bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of inhibition of NO synthase on vascular reactivity in a rat model of hyperdynamic sepsis
Authors: Fox G. A. , Paterson N. A. , McCormack D. G.
Published: December 2017

To evaluate the role of nitric oxide (NO) in the attenuated vascular reactivity observed in sepsis, we utilized the specific NO synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME). Male Sprague-Dawley rats (n = 16) were randomized to either sepsis induced by cecal ligation and perforation (CLP; n = 8) or sham procedure (Sham; n = 8). Vascular reactivity was assessed by measuring the pulmonary pressor response to hypoxia (HPV) (fractional inspired O2 concentration = 0.08) and the pulmonary and systemic pressor response to an intravenous infusion of phenylephrine (1.5-6.0 micrograms.kg-1.min-1). Twenty-four hours after surgery, CLP animals had significantly attenuated HPV compared with Sham animals. In response to hypoxia the change in total pulmonary vascular resistance during hypoxia was 0.008 +/- 0.004 and 0.021 +/- 0.006 mmHg.min-ml-1 in CLP and Sham animals, respectively (P < 0.05). The pulmonary and systemic blood pressure response to phenylephrine was also attenuated in CLP compared with Sham animals. After L-NAME infusion (15 mg/kg), there was a significant augmentation of the HPV response in Sham animals. In contrast, the HPV response in CLP animals was unchanged after L-NAME. The attenuated pressor response to phenylephrine in neither the pulmonary nor the systemic circulation was changed after the administration of L-NAME. These data suggest that in rats, excess NO is not an important mediator of the attenuated vascular reactivity observed in sepsis.
AICA riboside improves myocardial ischemia in coronary microembolization in dogs
Authors: Hori M. , Kitakaze M. , Takashima S. , Morioka T. , Sato H. , Minamino T. , Node K. , Komamura K. , Inoue M. , Kamada T.
Published: December 2017

This study was undertaken to examine whether 5-amino-4-imidazolecarboxamide (AICA) riboside (acadesine), which augments adenosine release in ischemic myocardium, further attenuates ischemic injury after acute coronary microembolization. The left anterior descending coronary artery was cannulated and perfused with blood from the left carotid artery in 46 dogs, and coronary blood flow (CBF) of the perfused area was measured. In 12 dogs, 15-microns microspheres (5.0 x 10(4)/ml) were injected repeatedly until CBF approached zero. Changes in CBF, fractional shortening, lactate extraction ratio, and adenosine release were measured with and without administration of AICA riboside. In the control group (n = 7), CBF increased to 154 +/- 11 ml.100 g-1.min-1 at 16-30% of total coronary embolization, and adenosine release was 6.1 +/- 1.0 nmol.100 g-1.min-1. Administration of AICA riboside (n = 5) enhanced coronary hyperemia (187 +/- 8 ml.100 g-1.min-1, P < 0.05), adenosine release (11.9 +/- 0.9 nmol.100 g-1.min-1, P < 0.001), and myocardial adenosine content (0.434 +/- 0.069 vs. 0.118 +/- 0.019 nmol/mg wet wt, P < 0.01) and attenuated decreases in fractional shortening and lactate extraction ratio. AICA riboside preserved myocardial tissue ATP content of the embolized area. The administrations of 8-phenyltheophylline (n = 12) and alpha,beta-methyleneadenosine 5'-diphosphate (n = 10) abolished the beneficial effects of AICA riboside. Furthermore, AICA riboside increased ectosolic and cytosolic 5'-nucleotidase activity of the embolized myocardium (n = 12). Thus we conclude that AICA riboside attenuates contractile and metabolic dysfunction by enhancing adenosine release via activation of ectosolic 5'-nucleotidase and inducing local hyperemia in acute coronary microembolization.
Functional origin of reflected pressure waves in a multibranched model of the human arterial system
Authors: Karamanoglu M. , Gallagher D. E. , Avolio A. P. , O'Rourke M. F.
Published: December 2017

The effects of wave travel and wave reflection were simulated in a mathematical model of the whole arterial tree consisting of 142 uniform transmission line segments. The arterial model was partitioned into three separate segments: upper limbs, trunk, and lower limbs. Aging was simulated by increasing average pulse wave velocities of these segments (10.9–12.9, 8.0–11.7, and 9.0–11.3 m/s for upper limbs, trunk, and lower limbs, respectively). Reflection coefficients at the terminal elements were altered to simulate vasodilation (0.0) and vasoconstriction (0.95). The impedance patterns and spatial distribution of pressure waveforms generated by the model simulating aging and vasoconstriction were similar to in vivo measurements by other investigators. Reflected pressure waves from each segment reached the ascending aorta and contributed differently to the late systolic peak on the aortic pressure wave. Aging does not alter the origin of these reflected pressure waves in the trunk. Aortic impedance and pressure wave changes induced by simulation of dilation of splanchnic bed were similar to those observed experimentally with nitroglycerin.
Vascular cell interactions modulate the expression of endothelin-1 and platelet-derived growth factor BB
Authors: Bonin L. R. , Damon D. H.
Published: December 2017

Endothelin (ET)-1 and platelet-derived growth factor (PDGF) BB are important regulators of vascular cell growth and contractile function. We tested the hypothesis that interactions between endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) regulate the expression of these two factors. Bovine and rat cocultures of EC-VSMC that allowed cell contact and exchange of soluble mediators were studied. In bovine cocultures, ET-1 and PDGF B transcription decreased. Minimum levels of transcription were 39 +/- 9% of control for ET-1 and 31 +/- 6% of control for PDGF B. In contrast, steady-state mRNA levels transiently increased in coculture; maximum mRNA levels were 579 +/- 248 and 267 +/- 41% of control for ET-1 and PDGF B, respectively. ET-1 and PDGF BB protein levels were decreased in bovine cocultures. The amount of ET-1 in cocultures was 51% less and the amount of PDGF BB was 25% less than that in homotypic cultures. In rat cocultures, ET-1 protein levels were transiently increased compared with homotypic cultures; the maximum difference was 99 +/- 26%. These results indicate that EC-VSMC interactions regulate ET-1 and PDGF BB expression in EC-VSMC cocultures via multiple mechanisms. Furthermore, the interactive regulation appears to be species specific. These data suggest a novel mechanism for the regulation of these two vasoactive factors that may play an important role in cardiovascular physiology and/or pathology.
In vitro endotoxin exposure induces contractile dysfunction in adult rat cardiac myocytes
Authors: Tao S. , McKenna T. M.
Published: December 2017

In vivo endotoxin treatment causes a nitric oxide-mediated hypocontractility in cardiac myocytes. The objective of this study was to assess whether in vitro endotoxin exposure confers similar contractile defects in adult rat cardiac cells. We found that incubation of cardiac myocytes for 6 h with 10-100 ng/ml endotoxin resulted in progressive time- and protein synthesis-dependent decreases in electrically stimulated twitch magnitudes and increased contraction and relaxation times. Serum was not required for the endotoxin-induced hypocontractility. The endotoxin-induced defect in contractility was reversed over time, since myocytes continuously incubated with endotoxin for 24 h exhibited normal contractility; in contrast, control cells incubated for 18 h were suppressed by a subsequent 6-h exposure to endotoxin. Nitric oxide synthase activity was increased after a 6-h endotoxin treatment as evidenced by a dose-dependent enhanced conversion of [3H]arginine to [3H]citrulline and by elevated guanosine 3',5'-cyclic monophosphate levels. Superfusion of endotoxin-incubated cells with N omega-nitro-L-arginine methyl ester restored contractile function, whereas superfusion with L-arginine reimposed abnormal contractility. Naive myocytes superfused with 8-bromoguanosine 3',5'-cyclic monophosphate expressed contractile defects similar to those induced by endotoxin. These findings demonstrate that endotoxin has direct negative effects on cardiac cell contractile function and that induction of NO synthase activity is a primary intracellular mediator of the diminished contractility.
Intracellular calcium activates a chloride current in canine ventricular myocytes
Authors: Zygmunt A. C.
Published: December 2017

The contribution of chloride and potassium to the 4-aminopyridine (4-AP)-resistant transient outward current was investigated in dog cardiac myocytes. Whole cell currents were recorded at 37 degrees C in single cells dissociated from epicardial and midmyocardial regions of the canine ventricle. Sodium-calcium exchange current and voltage-dependent transient outward potassium current (IA) were blocked in sodium-free solutions containing 2 mM 4-AP; sodium channels were inactivated by the -50-mV holding potential. When patch pipettes contained 0.4–0.8 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, voltage-clamp steps over the range -20 to +50 mV activated an inward calcium current (ICa) and a Ca(2+)-activated chloride current [ICl(Ca)]. ICl(Ca) was blocked by 200 microM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, 1 mM 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS), or reduction of external chloride. Independent of the presence of potassium, the reversal potential of the SITS-sensitive current varied with extracellular chloride, as predicted for a chloride-selective conductance. The bell-shaped current-voltage relation of ICl(Ca) has a threshold of -20 mV and a peak at +40 mV. No evidence could be found for a Ca(2+)-activated potassium current or a Ca(2+)-activated nonspecific cation current under these conditions. ICl(Ca) contributed to oscillatory inward currents at diastolic potentials in cells superfused by isoproterenol and high Ca2+, suggesting a role for this current in triggered arrhythmias associated with delayed afterdepolarizations. In the normal heart, ICl(Ca) is likely to contribute to rate- and rhythm-dependent repolarization of the cardiac action potential.
ATP promotes development of afterdepolarizations and triggered activity in cardiac myocytes
Authors: Song Y. , Belardinelli L.
Published: December 2017

The effect of extracellular ATP on transient inward current (Iti), delayed afterdepolarization (DAD), early afterdepolarization (EAD), and triggered activity were investigated in guinea pig isolated ventricular myocytes. ATP alone did not induce afterdepolarizations nor did it significantly alter the resting membrane potentials and action potentials. However, when it was applied with drugs known to increase intracellular Ca2+, ATP facilitated the induction of afterdepolarizations and triggered activity in approximately 60% of the cells. In the presence of isoproterenol, ATP increased the amplitude of Iti and DADs by 55 and 206%, respectively, and caused increases in the amplitude of L-type Ca2+ current (ICa) and EADs, which occasionally led to triggered activity. Similarly, addition of ATP increased the amplitude of Iti and DADs induced by elevated extracellular Ca2+ by 110 and 83%, respectively. Ryanodine inhibited the ATP-induced increase in Iti but not the increase in ICa. In the presence of BAY K 8644 or quinidine, ATP not only further prolonged the action potential durations by 18 +/- 4 and 17 +/- 4%, respectively, but also increased the amplitude of EADs. The present results show a novel arrhythmogenic effect of extracellular ATP, which facilitates the genesis of triggered arrhythmias when Ca2+ influx is increased, probably by further increasing Ca2+ influx from extracellular medium and Ca2+ release from intracellular stores.
Morphometry of pig coronary venous system
Authors: Kassab G. S. , Lin D. H. , Fung Y. C.
Published: December 2017

This is a third part of tripartite morphometric data of the pig coronary blood vessels, giving a complete quantitative description of the arterial tree [Kassab et al., Am. J. Physiol. 265 (Heart Circ. Physiol. 34): H350-H365, 1993], capillary network [Kassab and Fung, Am. J. Physiol. 267 (Heart Circ. Physiol. 36): H319-H325, 1994], and venous tree (this article). Together they provide the quantitative anatomic foundation for coronary hemodynamics. The coronary venules have a unique morphology. Unlike coronary arterioles, which have cylindrical cross sections and a fairly constant diameter in each segment, the venules have approximately elliptical cross sections, are usually wavy in the longitudinal direction, and often converge like fingers to a hand. Measurements were made with the silicone elastomer casting method on five pig hearts. Data on smaller vessels were obtained from histological specimens by optical sectioning. Data on larger vessels were obtained from vascular casts. Arcading veins and anastomoses on the epicardial surface have a unique topology. Data on the number of vessels in each order, the major and minor axes, length, connectivity matrix, and the fractions of the vessels of a given order connected in series in all orders of vessels of the sinusal and thebesian veins are presented. It is shown that of the blood in the coronary blood vessels of a pig heart 27.4% is in the arteries (> 200 microns), 37.1% is in veins (> 200 microns), and 35.5% is in microcirculation (< 200 microns), of which 89.4% is in the capillaries.
Regulation of ANP secretion by endothelin-1 in cultured atrial myocytes: desensitization and receptor subtype
Authors: Leite M. F. , Page E. , Ambler S. K.
Published: December 2017

We examined endothelin-1 (ET-1) binding and ET-1-regulated atrial natriuretic peptide (ANP) secretion in primary cultures of adult rat atrial myocytes. ET-1 binding was analyzed as a reversible bimolecular reaction, with bimolecular association rate constant = 1.9 x 10(9) M-1.h-1, dissociation rate constant = 0.028 h-1, and a dissociation constant, calculated from these values = 0.015 nM. ET-1 increased ANP secretion with a one-half effective concentration (EC50) of 0.62 nM, which correlated with EC50 receptor occupancy under equivalent experimental conditions (0.75 nM). The secretory response rapidly desensitized (half-time = 10 min at 10 nM ET-1). The time courses for ET-1 binding, ET-1-stimulated secretion, and desensitization were all comparable. Recovery from desensitization was slow and paralleled the recovery of 125I-labeled ET-1 binding. The ETA receptor subtype-selective antagonist, BQ-123, inhibited 125I-ET-1 binding and ET-1-activated ANP secretion with high affinity, whereas the ETB-selective agonists, endothelin-3 and sarafotoxin S6c, inhibited binding with low affinity and did not effectively stimulate ANP secretion. We conclude that 1) ET-1 can stimulate ANP secretion by direct action on the atrial myocytes; 2) primary cultures of adult rat atrial myocytes express only the ETA receptor subtype; 3) the ANP secretory response to ET-1 desensitizes rapidly but recovers slowly; and 4) occupation of the ETA receptors by ET-1 initiates the unidirectional sequence of receptor activation, signal transduction, ANP secretion, and finally, desensitization.
Enhanced pulmonary arterial dilation to arginine vasopressin in chronically hypoxic rats
Authors: Eichinger M. R. , Walker B. R.
Published: December 2017

Chronic hypoxic exposure elicits pulmonary vascular remodeling and may alter normal pulmonary endothelial function. We examined the vasodilatory response to the receptor-mediated endothelium-dependent dilator arginine vasopressin (AVP), the non-receptor-mediated endothelium-dependent dilator A-23187, and the nitric oxide (NO) donor sodium nitroprusside in lungs isolated from control or chronically hypoxic rats. Lungs were isolated from male Sprague-Dawley rats and perfused with a physiological saline solution containing 4% albumin. Arterial and venous pressures were monitored and microvascular pressure was estimated by double occlusion, allowing assessment of segmental resistances. After equilibration, lungs were constricted with the thromboxane mimetic U-46619. Upon development of a stable pressor response, lungs were dilated with one of the above agents. A series of doses of AVP was administered to separate groups of lungs from control or chronically hypoxic rats. Lungs from chronically hypoxic rats exhibited an augmented dilatory response to AVP compared with control lungs, and this effect was due to enhanced dilation of precapillary segments. The total and segmental vasodilatory responses to A-23187 and sodium nitroprusside were not different between the two groups of lungs, suggesting that chronic hypoxia did not upregulate the enzyme NO synthase or enhance the vascular smooth muscle responsiveness to NO. Thus our data suggest that the augmented total and pulmonary arterial dilation to AVP after chronic hypoxia is most likely due to altered receptor-mediated processes of the hormone.
Na+/H+ exchange and reperfusion arrhythmias: protection by intracoronary infusion of a novel inhibitor
Authors: Yasutake M. , Ibuki C. , Hearse D. J. , Avkiran M.
Published: December 2017

Activation of sarcolemmal Na+/H+ exchange has been proposed as a causal factor in reperfusion arrhythmogenesis. To test this hypothesis, we determined the antiarrhythmic efficacy of two structurally distinct but equipotent Na+H+ exchange inhibitors, 5-(N-ethyl-N-isopropyl)amiloride (EIPA) and the novel drug, 3-methylsulfonyl-4-piperidinobenzoyl guanidine (HOE-694), in isolated rat hearts (n = 12/group) subjected to independent dual coronary perfusion. After 15 min of aerobic perfusion of both beds, flow to the left coronary bed (LCB) was terminated for 10 min; this was followed by 5 min of reperfusion. Various concentrations of each drug were selectively infused into the LCB either during the 5-min period preceding ischemia plus during reperfusion or during reperfusion alone. With the former protocol, 0.01, 0.1, 1, and 10 microM EIPA reduced the incidence of reperfusion-induced ventricular fibrillation (VF) from 92% in controls to 83, 83, 50, and 0% (P < 0.05); the number of hearts in sinus rhythm at the end of reperfusion was increased from 17 to 42, 25, 83 (P < 0.05), and 100% (P < 0.05). HOE-694, at the same concentrations, reduced VF incidence from 92% in control to 83, 58, 50, and 8% (P < 0.05); 25, 67, 75 (P < 0.05), and 100% (P < 0.05) of hearts were in sinus rhythm, compared with 17% of controls, at the end of reperfusion. Even when infused during reperfusion alone, both drugs afforded significant protection against reperfusion-induced VF, which did not differ significantly from that observed when the drugs were also given before ischemia. The similar antiarrhythmic efficacy of EIPA and HOE-694 is consistent with an arrhythmogenic role for activation of Na+/H+ exchange during early reperfusion.
Mechanical determinants of left ventricular relaxation in isovolumically beating hearts
Authors: Tobias A. H. , Slinker B. K. , Kirkpatrick R. D. , Campbell K. B.
Published: December 2017

Both pressure and volume have been proposed to determine the speed of left ventricular (LV) relaxation, but their relative importance is not known. Accordingly, we used isolated, buffer-perfused, isovolumically beating ferret hearts to study the effects of maximal developed pressure (Pdmax) and LV volume (V) on the speed of LV relaxation. Experiments were performed at 30 degrees C, and the hearts were paced at a baseline interbeat interval (BI) of 800 ms. Pdmax was varied independently of V by use of seven BI (75 to 133% of baseline BI), which resulted in test beats that developed a range of Pdmax due to varying degrees of restitution. Pdmax was also varied by setting V at five levels (80 to 120% of baseline V) during the test beats. Speed of relaxation was quantified as the time period of pressure decay from 75 to 25% Pdmax (T75–25). Data were analyzed by multiple linear regression. Increases in both Pdmax and V independently prolonged T75-25, and T75–25 was 1.45 times more sensitive to Pdmax than to V. However, when Pdmax and V were combined to estimate maximal wall stress (sigma max), the effects of Pdmax and V, as well as relative circumferential muscle length (estimated by V1/3), were not important determinants, and T75–25 depended on sigma max alone. Thus we conclude that 1) Pdmax and V are both determinants of the speed of LV relaxation and that Pdmax is approximately 1.5 times more important than V, and 2) the effects of Pdmax and V on relaxation act via the common mechanism of sigma max.
Estimation of laser-Doppler flux biological zero using basilar artery flow velocity in the rabbit
Authors: Richards H. K. , Czosnyka M. , Kirkpatrick P. J. , Pickard J. D.
Published: December 2017

Laser-Doppler flowmetry has potential for continuous cerebral blood flow (CBF) measurement in man and experimental animals. However, laser-Doppler flux (LDFx) measured when perfusion is absent (the biological zero, 0biol) does not necessarily coincide with the instrument's electrical zero. To evaluate laser-Doppler flowmetry further we have compared LDFx in rabbits with continuous measurement of the maximum flow velocity (FVx) in the basilar artery using Doppler ultrasonography. Arterial blood pressure (ABP), FVx, and LDFx were measured continuously in anesthetized New Zealand White rabbits. ABP was altered by controlled hemorrhage with subsequent reinfusion. 0biol was estimated from regression analysis of FVx vs. LDFx and compared with 0biol obtained after death. There was a strong linear relationship between LDFx and FVx (r = 0.94). The absolute difference between estimated 0biol and true 0biol was 5.24% of control prehemorrhage LDFx. Variations in 0biol (range 4-409) suggest that percent changes in LDFx must be related to 0biol if results between individual animals are to be compared.
Transient rheological behavior of blood in low-shear tube flow: velocity profiles and effective viscosity
Authors: Alonso C. , Pries A. R. , Kiesslich O. , Lerche D. , Gaehtgens P.
Published: December 2017

Velocity profiles of human blood flowing through vertical and horizontal glass tubes (25–100 microns ID) were measured as a function of time following a sudden reduction of wall shear stress (tau w) from a high value to values ranging from 2 to 100 mPa. Cell velocities at various radial positions were determined off-line from video recordings by digital image analysis. In vertical tubes, symmetric velocity profiles were obtained that developed increasing bluntness with time, particularly at lower tau w and in smaller tubes. In horizontal tubes, velocity profiles developed strong asymmetry as a function of time. Red blood cell (RBC) sedimentation was associated with uniform low flow velocities in the concentrating cell sediment, whereas faster flow and almost parabolic profiles were observed in the supernatant plasma region. Calculations of effective blood viscosity showed a decrease with time at low tau w in vertical tubes but an increase in horizontal tubes. The differences between profile shape and effective viscosity in vertical and horizontal tubes disappeared at tau w > 50 mPa. These findings are related to the cross-sectional distribution of RBC, which depends on RBC aggregation and sedimentation.
Chronic pulmonary hypertension in utero impairs endothelium-dependent vasodilation
Authors: McQueston J. A. , Kinsella J. P. , Ivy D. D. , McMurtry I. F. , Abman S. H.
Published: December 2017

To determine whether endothelium-dependent pulmonary vasodilation is selectively impaired by chronic intrauterine pulmonary hypertension, we compared the hemodynamic effects of an endothelium-dependent agonist, acetylcholine (ACh), with an endothelium-independent agonist, atrial natriuretic peptide (ANP), before, during, and after development of pulmonary hypertension in five late-gestation fetal lambs. Pulmonary hypertension was produced over 9–12 days by progressive inflation of a vascular occluder around the ductus arteriosus. Age-matched fetal lambs (n = 5) without occluders served as controls. Mean pulmonary arterial pressure increased from 44 +/- 2 (baseline) to 65 +/- 4 Torr after 10-12 days of inflation (P < 0.05). Left lung pulmonary vascular resistance (PVR) increased from 0.52 +/- 0.06 to 0.72 +/- 0.11 Torr.ml-1.min over 10 days (P < 0.05). O2 saturation remained at > 40% during the study period. Although brief intrapulmonary infusions of ACh (1.5 micrograms over 15 min) lowered left lung PVR by 29 +/- 8% before ductus arteriosus compression, ACh-induced pulmonary vasodilation was absent after 9–12 days of pulmonary hypertension. In contrast, the vasodilator response to ANP remained intact throughout the study period. ACh- and ANP-induced vasodilation did not change with time in control animals. In five hypertensive animals delivered by cesarean section, inhaled NO (20 ppm) reduced left lung PVR from levels achieved during ventilation with 100% O2 alone (0.61 +/- 0.31 to 0.24 +/- 0.007 Torr.ml-1.min), increased arterial O2 saturation from 51 +/- 14 to 84 +/- 13%, and increased arterial PO2 from 29 +/- 11 to 106 +/- 34 Torr.(ABSTRACT TRUNCATED AT 250 WORDS)
Hypoxic vasoconstriction and intracellular Ca2+ in pulmonary arteries: evidence for PKC-independent Ca2+ sensitization
Authors: Robertson T. P. , Aaronson P. I. , Ward J. P.
Published: December 2017

The effect of hypoxia on intracellular Ca2+ ([Ca2+]i) and tension in small intrapulmonary arteries (IPA) of the rat was examined using the Ca2+ fluorophore fura 2. Induction of hypoxia in IPA preconstricted with 3 microM prostaglandin F2 alpha (PGF2 alpha) resulted in a biphasic contractile response, the first phase of which was associated with a transient rise in [Ca2+]i. No additional rise in [Ca2+]i was observed during the more slowly developing second phase constriction. Upon reoxygenation [Ca2+]i and tension returned to prehypoxic levels. Ro-31-8220 [a specific protein kinase C (PKC) inhibitor] reduced the first phase in IPA preconstricted with PGF2 alpha or 20 mM KCl, but had no effect on the second phase constriction in either of these groups. These results demonstrate that the first phase of the hypoxic constriction is associated with a transient rise in [Ca2+]i via either Ca2+ influx and/or release, and may have a PKC-dependent component, whereas the second phase involves a PKC-independent sensitization of the contractile machinery to Ca2+.
Eicosanoid synthesis in cardiomyocytes: influence of hypoxia, reoxygenation, and polyunsaturated fatty acids
Authors: Oudot F. , Grynberg A. , Sergiel J. P.
Published: December 2017

The synthesis of eicosanoids was investigated in cultured rat ventricular myocytes. Under normoxia, the cardiomyocytes released 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha) and prostaglandin (PG) E2 and smaller amounts of PGF2 alpha and thromboxane B2. Hypoxia enhanced the production of PGE2 and PGF2 alpha, whereas the synthesis of 6-keto-PGF1 alpha was not affected. Conversely, posthypoxic reoxygenation greatly increased the synthesis of 6-keto-PGF1 alpha, whereas the synthesis of PGF2 alpha, was not affected and that of PGE2 was reduced. The cardiomyocyte polyunsaturated fatty acid (PUFA) profile was altered by arachidonic acid or eicosapentaenoic acid and docosahexaenoic acid. Under normoxia, the eicosanoid production appeared to be roughly related to the cell phospholipid arachidonic acid content. Conversely, during posthypoxic reoxygenation, the production of eicosanoids was related to the cell phospholipid n-3 PUFA content, with the n-3-rich cells displaying a marked inhibition of the synthesis. This inhibition was mainly attributed to eicosapentaenoic acid and/or docosapentaenoic acid. Whether this inhibition occurs in vivo during postischemic reperfusion, it may contribute to the beneficial effect of n-3 PUFA on the heart.
Hemodynamic and microcirculatory changes during development of renal hypertension
Authors: Hernandez I. , Greene A. S.
Published: December 2017

To study the progression of vessel loss (rarefaction) during the development of hypertension, a plastic window was chronically implanted over the biceps femoralis muscle of reduced renal mass (RRM) and sham-operated control (SOC) rats on a low-salt diet (0.4%). Blood pressure was measured directly via a catheter implanted in the femoral artery, and tissue blood flow was measured by laser-Doppler flowmetry before and after local topical application of sodium nitroprusside. Measurements were made on the control day and after an increase in sodium intake (4.0%) in RRM rats on days 5, 10, 14, 21, and 28. SOC rats on a low-salt diet served as the control group. RRM rats became hypertensive (167 mmHg), and vascular resistance increased after a change in sodium intake. Resting tissue blood flow decreased by 19% by day 28 in RRM but did not change in SOC. Sodium nitroprusside administration reduced vascular resistance to the same level in both RRM and SOC during control and at day 10; however, on all other days, sodium nitroprusside was not able to fully dilate the RRM microcirculation compared with that of SOC. At the same time, microvascular density estimated by computer fluorescence microscopy was decreased by 25% in RRM rats. These studies indicate that the development of RRM hypertension is characterized by a transition from increased tone and vessel closure (functional rarefaction) to anatomic vessel loss (structural rarefaction).
Effects of hyperthyroidism on muscle blood flow during exercise in rats
Authors: McAllister R. M. , Sansone J. C. , Laughlin M. H.
Published: December 2017

Hyperthyroidism is associated with exercise intolerance. Previous research, however, has shown that cardiac output is either normal or enhanced during exercise in the hyperthyroid state. We therefore hypothesized that blood flow to working skeletal muscle is augmented in hyperthyroid animals during in vivo submaximal exercise and, consequently, that noncardiovascular factors are responsible for intolerance to exercise. To test this hypothesis, rats were made hyperthyroid (Hyper) over 6–12 wk with injections of triiodothyronine (300 micrograms/kg). Hyperthyroidism was evidenced by left ventricular hypertrophy [euthyroid (Eut), 2.12 +/- 0.05 mg/g body wt; Hyper, 2.78 +/- 0.06; P < 0.005], 25–60% increases in citrate synthase activities in Hyper hindlimb muscles over those of Eut rats, and higher preexercise heart rates (Eut, 415 +/- 18 beats/min; Hyper, 479 +/- 19; P < 0.025). Regional blood flows were determined by the radiolabeled microsphere method, preexercise, and at 1–2 min of treadmill running at 15 m/min (0% grade). Total hindlimb muscle blood flow preexercise was unaffected (Eut, 31 +/- 4 ml.min-1.(100) g-1, n = 11; Hyper, 40 +/- 6, n = 9; not significant) but was higher (P < 0.025) in Hyper (127 +/- 17, n = 9) compared with Eut (72 +/- 11, n = 9) during treadmill running. During exercise, flows to individual muscles and muscle sections were approximately 50–150% higher in Hyper compared with Eut rats. Visceral blood flows were largely similar between groups. These findings indicate that hyperthyroidism is associated with augmented blood flow to skeletal muscle during submaximal exercise. Thus hypoperfusion of skeletal muscle does not account for the poor exercise tolerance characteristic of hyperthyroidism.
NEM inhibits transcytosis, endocytosis, and capillary permeability: implication of caveolae fusion in endothelia
Authors: Schnitzer J. E. , Allard J. , Oh P.
Published: December 2017

Various vesicular carriers transport select molecular cargo between intracellular compartments utilizing a budding mechanism with docking and fusion of individual vesicles with their target membranes. This fusion requires key intracellular component(s) that are sensitive to alkylation with N-ethylmaleimide (NEM). In endothelium, caveolae may mediate endocytosis and transcytosis of select macromolecules. If caveolae utilize a mechanism similar to other vesicular carriers, then their transport should also be sensitive to NEM. The following tracers were chosen based on their pathway specificity: 1) albumin-gold complexes (A-Au) that bind gp30 and gp18 for endocytosis by caveolae, 2) native albumin that binds albondin and is transported by caveolae, 3) ferritin as a fluid-phase probe transcytosed by caveolae, and 4) inulin as a paracellular probe. In culture, NEM significantly inhibited A-Au uptake and delivery to endosomes but not endothelial cell surface binding. In rat lung, NEM reduced capillary permeability to albumin and the tissue uptake of ferritin and A-Au, but not inulin, indicating inhibition of caveolae-mediated but not paracellular transport. Neutral but not charged alkylating agents inhibited A-Au uptake, consistent with their relative abilities to cross membranes and modify intracellular factors. Like other vesicular pathways, endothelial caveolae transport their select ligands utilizing a NEM-sensitive mechanism, apparently requiring vesicle-membrane fusion.
Dietary Na+ and cardiopulmonary baroreflex control of renal sympathetic nerve activity in SHR
Authors: Huang B. S. , Leenen F. H.
Published: December 2017

In young Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) with or without chronic sinoaortic denervation (SAD), we evaluated the effects of low, regular, and high dietary sodium intake (L-Na, R-Na, and H-Na, respectively) from 4 to 8 wk of age on cardiopulmonary baroreflex function, which was assessed by changes in renal sympathetic nerve activity (RSNA) and heart rate (HR) in response to acute volume expansion. In intact SHR H-Na increased blood pressure (BP), whereas L-Na decreased BP. No changes were observed in intact WKY. The gain of the cardiopulmonary baroreflex control of both HR and RSNA was significantly attenuated in SHR vs. WKY on R-Na. In both SHR and WKY, L-Na had no effects on the gain of RSNA and HR responses. In both strains, H-Na did not affect the gain of HR but attenuated the gain of the RSNA response. H-Na attenuated the gain of RSNA response more in SHR with SAD vs. intact SHR (52 vs. 69% of corresponding R-Na control) but less in WKY with SAD vs. intact WKY (80 vs. 71% of corresponding R-Na control). These data indicate that in SHR, H-Na further desensitizes the already impaired cardiopulmonary baroreflex control of RSNA. After SAD, this attenuation is more prominent in SHR but becomes less prominent in WKY. High sodium intake, therefore, modulates the interaction between the arterial and cardiopulmonary baroreflexes in the control of RSNA oppositely in WKY vs. SHR.
Mechanisms of hypercapnia-stimulated PG production in piglet cerebral microvascular endothelial cells
Authors: Hsu P. , Albuquerque M. L. , Leffler C. W.
Published: December 2017

High CO2 stimulates dilator prostanoid (prostaglandin; PG) synthesis by piglet cerebral microvascular endothelial cells, but the mechanism of stimulation is unclear. We address the hypothesis that intracellular pH (pHi) and Ca2+ signaling are involved. When extracellular pH (pHe) and PCO2 were constant and pHi was rapidly reduced (propionate or nigericin), PG synthesis was stimulated. When pHe was lowered by reducing NaHCO3, pHi fell slowly, but PG synthesis was not altered. When pHe was decreased by increasing PCO2 or returned to 7.4 by increasing NaHCO3, with a constant PCO2 of 100 mmHg, pHi dropped quickly and PG synthesis was stimulated. When pHi was reduced slowly by changing CO2 slowly, or by stepwise addition of propionate, PG synthesis was increased regardless of pHe, suggesting that the rapid decline of pHi plays a central role in mediating the PG synthesis. Ca2+ signaling is a potential mechanism by which pHi increases PG synthesis. However, extracellular Ca2+ removal did not affect PG synthesis induced by propionate or hypercapnia. Furthermore, neither rapid nor slow decreases of pHi altered cytosolic free Ca2+ concentration. Therefore, Ca2+ signals do not appear to be involved in the CO2 stimulation of PG synthesis.
Influence of sympathetic tone on mechanical properties of muscular arteries in humans
Authors: Joannides R. , Richard V. , Moore N. , Godin M. , Thuillez C.
Published: December 2017

Although smooth muscle tone is a key determinant of mechanical properties of arteries in animal experiments, it has not yet been studied in humans because of technical limitations. To assess the influence of tone on arterial properties in humans and to emphasize the interest of calculation at specific stress, we used echo tracking and photoplethysmographic measurement of arterial pressure to study radial arterial mechanics during a cold pressor test (CPT) in 12 healthy volunteers (28 +/- 2 yr). During CPT, mean arterial pressure rose from 83 +/- 3 to 106 +/- 5 mmHg (P < 0.05), internal diameter decreased from 2.75 +/- 0.15 to 2.54 +/- 0.14 mm (P < 0.05), and wall thickness increased from 0.576 +/- 0.027 to 0.634 +/- 0.029 mm (P < 0.05). At a specific pressure (105 mmHg), midwall stress and incremental modulus decreased whereas arterial compliance increased. The incremental modulus of elasticity and compliance were fitted as functions of pressure and of midwall stress. CPT decreased the modulus about equally at all wall stresses measured. The modulus decreased and the compliance increased at every level of pressure measured. At all levels of midwall stress, the compliance was decreased. Thus acute sympathetic stimulation induced by CPT decreases the wall stiffness of human arteries in vivo. This may be explained by an unloading of stiffer wall components during active arterial constriction.
Effects of hypertonic saline and dextran 70 on cardiac functions after burns
Authors: Suzuki K. , Ogino R. , Nishina M. , Kohama A.
Published: December 2017

The effects of hypertonic saline-dextran (HSD) on cardiac contractility and hemodynamics after burns were studied in anesthetized animals with full-thickness 50% total body surface area burns that were resuscitated with HSD or lactated Ringer solution (LR) alone. No significant difference in cardiac contractility during 6 h postburn was observed between the two groups, as assessed by the end-systolic pressure-volume relationship and the stroke work-end-diastolic volume relationship. An additional bolus of HSD at 6 h postburn caused no significant changes in the end-systolic pressure-volume relationship and stroke work-end-diastolic volume relationship in the burned and sham-burned animals, both of which were resuscitated with HSD. Ten minutes of hemodynamic changes following HSD infusion at 30 min postburn revealed a sudden increase in stroke volume with biphasic responses in left ventricular systolic pressure, which first decreased, then increased, and finally returned to the pre-HSD value. End-diastolic volume was maintained at approximately 110% of the pre-HSD value during this period. We concluded that HSD does not enhance cardiac contractility after severe burns but does produce direct effects on postburn circulation to reduce afterload and augment preload, resulting in a short-lived increase in cardiac output.
Effects of sarcoplasmic reticulum Ca2+ load on the gain function of Ca2+ release by Ca2+ current in cardiac cells
Authors: Janczewski A. M. , Spurgeon H. A. , Stern M. D. , Lakatta E. G.
Published: December 2017

We studied the effects of variable sarcoplasmic reticulum (SR) Ca2+ loading on changes in the gain index of Ca2+ release from the SR, measured as the ratio of the amount of Ca2+ released to the magnitude of the Ca2+ current (ICa) integrated for the initial 20 ms of the depolarization, in whole cell voltage-clamped rat ventricular myocytes dialyzed with the Ca2+ indicator indo 1 salt at 23 degrees C. Changes in ICa were measured directly, and changes in the SR Ca2+ release were indexed by changes in the amplitudes and rates of rise of cytosolic Ca2+ (Ca2+i) transients. The SR Ca2+ load was graded by the duration of conditioning voltage-clamp steps and verified by caffeine-dependent Ca2+i transients. A train of abbreviated (from 100 to 20 ms) voltage-clamp depolarizations, which triggers SR Ca2+ release but fails to replenish the SR with Ca2+, diminished the SR Ca2+ load by 56 +/- 5%, did not alter peak ICa but reduced the amplitudes of the ICa-dependent Ca2+i transients by 52 +/- 3%, and decreased the gain index by 60 +/- 3% (SE; n = 5 or 6). Changes in the amplitudes of Ca2+i transients elicited by ICa and changes in the gain index were linearly correlated (r2 = 0.83 and 0.79, respectively; P < 0.001 for each) with changes in amplitudes of Ca2+i transients elicited by caffeine pulses applied in lieu of the respective voltage-clamp pulses.(ABSTRACT TRUNCATED AT 250 WORDS)
Presence and secretion of atrial natriuretic peptide from cultured human aortic endothelial cells
Authors: Brandt R. R. , Heublein D. M. , Mattingly M. T. , Pittelkow M. R. , Burnett J. C.
Published: December 2017

The endothelium is the production site of several potent vasoactive substances that modulate vascular tone and growth. The present study was undertaken to investigate the presence and secretion of atrial natriuretic peptide (ANP) immunoreactivity from vascular endothelial cells. ANP immunoreactivity was present in cultured human aortic endothelial cells by both immunohistochemical staining and radioimmunoassay. ANP immunoreactivity was also detectable in culture medium from human aortic endothelial cells in low picogram concentrations. These findings suggest that vascular endothelium is a site of ANP production and secretion of ANP. There was a differential distribution of ANP and endothelin-1 (ET-1), with a higher ANP concentration in cell extracts and a higher ET-1 concentration in cell culture media. Although ANP has been conceived as a circulating endocrine hormone, these findings are consistent with ANP functioning also as an autocrine and paracrine modulator in the regulation of vascular tone and growth.
Phosphorylation by protein kinase A enhances delayed rectifier K+ current in rabbit vascular smooth muscle cells
Authors: Aiello E. A. , Walsh M. P. , Cole W. C.
Published: December 2017

The effect of adenosine 3',5'-cyclic monophosphate-dependent protein kinase (PKA) activity on 4-aminopyridine (4-AP)-sensitive delayed rectifier current (IdK) in isolated rabbit portal vein smooth muscle cells was studied via whole cell voltage clamp (20–22 degrees C). A threefold increase in 4-AP-sensitive (5 mM) IdK was recorded after gaining cell access during dialysis with 5 mM intracellular ATP and internal Ca2+ buffered to a low level with 5 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid. Dialysis with the nonhydrolyzable ATP analogue 5'-adenylylimidodiphosphate (5 mM) or the specific peptide inhibitor of PKA (PKI; 10 microM) reduced current runup by 50 and 70%, respectively. Delayed dialysis with PKI reversed runup and inhibited IdK to below initial levels. Forskolin (1 microM) caused a reversible increase in IdK, which was inhibited by 4-AP (5 mM). Isoproterenol (1 microM) reversibly enhanced IdK; the increase was sensitive to propranolol (2 microM) and 4-AP (5 mM) and was prevented by dialysis with PKI (10 microM). IdK was enhanced over the entire voltage range of activation and associated with a negative shift in reversal potential of net whole cell current, consistent with hyperpolarization of resting membrane potential. The data provide the first evidence for a signal transduction mechanism involving beta-adrenoceptors, adenylate cyclase, and a phosphotransferase reaction mediated by PKA for the regulation of delayed rectifier K+ channels in vascular smooth muscle.
Angiotensin II induces transcription and expression of alpha 1-adrenergic receptors in vascular smooth muscle cells
Authors: Hu Z. W. , Shi X. Y. , Okazaki M. , Hoffman B. B.
Published: December 2017

Angiotensin II (ANG II) induces vascular smooth muscle contraction and functions as a growth factor stimulating vascular smooth muscle cell (VSMC) hypertrophy. We wondered whether ANG II might induce expression of alpha 1-adrenergic receptors (ARs) in cultured VSMCs, which would then potentially accentuate the effects of catecholamines in the cells. Rat VSMCs were preincubated with phenoxybenzamine to inactivate alpha 1-ARs; the cells were then treated with ANG II for 24 h. ANG II-treated cells expressed an increased number of alpha 1-ARs compared with controls, suggesting that ANG II increased the rate of alpha 1-AR synthesis. ANG II markedly induced accumulation of alpha 1A/D- and alpha 1B-AR mRNAs in a concentration- and time-dependent manner. This effect of ANG II was blocked by the specific ANG II-receptor agonist [Sar1-Ile8]ANG II. ANG II-induced accumulation of alpha 1A/D-AR mRNAs was completely abolished by transcriptional inhibitor actinomycin D. ANG II markedly increased the transcriptional rate of the alpha 1A/D-AR gene without changing stability of alpha 1A/D-AR mRNAs. Protein kinase C (PKC) activator 4 beta-phorbol 12-myristate 13-acetate also induced accumulation of alpha 1A/D-AR mRNAs, and PKC inhibitor H-7 completely blocked ANG II-induced accumulation of the alpha 1A/D-AR mRNAs. Neither the biologically inactive ANG II analogue des-Phe8-ANG II nor the calcium ionophores A-23187 and BAY K-8466 induced alpha 1A/D-AR mRNAs. Finally, ANG II preincubation increased alpha 1-AR agonist phenylephrine-stimulated expression of the c-fos gene.(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of cGMP on calcium handling in ATP-stimulated rat resistance arteries
Authors: Andriantsitohaina R. , Lagaud G. J. , Andre A. , Muller B. , Stoclet J. C.
Published: December 2017

The mechanisms by which guanosine 3',5'-cyclic monophosphate (cGMP) modulates the contraction induced by ATP were investigated in small mesenteric resistance arteries of the rat. The nitric oxide donors 3-morpholinosydnonimine (SIN-1, 10 microM) and sodium nitroprusside (SNP, 10 microM) increased cGMP but not adenosine 3',5'-cyclic monophosphate (cAMP) content of the tissue. SIN-1, SNP, and 8-bromoguanosine 3',5'-cyclic monophosphate (8-BrcGMP, 100 microM) inhibited the myosin light chain phosphorylation and the contractile response to ATP. Both effects were completely reversed by the selective inhibitor of cGMP protein kinase, Rp-8-bromoguanosine 3',5'-cyclic monophosphorothioate (30 microM). The sensitivity to Ca2+ of arteries permeabilized with Staphylococcus aureus alpha-toxin (4,000 hemolytic units/ml) was not affected by 8-BrcGMP. The two nitric oxide donors and 8-BrcGMP decreased the rise in intracellular Ca2+ induced by ATP. The vasodilator agents abolished the contractile response to the exogenous calcium in vessels that were exposed to 3 mM ATP after depletion of intracellular Ca2+ stores. Thapsigargin (1 microM), an inhibitor of the sarcoplasmic reticulum Ca(2+)-adenosinetriphosphatase, reversed the inhibitory effect of the vasodilator agents when the contraction induced by ATP was elicited in the presence of the Ca2+ entry blocker nitrendipine (1 microM) or in Ca(2+)-free medium. These results show that cGMP inhibits ATP-induced contraction by decreasing intracellular Ca2+ concentration in small resistance arteries. They indicate that this effect results from decreased Ca2+ influx and enhanced Ca2+ sequestration through a thapsigargin-sensitive pump via activation of a cGMP protein kinase.