Role of muscular eNOS in skeletal arteries: Endothelium-independent hypoxic vasoconstriction of the femoral artery is impaired in eNOS-deficient mice

Abstract

We previously reported that hypoxia augments α-adrenergic contraction (hypoxic vasoconstriction, HVC) of skeletal arteries in rats. The underlying mechanism may involve hypoxic inhibition of endothelial nitric oxide synthase (eNOS) expressed in skeletal arterial myocytes (16). To further explore the novel role of muscular eNOS in the skeletal artery, we compared HVC in femoral arteries (FAs) from eNOS knockout (KO) mice with that from wild-type (WT) and heterozygous (HZ) mice. Immunohistochemical assays revealed that, in addition to endothelia, eNOS is also expressed in the medial layer of FAs, albeit at a much lower level. However, the medial eNOS signal was not evident in HZ FAs, despite strong expression in the endothelium; similar observations were made in WT carotid arteries (CAs). The amplitude of contraction induced by 1 μM phenylephrine (PhE) was greater in HZ than in WT FAs. Hypoxia (3% Po2) significantly augmented PhE-induced contraction in WT FAs but not in HZ or KO FAs. No HVC was observed in PhE-pretreated WT CAs. The NOS inhibitor nitro-l-arginine methyl ester (0.1 mM) also augmented PhE contraction in endothelium-denuded WT FAs but not in WT CAs. Inhibitors specific to neuronal NOS and inducible NOS did not augment PhE-induced contraction of WT FAs. NADPH oxidase 4 (NOX4) inhibitor (GKT137831, 5 μM), but not NOX2 inhibitor (apocynin, 100 μM), suppressed HVC. Consistent with the role of reactive oxygen species (ROS), HVC was also inhibited by pretreatment with tiron or polyethylene glycol-catalase. Taken together, these data suggest that the eNOS expressed in smooth muscle cells in FAs attenuates α-adrenergic vasoconstriction; this suppression is alleviated under hypoxia, which potentiates vasoconstriction in a NOX4/ROS-dependent mechanism.

Senescent murine femoral arteries undergo vascular remodelling associated with accelerated stress‐induced contractility and reactivity to nitric oxide

“…Like in other mammalian conduit vessels, it responds to various contractile stimuli, i.e., α 1 ‐adrenoreceptor agonists, 5‐hydroxythryptamin, endothelin‐1, eicosanoids, NO inhibition, etc 4–8 . It is common knowledge that basal and agonist‐induced contractility of the FA could be altered by pathological conditions such as hypoxia, gram‐negative bacterial endotoxins, diabetes or microgravity 5,9–11 . Augmented vascular tone often coincides with advanced age, as at present, it is well appreciated that ageing increases muscle sympathetic nerve activity 12 .…”

“…[4][5][6][7][8] It is common knowledge that basal and agonist-induced contractility of the FA could be altered by pathological conditions such as hypoxia, gram-negative bacterial endotoxins, diabetes or microgravity. 5,[9][10][11] Augmented vascular tone often coincides with advanced age, as at present, it is well appreciated that ageing increases muscle sympathetic nerve activity. 12 It has also recently been shown that on the level of smooth muscle cells, ageing induces a diminution of the Ca 2+ -dependent chloride conductance and a rise in agonistinduced contractility.…”

Vascular characteristics and expression of hypoxia genes in Tibetan pigs’ hearts

“…VEGF could be positively regulated by HIF ‐ 1α and the expression of VEGF was higher in Tibetan pigs than that of Landrace pigs, which could promote endothelial cell proliferation and neovascularization, increasing vascular permeability to promote the development of cardiovascular system as a key vascular related factor (Srinivasan et al., 2015 ; Wang et al., 2020 ; Yu et al., 2018 ). The expression of eNOS and the relative vascular diameter were the highest in the high‐altitude Tibetan pigs, and it is believed that eNOS can regulate blood pressure and vascular permeability by influencing the vascular diameter (Janaszak‐Jasiecka et al., 2018 ; Kim et al., 2016 ).…”

“…The expression of eNOS and the relative vascular diameter were the highest in the high-altitude Tibetan pigs, and it is believed that eNOS can regulate blood pressure and vascular permeability by influencing the vascular diameter (Janaszak-Jasiecka et al, 2018;Kim et al, 2016).…”