Pregnancy-induced alterations of vascular function in mouse mesenteric and uterine arteries

Normal pregnancy involves dramatic changes to maternal vascular function, while abnormal vascular adaptations may contribute to pregnancy-associated diseases such as preeclampsia. Many genetic mouse models have recently emerged to study vascular pathologies of pregnancy. However, vascular adaptations to pregnancy in normal mice are not fully understood. Thus, we studied changes in vascular reactivity during normal mouse pregnancy. We hypothesized that pregnant mice will have enhanced endothelial-dependent vasodilation compared with nonpregnant mice, via an enhancement of the nitric oxide synthase (NOS) prostaglandin H synthase (PGHS), and other endothelial-derived hyperpolarizing pathways. Late pregnant (Day 17-18) C57BL/6J mice (n = 10) were compared with nonpregnant mice (n = 7). Uterine and mesenteric arteries were mounted on a wire myograph system and assessed for endothelium-dependent (methacholine) and -independent (sodium nitroprusside; SNP) relaxation responses. Endothelial-dependent relaxation was enhanced in pregnant uterine and mesenteric arteries, which was blunted after the addition of inhibitors of the PGHS or NOS pathways. In nonpregnant mice, these pathways had no effect in modulating relaxation in uterine arteries, whereas vasodilation in mesenteric arteries was reduced only by NOS inhibition. Both uterine and mesenteric vessels had nonnitric oxide- and nonprostaglandin-mediated relaxation, but this relaxation was not enhanced during pregnancy. Endothelial-independent relaxation was also enhanced in pregnant uterine but not mesenteric arteries. Our data indicate that uterine and mesenteric arteries from pregnant mice have enhanced vasodilation. Understanding vascular adaptations to normal mouse pregnancy is crucial for interpreting changes that may occur in genetic mouse models.     

Effect of nitric oxide synthase inhibition on mitochondrial biogenesis in rat skeletal muscle.

The purpose of this study was to determine whether nitric oxide synthase (NOS) inhibition decreased basal and exercise-induced skeletal muscle mitochondrial biogenesis. Male Sprague-Dawley rats were assigned to one of four treatment groups: NOS inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME, ingested for 2 days in drinking water, 1 mg/ml) followed by acute exercise, no l-NAME ingestion and acute exercise, rest plus l-NAME, and rest without l-NAME. The exercised rats ran on a treadmill for 53 +/- 2 min and were then killed 4 h later. NOS inhibition significantly (P < 0.05; main effect) decreased basal peroxisome proliferator-activated receptor-gamma coactivator 1beta (PGC-1beta) mRNA levels and tended (P = 0.08) to decrease mtTFA mRNA levels in the soleus, but not the extensor digitorum longus (EDL) muscle. This coincided with significantly reduced basal levels of cytochrome c oxidase (COX) I and COX IV mRNA, COX IV protein and COX enzyme activity following NOS inhibition in the soleus, but not the EDL muscle. NOS inhibition had no effect on citrate synthase or beta-hydroxyacyl CoA dehydrogenase activity, or cytochrome c protein abundance in the soleus or EDL. NOS inhibition did not reduce the exercise-induced increase in peroxisome proliferator-activated receptor-gamma coactivator 1alpha (PGC-1alpha) mRNA in the soleus or EDL. In conclusion, inhibition of NOS appears to decrease some aspects of the mitochondrial respiratory chain in the soleus under basal conditions, but does not attenuate exercise-induced mitochondrial biogenesis in the soleus or in the EDL.     

Regulation of baseline Ca2+ sensitivity in permeabilized uterine arteries: effect of pregnancy

The adaptation of contractile mechanisms of the uterine artery to pregnancy is not fully understood. The present study examined the effect of pregnancy on the uterine artery baseline Ca2+ sensitivity. In beta-escin-permeabilized arterial preparations, Ca2+ -induced concentration-dependent contractions were significantly decreased in uterine arteries from pregnant animals compared with those of nonpregnant animals. Time-course studies showed that Ca2+ increased phosphorylation of 20-kDa myosin light chain (MLC20), which preceded the tension development in vessels from both pregnant and nonpregnant animals. When compared with vessels from nonpregnant animals, there was a significant increase in the protein level of MLC20 and an accordance increase in the level of Ca2+ -induced phosphorylated MLC20 (MLC20-P) in uterine arteries during pregnancy. Simultaneous measurements of MCL20-P levels and contractions stimulated with Ca2+ in the same tissues demonstrated a significant attenuation in the tension-to-MLC20-P ratio in uterine arteries during pregnancy. Activation of PKC with phorbol 12,13-dibutyrate (PDBu) potentiated Ca2+ -induced contractions in uterine arteries from nonpregnant but not pregnant animals. Accordingly, inhibition of PKC attenuated Ca2+ -induced contractions in uterine arteries from nonpregnant but not pregnant animals. PDBu produced contractions in the presence or absence of Ca2+ in the beta-escin-permeabilized arteries, which were significantly decreased in uterine arteries from pregnant compared with nonpregnant animals. The results suggest that pregnancy upregulates the thick-filament regulatory pathway by increasing MLC20 phosphorylation but downregulates the thin-filament regulatory pathway by decreasing the contractile sensitivity of MLC20-P, resulting in attenuated baseline Ca2+ sensitivity in the uterine artery. In addition, PKC plays an important role in the regulation of basal Ca2+ sensitivity, which is downregulated during pregnancy.     

Pregnancy prevents hypertensive remodeling and decreases myogenic reactivity in posterior cerebral arteries from Dahl salt-sensitive rats: a role in eclampsia?

Previous studies have demonstrated that pregnancy prevents protective hypertension-induced remodeling of cerebral arteries using nitric oxide synthase (NOS) inhibition to raise mean arterial pressure (MAP). In the present study, we investigated whether this effect of pregnancy was specific to NOS inhibition by using the Dahl salt-sensitive (SS) rat as a model of hypertension. Nonpregnant (n = 16) and late-pregnant (n = 17) Dahl SS rats were fed either a high-salt diet (8% NaCl) to raise blood pressure or a low-salt diet (<0.7% NaCl). Third-order posterior cerebral arteries were isolated and pressurized in an arteriograph chamber to measure active responses to pressure and passive remodeling. Several vessels from each group were stained for protein gene product 9.5 to determine perivascular nerve density. Blood pressure was elevated in both groups on high salt. The elevated MAP was associated with significantly smaller active and passive diameters (P < 0.05) and inward remodeling in the nonpregnant hypertensive group only. Whereas no structural changes were observed in the late-pregnant hypertensive animals, both late-pregnant groups had diminished myogenic reactivity (P < 0.05). Nerve density in both the late-pregnant groups was significantly greater when compared with the nonpregnant groups, suggesting that pregnancy has a trophic influence on perivascular innervation of the posterior cerebral artery. However, hypertension lowered the nerve density in both nonpregnant and late-pregnant animals. It therefore appears that pregnancy has an overall effect to prevent hypertension-induced remodeling regardless of the mode of hypertension. This effect may predispose the brain to autoregulatory breakthrough, hyperperfusion, and eclampsia when MAP is elevated.     

Nitric oxide synthase-inhibition hypertension is associated with altered endothelial cyclooxygenase function

We reported previously that endothelium-intact superior mesenteric arteries (SMA) from N(omega)-nitro-L-arginine (L-NNA)-treated hypertensive rats (LHR) contract more to norepinephrine (NE) than SMA from control rats. Others have shown that nitric oxide (NO) synthase (NOS) inhibition increases cyclooxygenase (COX) function and expression. We hypothesized that augmented vascular sensitivity to NE in LHR arteries is caused by decreased NOS-induced dilation and increased COX product-induced constriction. We observed that the EC50 for NE is lower in LHR SMA compared with control SMA (control -6.37 +/- 0.04, LHR -7.89 +/- 0.09 log mol/l; P <0.05). Endothelium removal lowered the EC50 (control -7.95 +/- 0.11, LHR -8.44 +/- 0.13 log mol/l; P <0.05) and increased maximum tension in control (control 1,036 +/- 38 vs. 893 +/- 21 mg; P <0.05) but not LHR (928 +/- 30 vs. 1,066 +/- 31 mg) SMA. Thus augmented NE sensitivity in LHR SMA depends largely on decreased endothelial dilation. NOS inhibition (L-NNA, 10(-4) mol/l) increased maximum tension and EC50 in control arteries but not in LHR arteries. In contrast, COX inhibition decreased maximum tension in control arteries, suggesting that COX products augment contraction. Indomethacin did not affect NE-induced contraction in L-NNA-treated or denuded arteries. In control SMA loaded with the fluorescent NO indicator 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate, indomethacin increased and L-NNA decreased NO release. Therefore, COX products appear to inhibit NO production to augment NE-induced contraction. With chronic NOS inhibition, this modulating influence is greatly diminished. Thus, in NOS-inhibition hypertension, decreased activity of both COX and NOS pathways profoundly disrupts endothelial modulation of contraction.     

Chronic hypoxia, pregnancy, and endothelium-mediated relaxation in guinea pig uterine and thoracic arteries

Vasodilation that occurs during normal pregnancy is associated with enhanced relaxation and decreased contractile response to agonists, which are in part due to increased stimulated and basal nitric oxide (NO). In preeclampsia and/or pregnancies carried at high altitude (HA), this normal vascular adjustment is reversed or diminished. We previously reported that HA exposure did not inhibit the pregnancy-associated decrease in contractile response to agonist or basal NO in guinea pig uterine arteries (UA). We therefore sought to determine whether altitude interfered with effects of pregnancy on endothelium-dependent relaxation through a reduction in stimulated NO. We examined the relaxation response to ACh in UA and bradykinin in thoracic arteries (TA) and effects of NO inhibition with 200 microM N(G)-nitro-L-arginine (L-NNA) in arterial rings isolated from nonpregnant and pregnant guinea pigs exposed throughout gestation to low altitude (LA, 1,600 m, n = 26) or HA (3,962 m, n = 22). In pregnant UA, relaxation to ACh was enhanced (P < 0.05) at both altitudes and NO inhibition diminished, but did not reverse, ACh relaxation. The effect of L-NNA on the relaxation response to ACh was less in HA than in LA animals (P = 0.0021). In nonpregnant UA, relaxation to ACh was similar in LA and HA animals. L-NNA reversed the relaxation response to ACh at HA but not at LA. In TA, relaxation to bradykinin was unaltered by pregnancy or altitude and was completely reversed by NO inhibition. These data suggest that effects of NO inhibition are diminished in UA during pregnancy at HA. Additional studies are needed to confirm whether these effects are mediated through inhibition of stimulated NO. HA exposure did not inhibit relaxation to ACh, perhaps because of stimulation of other vasodilators.     

Differential expression of uterine NO in pregnant and nonpregnant rats with intrauterine bacterial infection

Previous studies have demonstrated that nitric oxide (NO) is involved in the uterine host defense against bacterial infection. In nonpregnant rats, NO production in the uterus was shown to be lower, and inducible NO synthase (NOS) expression was undetectable. However, studies in pregnant rats show abundant expression of inducible NOS with significant elevation in NO production in the uterus. We have recently reported that intrauterine Escherichia coli infection caused a localized increase in uterine NO production and inducible NOS expression in the nonpregnant rat. In our present study, we examined whether the uterine NO production, NOS expression, and uterine tumor necrosis factor-alpha protein are increased in pregnant rats with intrauterine pathogenic Escherichia coli infection. Unlike the nonpregnant state, the NO production in the infected uterine horn of pregnant rats was not significantly elevated after bacterial inoculation compared with the contralateral uterine horn. The expression of uterine NOS (types II and III) also did not show significant upregulation in the infected horn. This is in contrast to that in nonpregnant animals, in which type II NOS was induced in the uterus on infection. Moreover, intrauterine infection induced an elevated expression of tumor necrosis factor-alpha protein in the infected horn both of nonpregnant and of pregnant rats. These data suggest that the sequential stimulation of NOS expression, especially the inducible isoform, and generation of uterine NO are lacking during pregnancy despite an elevated tumor necrosis factor-alpha after infection. In summary, NO synthesis response may be maximal at pregnancy, and infection may not further induce the NO system. Present studies, together with our previous report that intrauterine infection-induced lethality in pregnancy rats was amplified with the inhibition of NO, suggest that pregnancy is a state predisposed for increased complications associated with intrauterine infection and that the constitutively elevated uterine NO during pregnancy may help contain or even reduce the risk of infection-related complications.     

Connexin 43 mediates endothelium-derived hyperpolarizing factor-induced vasodilatation in subcutaneous resistance arteries from healthy pregnant women

The role of gap junctions in endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxation of human arteries was assessed using connexin mimetic peptides (CMPs) designated (37,43)Gap27, (40)Gap27, and (43)Gap26 according to homology with the major vascular connexins (Cx37, Cx40, and Cx43). Resistance arteries were obtained from subcutaneous fat biopsies of healthy pregnant women undergoing elective cesarean section. Endothelium-dependent vasodilatation to bradykinin (BK) was assessed using wire myography. N(omega)-nitro-l-arginine methyl ester (l-NAME) and indomethacin (nitric oxide synthase and cyclooxygenase inhibitors, respectively) attenuated maximal relaxation to BK (R(max)) by approximately 50%. Coincubation with l-NAME, indomethacin, and the combined CMPs ((37,43)Gap27, (40)Gap27, and (43)Gap26) almost abolished relaxation to BK (R(max) = 12.2 +/- 3.7%). In arteries incubated with l-NAME and indomethacin, the addition of either (37,43)Gap27 or (40)Gap27 had no significant effect on R(max), whereas (43)Gap26 caused marked inhibition (R(max) = 21 +/- 6.4%, P = 0.005 vs. l-NAME plus indomethacin alone) that was similar to that of the triple combination. Endothelium-independent vasorelaxation was unaffected by CMPs, l-NAME, or indomethacin. Immunohistochemistry demonstrated Cx37, Cx40, and Cx43 expression in the endothelium and vascular smooth muscle. In pregnant women, EDHF-mediated vasorelaxation of subcutaneous resistance arteries is dependent on Cx43 and gap junctions.     

Role of protein kinase C isozymes in the regulation of alpha1-adrenergic receptor-mediated contractions in ovine uterine arteries

Previously, we demonstrated that activation of protein kinase C (PRKC) enhanced alpha(1)-adrenergic receptor-induced contractions in nonpregnant ovine uterine arteries but inhibited the contractions in pregnant ovine uterine arteries. The present study tested the hypothesis that differential regulation of PRKC isozyme activities contributes to the different effects of phorbol 12, 13-dibutyrate (PDBu) on alpha(1)-adrenergic receptor-mediated contractions between the pregnant and nonpregnant ovine uterine arteries. Phenylephrine-induced contractions of ovine nonpregnant and pregnant uterine arteries were determined in the absence or presence of the PRKC activator PDBu and/or in combination with conventional and novel PRKC isozyme inhibitor GF109203X, PRKC isozyme-selective inhibitory peptides for conventional PRKC, PRKCB1, PRKCB2, and PRKCE. GF109203X produced a concentration-dependent inhibition of phenylephrine-induced contractions in both nonpregnant and pregnant uterine arteries, and it reversed the PDBu-mediated potentiation and inhibition of phenylephrine-induced contractions in nonpregnant and pregnant uterine artieries, respectively. In addition, PRKCB1, PRKCB2, and PRKCE inhibitory peptides blocked the PDBu-mediated responses in both nonpregnant and pregnant uterine arteries. Western blot analysis showed that PDBu induced a membrane translocation of PRKCA, PRKCB1, PRKCB2, and PRKCE in pregnant uterine arteries, and PRKCB1, PRKCB2, and PRKCE in nonpregnant uterine arteries. The results disprove the hypothesis that the dichotomy of PRKC mechanisms in the regulation of alpha(1)-adrenergic receptor-induced contractions in nonpregnant and pregnant uterine arteries is caused by the activation of different PRKC isozymes, and suggest downstream mechanisms of differential subcellular distributions for the distinct functional effects of PRKC isozymes in the adaptation of uterine arteries to pregnancy.     

Pregnancy and estradiol decrease GTPase activity in the guinea pig uterine artery

The mechanisms by which pregnancy redistributes cardiac output in an organ-specific manner are poorly understood. We propose that it is consequential to estrogen-mediated alterations in G protein-mediated signal transduction. Aortas and uterine (UAs) and mesenteric arteries (MAs) were obtained from late-pregnant, nonpregnant, or ovariectomized guinea pigs chronically treated with 17beta-estradiol. High-affinity GTPase activity was assayed enzymatically. The cGMP generated in response to the endothelium-dependent agonist ACh was measured in UAs incubated with or without cholera toxin (CTX, which inhibits G(s)alpha). Pregnancy significantly decreased UA but not aorta or MA GTPase activity. 17beta-Estradiol decreased UA GTPase activity compared with untreated ovariectomized animals. ACh increased cGMP in pregnant but not nonpregnant UAs. Pretreatment of nonpregnant UAs with CTX increased ACh-induced cGMP levels similar to pregnancy. Thus pregnancy and estradiol decrease the GTPase activity of a CTX-sensitive G protein in UAs, increasing receptor-dependent cGMP release. This alteration in receptor-mediated G protein coupling in UAs may contribute to the characteristic cardiovascular adaptation to pregnancy.     

Adaptation of uterine artery thick- and thin-filament regulatory pathways to pregnancy

Little is known about the adaptation of uterine artery smooth muscle contractile mechanisms to pregnancy. The present study tested the hypothesis that pregnancy differentially regulates thick- and thin-filament regulatory pathways in uterine arteries. Isometric tension, intracellular free Ca(2+) concentration, and phosphorylation of 20-kDa myosin light chain (MLC(20)) were measured simultaneously in uterine arteries isolated from nonpregnant and near-term (140 days gestation) pregnant sheep. Phenylephrine-mediated intracellular free Ca(2+) concentration, MLC(20) phosphorylation, and contraction tension were significantly increased in uterine arteries of pregnant compared with nonpregnant animals. In contrast, phenylephrine-mediated Ca(2+) sensitivity of MLC(20) phosphorylation was decreased in the uterine arteries of pregnant sheep. Simultaneous measurement of phenylephrine-stimulated tension and MLC(20) phosphorylation in the same tissue indicated a decrease in MLC(20) phosphorylation-independent contractions in the uterine arteries of pregnant sheep. In addition, activation of PKC produced significantly lower sustained contractions in uterine arteries of pregnant compared with nonpregnant animals in the absence of changes in MLC(20) phosphorylation levels in either vessels. In uterine arteries of nonpregnant sheep, the mitogen-activated protein kinase kinase/extracellular signal-regulated kinase inhibitor PD-098059 significantly increased phenylephrine-mediated, MLC(20) phosphorylation-independent contractions. The results suggest that in uterine arteries, pregnancy upregulates alpha(1)-adrenoceptor-mediated Ca(2+) mobilization and MLC(20) phosphorylation. In contrast, pregnancy downregulates the Ca(2+) sensitivity of myofilaments, which is mediated by both thick- and thin-filament pathways.     

Vasorelaxant action of 17 -estradiol in rat uterine arteries: role of nitric oxide synthases and estrogen receptors

The uterine vasculature plays an important role during pregnancy by providing adequate perfusion of the maternal-fetal interface. To this end, substantial remodeling of the uterine vasculature occurs with consequent changes in responsiveness to contractile agents. The purpose of our study was to characterize the vasorelaxant effects of estrogens on vascular smooth muscles of the rat uterine artery during pregnancy and to evaluate the involvement of estrogen receptors (ESR) and nitric oxide synthases (NOS). To do so, we measured NOS expression in the whole uterine and mesenteric circulatory bed by Western blotting. Vasorelaxant effects of 17beta-estradiol (17beta-E(2)) were assessed on endothelium-denuded uterine arteries with wire myographs in the absence and presence of pharmacological modulators [nitro-L-arginine methyl ester (L-NAME), ICI-182780, tamoxifen]. All experiments were performed on arteries from nonpregnant (NP) and late pregnant (P) rats. In the uterine vasculature of the latter group, NOS3 (endothelial NOS) expression was increased, while NOS1 (neuronal NOS) was reduced compared with NP rats. Expression of the NOS2 (inducible NOS) isoform was undetectable in the two groups. Both 17beta-E(2) and 17alpha-E(2) induced uterine artery relaxation, but the latter evoked lower responses. Endothelium-denuded arteries from NP rats showed larger relaxation with 17beta-E(2) than P rats. This larger relaxation disappeared in the presence of L-NAME. The ESR antagonist ICI-182780 did not affect acute relaxation with 17beta-E(2) and 17alpha-E(2). Moreover, membrane-nonpermeant 17beta-E(2):BSA (estradiol conjugated to bovine serum albumin) did not induce any vasorelaxation. Our results indicate that estrogens exert direct acute vasorelaxant effects in smooth muscles of the rat uterine artery that are mediated by mechanisms independent of ESR activation, but with some stereospecificity. Part of this effect, in NP rats only, is due to nitric oxide produced from muscle NOS1.     

Cortisol-mediated regulation of uterine artery contractility: effect of chronic hypoxia

We previously demonstrated that cortisol regulated alpha(1)-adrenoceptor-mediated contractions differentially in nonpregnant and pregnant uterine arteries. Given that chronic hypoxia during pregnancy has profound effects on maternal uterine artery reactivity, the present study investigated the effects of chronic hypoxia on cortisol-mediated regulation of uterine artery contractions. Pregnant (day 30) and nonpregnant ewes were divided between normoxic control and chronically hypoxic [maintained at high altitude (3,820 m), arterial Po(2): 60 mmHg for 110 days] groups. Uterine arteries were isolated and contractions measured. In hypoxic animals, cortisol (10 ng/ml for 24 h) increased norepinephrine-induced contractions in pregnant, but not in nonpregnant, uterine arteries. The 11beta-hydroxysteroid dehydrogenase inhibitor carbenoxolone did not change cortisol effects in nonpregnant uterine arteries, but abolished it in pregnant uterine arteries by increasing norepinephrine pD(2) (-log EC(50)) in control tissues. The dissociation constant of norepinephrine-alpha(1)-adrenoceptors was not changed by cortisol in nonpregnant, but decreased in pregnant uterine arteries. There were no differences in the density of glucocorticoid receptors between normoxic and hypoxic tissues. Cortisol inhibited the norepinephrine-induced increase in Ca(2+) concentrations in nonpregnant arteries, but potentiated it in pregnant arteries. In addition, cortisol attenuated phorbol 12,13-dibutyrate-induced contractions in normoxic nonpregnant and pregnant uterine arteries, but had no effect on the contractions in hypoxic arteries. The results suggest that cortisol differentially regulates alpha(1)-adrenoceptor- and PKC-mediated contractions in uterine arteries. Chronic hypoxia suppresses uterine artery sensitivity to cortisol, which may play an important role in the adaptation of uterine vascular tone and blood flow in response to chronic stress of hypoxia during pregnancy.     

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.     

Maternal hypoxic ventilatory response, ventilation, and infant birth weight at 4,300 m

To test the hypothesis that increased hypoxic ventilatory responsiveness (HVR) raised maternal ventilation and arterial oxygenation during high-altitude pregnancy and related to the birth weight of the offspring, we studied 21 residents of Cerro de Pasco, Peru (4,300 m), while eight of them were 36 +/- 0 wk pregnant and 15 of them 13 +/- 0 wk postpartum. HVR was low in the nonpregnant women (mean +/- SE shape parameter A = 23 +/- 8) but increased nearly fourfold with pregnancy (A = 87 +/- 17). The increase in HVR appeared to account for the 25% rise in resting ventilation with pregnancy (delta VE observed = 2.4 +/- 0.7 l/min BTPS vs. delta VE predicted from delta HVR = 2.6 +/- 1.7 l/min BTPS, P = NS). Hyperoxia decreased ventilation in the pregnant women (P less than 0.01) to levels similar to those measured when nonpregnant. The increased ventilation of pregnancy raised arterial O2 saturation (SaO2) from 83 +/- 1 to 87 +/- 0%, and SaO2 was correlated positively with HVR in the pregnant women. The rise in SaO2 compensated for a 0.9 g/100 ml decrease in hemoglobin concentration to preserve arterial O2 content at levels present when nonpregnant. Cardiac output in the 36th wk of pregnancy did not differ significantly from values measured postpartum. The increase in HVR correlated positively with infant birth weight. An increase in HVR may be an important contributor to increased maternal ventilation with pregnancy and infant birth weight at high altitude.     

Roles of nitric oxide and angiotensin II in the impaired baroreflex gain of pregnancy

The present study tested the hypothesis that nitric oxide (NO) contributes to impaired baroreflex gain of pregnancy and that this action is enhanced by angiotensin II. To test these hypotheses, we quantified baroreflex control of heart rate in nonpregnant and pregnant conscious rabbits before and after: 1) blockade of NO synthase (NOS) with Nomega-nitro-L-arginine (20 mg/kg iv); 2) blockade of the angiotensin II AT1 receptor with L-158,809 (5 microg x kg(-1) x min(-1) iv); 3) infusion of angiotensin II (1 ng x kg(-1) x min(-1) nonpregnant, 1.6-4 ng x kg(-1) x min(-1) pregnant iv); 4) combined blockade of angiotensin II AT(1) receptors and NOS; and 5) combined infusion of angiotensin II and blockade of NOS. To determine the potential role of brain neuronal NOS (nNOS), mRNA and protein levels were measured in the paraventricular nucleus, nucleus of the solitary tract, caudal ventrolateral medulla, and rostral ventrolateral medulla in pregnant and nonpregnant rabbits. The decrease in baroreflex gain observed in pregnant rabbits (from 23.3 +/- 3.6 to 7.1 +/- 0.9 beats x min(-1) x mmHg(-1), P < 0.05) was not reversed by NOS blockade (to 8.3 +/- 2.5 beats x min(-1) x mmHg(-1)), angiotensin II blockade (to 5.0 +/- 1.1 beats x min(-1) x mmHg(-1)), or combined blockade (to 12.3 +/- 4.8 beats x min(-1) x mmHg(-1)). Angiotensin II infusion with (to 5.7 +/- 1.0 beats x min(-1) x mmHg(-1)) or without (to 8.4 +/- 2.4 beats x min(-1) x mmHg(-1)) NOS blockade also failed to improve baroreflex gain in pregnant or nonpregnant rabbits. In addition, nNOS mRNA and protein levels in cardiovascular brain regions were not different between nonpregnant and pregnant rabbits. Therefore, we conclude that NO, either alone or via an interaction with angiotensin II, is not responsible for decrease in baroreflex gain during pregnancy.     

Plasma protein carbonyls in nonpregnant, healthy pregnant and preeclamptic women

Increased reactive oxygen species (ROS) and lipid peroxidation may be implicated in the pathogenesis of preeclampsia by causing cell (membrane) damage and impaired endothelial function. Carbonyl derivatives of proteins, or protein carbonyls, may be sensitive biomarkers of ROS-mediated damage. The aim of the study was to compare levels of protein carbonyls in plasma of preeclamptic, healthy pregnant and healthy nonpregnant women. Plasma protein carbonyls were measured in 47 preeclamptic, 45 healthy pregnant and 22 healthy nonpregnant women by using a sensitive ELISA-method. ANOVA, the unpaired t-test and Pearson's correlation were used for statistical analysis. Preeclamptic women had significantly higher plasma protein carbonyl levels than healthy pregnant women (P < 0.0001). Healthy pregnant women showed significantly higher protein carbonyl levels (P < 0.001) as compared to nonpregnant controls. The higher levels of protein carbonyls as compared to nonpregnant controls suggest that increased oxygen free radical damage occurs in normal pregnancy and to a much higher extent in preeclampsia.     

Endothelial vasodilator production by uterine and systemic arteries. IV. Cyclooxygenase isoform expression during the ovarian cycle and pregnancy in sheep

Uterine artery endothelial production of the potent vasodilator, prostacyclin, is greater in pregnant versus nonpregnant sheep and in whole uterine artery from intact versus ovariectomized ewes. We hypothesized that uterine artery cyclooxygenase (COX)-1 and/or COX-2 expression would be elevated during pregnancy (high estrogen and progesterone) and the follicular phase of the ovarian cycle (high estrogen/low progesterone) as compared to that in luteal phase (low estrogen/high progesterone) or in ovariectomized (low estrogen and progesterone) ewes. Uterine and systemic (omental) arteries were obtained from nonpregnant luteal-phase (LUT; n = 10), follicular-phase (FOL; n = 11), and ovariectomized (OVEX; n = 10) sheep, as well as from pregnant sheep (110-130 days gestation; term = 145 +/- 3 days; n = 12). Endothelial and vascular smooth muscle (VSM) COX-1 protein levels and uterine artery endothelial cell COX-1 mRNA levels were compared. Using immunohistochemistry and Western analysis, the primary location of COX-1 protein was the endothelium; that is, we observed 2.2-fold higher COX-1 protein levels in intact versus endothelium-denuded uterine artery and a 6.1-fold higher expression in the endothelium versus VSM (P < 0.05). COX-2 protein expression was not detectable in either uterine artery endothelium or VSM. COX-1 protein levels were observed to be higher (1.5-fold those of LUT) in uterine artery endothelium from FOL versus either OVEX or LUT nonpregnant ewes (P < 0.05), with substantially higher COX-1 levels seen in pregnancy (4.8-fold those of LUT). Increases in uterine artery endothelial COX-1 protein were highly correlated to increases in the level of COX-1 mRNA (r(2) = 0.66; P < 0.01) for all treatment groups (n = 6-8 per group), suggesting that increased COX-1 protein levels are regulated at the level of increased COX-1 mRNA. No change in COX-1 expression was observed between groups in a systemic (omental) artery. In conclusion, COX-1 expression is specifically up-regulated in the uterine artery endothelium during high uterine blood flow states such as the follicular phase and, in particular, pregnancy.     

Mechanisms involved in calcitonin gene-related Peptide-induced relaxation in pregnant rat uterine artery

Human and rodent studies have demonstrated that calcitonin gene-related peptide (CGRP), a potent vasodilator, relaxes uterine tissue during pregnancy but not during labor. The vascular sensitivity to CGRP is enhanced during pregnancy, compared to nonpregnant human uterine arteries. In the present study, we hypothesized that uterine artery relaxation effects of CGRP are enhanced in pregnant rats compared to nonpregnant diestrus rats (NP-DE) and that several secondary messenger systems are involved in this process. We also hypothesized that the expression of CGRP-A receptor components, calcitonin receptor-like receptor (CRLR), receptor activity-modifying protein (RAMP1), and CGRP-B receptors are greater in pregnant rats. For vascular relaxation studies, uterine arteries from either NP-DE or Day 18 pregnant rats were isolated, and responsiveness of the vessels to CGRP was examined with a small vessel myograph. CGRP-A and CGRP-B receptor expressions were assessed by RT-PCR and Western immunoblotting, respectively. CGRP (10(-10)--10(-7) M) produced a concentration-dependent relaxation of norepinephrine-induced contractions in both NP-DE and Day 18 pregnant rat uterine arteries. Pregnancy increased the vasodilator sensitivity to CGRP significantly (P < 0.05) compared to NP-DE rats. CGRP receptor antagonist, CGRP8-37, inhibited CGRP-induced relaxation of pregnant uterine arteries. The CGRP-induced relaxation was not affected by NG-nitro-l-arginine methyl ester (L-NAME) (nitric oxide inhibitor, 10(-4) M) but was significantly (P < 0.05) attenuated by inhibitors of guanylate cyclase (ODQ, 10(-5) M) and adenylate cyclase (SQ 22536, 10(-5) M). CGRP-induced vasorelaxation was significantly (P < 0.05) attenuated by potassium channel blockers KATP (glybenclamide, 10(-5) M) and K(CA) (tetraethylammonium, 10(-3) M). The expression of CRLR and RAMP1 was significantly (P < 0.05) elevated during pregnancy compared to nonpregnant diestrus state (NP-DE). However, CGRP-B receptor proteins in uterine arteries were not altered with pregnancy compared to those of NP-DE. These studies suggest that CGRP-induced increases in uterine artery relaxation may play a role in regulating blood flow to the uterus during pregnancy and, therefore, in fetal growth and survival.