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      Enhanced Vascular Smooth Muscle Calcium Sensitivity and Loss of Endothelial Vasodilator Influence Contribute to Myogenic Tone Development in Rat Radial Uterine Arteries during Gestation

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          Uterine artery myogenic tone (MT) develops during pregnancy in hemochorial placentates such as rats and humans. The physiological reason for its appearance is not clear, and we reasoned that it may be a late pregnancy (LP) event in preparation for controlling hemorrhage during parturition. We also hypothesized that gestational increases in RhoA-induced vascular smooth muscle (VSM) calcium sensitivity are contributory and occur under the tonic influence of nitric oxide (NO). Second-order pre-placental radial arteries from early-pregnant (day 12, n = 5), mid-pregnant (day 16, n = 5) and LP (day 20, n = 20) rats were used in combination with arteriography, VSM calcium measurements, pharmacological RHO/Rho-associated protein kinase (ROCK) and nitric oxide synthase (NOS) inhibition, and Western blotting. A subgroup of LP animals (LP + LN; n = 5) treated with L-NAME from gestational days 10 to 20 were used to determine the effects of NOS inhibition on MT and RhoA expression. MT was evident throughout pregnancy, but its expression in pressurized vessels was masked by endothelial NO-induced vasodilation during early gestation. RhoA protein expression was upregulated in LP and attenuated by in vivo NOS inhibition (as was MT). In vitro RHO/ROCK inhibition decreased MT in a concentration-dependent manner without reducing VSM calcium. In summary, pressure-dependent uterine artery tone increases with gestational age due to a combination of RhoA-mediated increases in VSM calcium sensitivity and a loss of endothelial NO influence.

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          Rheological and Physiological Consequences of Conversion of the Maternal Spiral Arteries for Uteroplacental Blood Flow during Human Pregnancy

          Physiological conversion of the maternal spiral arteries is key to a successful human pregnancy. It involves loss of smooth muscle and the elastic lamina from the vessel wall as far as the inner third of the myometrium, and is associated with a 5–10-fold dilation at the vessel mouth. Failure of conversion accompanies common complications of pregnancy, such as early-onset preeclampsia and fetal growth restriction. Here, we model the effects of terminal dilation on inflow of blood into the placental intervillous space at term, using dimensions in the literature derived from three-dimensional reconstructions. We observe that dilation slows the rate of flow from 2 to 3 m/s in the non-dilated part of an artery of 0.4–0.5 mm diameter to approximately 10 cm/s at the 2.5 mm diameter mouth, depending on the exact radius and viscosity. This rate predicts a transit time through the intervillous space of approximately 25 s, which matches observed times closely. The model shows that in the absence of conversion blood will enter the intervillous space as a turbulent jet at rates of 1–2 m/s. We speculate that the high momentum will damage villous architecture, rupturing anchoring villi and creating echogenic cystic lesions as evidenced by ultrasound. The retention of smooth muscle will also increase the risk of spontaneous vasoconstriction and ischaemia–reperfusion injury, generating oxidative stress. Dilation has a surprisingly modest impact on total blood flow, and so we suggest the placental pathology associated with deficient conversion is dominated by rheological consequences rather than chronic hypoxia.
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            Pharmacological properties of Y-27632, a specific inhibitor of rho-associated kinases.

            Y-27632 [(+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl)cyclohexanecarboxamide++ + dihydrochloride] is widely used as a specific inhibitor of the Rho-associated coiled-coil forming protein serine/threonine kinase (ROCK) family of protein kinases. This study examined the inhibition mechanism and profile of actions of Y-27632 and a related compound, Y-30141 [(+)-(R)-trans- 4-(1-aminoethyl)-N-(1H-pyrrolo[2, 3-b]pyridin-4-yl)cyclohexan-ecarboxamide dihydrochloride]. Y-27632 and Y-30141 inhibited the kinase activity of both ROCK-I and ROCK-II in vitro, and this inhibition was reversed by ATP in a competitive manner. This suggests that these compounds inhibit the kinases by binding to the catalytic site. Their affinities for ROCK kinases as determined by K(i) values were at least 20 to 30 times higher than those for two other Rho effector kinases, citron kinase and protein kinase PKN. [(3)H]Y-30141 was taken up by cells in a temperature- and time-dependent and saturable manner, and this uptake was competed with unlabeled Y-27632. No concentrated accumulation was found, suggesting that the uptake is a carrier-mediated facilitated diffusion. Y-27632 abolished stress fibers in Swiss 3T3 cells at 10 microM, but the G(1)-S phase transition of the cell cycle and cytokinesis were little affected at this concentration. Y-30141 was 10 times more potent than Y-27632 in inhibiting the kinase activity and stress fiber formation, and it caused significant delay in the G(1)-S transition and inhibition of cytokinesis at 10 microM.
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              Signaling mechanisms underlying the vascular myogenic response.

              The vascular myogenic response refers to the acute reaction of a blood vessel to a change in transmural pressure. This response is critically important for the development of resting vascular tone, upon which other control mechanisms exert vasodilator and vasoconstrictor influences. The purpose of this review is to summarize and synthesize information regarding the cellular mechanism(s) underlying the myogenic response in blood vessels, with particular emphasis on arterioles. When necessary, experiments performed on larger blood vessels, visceral smooth muscle, and even striated muscle are cited. Mechanical aspects of myogenic behavior are discussed first, followed by electromechanical coupling mechanisms. Next, mechanotransduction by membrane-bound enzymes and involvement of second messengers, including calcium, are discussed. After this, the roles of the extracellular matrix, integrins, and the smooth muscle cytoskeleton are reviewed, with emphasis on short-term signaling mechanisms. Finally, suggestions are offered for possible future studies.

                Author and article information

                J Vasc Res
                Journal of Vascular Research
                S. Karger AG
                May 2020
                27 February 2020
                : 57
                : 3
                : 126-135
                aDepartment of Obstetrics, Gynecology and Reproductive Sciences, University of Vermont Larner College of Medicine, Burlington, Vermont, USA
                bDepartment of Biology, Ecology and Earth Science, University of Calabria, Arcavacata di Rende, Italy
                Author notes
                *Dr. George Osol, Department of Obstetrics, Gynecology and Reproductive Sciences, University of Vermont Larner College of Medicine, Given C-217A, 89 Beaumont Ave., Burlington, VT 05405 (USA), gosol@med.uvm.edu
                505670 J Vasc Res 2020;57:126–135
                © 2020 S. Karger AG, Basel

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                Page count
                Figures: 5, Tables: 1, Pages: 10
                Research Article


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