Given that cortisol plays an important role in the regulation of vascular reactivity, the present study investigated the potential role of cortisol in potentiation of uterine artery (UA) contractility and tested the hypothesis that pregnancy downregulated the cortisol-mediated potentiation. In vitro cortisol treatment (3, 10, or 30 ng/ml for 24 h) produced a dose-dependent increase in norepinephrine (NE)-induced contractions in both nonpregnant and pregnant (138-143 days gestation) sheep UA. However, this cortisol-mediated response was significantly attenuated by approximately 50% in pregnant UA. The 11 beta-hydroxysteroid dehydrogenase (11-beta HSD) inhibitor carbenoxolone did not change the effect of cortisol in nonpregnant UA but abolished its effect in pregnant UA by increasing the NE pD(2) in control tissues from 6.20 +/- 0.05 to 6.59 +/- 0.11. The apparent dissociation constant value of NE alpha(1)-adrenoceptors was not changed by cortisol in pregnant UA but was decreased in nonpregnant UA. There was no difference in glucocorticoid receptor density between nonpregnant and pregnant UA. Cortisol significantly decreased endothelial nitric oxide (NO) synthase protein levels and NO release in both nonpregnant and pregnant UA, but the effect of cortisol was attenuated in pregnant UA by approximately 50%. Carbenoxolone alone had no effects on NO release in nonpregnant UA but was decreased in pregnant UA. These results suggest that cortisol potentiates NE-mediated contractions by decreasing NO release and increasing NE-binding affinity to alpha(1)-adrenoceptors in nonpregnant UA. Pregnancy attenuates UA sensitivity to cortisol, which may be mediated by increasing type-2 11-beta HSD activity in UA.     

Calcium homeostasis and contraction of the uterine artery: effect of pregnancy and chronic hypoxia

The present study tested the hypothesis that chronic hypoxia alters pregnancy-mediated adaptation of Ca2+ homeostasis and contractility in the uterine artery. Uterine arteries were isolated from nonpregnant and near-term pregnant ewes of normoxic control or high-altitude (3820 m) hypoxic (oxygen pressure in the blood [PaO2], 60 mm Hg) treatment for 110 days. Contractions and intracellular-free Ca2+ concentration ([Ca2+]i) were measured simultaneously in the same tissue. In normoxic animals, pregnancy increased norepinephrine (NE), but not 5-hydroxy-thymide (5-HT) or KCl, contractile sensitivity in the uterine artery. Chronic hypoxia significantly attenuated NE-induced contractions in the pregnant, but not nonpregnant, uterine arteries. Similarly, 5-HT-mediated contractions of nonpregnant arteries were not changed. In the pregnant uterine artery, chronic hypoxia significantly increased NE-mediated Ca2+ mobilization, but decreased the Ca2+ sensitivity. In addition, hypoxia increased the calcium ionophore A23187-induced relaxation in pregnant, but not nonpregnant, uterine arteries. However, the A23187-mediated reduction of [Ca2+]i was significantly impaired in hypoxic arteries. In contrast, hypoxia significantly increased the slope of the [Ca2+]i-tension relationship of A23187-induced reductions in [Ca2+]i and tension in the pregnant uterine artery. The results suggest that the contractility of nonpregnant uterine artery is insensitive to moderate chronic hypoxia, but the adaptation of sympathetic tone that normally occurs in the uterine artery during pregnancy is inhibited by chronic hypoxia. In addition, changes in Ca2+ sensitivity of myofilaments play a predominant role in the adaptation of uterine artery contractility to pregnancy and chronic hypoxia.     

Estrogen-dependent regulation of neurokinin 3 receptor-mediated uterine contractility in the rat

The receptors for neurokinin 1 (NK1-R), neurokinin 2 (NK2-R), and neurokinin 3 (NK3-R) are expressed and functionally active in the uterus, promoting strong contractions of the myometrium. Previously, we demonstrated that myometrial contractility activated by the NK-Rs is regulated by estrogen. In the current study, we furthered our investigations of the role of estrogen in the regulation of NK3-R-mediated myometrial contractility. Estrogen promotes both heterologous and homologous desensitization of NK3-R-mediated uterine contractility. In tissue obtained from estrogen-dominated rats (ovariectomized estrogen-treated rats and rats in estrus), the magnitude of uterine contractions decreased in response to consecutive additions of the NK3-R-selective agonist senktide. By addition of the fourth dose of agonist, the contractile response was routinely barely above baseline. In contrast, in tissue obtained from non-estrogen-dominated rats consecutive doses of senktide resulted in contractions of identical magnitude. The homologous desensitization was specific to the NK3-R, and the desensitization of the NK3-R-mediated response did not affect the magnitude or nature of uterine contractions in response to NK1-R or NK2-R activation. Furthermore, heterologous and homologous desensitization of NK3-R-mediated contractility is dependent upon the duration of exposure to estrogen. This complex mechanism appears to be important in intact tissue; capsaicin-mediated release of endogenous neuropeptides resulted in a desensitization of response to subsequent stimulation with senktide in estrogen-dominated uterine tissue.     

Inhibitory effect of GnRH on isolated rat uterine muscle contractility

The effect of GnRH upon uterine contractions of both non-pregnant and pregnant rats was examined in vitro. In the non-pregnant rat uterus, GnRH inhibited in a concentration-and-time dependent manner the contractions induced by acetylcholine and oxytocin, but not those caused by bradykinin and angiotensin II. GnRH also inhibited the rhythmic contractions induced by oxytocin in uterine strips from late pregnant rats. These findings show that GnRH has a direct inhibitory effect on the rat uterine contractions, suggesting that GnRH-like substances may exert modulatory influences upon rat uterine contractility.     

Mechanism of glucose-6-phosphate dehydrogenase-mediated regulation of coronary artery contractility

We previously identified glucose-6-phosphate dehydrogenase (G6PD) as a regulator of vascular smooth muscle contraction. In this study, we tested our hypothesis that G6PD activated by KCl via a phosphatase and tensin homologue deleted on chromosome 10 (PTEN)-protein kinase C (PKC) pathway increases vascular smooth muscle contraction and that inhibition of G6PD relaxes smooth muscle by decreasing intracellular Ca(2+) ([Ca(2+)](i)) and Ca(2+) sensitivity to the myofilament. Here we show that G6PD is activated by membrane depolarization via PKC and PTEN pathway and that G6PD inhibition decreases intracellular free calcium ([Ca(2+)](i)) in vascular smooth muscle cells and thus arterial contractility. In bovine coronary artery (CA), KCl (30 mmol/l) increased PKC activity and doubled G6PD V(max) without affecting K(m). KCl-induced PKC and G6PD activation was inhibited by bisperoxo(pyridine-2-carboxyl)oxovanadate (Bpv; 10 μmol/l), a PTEN inhibitor, which also inhibited (P < 0.05) KCl-induced CA contraction. The G6PD blockers 6-aminonicotinamide (6AN; 1 mmol/l) and epiandrosterone (EPI; 100 μmol/l) inhibited KCl-induced increases in G6PD activity, [Ca(2+)](i), Ca(2+)-dependent myosin light chain (MLC) phosphorylation, and contraction. Relaxation of precontracted CA by 6AN and EPI was not blocked by calnoxin (10 μmol/l), a plasma membrane Ca(2+) ATPase inhibitor or by lowering extracellular Na(+), which inhibits the Na(+)/Ca(2+) exchanger (NCX), but cyclopiazonic acid (200 μmol/l), a sarcoplasmic reticulum Ca(2+) ATPase inhibitor, reduced (P < 0.05) 6AN- and EPI-induced relaxation. 6AN also attenuated phosphorylation of myosin phosphatase target subunit 1 (MYPT1) at Ser855, a site phosphorylated by Rho kinase, inhibition of which reduced (P < 0.05) KCl-induced CA contraction and 6AN-induced relaxation. By contrast, 6AN increased (P < 0.05) vasodilator-stimulated phosphoprotein (VASP) phosphorylation at Ser239, indicating that inhibition of G6PD increases PKA or PKG activity. Inhibition of PKG by RT-8-Br-PET-cGMPs (100 nmol/l) diminished 6AN-evoked VASP phosphorylation (P < 0.05), but RT-8-Br-PET-cGMPs increased 6AN-induced relaxation. These findings suggest G6PD inhibition relaxes CA by decreasing Ca(2+) influx, increasing Ca(2+) sequestration, and inhibiting Rho kinase but not by increasing Ca(2+) extrusion or activating PKG.     

The role of voltage-gated potassium channels in the regulation of mouse uterine contractility

Background  

Uterine smooth muscle cells exhibit ionic currents that appear to be important in the control of uterine contractility, but how these currents might produce the changes in contractile activity seen in pregnant myometrium has not been established. There are conflicting reports concerning the role of voltage-gated potassium (Kv) channels and large-conductance, calcium-activated potassium (BK) channels in the regulation of uterine contractility. In this study we provide molecular and functional evidence for a role for Kv channels in the regulation of spontaneous contractile activity in mouse myometrium, and also demonstrate a change in Kv channel regulation of contractility in pregnant mouse myometrium.     

Upregulation of eNOS in pregnant ovine uterine arteries by chronic hypoxia

We tested the hypothesis that chronic high-altitude (3,820 m) hypoxia during pregnancy was associated with the upregulation of endothelial nitric oxide (NO) synthase (eNOS) protein and mRNA in ovine uterine artery endothelium and enhanced endothelium-dependent relaxation. In pregnant sheep, norepinephrine-induced dose-dependent contractions were increased by removal of the endothelium in both control and hypoxic uterine arteries. The increment was significantly higher in hypoxic tissues. The calcium ionophore A23187-induced relaxation of the uterine artery was significantly enhanced in hypoxic compared with control tissues. However, sodium nitroprusside- and 8-bromoguanosine 3',5'-cyclic monophosphate-induced relaxations were not changed. Accordingly, chronic hypoxia significantly increased basal and A23187-induced NO release. Chronic hypoxia increased eNOS protein and mRNA levels in the endothelium from uterine but not femoral or renal arteries. In nonpregnant animals, chronic hypoxia increased eNOS mRNA in uterine artery endothelium but had no effects on eNOS protein, NO release, or endothelium-dependent relaxation. Chronic hypoxia selectively augments pregnancy-associated upregulation of eNOS gene expression and endothelium-dependent relaxation of the uterine artery.     

Chronic hypoxia opposes pregnancy-induced increase in uterine artery vasodilator response to flow

We tested the hypotheses that pregnancy increases the uterine artery (UA) vasodilator response to flow and that this increase is impaired under conditions of chronic hypoxia (30 days, simulated elevation 3,960 m). UA were isolated from 24 normoxic or chronically hypoxic midpregnant guinea pigs and studied with the use of pressure myography. Normoxic pregnancy increased UA flow vasodilator response and protected against a rise in wall shear stress (WSS). Chronic hypoxia opposed these effects, prompting vasoconstriction at high flow and increasing WSS above levels seen in normoxic pregnant UA. The nitric oxide synthase inhibitor N(G)-nitro-l-arginine (l-NNA) eliminated the pregnancy-associated increase in flow vasodilation in normoxic UA, suggesting that increased nitric oxide production was responsible. The considerable residual vasodilation after nitric oxide synthase and cyclooxygenase inhibition implicated endothelial-derived hyperpolarizing factor (EDHF) as an additional contributor to flow vasodilation. l-NNA increased flow vasodilation in UA from chronically hypoxic animals, suggesting that chronic hypoxia may have lowered EDHF or elevated peroxynitrite production. In conclusion, flow is an important physiological vasodilator for the acute and more chronic UA dimensional changes required to increase uteroplacental blood flow during normal pregnancy. Chronic hypoxia may be a mechanism that opposes the pregnancy-associated rise in UA flow vasodilation, thereby increasing the incidence of preeclampsia and intrauterine growth restriction at a high altitude.     

Mechanisms of uterine contractility in laying hens

The physiological basis of uterine contractility in laying hens is not well understood, but a better understanding is important for understanding the mechanisms governing egg laying. The characteristics of uterine contractility arising spontaneously or by prostaglandin F_2α (PGF_2α) stimulation were therefore examined and the underlying mechanisms investigated. Uterine strips were isolated from laying hens 4 h before oviposition and force measured. These strips remained healthy in vitro and produced regular spontaneous contractions. The contractions were phasic and could be recorded for several hours. Exposure to nifedipine, the specific L-type Ca channel blocker, led to the abolition of force. The contraction amplitude and frequency were significantly increased when Bay K8644, an agonist of L-type Ca channels, was applied or when the concentration of extracellular Ca was elevated. Spontaneous contractions were also significantly inhibited by wortmannin, the specific inhibitor of myosin light chain kinase (MLCK). When 1 μM PGF_2α was applied to spontaneously contracting uterus, it significantly increased their amplitude and frequency of the contractions. As with spontaneous contractions, PGF_2α-induced force production was abolished by nifedipine and wortmannin. In the absence of extracellular Ca, a small but tonic force was generated upon application of PGF_2α which was not affected by wortmannin. Thus, extracellular Ca entry and MLCK phosphorylation are essential for uterine force production occurring spontaneously or by PGF_2α stimulation. Our data supports the conclusion that the pathway dependent on extracellular Ca entry and MLCK phosphorylation predominates during PGF_2α stimulation but suggests some involvement of an alternative force-producing pathway, presumably Ca-sensitization.     

Changes in the fast uterine muscle biopotentials in rabbits with chronic hypoxia

Changes of the high-frequency electrical activity in the myometrium after a separate and simultaneous ligation the uterine and ovarian vessels were studied in chronic experiments (137 experiments on 18 non-pregnant rabbits which had already had pregnancies in the past). The highest and most prolonged (up to 45 days) inhibition of the amplitude and frequency of rapid (peak) potentials of the myometrium follows a simultaneous ligation of the uterine and ovarian arteries and veins. The amplitude and frequency of biopotentials is gradually restored with the compensation of blood circulation by the collateral blood channels.     

Role of the calcium store in uterine contractility

This article assesses the nature of the sarcoplasmic reticulum (SR) in uterine smooth muscle. Modern imagining techniques have revealed new information about the location and density of Ca storage and release. Release mechanisms, including IP(3) and Ca itself, via ryanodine receptors (RyR), as well as possible roles for cyclic ADP ribose, and the contribution of the SR to relaxation are detailed. The role of the SR Ca-ATPase in both decay of the Ca transient and maintaining Ca homeostasis is reviewed. Recent data on the role of local Ca signals from the SR in contributing to membrane excitability and contractility are discussed, along with interactions with ion channels in lipid microdomains.     

Effects of adipokines and obesity on uterine contractility

Obesity is a major public health problem. The prevalence of obesity has significantly increased in developed countries, particularly in France with an overall increase of 76% over the last 15 years. In pregnant women, obesity is associated with alterations in the quality of labor, such as delayed onset of labor, a higher rate of prolonged pregnancies, prolonged labor, and higher oxytocin requirements. There is also an increased prevalence of Cesarean sections, particularly during the active phase of labor, and perinatal complications (postpartum hemorrhage).It seems that some of these functional changes and their consequences can be attributed to a disruption of hormonal balance encountered in obese women and involving adipokines (apelin, ghrelin, visfatin, leptin), but also to the interactions between adipose tissue and the “oxytocin (OT) – oxytocin receptor (OTR)”.In this review, we detailed mechanisms to understand the impact of specific metabolic alterations in obesity on uterine contractility.Better knowledge of the impact of obesity on labor and delivery pathophysiology should strengthen the prevention of obesity in women of childbearing age and provide a suitable and effective management. The beneficial effect of weight loss and exercise in non-pregnant women on the correction of metabolic disorders secondary to obesity should be studied in populations of overweight women to demonstrate its effectiveness.     

Cardioprotective effect of chronic hypoxia is blunted by concomitant hypercapnia

The effect of chronic hypercapnia on cardioprotection induced by chronic hypoxia was investigated in adult male Wistar rats exposed to isobaric hypoxia (10 % O(2)) for three weeks. In the first experimental group, CO(2) in the chamber was fully absorbed; in the second group, its level was increased to 4.1 %. Normoxic controls were kept in atmospheric air. Anesthetized open-chest animals were subjected to 20-min LAD coronary artery occlusion and 3-h reperfusion for infarct size determination (TTC staining). Chronic hypoxia alone reduced body weight and increased hematocrit; these effects were significantly attenuated by hypercapnia. The infarct size was reduced from 61.9+/-2.2 % of the area at risk in the normoxic controls to 44.5+/-3.3 % in the hypoxic group (P<0.05). Hypercapnia blunted the infarct size-limiting effect of hypoxia (54.8+/-2.4 %; P<0.05). It is concluded that increased CO(2) levels in the inspired air suppress the development of the chronic hypoxia-induced cardioprotective mechanism, possibly by interacting with ROS signalling pathways.     

Acute and chronic effects of oral enprostil, a synthetic dehydroprostaglandin E2, on uterine contractility

In acute experiments eleven nonpregnant women received a single oral dose of enprostil (prostaglandin E2 analogue) 35-140 mcg. Uterine activity was measured by a microtransducer-tipped Millar catheter. A single, oral dose of enprostil caused a long-lasting contracture response of the uterus. 3 h after enprostil, uterine resting pressure (RP) was still high. In chronic experiments, eleven women with regular menstrual cycles received 35 mcg or 70 mcg BID enprostil and placebo in a crossover, double-blind fashion from cycle day 10 +/- 3 for four weeks, then had a washout period of four weeks followed by another four-week treatment period. An increase of uterine RP after enprostil was dose-dependent. After two weeks of twice-daily administration of enprostil, the baseline RP was lower than after placebo (p less than 0.01) and the increase in RP after the morning enprostil less than that seen on the first day. In eight patients studied, the mean values of plasma progesterone were normal, both during placebo--and enprostil--treated cycles.