Smooth muscle ATP-sensitive potassium channels mediate migraine-relevant hypersensitivity in mouse models

Background Opening of KATP channels by systemic levcromakalim treatment triggers attacks in migraine patients and hypersensitivity to von Frey stimulation in a mouse model. Blocking of these channels is effective in several preclinical migraine models. It is unknown in what tissue and cell type KATP-induced migraine attacks are initiated and which KATP channel subtype is targeted. Methods In mouse models, we administered levcromakalim intracerebroventricularly, intraperitoneally and intraplantarily and compared the nociceptive responses by von Frey and hotplate tests. Mice with a conditional loss-of-function mutation in the smooth muscle KATP channel subunit Kir6.1 were given levcromakalim and GTN and examined with von Frey filaments. Arteries were tested for their ability to dilate ex vivo. mRNA expression, western blotting and immunohistochemical stainings were made to identify relevant target tissue for migraine induced by KATP channel opening. Results Systemic administration of levcromakalim induced hypersensitivity but central and local administration provided antinociception respectively no effect. The Kir6.1 smooth muscle knockout mouse was protected from both GTN and levcromakalim induced hypersensitivity, and their arteries had impaired dilatory response to the latter. mRNA and protein expression studies showed that trigeminal ganglia did not have significant KATP channel expression of any subtype, whereas brain arteries and dura mater primarily expressed the Kir6.1 + SUR2B subtype. Conclusion Hypersensitivity provoked by GTN and levcromakalim in mice is dependent on functional smooth muscle KATP channels of extracerebral origin. These results suggest a vascular contribution to hypersensitivity induced by migraine triggers.

Sex-dependent change in the reactivity of isolated pulmonary arteries of gonadectomized rats under the intermittent hypoxia of different degree

Introduction. Pulmonary vasoconstriction is one of factors of hypoxic pulmonary hypertension (HPH). The progression of this disease depends on the degree of hypoxiа and seх. The aim of this study was to investigate the reactivity of isolated pulmonary vessels of male and female rats with HPH to vasoactive factors. Materials and methods. The experiments were on male and female of Wistar rats 190–200 g, which were gonadectomized. All animals were divided into 4 groups. One group of males and female rats was kept in a vivarium (21 % О2 ). To simulate HPH, other rats were exposed to hypobaric hypoxia for 10 hours a day at an oxygen content in the inhaled air equal to 13 % (pP O2 103.7 mmHg) or 10 % (pP O2 78,2 mmHg), or 8 % (pP O2 63,5 mmHg) as compared to its content at 21 % (pP О2 159 mmHg). After that, a third-order pulmonary vessel was perfused at a constant flow rate with vasoconstrictors and vasodilators. The reaction was recorded by the change in perfusion pressure. Results. In females with HРН 10 %O2 , constricting response to serotonin were greater than in males. In normotensive males, the dilatory response to sodium nitroprusside (NP) was less than in female. Exposure to hypoxia induced an increase in NP responses. Conclusion. Increased reactivity of pulmonary vessels to serotonin is a factor of pathogenesis of HPH in females, in contrast to males. Increased reactivity to NO donor in males exposed to hypoxia сan be used for a pharmacological target for HPH.

18b-glycyrrhetinic acid increases blood pressure in rats through the action on myoendothelial gap junctions

18b-glycyrrhetinic acid (GA), a pentacyclic triterpenoid found in the roots of licorice plants (Glycyrrhiza glabra), posseses high biological activity, including anti-inflammatory and antimicrobial properties. Additionally, it effectively blocks myoendothelial gap junctions. Our experiments on adult Wistar rats have shown that GA administration via gavage in the dose 0.015 g per 100 g of body weight caused a significant increase in arterial blood pressure measured both invasively and non-invasively as early as on the 7th day after beginning of the treatment. Further administration of GA up to 21 days did not change blood pressure significantly. Thoracic aortic rings obtained from GA-treated animals demonstrated a decreased ability to relax in response to acetylcholine (ACh): the maximal dilatory response and the sensitivity of the vascular preparations to ACh measured as pD2 (-log ЕС50) were significantly suppressed compared to the relaxant responses of rings from untreated rats. GA externally applied to intact tissues at a concentration of 2×10-5 M inhibited the ACh-induced relaxation. The inhibition was more pronounced than that observed in vascular rings obtained from the GA-treated animals. Nevertheless, it was smaller than that observed under combined action of the nitric oxide synthase inhibitor, L-NAME, and indomethacin, indicating that GA affects preferentially EDHF-dependent component of the ACh-induced relaxation. These results may suggest that damage of myoendothelial gap junctions that provide electrical communication between the endothelium and the smooth muscle layers may, at least partially, cause the development of arterial hypertension under GA treatment.

Endothelial alpha globin is a nitrite reductase

Small artery vasodilation in response to hypoxia is essential for matching oxygen supply to tissue oxygen demand. One source of hypoxic dilation via nitric oxide (NO) signaling is nitrite reduction by erythrocytic hemoglobin (α2β2). However, the alpha subunit of hemoglobin is also expressed in resistance artery endothelium and localized to myoendothelial junctions, a subcellular domain that contacts underlying vascular smooth muscle cells. We hypothesized that nitrite reduction mediated by endothelial alpha globin may occur at myoendothelial junctions to regulate hypoxic vasodilation. To test this concept, we created two novel mouse strains: one lacking alpha globin specifically in endothelium (EC Hba1Δ/Δ) and one where alpha globin is mutated such that its inhibitory association with endothelial NO synthase (eNOS) is prevented (Hba1WT/Δ36-39). In EC Hba1Δ/Δ or Hba1WT/Δ36-39 mice hemoglobin levels, hematocrit and erythrocyte counts were unchanged from littermate controls. Loss of the full alpha globin protein from the endothelium in the EC Hba1Δ/Δ model was associated with decreased exercise capacity and decreased intracellular nitrite utilization in hypoxic conditions. These effects were not seen in Hba1WT/Δ36-39 animals. Hypoxia induced vasodilation was decreased by 60% in isolated thoracodorsal arteries from EC Hba1Δ/Δ, while infusion of erythrocytes only partially rescued the dilatory response. Lastly, unlike other models where blood pressure is decreased, EC Hba1Δ/Δ blood pressure was not altered in response to hypoxia. Overall, we conclude that alpha globin in the resistance artery endothelium can act as a nitrite reductase to provide a local vasodilatory response to hypoxia.

A Paradoxical Vasodilatory Nutraceutical Intervention for Prevention and Attenuation of Migraine—A Hypothetical Review

Studies suggest that migraine pain has a vascular component. The prevailing dogma is that peripheral vasoconstriction activates baroreceptors in central, large arteries. Dilatation of central vessels stimulates nociceptors and induces cortical spreading depression. Studies investigating nitric oxide (NO) donors support the indicated hypothesis that pain is amplified when acutely administered. In this review, we provide an alternate hypothesis which, if substantiated, may provide therapeutic opportunities for attenuating migraine frequency and severity. We suggest that in migraines, heightened sympathetic tone results in progressive central microvascular constriction. Suboptimal parenchymal blood flow, we suggest, activates nociceptors and triggers headache pain onset. Administration of NO donors could paradoxically promote constriction of the microvasculature as a consequence of larger upstream central artery vasodilatation. Inhibitors of NO production are reported to alleviate migraine pain. We describe how constriction of larger upstream arteries, induced by NO synthesis inhibitors, may result in a compensatory dilatory response of the microvasculature. The restoration of central capillary blood flow may be the primary mechanism for pain relief. Attenuating the propensity for central capillary constriction and promoting a more dilatory phenotype may reduce frequency and severity of migraines. Here, we propose consideration of two dietary nutraceuticals for reducing migraine risk: L-arginine and aged garlic extracts.

Impaired peripheral vasodilation during graded systemic hypoxia in healthy older adults: role of the sympathoadrenal system

Systemic hypoxia is a physiological and pathophysiological stress that activates the sympathoadrenal system and, in young adults, leads to peripheral vasodilation. We tested the hypothesis that peripheral vasodilation to graded systemic hypoxia is impaired in older healthy adults and that this age-associated impairment is due to attenuated β-adrenergic mediated vasodilation and elevated α-adrenergic vasoconstriction. Forearm blood flow was measured (Doppler ultrasound), and vascular conductance (FVC) was calculated in 12 young (24 ± 1 yr) and 10 older (63 ± 2 yr) adults to determine the local dilatory responses to graded hypoxia (90, 85, and 80% O2 saturations) in control conditions, following local intra-arterial blockade of β-receptors (propranolol), and combined blockade of α- and β-receptors (phentolamine + propranolol). Under control conditions, older adults exhibited impaired vasodilation to hypoxia compared with young participants at all levels of hypoxia (peak ΔFVC at 80% [Formula: see text] = 4 ± 6 vs. 35 ± 8%; P < 0.01). During β-blockade, older adults actively constricted at 85 and 80% [Formula: see text] (peak ΔFVC at 80% [Formula: see text] = −13 ± 6%; P < 0.05 vs. control), whereas the response in the young was not significantly impacted (peak ΔFVC = 28 ± 8%). Combined α- and β-blockade increased the dilatory response to hypoxia in young adults; however, older adults failed to significantly vasodilate (peak ΔFVC at 80% [Formula: see text]= 12 ± 11% vs. 58 ± 11%; P < 0.05). Our findings indicate that peripheral vasodilation to graded systemic hypoxia is significantly impaired in older adults, which cannot be fully explained by altered sympathoadrenal control of vascular tone. Thus, the impairment in hypoxic vasodilation is likely due to attenuated local vasodilatory and/or augmented vasoconstrictor signaling with age. NEW & NOTEWORTHY We found that the lack of peripheral vasodilation during graded systemic hypoxia with aging is not mediated by the sympathoadrenal system, strongly implicating local vascular control mechanisms in this impairment. Understanding these mechanisms may lead to therapeutic advances for improving tissue blood flow and oxygen delivery in aging and disease.

Impact of age on cerebrovascular dilation versus reactivity to hypercapnia

This study quantified the effect of age on cerebrovascular reactivity and cerebrovascular conductance while accounting for differences in grey matter volume in younger (YA: n = 12; 24 ± 4 years, six females) and older adults (OA: n = 10; 66 ± 7 years; five females). Cerebral blood flow velocity (CBFV; transcranial Doppler) in the middle cerebral artery (MCA), MCA cross-sectional area (CSA), intracranial volumes (magnetic resonance imaging), and mean arterial pressure (MAP; Finometer), were measured under normocapnic and hypercapnic (6% carbon dioxide) conditions. Cerebral blood flow (CBF) was quantified from CBFV and MCA CSA and normalized to grey matter volume. Grey matter volume was 719 ± 98 mL in YA and 622 ± 50 mL in OA ( P = 0.009). Cerebrovascular reactivity (%ΔCBF/ΔPETCO2) was not different between YA and OA. In contrast, cerebrovascular conductance (CBF/MAP) in response to hypercapnia was reduced in OA ( P = 0.02). Of note, MAP increased more with hypercapnia in OA compared with YA. Therefore, the central hemodynamic response to hypercapnia compensated for a diminished dilatory response downstream from the MCA so that the CBF response to hypercapnia per unit of brain mass was not affected by age. This impairment was not detected by traditional measures of cerebrovascular reactivity.

Piezocone dissipation tests at the Canadian Test Site No. 1, Gloucester, Ontario

A series of pore-water pressure dissipation records were acquired using a type 2 piezocone penetrometer sounding that was performed in the sensitive Leda clays underlying the Canadian Geotechnical Research site in South Gloucester, Ontario. This note presents the results of the piezocone penetration test (CPTu) sounding and the individual pore-water pressure decays with time that were measured at 1 m vertical intervals, ranging from depths of 2 to 23 m at the site. Using soil behavioral charts, the sounding confirmed the presence of soft sensitive clays. While many of the dissipations were predominantly monotonic, some dilatory response was also observed at shallow depths. Thus, a grouping of dissipatory behaviors was used to infer layers of similar clay characteristics. The results are offered as complementary data to existing in situ and laboratory information that have been collected at this important experimental test site.