Vascular development in early ovine gestation: carotid smooth muscle function, phenotype, and biochemical markers

Carotid smooth muscle contractility changes after severe burn

Severe burns result in cardiovascular dysfunction, but responses in the peripheral vasculature are unclear. We hypothesize that severe burns disturb arterial contractility through acute changes in adrenergic and cholinergic receptor function. To address this, we investigated the changes in carotid artery contractility and relaxation following a severe burn. Thirty-four adult Sprague–Dawley male rats received a 40% total body surface area (TBSA) scald burn and fluid resuscitation using the Parkland formula. Control animals received sham burn procedure. Animals were serially euthanized between 6 h and 14 days after burn and endothelium-intact common carotid arteries were used for ex vivo force/relaxation measurements. At 6 h after burn, carotid arteries from burned animals demonstrated a > 50% decrease in cumulative dose-responses to norepinephrine (p < 0.05) and to 10⁻⁷ M angiotensin II (p < 0.05). Notably, pre-constricted carotid arteries also demonstrated reduced relaxation responses to acetylcholine (p < 0.05) 6 h after burn, but not to sodium nitroprusside. Histologic examination of cross-sectional planes revealed significant increases in carotid artery wall thickness in burned rats at 6 h versus 3 days, with increased collagen expression in tunica media at 3 days (p < 0.05). Carotid artery dysfunction occurs within 6 h after severe burn, demonstrating decreased sensitivity to adrenergic- and angiotensin II-induced vasoconstriction and acetylcholine-induced relaxation.

Cardiovascular effects of prenatal stress-Are there implications for cerebrovascular, cognitive and mental health outcome?

Prenatal stress programs offspring cognitive and mental health outcome. We reviewed whether prenatal stress also programs cardiovascular dysfunction which potentially modulates cerebrovascular, cognitive and mental health disorders. We focused on maternal stress and prenatal glucocorticoid (GC) exposure which have different programming effects. While maternal stress induced cortisol is mostly inactivated by the placenta, synthetic GCs freely cross the placenta and have different receptor-binding characteristics. Maternal stress, particularly anxiety, but not GC exposure, has adverse effects on maternal-fetal circulation throughout pregnancy, probably by co-activation of the maternal sympathetic nervous system, and by raising fetal catecholamines. Both effects may impair neurodevelopment. Experimental data also suggest that severe maternal stress and GC exposure during early and mid-gestation may increase the risk for cardiovascular disorders. Human data are scarce and especially lacking for older age. Programming mechanisms include aberrations in cardiac and kidney development, and functional changes in the renin-angiotensin-aldosterone-system, stress axis and peripheral and coronary vasculature. Adequate experimental or human studies examining the consequences for cerebrovascular, cognitive and mental disorders are unavailable.

Mechanisms of Sex Disparities in Cardiovascular Function and Remodeling

Epidemiological studies demonstrate disparities between men and women in cardiovascular disease prevalence, clinical symptoms, treatments, and outcomes. Enrollment of women in clinical trials is lower than men, and experimental studies investigating molecular mechanisms and efficacy of certain therapeutics in cardiovascular disease have been primarily conducted in male animals. These practices bias data interpretation and limit the implication of research findings in female clinical populations. This review will focus on the biological origins of sex differences in cardiovascular physiology, health, and disease, with an emphasis on the sex hormones, estrogen and testosterone. First, we will briefly discuss epidemiological evidence of sex disparities in cardiovascular disease prevalence and clinical manifestation. Second, we will describe studies suggesting sexual dimorphism in normal cardiovascular function from fetal life to older age. Third, we will summarize and critically discuss the current literature regarding the molecular mechanisms underlying the effects of estrogens and androgens on cardiac and vascular physiology and the contribution of these hormones to sex differences in cardiovascular disease. Fourth, we will present cardiovascular disease risk factors that are positively associated with the female sex, and thus, contributing to increased cardiovascular risk in women. We conclude that inclusion of both men and women in the investigation of the role of estrogens and androgens in cardiovascular physiology will advance our understanding of the mechanisms underlying sex differences in cardiovascular disease. In addition, investigating the role of sex-specific factors in the development of cardiovascular disease will reduce sex and gender disparities in the treatment and diagnosis of cardiovascular disease. © 2019 American Physiological Society. Compr Physiol 9:375-411, 2019.

Fetal Sheep Mesenteric Resistance Arteries: Functional and Structural Maturation

BACKGROUND

Fetal blood pressure increases during late gestation; however, the underlying vascular mechanisms are unclear. Knowledge of the maturation of resistance arteries is important to identify the mechanisms and vulnerable periods for the development of vascular dysfunction in adulthood.

METHODS

We determined the functional and structural development of fetal sheep mesenteric resistance arteries using wire myography and immunohistochemistry.

RESULTS

Media mass and distribution of myosin heavy-chain isoforms showed no changes between 0.7 (100 ± 3 days) and 0.9 (130 ± 3 days) gestation. However, from 0.7 to 0.9 gestation, the resting wall tension increased accompanied by non-receptor-dependent (potassium) and receptor-dependent (noradrenaline; endothelin-1) increases in vasocontraction. Angiotensin II had no contractile effect at both ages. Endothelium-dependent relaxation to acetylcholine and prostaglandin E2 was absent at 0.7 but present at 0.9 gestation. Augmented vascular responsiveness was paralleled by the maturation of sympathetic and sensory vascular innervation. Non-endothelium-dependent relaxation to nitric oxide showed no maturational changes. The expression of vasoregulator receptors/enzymes did not increase between 0.7 and 0.9 gestation.

CONCLUSION

Vascular maturation during late ovine gestation involves an increase in resting wall tension and the vasoconstrictor and vasodilator capacity of the mesenteric resistance arteries. Absence of structural changes in the tunica media and the lack of an increase in vasoregulator receptor/enzyme expression suggest that vasoactive responses are due to the maturation of intracellular pathways at this gestational age.

Vasotrophic regulation of age-dependent hypoxic cerebrovascular remodeling

Hypoxia can induce functional and structural vascular remodeling by changing the expression of trophic factors to promote homeostasis. While most experimental approaches have been focused on functional remodeling, structural remodeling can reflect changes in the abundance and organization of vascular proteins that determine functional remodeling. Better understanding of age-dependent hypoxic macrovascular remodeling processes of the cerebral vasculature and its clinical implications require knowledge of the vasotrophic factors that influence arterial structure and function. Hypoxia can affect the expression of transcription factors, classical receptor tyrosine kinase factors, non-classical G-protein coupled factors, catecholamines, and purines. Hypoxia's remodeling effects can be mediated by Hypoxia Inducible Factor (HIF) upregulation in most vascular beds, but alterations in the expression of growth factors can also be independent of HIF. PPARγ is another transcription factor involved in hypoxic remodeling. Expression of classical receptor tyrosine kinase ligands, including vascular endothelial growth factor, platelet derived growth factor, fibroblast growth factor and angiopoietins, can be altered by hypoxia which can act simultaneously to affect remodeling. Tyrosine kinase-independent factors, such as transforming growth factor, nitric oxide, endothelin, angiotensin II, catecholamines, and purines also participate in the remodeling process. This adaptation to hypoxic stress can fundamentally change with age, resulting in different responses between fetuses and adults. Overall, these mechanisms integrate to assure that blood flow and metabolic demand are closely matched in all vascular beds and emphasize the view that the vascular wall is a highly dynamic and heterogeneous tissue with multiple cell types undergoing regular phenotypic transformation.

Chronic hypoxia and VEGF differentially modulate abundance and organization of myosin heavy chain isoforms in fetal and adult ovine arteries

Chronic hypoxia increases vascular endothelial growth factor (VEGF) and thereby promotes angiogenesis. The present study explores the hypothesis that hypoxic increases in VEGF also remodel artery wall structure and contractility through phenotypic transformation of smooth muscle. Pregnant and nonpregnant ewes were maintained at sea level (normoxia) or 3,820 m (hypoxia) for the final 110 days of gestation. Common carotid arteries harvested from term fetal lambs and nonpregnant adults were denuded of endothelium and studied in vitro. Stretch-dependent contractile stresses were 32 and 77% of normoxic values in hypoxic fetal and adult arteries. Hypoxic hypocontractility was coupled with increased abundance of nonmuscle myosin heavy chain (NM-MHC) in fetal (+37%) and adult (+119%) arteries. Conversely, hypoxia decreased smooth muscle MHC (SM-MHC) abundance by 40% in fetal arteries but increased it 123% in adult arteries. Hypoxia decreased colocalization of NM-MHC with smooth muscle α-actin (SM-αA) in fetal arteries and decreased colocalization of SM-MHC with SM-αA in adult arteries. Organ culture with physiological concentrations (3 ng/ml) of VEGF-A(165) similarly depressed stretch-dependent stresses to 37 and 49% of control fetal and adult values. The VEGF receptor antagonist vatalanib ablated VEGF's effects in adult but not fetal arteries, suggesting age-dependent VEGF receptor signaling. VEGF replicated hypoxic decreases in colocalization of NM-MHC with SM-αA in fetal arteries and decreases in colocalization of SM-MHC with SM-αA in adult arteries. These results suggest that hypoxic increases in VEGF not only promote angiogenesis but may also help mediate hypoxic arterial remodeling through age-dependent changes in smooth muscle phenotype and contractility.

Differential sensitivity to angiotensin II and norepinephrine in human uterine arteries

BACKGROUND

During pregnancy, uteroplacental responses to norepinephrine (NE) exceed systemic responses. In contrast, uteroplacental responses to angiotensin II (ANG II) are less than systemic. The explanation for these differences in uteroplacental sensitivity remain unclear but may reflect type 2 ANG II receptor (AT(2)R) predominance in uterine artery (UA) vascular smooth muscle (VSM).

OBJECTIVE

The objective of the study was to examine VSM sensitivity to KCl, NE, and ANG II in UA from nonpregnant (NP) and pregnant (P) women and determine VSM ANG II receptor subtype expression.

METHODS

Responses to KCl, NE, and ANG II were examined in endothelium-denuded UA rings from NP (n = 28) and P (n = 13; 34-40 wk gestation) women, and ANG II receptor subtype, α(1)-receptor and contractile proteins were measured.

RESULTS

KCl and NE dose dependently contracted UA (P < 0.001), P exceeding NP 2-fold or greater; but α(1)-receptor expression was unchanged. ANG II did not elicit dose effects in NP or P UA; however, P responses exceeded NP approximately 2-fold (P < 0.001) and were approximately 2.5-fold less than NE (P < 0.001). AT(2)R and AT(1)R expression were similar (P > 0.1) in VSM from NP and term P women. AT(1)R blockade abolished ANG II contractions (P < 0.001); AT(2)R blockade did not enhance ANG II sensitivity in UA with or without endothelium. Actin contents increased approximately 2-fold in term UA.

CONCLUSIONS

Sensitivity to α-stimulation exceeds ANG II in NP and P UA, explaining the differential uteroplacental sensitivity in pregnancy. Because AT(2)R predominate in UA VSM throughout reproduction, this contributes to the inherent refractoriness to ANG II in the uterine vasculature. The increase in UA contractile proteins at term P suggests remodeling, explaining the enhanced contractility seen.

Ovine middle cerebral artery characterization and quantification of ultrastructure and other features: changes with development

Regulation of tone, blood pressure, and blood flow in the cerebral vasculature is of vital importance, particularly in the developing infant. We tested the hypothesis that, in addition to accretion of smooth muscle cells (SMCs) in cell layers with vessel thickening, significant changes in smooth muscle structure, as well as phenotype, extracellular matrix, and membrane proteins, in the media of cerebral arteries (CAs) during the course of late fetal development account for associated changes in contractility. Using transmission electron, confocal, wide-field epifluorescence, and light microscopy, we examined the structure and ultrastructure of CAs. Also, we utilized wire myography, Western immunoblotting, and real-time quantitative PCR to examine several other features of these arteries. We compared the main branch ovine middle CAs of 95- and 140-gestational day (GD) fetuses with those of adults (n = 5 for each experimental group). We observed a graded increase in phenylephrine- and KCl-induced contractile responses with development. Structurally, lumen diameter, media thickness, and media cross-sectional area increased dramatically from one age group to the next. With maturation, the cross-sectional profiles of CA SMCs changed from flattened bands in the 95-GD fetus to irregular ovoid-shaped fascicles in the 140-GD fetus and adult. We also observed a change in the type of collagen, specific integrin molecules, and several other parameters of SMC morphology with maturation. Ovine CAs at 95 GD appeared morphologically immature and poorly equipped to respond to major hemodynamic adjustments with maturation.

Defining the differential sensitivity to norepinephrine and angiotensin II in the ovine uterine vasculature

The intact ovine uterine vascular bed (UVB) is sensitive to α-agonists and refractory to angiotensin II (ANG II) during pregnancy; the converse occurs in the systemic circulation. The mechanism(s) responsible for these differences in uterine sensitivity are unclear and may reflect predominance of nonconstricting AT(2) receptors (AT(2)R) in uterine vascular smooth muscle (UVSM). The contribution of the placental vasculature also is unclear. Third generation and precaruncular/placental arteries from nonpregnant (n = 16) and term pregnant (n = 23) sheep were used to study contraction responses to KCl, norepinephrine (NE), and ANG II (with/without ATR specific inhibitors) and determine UVSM ATR subtype expression and contractile protein content. KCl and NE increased third generation and precaruncular/placental UVSM contractions in a dose- and pregnancy-dependent manner (P ≤ 0.001). ANG II only elicited modest contractions in third generation pregnant UVSM (P = 0.04) and none in precaruncular/placental UVSM. Moreover, compared with KCl and NE, ANG II contractions were diminished ≥ 5-fold. Whereas KCl and ANG II contracted third generation>>precaruncular/placental UVSM, NE-induced contractions were similar throughout the UVB. However, each agonist increased third generation contractions ≥ 2-fold at term, paralleling increased actin/myosin and cellular protein content (P ≤ 0.01). UVSM AT(1)R and AT(2)R expression was similar throughout the UVB and unchanged during pregnancy (P > 0.1). AT(1)R inhibition blocked ANG II-mediated contractions; AT(2)R blockade, however, did not enhance contractions. AT(2)R predominate throughout the UVB of nonpregnant and pregnant sheep, contributing to an inherent refractoriness to ANG II. In contrast, NE elicits enhanced contractility throughout the ovine UVB that exceeds ANG II and increases further at term pregnancy.

Central stiffening in adulthood linked to aberrant aortic remodeling under suboptimal intrauterine conditions

This study examined perturbed aortic development and subsequent wall stiffening as a link to later cardiovascular disease. Placental insufficiency was induced in pregnant guinea pigs at midgestation by uterine artery ligation. Near term, fetuses were killed and defined as normal birth weight (NBW), low birth weight (LBW), and intrauterine growth restricted (IUGR). Offspring were classified according to birth weight and killed in adulthood. Collagen and elastin content of aortas were analyzed using Sirius red and orcein staining, respectively. Immunofluorescence was used for detection of α-actin and nonmuscle myosin heavy chain (MHC-B), a marker of synthetic-type vascular smooth muscle cells (VSMCs). Ex vivo generation of length-tension curves was performed with aortic rings from adult offspring. Relative elastic fiber content was decreased by 10% in LBW and 14% in IUGR compared with NBW fetuses. In adulthood, relative elastic fiber content was 51% lower in LBW vs. NBW, and the number of elastic laminae adjusted for wall thickness was 25% lower in LBW (P < 0.01). The percent area stained for MHC-B was sixfold higher in LBW vs. NBW fetuses (P < 0.0001) and threefold higher in LBW vs. NBW adult offspring (P < 0.05). The increase in MHC-B in LBW offspring concurred with a 41% increase in total collagen content and a 33 and 56% increase in relative and total α-actin content, respectively (P < 0.05). Thus aortic wall stiffening in adulthood can be traced to altered matrix composition established under suboptimal intrauterine conditions that is amplified postnatally by the activity of synthetic VSMCs.

Chronic intrauterine hypoxia interferes with aortic development in the late gestation ovine fetus

This study explored arterial remodelling in fetuses growth restricted by hypoxia. Chronically catheterized fetal sheep were made moderately or severely hypoxic by placental embolization for 15 days starting at gestational age 116-118 (term ∼147 days). Cross-sections of the aorta were analysed for collagen and elastin content using histological procedures, while immunofluorescence was applied to measure markers of vascular smooth muscle cell (VSMC) type. In frozen aortae quantitative PCR was used to measure mRNA levels of extracellular matrix (ECM) precursor proteins as well as molecular regulators of developmental and pathological remodelling. Relative to Control (n =6), aortic wall thickness was increased by 23% in the Moderate group (n =5) and 33% (P <0.01) in the Severe group (n =5). Relative to Control, the Severe group exhibited a 5-fold increase in total collagen content (P <0.01) that paralleled increases in mRNA levels of procollagen I (P <0.05) and III and transforming growth factor β (TGF-β1) (P <0.05). The percentage area stained for α-actin was inversely related to fetal arterial oxygen saturation (P <0.05) and total α-actin content was 45% higher in the Moderate group and 65% (P <0.05) higher in the Severe group, compared to Control. A 12% and 39% (P <0.05) reduction in relative elastic fibre content was observed in Moderate and Severe fetuses, respectively. mRNA levels of the elastolytic enzyme, matrix metalloproteinase-2 (MMP-2) were inversely correlated with fetal arterial oxygen saturation (P <0.05) (Fig. 7) and mRNA levels of its activator, membrane-type MMP (MTI-MMP), were elevated in the Severe group (P <0.05). Marked neointima formation was apparent in Severe fetuses (P <0.05) concomitant with an increase in E-selectin mRNA expression (P <0.05). Thus, aberrant aortic formation in utero mediated by molecular regulators of arterial growth occurs in response to chronic hypoxaemia.

Pregnancy modifies the large conductance Ca2+-activated K+ channel and cGMP-dependent signaling pathway in uterine vascular smooth muscle

Regulation of uteroplacental blood flow (UPBF) during pregnancy remains unclear. Large conductance, Ca(2+)-activated K(+) channels (BK(Ca)), consisting of alpha- and regulatory beta-subunits, are expressed in uterine vascular smooth muscle (UVSM) and contribute to the maintenance of UPBF in the last third of ovine pregnancy, but their expression pattern and activation pathways are unclear. We examined BK(Ca) subunit expression, the cGMP-dependent signaling pathway, and the functional role of BK(Ca) in uterine arteries (UA) from nonpregnant (n = 7), pregnant (n = 38; 56-145 days gestation; term, approximately 150 days), and postpartum (n = 15; 2-56 days) sheep. The alpha-subunit protein switched from 83-87 and 105 kDa forms in nonpregnant UVSM to 100 kDa throughout pregnancy, reversal occurring >30 days postpartum. The 39-kDa beta(1)-subunit was the primary regulatory subunit. Levels of 100-kDa alpha-subunit rose approximately 70% during placentation (P < 0.05) and were unchanged in the last two-thirds of pregnancy; in contrast, beta(1)-protein rose throughout pregnancy (R(2) = 0.996; P < 0.001; n = 13), increasing 50% during placentation and approximately twofold in the remainder of gestation. Although UVSM soluble guanylyl cyclase was unchanged, cGMP and protein kinase G(1alpha) increased (P < 0.02), paralleling the rise and fall in beta(1)-protein during pregnancy and the puerperium. BK(Ca) inhibition not only decreased UA nitric oxide (NO)-induced relaxation but also enhanced alpha-agonist-induced vasoconstriction. UVSM BK(Ca) modify relaxation-contraction responses in the last two-thirds of ovine pregnancy, and this is associated with alterations in alpha-subunit composition, alpha:beta(1)-subunit stoichiometry, and upregulation of the cGMP-dependent pathway, suggesting that BK(Ca) activation via NO-cGMP and beta(1) augmentation may contribute to the regulation of UPBF.

Notch and Vascular Smooth Muscle Cell Phenotype

The Notch signaling pathway is critical for cell fate determination during embryonic development, including many aspects of vascular development. An emerging paradigm suggests that the Notch gene regulatory network is often recapitulated in the context of phenotypic modulation of vascular smooth muscle cells (VSMC), vascular remodeling, and repair in adult vascular disease following injury. Notch ligand receptor interactions lead to cleavage of receptor, translocation of the intracellular receptor (Notch IC), activation of transcriptional CBF-1/RBP-Jκ–dependent and –independent pathways, and transduction of downstream Notch target gene expression. Hereditary mutations of Notch components are associated with congenital defects of the cardiovascular system in humans such as Alagille syndrome and cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). Recent loss- or gain-of-function studies have provided insight into novel Notch-mediated CBF-1/RBP-Jκ–dependent and –independent signaling and cross-regulation to other molecules that may play a critical role in VSMC phenotypic switching. Notch receptors are critical for controlling VSMC differentiation and dictating the phenotypic response following vascular injury through interaction with a triad of transcription factors that act synergistically to regulate VSMC differentiation. This review focuses on the role of Notch receptor ligand interactions in dictating VSMC behavior and phenotype and presents recent findings on the molecular interactions between the Notch components and VSMC-specific genes to further understand the function of Notch signaling in vascular tissue and disease.

Large conductance Ca2+-activated K+ channels contribute to vascular function in nonpregnant human uterine arteries

Large conductance K( +) channels (BK(Ca)) are expressed in uterine artery (UA) smooth muscle from nonpregnant and pregnant sheep and contribute to the regulation of basal vascular tone and responses to estrogen and vasoconstrictors. To determine if BK(Ca) are expressed in women and contribute to UA function, we collected UA from nonpregnant women (n = 31) at elective hysterectomy and analyzed for subunit protein, localization with immunohistochemistry, and function using endothelium-denuded rings. UA expresses BK(Ca) alpha -, beta1- and beta2-subunit protein. KCl and phenylephrine (PE, an alpha(1)-agonist) caused dose-dependent vasoconstriction (P < .001), and UA precontracted with PE dose-dependently relaxed with sodium nitroprusside (SNP; P < .001).Tetraethylammonium chloride (TEA, 0.2-1.0 mM), a BK(Ca) inhibitor, dose-dependently increased resting tone (P = .004; 28% +/- 5.3% with 1.0 mM), enhanced PE-induced (10(-)(6) M) vasoconstriction (P < .04), and attenuated SNP-induced relaxation at 1.0 mM (P = .02). BK( Ca) are expressed in human UA and modulate vascular function by attenuating vasoconstrictor responses and contributing to nitric oxide-induced vasorelaxation.

Metabolism and synthesis of arginine vasopressin in conscious newborn sheep

Arginine vasopressin (AVP) is an important regulator of cardiovascular homeostasis in the fetus, but its role after birth is unclear. Although infused AVP increases mean arterial pressure (MAP) during the 1st mo after birth, pressor responses are unchanged, suggesting that vascular responsiveness is also unchanged. Alternatively, this could reflect increases in AVP metabolic clearance rate (MCR(AVP)). However, newborn AVP metabolism and synthesis are poorly studied. Therefore, we examined the pressor responses to infused AVP and the pattern of circulating AVP, AVP production rate (PR(AVP)), and MCR(AVP) in conscious newborn sheep (n = 5) at 9-38 days after birth. Basal MAP rose and heart rate (HR) fell during the study period (P < or = 0.02), while circulating AVP was unchanged (P > 0.1), averaging 3.01 +/- 0.86 pg/ml. Infused AVP elicited steady-state responses at 10-40 min, increasing plasma AVP and MAP and decreasing HR (P < 0.001). Although pressor responses were unchanged between 9 and 38 days, the rise in MAP correlated with increases in plasma AVP (R = 0.47, P = 0.02, n = 24). MCR(AVP) was unchanged throughout the 1st mo (P > 0.2), averaging 205 +/- 17 ml.kg(-1).min(-1), and was associated with an elevated PR(AVP), 973 +/- 267 pg.kg(-1).min(-1), which also was unchanged (P > 0.1). After birth, MCR(AVP) and PR(AVP) are elevated, probably accounting for the stable plasma AVP levels. The former is also likely to account for the stable pressor responses to infused AVP during the 1st mo. The reason for the elevated PR(AVP) is unclear but may relate to increases in vascular volume associated with postnatal growth.