bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence for NO involvement in regulating vascular reactivity in balloon-injured rat carotid artery
Authors: Major T. C. , Overhiser R. W. , Panek R. L.
Published: December 2017

The present study evaluated the influence of this newly formed intima on vascular reactivity in balloon-injured carotid arteries and the regulatory role of the vasodilator, nitric oxide (NO). Balloon injury was performed using a 2-F Fogarty catheter. After 2 and 4 wk, carotid artery segments were removed for both histomorphometric analysis and determination of in vitro contractile responses. Histomorphometric analysis showed a marked intimal thickening with an intima-to-media ratio of 126 +/- 19% (n = 5). The lack of factor VIII staining in injured carotid arteries revealed the absence of endothelium, since factor VIII-related antigen is a glycoprotein synthesized by endothelial cells. Functionally, maximal contractile responses to norepinephrine, angiotensin II (ANG II), endothelin-1, and serotonin were all attenuated in the injured vessels compared with the uninjured carotid arteries [0.38 +/- 0.11 vs. 0.73 +/- 0.10 g (n = 5), norepinephrine; 0.15 +/- 0.06 vs. 0.38 +/- 0.05 g (n = 4), ANG II; 0.60 +/- 0.14 vs. 1.05 +/- 0.12 g (n = 4), endothelin-1; 0.23 +/- 0.07 vs. 0.60 +/- 0.06 g (n = 12), serotonin]. Contractile responses induced by KCl were not affected by the balloon injury (0.62 +/- 0.10 vs. 0.64 +/- 0.09 g, n = 4). Interestingly, carbachol, a muscarinic agonist and vasodilator, caused concentration-dependent relaxations in 2- as well as 4-wk postinjured vessels despite the absence of endothelium. The NO synthase inhibitors, N omega-L-arginine methyl ester (L-NAME) and N omega-nitro-L-arginine (L-NNA), blocked the relaxation responses evoked by carbachol. Exogenously administered L-arginine reversed this blockade of the NOS inhibitors on the carbachol-induced relaxations. In addition, L-NAME partially reversed in a concentration-dependent manner the reduced maximal contractile force elicited by serotonin in the injured carotid artery.(ABSTRACT TRUNCATED AT 250 WORDS)
Role of angiotensin-converting enzyme and angiotensin II in development of hypoxic pulmonary hypertension
Authors: Morrell N. W. , Morris K. G. , Stenmark K. R.
Published: December 2017

Although angiotensin converting enzyme (ACE) inhibitors are known to attenuate the development of hypoxic pulmonary hypertension in rats, the precise mechanism of this protective effect remains unknown. Thus we utilized specific angiotensin II (ANG II)-receptor antagonists to investigate whether ANG II is involved directly in the hemodynamic and structural changes of pulmonary hypertension, and we tested whether the protective effects of ACE inhibition can be attributed partly to potentiation of bradykinin. During 14 days of hypobaric hypoxia, rats received, via intraperitoneal osmotic minipumps, either 1) the ACE inhibitor captopril, 2) captopril plus the bradykinin B2-receptor antagonist CP-0597, 3) the ANG II type 1 receptor antagonist losartan, 4) the ANG II type 2 receptor antagonist PD-123319, or 5) saline. At 14 days, mean pulmonary arterial pressure (MPAP) was reduced (P < 0.05) in hypoxic rats treated with captopril (26.6 +/- 0.8 mmHg) or losartan (24.4 +/- 1.0 mmHg) compared with saline (32.0 +/- 1.4 mmHg) but was unaffected by PD-123319 (29.5 +/- 1.7 mmHg). Right ventricular hypertrophy was reduced in hypoxic rats treated with captopril or losartan compared with saline-treated rats. Morphometry showed less medial thickening and peripheral muscularization of small pulmonary arteries in hypoxic animals treated with captopril or losartan. Coadministration of CP-0597 did not reverse the protective effects of captopril on pulmonary vascular remodeling. These results suggest a novel role for endogenous ANG II, acting through the type 1 receptor, in the vascular remodeling associated with hypoxic pulmonary hypertension. The beneficial effects of ACE inhibition in this model can be attributed to reduced ANG II production rather than potentiation of bradykinin.
Acute effects of glucose on reactivity of cerebral microcirculation: role of activation of protein kinase C
Authors: Mayhan W. G. , Patel K. P.
Published: December 2017

Our first goal was to determine whether acute hyperglycemia alters endothelium-dependent reactivity of rat cerebral arterioles. Our second goal was to investigate a possible mechanism for impaired reactivity during acute hyperglycemia. Diameter of pial arterioles was measured during suffusion with ADP, acetylcholine, histamine, N-methyl-D-aspartate (NMDA), and nitroglycerin before and during application of a suffusate containing D-glucose (5, 10, 20, and 25 mM). ADP, acetylcholine, histamine, NMDA, and nitroglycerin produced dose-related vasodilation before application of D-glucose. Vasodilatation in response to the agonists was not altered by 5 and 10 mM D-glucose. In contrast, vasodilatation in response to ADP, acetylcholine, histamine, and NMDA was impaired during application of 20 and 25 mM D-glucose. Dilatation in response to nitroglycerin was not altered. Application of the protein kinase C inhibitor calphostin C (1.0 nM) or chelerythrine (10 nM) restored endothelium-dependent vasodilatation during application of 25 mM D-glucose. Thus acute hyperglycemia impairs endothelium-dependent responses of cerebral arterioles via the activation of protein kinase C.
Changes in endothelial actin cytoskeleton in venules with time after histamine treatment
Authors: Baldwin A. L. , Thurston G.
Published: December 2017

In this study the time course of development and recovery of histamine-induced venular leaks was followed in conjunction with rearrangement of endothelial actin fibers. The microvasculature of a single mesenteric window of anesthetized Sprague-Dawley rats was perfused with buffered saline, with or without 10(-4) M histamine, for 3-30 min. Fluorescein isothiocyanate (FITC)-albumin was added for the last 3 min. The microvasculature was perfusion fixed, stained with rhodamine phalloidin (for filamentous actin), and viewed using confocal microscopy. The number and relative size of FITC-albumin leaks per venule length were measured. After 3 min of histamine application focal leaks appeared in some of the venules. Most focal leaks were accompanied by local breaks in the endothelial peripheral actin rim. Larger leaks were also present, accompanied by greater disruption of the venular endothelial peripheral actin rim, diffuse F-actin staining, and adherent platelets and leukocytes. Few central actin fibers were visible even in endothelial cells associated with large leaks. After 10-15 min of histamine exposure, larger leaks were more abundant but with fewer adherent cells. Central actin fibers in endothelial cells increased in number, peaking after 20 min of histamine, while the diffuse actin staining declined. Leak area per micrometer of venule peaked at 10-15 min, but the numbers of leaks per micrometer did not vary significantly from 3 to 30 min. These data suggest that the central fibers are not involved with the phase of increasing permeability, but they may play a role in the structural and functional recovery of endothelial cells perturbed by histamine.
Simultaneous ipsilateral and contralateral measurements of vasomotion in conduit arteries of human upper limbs
Authors: Porret C. A. , Stergiopulos N. , Hayoz D. , Brunner H. R. , Meister J. J.
Published: December 2017

We investigated the patterns of vasomotion in various conduit arteries of the human arm. The internal diameter of the brachial, radial, ulnar, and digital artery was measured noninvasively in 17 healthy volunteers (aged 24-40 yr), using a high-precision ultrasonic echotracking device. Under resting conditions, the radial, ulnar, and digital internal diameter exhibited spontaneous oscillations (vasomotion) with a relative amplitude ranging from 1 to 5% of the mean diameter and a fundamental frequency ranging from 0.01 to 0.05 Hz. This oscillatory behavior was either quasi-periodic or irregular. The low-frequency mode (f <or = 0.05 Hz) present in the diameter signal was identified neither in the heart rate nor in the blood pressure signal. To determine whether the oscillatory activity was propagative, simultaneous measurements of diameter at two sites on the right radial artery were performed and revealed no significant consistent phase shift. Ipsilateral radial and ulnar diameters, measured at the wrist level, exhibited similar and synchronous vasomotion patterns, despite differences in the amplitude. For all subjects, contralateral measurements, performed at two symmetrical sites of the radial arteries, showed similar oscillatory patterns with a strong correlation (0.85 < r < 0.99, n = 12). These results suggested the existence of a global regulatory mechanism that coordinates vasomotion in the large conduit arteries of the human arm.
Regional differences in constitutive and induced ICAM-1 expression in vivo
Authors: Panes J. , Perry M. A. , Anderson D. C. , Manning A. , Leone B. , Cepinskas G. , Rosenbloom C. L. , Miyasaka M. , Kvietys P. R. , Granger D. N.
Published: December 2017

The aim of the present study was to characterize and compare the expression of intercellular adhesion molecule 1 (ICAM-1) on unstimulated and endotoxin-challenged endothelial cells in different tissues of the rat. ICAM-1 expression was measured using 125I-labeled anti-rat ICAM-1 monoclonal antibody (MAb) and an isotype-matched control MAb labeled with 131I (to correct for nonspecific accumulation of the binding MAb). Under baseline conditions, ICAM-1 MAb binding was observed in all organs. The binding of 125I-ICAM-1 MAb varied widely among organs, with the largest accumulation (per g tissue) in the lung, followed by heart (1/30th of lung activity), splanchnic organs (1/50th of lung activity), thymus (1/100th of lung activity), testes (1/300th of lung activity), and skeletal muscle (1/800th of lung activity). Endotoxin induced an increase in ICAM-1 MAb binding in all organs except the spleen. Endotoxin-induced upregulation of ICAM-1 was greatest in heart and skeletal muscle (5- to 10-fold), whereas the remaining organs exhibited a two- to fourfold increase in ICAM-1 expression. Maximal upregulation of ICAM-1 occurred at 9-12 h after endotoxin administration. A dose-dependent increase in ICAM-1 expression was elicited by 0.1-10 microgram/kg, with higher doses (up to 5 mg/kg) producing no further increment. Induction of ICAM-1 mRNA after endotoxin was observed in all tissues examined (lung, heart, intestine), peaked at 3 h, and then rapidly returned to control levels. These findings indicate that ICAM-1 is constitutively expressed on vascular endothelium in all organs of the rat and that there are significant regional differences in the magnitude and time course of endotoxin-induced ICAM-1 expression.
Endothelin-1 vasoactive responses in lambs with pulmonary hypertension and increased pulmonary blood flow
Authors: Wong J. , Reddy V. M. , Hendricks-Munoz K. , Liddicoat J. R. , Gerrets R. , Fineman J. R.
Published: December 2017

Increased concentrations of endothelin-1 (ET-1) are found in children with congenital heart diseases that produce increased pulmonary blood flow and pulmonary hypertension, but the role of ET-1 in the pathophysiology of pulmonary hypertension is unclear. Therefore, we investigated ET-1-induced vasoactive responses and ET-1 concentrations in an animal model of pulmonary hypertension and increased pulmonary blood flow. Vascular shunts were placed between the ascending aorta and main pulmonary artery in seven late-gestation fetal sheep. Four weeks after spontaneous delivery, ET-1 increased pulmonary vascular resistance by 29.7 +/- 34.4% (P < 0.05), the ETb-receptor agonist [Ala1,3,11,15]ET-1 (4AlaET-1) had no effect, and the ETa-receptor antagonist cyclo(D-Asp-L-Pro-D-Val-L-Leu-D-Trp) (BQ-123) decreased pulmonary vascular resistance by -16.0 +/- 5.6% (P < 0.05). In contrast, in six control lambs with a similar degree of pulmonary hypertension induced by U-46619, ET-1 and 4AlaET-1 decreased pulmonary vascular resistance by 24.8 +/- 17.6, and 20.0 +/- 13.8%, respectively (P < 0.05). In addition, systemic arterial concentrations of immunoreactive ET-1 were elevated in lambs with pulmonary hypertension (29.2 +/- 9.6 vs. 15.2 +/- 10.7 pg/ml, P < 0.05). Pulmonary hypertension and increased pulmonary blood flow alters the response of ET-1 from pulmonary vasodilation to vasoconstriction. These altered responses suggest a role for ET-1 and its receptors in the pathogenesis of pulmonary hypertension secondary to increased pulmonary blood flow.
Evidence for uneven distribution of L-type calcium channels in rat pulmonary circulation
Authors: Walker B. R.
Published: December 2017

Experiments were performed on isolated, perfused rat lungs to determine the segmental sites of vasoconstriction in response to factors that open voltage-sensitive, L-type calcium channels on vascular smooth muscle cells. Lungs from male Sprague-Dawley rats were perfused at constant flow with a physiological saline solution (PSS) containing albumin. Measurements were made of pulmonary arterial and venous pressure, whereas capillary pressure was estimated by the double-occlusion technique. After equilibration, lungs were constricted with depolarizing PSS containing high K+ (35 or 45 mM). With both stimuli, approximately 80% of the observed increase in vascular resistance occurred on the arterial side of the circulation. Both nifedipine and verapamil reversed this response; however, reversal was more consistent in the arterial segment. In additional experiments, the L-type channel activator (-)BAY K 8644 caused increased resistance in the arterial but not the venous segment. Another group of lungs constricted with the thromboxane mimetic U-46619 demonstrated equal arterial and venous vasoconstriction. In U-46619-constricted lungs, nifedipine caused a 28% reversal of the agonist-induced increase in arterial resistance but was without effect on the venous circulation. These data suggest that a greater density of L-type calcium channels may exist within the arterial segment of the pulmonary circulation than in the veins.
Surface thrombomodulin modulates thrombin receptor responses on vascular smooth muscle cells
Authors: Grinnell B. W. , Berg D. T.
Published: December 2017

Vascular smooth muscle cells produce the proteolytically activated thrombin receptor. Under certain conditions, they have been reported to synthesize thrombomodulin (TM), another thrombin receptor known to convert the specificity of thrombin from cleavage of procoagulant/proinflammatory substrates to the cleavage of the anticoagulant/anti-inflammatory factor protein C. In this study, we examined the role of TM in modulating thrombin-mediated cellular responses. Using a thrombin receptor-positive TM-negative rabbit intimal smooth muscle cell line (RIC), we isolated cells expressing varying levels of functional surface TM after transfection with an expression vector containing the cDNA for full-length TM. The parent RIC (TM negative) line responded to alpha-thrombin and to agonist peptide (SFLLRN-PNDKYEPF; abbreviated SFLL) with both mitogenic response and phosphoinositol release. However, transfected cells producing high levels of TM, equivalent to the level on rabbit aortic endothelial cells, responded to SFLL but not to alpha-thrombin. Whereas alpha-thrombin, SFLL, and the combination of SFLL and thrombin resulted in a mitogenic response in the TM-negative RIC line, the response to the agonist peptide could be blocked by thrombin in the TM-producing cell line. The degree to which thrombin receptor activation was blocked directly correlated with the level of TM on the cell surface, and high levels of thrombin could overcome the inhibitory effect. Our data demonstrate that the coexpression of TM with thrombin receptor on vascular smooth muscle cells can result in a modulation of cellular responses to thrombin, which could control thrombin-induced proliferative events following vessel injury or insult.
Cholinergic stimulation modulates negative inotropic effect of cocaine on ferret ventricular myocardium
Authors: Miao L. , Qiu Z. , Morgan J. P.
Published: December 2017

We tested the hypothesis that the negative inotropic effect (NIE) of cocaine is mediated, at least in part, by cholinergic stimulation and can be correlated with the degree of adenosine 3',5'-cyclic monophosphate (cAMP) dependency of the inotropic state. Cardiac myocytes were isolated from left ventricles of ferrets and loaded with the fluorescent Ca2+ indicator indo 1. Cells were placed in physiological solution containing 2.0 mM Ca2+ and stimulated at 0.5 Hz and 30 degrees C. Cocaine decreased peak cell shortening and peak intracellular Ca2+ in a concentration-dependent manner (10(-8)-10(-4) M). The concentration-response curve of cocaine was shifted significantly downward compared with those of lidocaine and procaine in the same range of concentrations. Atropine (10(-6) M) shifted the concentration-response curve of cocaine, but not those of lidocaine and procaine, rightward, with a pA2 value (7.66) similar to that obtained with carbachol (7.99). With prior addition of isoproterenol (ISO, 10(-8) M) or increased Ca2+ (4.0 mM) to increase cell shortening to the same degree (approximately 60%), cocaine and carbachol decreased contractility to a significantly greater extent in ISO-stimulated myocytes. To clarify whether these treatments changed responsiveness of the contractile elements to Ca2+, the effect of 2,3-butanedione monoxime, an agent that interferes with the interaction of myosin and actin, was tested with previous addition of ISO or increased Ca2+, and no differential effect occurred. Therefore, we postulate that 1) the NIE of cocaine on myocytes is caused by decreased Ca2+ availability; 2) this effect is due to specific stimulation of cholinergic receptors in addition to other direct myocardial (probably local anesthetic) effects; and 3) the NIE correlates with the level of cAMP dependence of the inotropic state.
Mechanism of negative lusitropic effect of alpha 1-adrenoceptor stimulation in cat papillary muscles
Authors: Vila-Petroff M. , Perez G. N. , Alvarez B. , Cingolani H. E. , Mattiazzi A.
Published: December 2017

Experiments were performed in cat papillary muscles to explore the mechanisms by which alpha 1-adrenoceptor stimulation affects myocardial relaxation. Phenylephrine (PE; 10 microM) + atenolol (1 microM; n = 8 experiments) produced a negative lusitropic effect, i.e., a prolongation of half-relaxation time (t1/2; time to 50% relaxation) by 30 +/- 10% (P < 0.05) and a proportionally smaller increase in maximal velocity of relaxation (-T) than in maximal velocity of contraction (+T), which significantly increased the ratio +T/-T. A similar increase in contractility, produced by increasing calcium, failed to significantly change t1/2 and +T/-T. PE-induced negative lusitropic effect was significantly inhibited by two protein kinase C (PKC) inhibitors, staurosporine (0.1 microM) and chelerythrine (10 microM). PE also increased intracellular pH by 0.18 +/- 0.05 pH units (P < 0.05, n = 4), as measured by the fluorescent dye 2'-7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. Intracellular alkalosis and the negative lusitropic effect of PE were prevented by the Na+/H+ exchanger inhibitor ethylisopropylamiloride (10 microM). No significant changes in calcium myofilament sensitivity and maximal tension were detected in trabeculae treated with PE either before or after chemical skinning. These results indicate that a Na+/H+ exchanger-induced intracellular alkalosis, possibly mediated by PKC activation, may fully account for the negative lusitropism of alpha 1-adrenoceptor stimulation.
Stress-induced mesenteric vasoconstriction in rats is mediated by neuropeptide Y Y1 receptors
Authors: Zukowska-Grojec Z. , Dayao E. K. , Karwatowska-Prokopczuk E. , Hauser G. J. , Doods H. N.
Published: December 2017

The physiological role of neuropeptide Y (NPY), a sympathetic cotransmitter and vasoconstrictor, has not been determined yet. We used a specific nonpeptide antagonist to the NPY Y1 receptor [BIBP-3226; (R)-N2-(diphenacetyl)-N-[(4-hydroxyphenyl) methyl]-D-arginineamide] to study the involvement of NPY in stress-induced vasoconstriction in the mesenteric bed. In rats subjected to cold water stress (COLD), plasma NPY immunoreactivity levels increased progressively from 0.15 +/- 0.01 to 0.32 +/- 0.05 pmol/ml and remained elevated during recovery. Administration of BIBP-3226 (3 mg.kg-1.h-1 infusion) tended to decrease the stress-induced pressor response and significantly attenuated the post-COLD elevation of blood pressure. The COLD-induced fall in the superior mesenteric artery blood flow and the increase of up to 300% in the mesenteric vascular resistance were either reduced or eliminated by BIBP-3226. Conversely, the Y1 antagonist had no effect on the COLD-induced tachycardia. This study provides the first evidence of the physiological role of NPY. The peptide is released during stress and increases mesenteric vascular resistance via activation of its Y1 receptors. Specific Y1-receptor antagonists may therefore be of potential benefit in prevention or treatment of stress-induced vasospasm.
Oxygen-elicited responses in calf coronary arteries: role of H2O2 production via NADH-derived superoxide
Authors: Mohazzab-H K. M. , Kaminski P. M. , Fayngersh R. P. , Wolin M. S.
Published: December 2017

Our previous studies in isolated endothelium-removed calf pulmonary arteries suggest that PO2-elicited responses are primarily mediated through modulation of guanosine 3',5'-cyclic monophosphate via changes in the generation of H2O2 originating from superoxide anion (O2-.) produced by NADH oxidase activity. In the present study we examined the importance of this mechanism in PO2-elicited responses of endothelium-removed calf coronary arteries. NADH oxidase activity was found to be the major source of O2-. in the homogenate of endothelium-removed calf coronary arteries detected by lucigenin-elicited chemiluminescence. Precontracted endothelium-removed calf coronary arteries show a relaxation to hypoxia, and reoxygenation causes a transient additional relaxation before the recovery of normoxic levels of force. Under these conditions the detection of O2-. was decreased by hypoxia and a transient overproduction was observed during reoxygenation. The relaxation to reoxygenation, but not to hypoxia, was significantly inhibited by a scavenger of O2-. that prevents the formation of H2O2 (nitro blue tetrazolium), an inhibitor of NAD(P)H oxidases and other O2(-.)-generating flavoproteins (diphenyliodonium), and inhibition of the stimulation of soluble guanylate cyclase (LY-83583). A scavenger of O2-. that promotes H2O2 formation (Tiron) did not inhibit the PO2-elicited responses examined. Hypoxia and diphenyliodonium (but not Tiron) decreased the metabolism of endogenous H2O2 by catalase (as measured by the H2O2-dependent co-oxidation of methanol to formaldehyde by catalase), and reoxygenation caused a stimulation of H2O2 metabolism by catalase. The presence of endothelium resulted in minor modifications of the PO2 responses, which were partially mediated via prostaglandins and nitric oxide on the basis of the effects of indomethacin and nitro-L-arginine, respectively. These results suggest that in calf coronary arteries the stimulation of guanylate cyclase via H2O2 originating from NADH-derived O2-(.) production contributes to the transient relaxation to posthypoxic reoxygenation, but not the response to hypoxia.
Regional cerebral blood flow response to vibrissal stimulation in mice lacking type I NOS gene expression
Authors: Ma J. , Ayata C. , Huang P. L. , Fishman M. C. , Moskowitz M. A.
Published: December 2017

The role of nitric oxide (NO) in cerebral blood flow-metabolism coupling was assessed in SV-129 wild-type (WT) and neuronal (type I) NO synthase (NOS) knockout mice (Kn). Regional cerebral blood flow (rCBF; laser-Doppler flowmetry) was measured over the contralateral cortical barrel field during unilateral mechanical vibrissal deflection (2-3 Hz, 60 s) under urethan anesthesia. The rCBF response was similar in WT and Kn and did not differ when recorded over the intact skull or closed cranial window preparations. Whisker stimulation increased rCBF by 41 +/- 8% (maximum) and 27 +/- 6% (mean) in WT (n = 6) and 41 +/- 7% (maximum) and 26 +/- 6% (mean) in Kn (n = 6) when recorded through a closed cranial window. After superfusion with topical N omega-nitro-L-arginine (L-NNA; 1 mM), the rCBF response was inhibited by approximately 45% in WT mice (P < 0.05), whereas there was no inhibition in Kn. Endothelium-dependent relaxation, assessed by pial vessel dilation in response to topical acetylcholine (100 microM) and inhibition by L-NNA (1 mM), was the same in both groups. Our results suggest that 1) endothelial NO production does not mediate the rCBF coupling to neuronal activity in Kn, 2) the inhibitory effect of L-NNA on the rCBF response to whisker stimulation in WT is a consequence of type I (neuronal) NOS inhibition, and 3) NO-independent mechanisms couple rCBF and metabolism during whisker stimulation in mice lacking expression of neuronal NOS.
Effect of cellular inhomogeneity on cardiac tissue mechanics based on intracellular control mechanisms
Authors: Landesberg A. , Markhasin V. S. , Beyar R. , Sideman S.
Published: December 2017

Our earlier description of the intracellular control (IC) of contraction of a single cell, based on coupling calcium kinetics with cross-bridge cycling, is extended here to study the performance of a multicellular inhomogeneous tissue common in pathophysiological situations. Inhomogeneity in calcium affinity or in cross-bridge kinetics is first simulated by analyzing two fiber segments connected as parallel or serial duplexes. The calculated characteristics of the parallel duplex are tested against our experimental data with two parallel nonuniform rat papillary fibers. The predicted serial duplex behavior is compared with reported experimental data of the effects of segmental hypoxia along a papillary fiber. Fiber inhomogeneity leads to polyphasic contraction of the fiber segments, reduces muscle length shortening, and affects the control of relaxation. We next investigated the force generated by a nonuniform tissue containing small areas of necrosis, evident in subendocardial infarction. Theoretical analysis suggests that the IC mechanism decreases the extension of cell necrosis by lowering the energy consumption of the viable cells in the ischemic zone. The study emphasizes the importance of IC in determining the global and local function of the inhomogeneous myocardium.
Role of summation of afferent input in cardiovascular reflexes from splanchnic nerve stimulation
Authors: Pan H. L. , Zeisse Z. B. , Longhurst J. C.
Published: December 2017

Stimulation of abdominal sympathetic visceral afferents reflexly excites the cardiovascular system. The present study examined the role of summation of afferent input in this reflex. Single-unit activity of A delta- and C-fiber afferents was recorded from the right thoracic sympathetic chain in anesthetized cats to determine the relationship between intensities of electrical stimulation and the types of nerve fibers within the right greater splanchnic nerve. The differential effect of cooling on A delta- and C-fiber axons in the sympathetic chain also was examined by recording single-unit afferent activity. Reflex cardiovascular responses were induced by electrical stimulation of the central cut end of the right greater splanchnic nerve. We observed that the numbers of A delta and C fibers activated by electrical stimulation were proportional to the intensity of stimulation. However, neither local cooling nor intensity of stimulation provided a means to separate A delta and C fibers contained in the sympathetic chain. The results demonstrate that the magnitude of excitatory cardiovascular reflexes is frequency dependent and is related directly to intensity of electrical stimulation, suggesting that both adequate discharge frequency of the afferent and sufficient numbers of afferents recruited are crucial factors for full expression of reflex cardiovascular responses.
Hypoxia-reoxygenation increases O2-. efflux which injures endothelial cells by an extracellular mechanism
Authors: Terada L. S.
Published: December 2017

The mechanisms by which superoxide anion (O2-.) injures reoxygenated vascular cells are not clearly understood. We hypothesized that O2-. formed in an intracellular compartment during reoxygenation may egress through plasmalemmal anion channels and mediate injury from an extracellular site. Bovine pulmonary artery endothelial cells (EC) kept hypoxic for 48 h had increased release of preloaded 51Cr upon reoxygenation. Evidence for an extracellular site of injury was the following. First, decreasing extracellular O2-. levels (measured by cytochrome c reduction) with the anion channel blocker 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) leads to decreased 51Cr leak. In contrast to its effect on extracellular O2-., DIDS increased intracellular O2-. levels (measured by nitroblue tetrazolium reduction) following reoxygenation. Second, treatment with exogenous superoxide dismutase (SOD), while having no significant effect on intracellular O2-. levels, also decreased 51Cr leak. Furthermore, cotreatment of EC with DIDS did not abrogate the protective effects of exogenous SOD, suggesting that SOD decreased injury by decreasing extracellular and not intracellular O2-. Finally, exposure of EC to extracellularly generated O2-. (xanthine oxidase/hypoxanthine system) caused injury, which was decreased by SOD but not by blockade of O2-. entry with DIDS. The mechanism by which O2-. injures EC may involve generation of .OH by surface-associated iron, since iron chelators and .OH scavengers of varying membrane permeability all decreased 51Cr release to a similar extent. Furthermore, the iron chelators and .OH scavengers also decreased EC 51Cr leak following exposure to exogenous xanthine oxidase/hypoxanthine but not following exposure to a O2(-.)-independent agent (A23187). We conclude that hypoxia-reoxygenation injures EC in a manner that is at least in part dependent on the efflux of O2-. into the extracellular space. Endogenous and exogenous strategies for protection against reoxygenation injury must target extracellular O2-. as a potentially harmful species.
Effect of arterial compliance on carotid sinus baroreceptor reflex control of the circulation
Authors: Potts J. T. , Hatanaka T. , Shoukas A. A.
Published: December 2017

Capacitive properties of the arterial and venous segments of the peripheral circulation are important in the regulation of cardiac output and arterial blood pressure. We examined whether an acute increase in arterial compliance C(a) would alter carotid sinus baroreflex control of the circulation. Eight mongrel dogs were anesthetized with pentobarbital sodium, and the carotid sinus regions were isolated and perfused with nonpulsatile pressures. Open-loop baroreflex response curves for systemic arterial pressure (SAP), heart rate (HR), aortic blood flow (ABF), peripheral vascular resistance (PVR), and left ventricular (LV) contractility were obtained when carotid sinus pressure (CSP) was changed in 25-mmHg steps between 50 and 200 mmHg under a control condition and when C(a) was increased by including two hydraulic compliant chambers to the arterial circulation (CS 1.72 ml/mmHg and CL 5.05 ml/mmHg). The compliant chambers significantly increased C(a) and altered the ratio of arterial to venous compliance C(a)/Cv). Changes in C(a)/Cv significantly decreased the maximal open-loop baroreflex gain (Gmax) for SAP (-2.3 +/- 0.5, -1.6 +/- 0.3, and -1.1 +/- 0.2 mmHg/mmHg, control vs. CS vs. CL, P < 0.05). Gmax for ABF was decreased by CS (-0.9 +/- 0.2 vs. -0.3 +/- 0.1 ml.kg-1.min-1, control vs. CS, P < 0.05), and CL reversed the reflex changes in ABF (Gmax: +0.6 +/- 0.3 ml.kg-1.min-1). Gmax for HR, PVR, and LV contractility was not altered when C(a) was increased (P > 0.05). These findings indicate that an increase in C(a) changes C(a)/Cv and alters carotid baroreflex control of SAP by modifying the ABF response. We conclude that a change in C(a)/Cv affects the reflex control of the circulation by altering the distribution of blood volume between the arterial and venous circulations.
Energetic basis for reduced contractile reserve in isolated rat hearts
Authors: Tian R. , Ingwall J. S.
Published: December 2017

To study the relationship between myocardial energetics and contractile reserve, we acutely and selectively inhibited creatine kinase (CK) activity in isolated perfused rat hearts, using increasing doses of iodoacetamide. 31P nuclear magnetic resonance spectroscopy was used to measure intracellular pH and the concentrations of ATP, phosphocreatine, and inorganic phosphate. Contractile reserve was assessed as the increase of rate-pressure product (RPP) from baseline during high-calcium perfusion. Contractile reserve was reduced by 9, 35, and 72% in hearts with 26, 6, and 1% CK activity, respectively. An inverse linear relationship between RPP and the free energy release from ATP hydrolysis ([delta G approximately P[) was shown for all groups. Furthermore, the maximal RPPs of all hearts were achieved at the same level of [delta G approximately P[ (52-53 kJ/mol), which is equal to the free energy requirement of sarcoplasmic reticulum Ca2+ adenosine 5'-triphosphatase (ATPase). We suggest that inhibition of the CK reaction caused a decrease of [delta G approximately P[ which, in turn, limits the Ca(2+)-handling capacity of sarcoplasmic reticulum Ca2+ ATPase. In this way, the ability of the heart to increase its contractile performance is restricted.
Functional antagonism between cAMP and cGMP on permeability of coronary endothelial monolayers
Authors: Hempel A. , Noll T. , Muhs A. , Piper H. M.
Published: December 2017

The role of the intracellular second messengers guanosine 3', 5'-cyclic monophosphate (cGMP) and adenosine 3', 5'-cyclic monophosphate (cAMP) in the control of macromolecule permeability was studied in cultured monolayers of microvascular coronary endothelial cells from rat. Macromolecule permeability was determined as passage of fluorescein isothiocyanate (FITC)-labeled albumin across the monolayers. Activation of adenylyl cyclase by the beta-adrenoceptor agonist isoproterenol (Iso; 10(-5) M) and the A2-adenosine receptor agonist 5'-(N-ethylcarboxamido)-adenosine (NECA; 10(-7) M) induced an increase in cellular cAMP contents that was accompanied by an increase in albumin flux. Effects of Iso and NECA on cellular cAMP level and albumin flux could be antagonized by a stimulator of the particular guanylyl cyclase, atrial natriuretic peptide (ANP; 10(-7) M), and stimulators of the soluble guanylyl cyclase, 3-morpholinosydnonimine (SIN-1; 10(-7) M) and sodium nitroprusside (SNP; 10(-6) M). ANP, SIN-1, and SNP also reduced cAMP content and basal macromolecule flux in unstimulated monolayers. 8-Bromoguanosine 3', 5'-cyclic monophosphate (8-BrcGMP; 5 x 10(-6) M), a stimulator of protein kinase G, reduced the increase in albumin flux under Iso (10(-5) M), NECA (10(-7) M), or 8-bromoadenosine 3', 5'-cyclic monophosphate (8-BrcAMP; 5 x 10(-6) M). The present study shows that cGMP and cAMP are functional antagonists in the control of macro molecule permeability.
Calcium channel activity increased by plasma from ischemic hindlimbs of rats: role of an endogenous NO synthase inhibitor
Authors: Jin J. S. , Wilde D. W. , Webb R. C. , D'Alecy L. G.
Published: December 2017

We tested the hypothesis that an endogenous nitric oxide synthase (NOS) inhibitor released from ischemic hindlimbs increases the activity of calcium channels in vascular smooth muscle, thus contributing to the increased contractile response to calcium agonists. Hindlimb ischemia was generated in rats by infrarenal aortic cross clamping for 5 h, after which plasma was obtained from femoral vein blood. Incubating naive aortic rings (endothelium intact) for 2 h in plasma collected from ischemic rats significantly reduced relaxation to acetylcholine in precontracted rings and increased contraction to the calcium channel agonist, BAY K 8644. However, in isolated smooth muscle cells (without endothelium) loaded with fura-2, no difference was noted in BAY K 8644-stimulated intracellular calcium concentration. The contractile responses to sodium fluoride, serotonin, and calcium ionophore A23187 were not different in either ischemic or control plasma-incubated rings. The augmentation of the contractile response to BAY K 8644 was significantly inhibited by nitroglycerin (10-8 M) and by exposure to calcium-free solution. N omega-nitro-L-arginine (without plasma incubation)-pretreated rings also demonstrated hyperresponsiveness to BAY K 8644. The increase in responsiveness to BAY K 8644 exhibited a negative correlation with the maximal relaxation to acetylcholine (r = -0.99), suggesting that the apparent increase in activity of calcium channels is mediated through inhibition of nitric oxide by an endogenous NOS inhibitor on endothelium.
Influence of L-type Ca channel alpha 2/delta-subunit on ionic and gating current in transiently transfected HEK 293 cells
Authors: Bangalore R. , Mehrke G. , Gingrich K. , Hofmann F. , Kass R. S.
Published: December 2017

We have measured ionic and gating currents in human embryonic kidney (HEK 293) cells transiently transfected with cDNAs encoding subunits of the cardiac voltage-gated L-type Ca2+ channel. Robust recombinant ionic current and associated nonlinear charge movement could be measured over a broad voltage range without contamination by endogenous channel activity. Coexpression of the alpha 2/delta-subunit along with alpha 1- and beta 2-subunits speeded activation and deactivation kinetics and significantly increased the maximal conductance of ionic current. Charge movement was measured at voltages negative to the threshold for activation of ionic current, and gating charge could be immobilized at positive holding potentials that did not inactivate ionic current. The ratio of maximal ionic conductance to maximal charge moved remained the same in the absence or presence of the alpha 2/delta-subunit. However, the maximal amount of charge moved was increased about twofold in the presence of the alpha 2/delta-subunit. These results suggest that coexpression of the alpha 2/delta-subunit enhances the expression of functional L-type channels and, in addition, provide evidence that most of the L-type channel-associated nonlinear charge movement is caused by transitions between nonconducting states of the channel protein that precede the open and inactivated states.
Fasting, lactate, and insulin improve ischemia tolerance in rat heart: a comparison with ischemic preconditioning
Authors: Doenst T. , Guthrie P. H. , Chemnitius J. M. , Zech R. , Taegtmeyer H.
Published: December 2017

We tested the hypothesis that improved ischemia tolerance in an isolated working rat heart preparation can be achieved by interventions other than ischemic preconditioning. Hearts were perfused at near-physiological workload with bicarbonate buffer containing glucose (10 mM). A preischemic period of 25 min was followed by 15 min of global ischemia and 30 min of reperfusion under preischemic conditions. Hearts came from either fed or fasted animals (groups 1 and 2). In group 3 lactate (10 mM) and insulin (10 mU/ml) were added to the perfusate of fasted animals. In group 4 hearts from fed animals were perfused with glucose (10 mM) and were ischemically preconditioned by one cycle of ischemia between 10 and 15 min of the preischemic perfusion. Cardiac power and glucose uptake were measured continuously to assess functional and metabolic recovery. In addition, we measured the time to return of aortic flow. Glucose metabolites and the ratio of latent of free citrate synthase activity (citrate synthase ratio, a marker for the structural integrity of mitochondria) were determined at selected time points. Groups 2, 3, and 4 recovered significantly faster than group 1, whereas recovery of power showed an improvement in groups 3 and 4 only. In addition, there was an early increase in glucose uptake during reperfusion in these two groups, suggesting an early need for glucose substrate. Glycogen levels decreased with ischemia in all groups and returned to preischemic levels in groups 2, 3, and 4. The citrate synthase ratio was low in the control group and preserved in the groups showing improved functional recovery. We conclude that metabolic interventions may be as effective as ischemic preconditioning in protecting the heart from ischemic injury.
Nitric oxide release in rat skeletal muscle capillary
Authors: Mitchell D. , Tyml K.
Published: December 2017

Nitric oxide (NO) has been shown to be a potent vasodilator released from endothelial cells (EC) in large blood vessels, but NO release has not been examined in the capillary bed. Because the capillary bed represents the largest source of EC, it may be the largest source of vascular NO. In the present study, we used intravital microscopy to examine the effect of the NO synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), on the microvasculature of the rat extensor digitorum longus muscle. L-NAME (30 mM) applied locally to a capillary (300 micron(s) from the feeding arteriole) reduced red blood cell (RBC) velocity [VRBC; control VRBC = 238 +/- 58 (SE) micron/s; delta VRBC = -76 +/- 8%] and RBC flux (4.4 +/- 0.7 to 2.8 +/- 0.7 RBC/s) significantly in the capillary, but did not change feeding arteriole diameter (Dcon = 6.3 +/- 0.7 micron, delta D = 5 +/- 7%) or draining venule diameter (Dcon = 10.1 +/- 0.6 micron, delta D = 4 +/- 2%). Because of the VRBC change, the flux reduction was equivalent to an increased local hemoconcentration from 1.8 to 5 RBCs per 100 micron capillary length. L-NAME also caused an increase in the number of adhering leukocytes in the venule from 0.29 to 1.43 cells/100 micron. L-NAME (30 mM) applied either to arterioles or to venules did not change capillary VRBC. Bradykinin (BK) locally applied to the capillary caused significant increases in VRBC (delta VRBC = 111 +/- 23%) and in arteriolar diameter (delta D = 40 +/- 5%). This BK response was blocked by capillary pretreatment with 30 mM L-NAME (delta VRBC = -4 +/- 27%; delta D = 5 +/- 9% after BK). We concluded that NO may be released from capillary EC both basally and in response to the vasodilator BK. We hypothesize that 1) low basal levels of NO affect capillary blood flow by modulating local hemoconcentration and leukocyte adhesion, and 2) higher levels of NO (stimulated by BK) may cause a remote vasodilation to increase microvascular blood flow.
Endogenous atrial natriuretic peptide inhibits endothelin-1 secretion in dogs with severe congestive heart failure
Authors: Wada A. , Tsutamato T. , Maeda Y. , Kanamori T. , Matsuda Y. , Kinoshita M.
Published: December 2017

Atrial natriuretic peptide (ANP) has been shown to counteract the response of endothelin-1 (ET-1), but whether endogenous ANP actually inhibits the systemic release of ET-1 in vivo has not yet been determined. We administered HS-142-1 (HS), a specific antagonist of the guanylate cyclase-coupled ANP receptor, to conscious dogs with severe congestive heart failure (CHF) produced by rapid right ventricular pacing (n = 5, for 22 days) at doses of 0.3, 1.0, and 3.0 mg/kg at 30-minutes intervals. In the present study, plasma ANP and ET-1 levels were significantly elevated in CHF(348 +/-58 and 4.54 +/- 0.60 pg/ml, respectively compared with those in control dogs (65 +/- 4, P < 0.01, 1.30 +/- 0.17 pg/ml, P < 0.001). HS inhibited plasma guanosine 3',5'-cyclic monophosphate (cGMP) levels, a biological market of endogenous ANP activity, in a dose-dependent manner from 21.8 +/- 2.2 to 7.2 +/- 1.4 pmol/ml (P < 0.001), with concomitant significant increases in plasma ET-1 levels from 4.54 +/- 0.60 to 6.60 +/- 0.72 pg/ml (P < 0.05). There was a significant negative correlation between the decrease in plasma cGMP and the increment in plasma ET-1 (r = -0.64, P < 0.01). Despite these responses, mean arterial pressure and pulmonary arterial pressure did not change significantly. Plasma angiotensin II and arginine vasopressin levels, both of which have been reported to stimulate ET-1 secretion in vitro, also showed no significant changes. These results strongly suggest that endogenous ANP directly inhibits endogenous ET-1 secretion through a cGMP-mediated pathway in chronic severe CHF.
Substrate-dependent alteration in O2 consumption and energy metabolism in vascular smooth muscle
Authors: Barron J. T. , Kopp S. J. , Tow J. , Parrillo J. E.
Published: December 2017

Energy metabolism and the substrate utilization pattern of intact porcine carotid artery were investigated in the presence or absence of glucose and/or octanoate during the phases of isometric contraction induced by K+ depolarization. During the early phase of contraction, there was a rapid increase in the rate of O2 uptake that was independent of the rate of force generation but dependent on the availability of intracellular pyruvate, the source of which was glucose and not glycogen. Lactate production increased linearly from the onset of contractile stimulation and was not suppressed by octanoate oxidation. There was no alteration from the basal resting state in the concentrations of the metabolites of the tricarboxylic acid cycle in the presence or absence of octanoate. During the phase of steady-state force maintenance, O2 consumption was increased compared with the basal unstimulated rate but was not increased when glucose and octanoate were present, which is consistent with the Crabtree effect. This was associated with increased aerobic lactic acid production and inhibition of the tricarboxylic acid cycle at the citrate synthase step. Alteration of the high-energy phosphate content could not account for the pattern of O2 consumption during contraction under different substrate conditions. In the absence of glucose, the energy from octanoate oxidation could substitute for the energy ordinarily derived from aerobic glycogen and lactic acid production. It is concluded that energy metabolism of vascular smooth muscle is coordinated during contraction by integration of the pathways of aerobic glycolysis and oxidative phosphorylation.
Xanthine oxidase mediates cyclic flow variations in a canine model of coronary arterial thrombosis
Authors: Kuwano K. , Ikeda H. , Oda T. , Nakayama H. , Koga Y. , Toshima H. , Imaizumi T.
Published: December 2017

We investigated the hypothesis that xanthine oxidase (XO) mediates platelet aggregation and cyclic flow variations (CFVs) in stenosed canine coronary arteries. CFVs were produced by an external constrictor placed at the site of the coronary artery with the injured endothelium. The severity of CFVs was evaluated by a pulsed Doppler flow probe. If CFVs developed, dogs intravenously received allopurinol, a specific XO inhibitor. The transcardiac gradient (difference between coronary vein and left atrium) of purine metabolites was determined during CFVs and after allopurinol administration. Allopurinol significantly reduced CFVs (from 8 +/- 1 to 1 +/- 1 cycles/h, P < 0.01, n = 14), whereas saline did not (from 8 +/- 1 to 7 +/- 1 cycles/h, n = 7). In seven dogs with CFVs, the transcardiac gradient of xanthine and uric acid concentrations significantly increased after the establishment of CFVs and significantly decreased after the administration of allopurinol. In vitro platelet studies showed that XO enhanced (from 30.9 +/- 2.0 to 47.6 +/- 1.5%, P < 0.0001, n = 10) and allopurinol inhibited ADP-induced platelet aggregation (from 48.3 +/- 1.3 to 24.8 +/- 1.5%, P < 0.0001, n = 10). Our results indicate that allopurinol inhibits platelet aggregation in vitro and provides a protection against CFVs in vivo. Thus XO may be an important mediator in this model.