bluuebunny/crossref_metadata_2025 huggingface dataset:
cGMP and cAMP in prostaglandin-induced pial artery dilation and increased CSF opioid concentration
Authors: Armstead W. M.
Published: December 2017

It has been observed that prostaglandins (PG) PGE2 and PGI2 increased cortical periarachnoid cerebrospinal fluid (CSF) methionine enkephalin (Met-enk) and leucine enkephalin (Leu-enk) concentrations in the newborn pig. It was also observed that PG-induced pial artery dilation was associated with elevated CSF guanosine 3',5'-cyclic monophosphate (cGMP) and adenosine 3',5'-cyclic monophosphate (cAMP) levels in the piglet. However, other studies have not always supported a role for cGMP in PG dilation. The present study used a pharmacological approach to test the hypothesis that both cGMP and cAMP contribute to PG-induced pial dilation and associated elevated CSF opioid concentration. PGE2 produced pial vasodilation that was blunted by the Rp diastereomer of bromoguanosine 3',5'-cyclic monophosphothioate [Rp-8-BrcGMPS (10(-5)M)], a cGMP antagonist (9 +/- 1, 16 +/- 1, and 23 +/- 1 vs. 4 +/- 1, 6 +/- 1, and 9 +/- 1% for 1, 10, and 100 ng/ml PGE2 before and after Rp-8-BrcGMPS, respectively). PGE2 elevated CSF Met-enk concentration, and these biochemical changes were also blunted by Rp-8-BrcGMPS (1,001 +/- 23, 1,424 +/- 54, and 1,973 +/- 56 vs. 804 +/- 41, 988 +/- 52, and 1,222 +/- 21 pg/ml for control, 10, and 100 ng/ml PGE2 in the absence and presence of Rp-8-BrcGMPS, respectively). Similar biochemical and vascular effects of Rp-8-BrcGMPS were observed for PGI2. Additionally, the Rp diastereomer of bromoadenosine 3',5'-cyclic monophosphothioate [Rp-8-BrcAMPS (10(-5)M)], a cAMP antagonist, blunted PGE2 dilation (10 +/- 1, 15 +/- 1, and 24 +/- 1 vs. 5 +/- 1, 8 +/- 1, and 12 +/- 1% for 1, 10, and 100 ng/ml PGE2 before and after Rp-8-BrcAMPS, respectively). PGE2-associated increases in CSF Met-enk and Leu-enk were similarly blunted by Rp-8-BrcAMPS. These data show that both cGMP and cAMP contribute to PG-induced pial dilation and that PG-associated elevated CSF cGMP and cAMP levels result in increased CSF Met-enk and Leu-enk concentration.
RSR-13, an allosteric effector of hemoglobin, increases systemic and iliac vascular resistance in rats
Authors: Kunert M. P. , Liard J. F. , Abraham D. J.
Published: December 2017

Tissue O2 delivery in excess of metabolic demand may be a factor in the development of high vascular resistance in experimental models of volume-expanded hypertension. This hypothesis was previously tested in rats with an exchange transfusion of red blood cells treated with inositol hexaphosphate or an intravenous infusion of RSR-4, allosteric effectors of hemoglobin. The binding of these drugs with hemoglobin effect a conformational change in the molecule, such that the affinity for O2 is reduced. However, in both preparations, the changes in vascular resistance could have been nonspecific. The present studies used intravenous infusions of RSR-13, which did not share some of the problematic characteristics of RSR-4 and inositol hexaphosphate. Conscious instrumented rats (an electromagnetic flow probe on ascending aorta or an iliac, mesenteric, or renal Doppler flow probe) were studied for 6 h after an RSR-13 infusion of 200 mg/kg in 15 min. This dose significantly increased arterial P50 (PO2 at which hemoglobin is 50% saturated) from 38 +/- 0.8 to 58 +/- 1.4 mmHg at 1 h after the start of the infusion. In the 3rd h cardiac output fell significantly from a control value of 358 +/- 33 to 243 +/- 24 ml.kg-1.min-1 and total peripheral resistance significantly increased from 0.31 +/- 0.03 to 0.43 +/- 0.04 mmHg.ml-1.kg.min. Cardiac output and P50 returned toward control over the next few hours. Neither cardiac output nor total peripheral resistance changed in the group of rats receiving vehicle alone. In a separate group of rats, iliac flow decreased significantly to 60% of control and iliac resistance increased to 160% of control. Iliac flow increased significantly in the group of rats that received vehicle only. Although the mechanism of these changes has not been established, these results suggest that a decreased O2 affinity leads to an increased total peripheral resistance and regional vascular resistance and support the hypothesis that O2 plays a role in the metabolic autoregulation of blood flow.
Response to cardiac sympathetic activation in transgenic mice overexpressing beta 2-adrenergic receptor
Authors: Du X. J. , Vincan E. , Woodcock D. M. , Milano C. A. , Dart A. M. , Woodcock E. A.
Published: December 2017

Transgenic mice have been created with 200-fold overexpression of beta 2-adrenergic receptors specifically in the heart. Cardiac function was studied in these transgenic mice and their controls at baseline and during isoproterenol perfusion or sympathetic nerve stimulation. The model used was an in situ buffer-perfused, innervated heart, and the left ventricle maximal derivative of pressure over time (dP/dtmax) and heart rate (HR) were measured. Basal HR and dP/dtmax were 30-40% higher in hearts from transgenic mice than controls. Electrical stimulation of sympathetic nerves (2, 4, and 8 Hz) or infusion of isoproterenol markedly increased HR and dP/dtmax in control hearts. Hearts from transgenic mice did not respond to isoproterenol. However, hearts from transgenic mice retained the HR response to nerve stimulation, and a small increase in dP/dtmax was also detected. Atenolol inhibited the response to nerve stimulation in control hearts but not that in hearts from transgenic mice. ICI-118551 inhibited the response in transgenic hearts. Basal HR and dP/dtmax were decreased by ICI-118551 only in transgenic hearts. Thus overexpression of cardiac beta 2-receptors modifies beta-adrenergic activity, but the responses to endogenous and exogenous adrenergic stimulation are affected differently.
Metalloprotease-mediated cleavage secretion of pulmonary ACE by vascular endothelial and kidney epithelial cells
Authors: Ramchandran R. , Kasturi S. , Douglas J. G. , Sen I.
Published: December 2017

The pulmonary isozyme of angiotensin-converting enzyme (ACEP) is present in the body both as a cell-associated protein in endothelial, epithelial, and monocytic cells and as a soluble protein in various body fluids including serum. The mechanism by which soluble ACEP is produced in vivo is unknown. Using in vitro transfected cell culture systems, we previously demonstrated that the rabbit testicular isozyme of ACE (ACET), which shares extensive homology with ACEP, is first synthesized as a plasma membrane-anchored ectoprotein and then secreted to the culture medium by cleavage removal of its COOH-terminal membrane-anchored tail. Here, using in vitro cultures of arterial endothelial cells and acutely isolated renal epithelial cells, we demonstrate that ACEP is also cleavage secreted from their natural producer cells. Biochemical and immunological characterization of the in vitro secreted ACEP protein revealed that it is missing the COOH-terminal membrane-anchored region of the cell-associated ACEP. Similar analysis of ACEP proteins present in rabbit serum, lung, and kidney established that ACEP secretion in vivo is also caused by the cleavage removal of the COOH-terminal region of the cell-associated protein. To characterize the proteolytic enzyme responsible for ACEP secretion, we employed rabbit renal proximal tubular epithelial cells and demonstrated significant inhibition of secretion by compound 3, a hydroxamic acid-based inhibitor of specific metalloproteases. In contrast, the inhibitors of chymotrypsin, trypsin, serine, aspartate, and cysteine proteases were ineffective. These results indicate that soluble ACEP production by vascular endothelial and renal epithelial cells, both in vitro and in vivo, is achieved by cleavage removal of its membrane-anchoring COOH-terminal tail by a metalloprotease.
Invariance of the resistance to venous return to carotid sinus baroreflex control
Authors: Hatanaka T. , Potts J. T. , Shoukas A. A.
Published: December 2017

Despite the well-established fact that the carotid sinus baroreflex system has profound control over the physical properties of the systemic circulation, the resistance to venous return (RVR) seems to be invariant of such control. We hypothesized that this apparent paradox may be explained from the baroreflex changes in systemic arterial compliance. In 12 pentobarbital-anesthetized mongrel dogs, RVR was measured at controlled carotid sinus pressures (CSP) of 50 and 200 mmHg with normal and artificially increased arterial compliance. Arterial compliance was determined from the arterial pressure decay when systemic blood flow was stopped with total vena caval occlusion. Changing CSP between 50 and 200 mmHg changed RVR significantly only under the condition of artificially increased arterial compliance. A four-parameter lumped model of the systemic circulation revealed that the baroreflex changes in arterial compliance and arterial resistance, which occurred in opposite directions, prevented a change in RVR when CSP was changed. The data also suggested that approximately 75% of RVR was attributed to large and conduit veins, the resistances along which were insensitive to baroreflex control. We concluded that the invariance of RVR results from a combination of 1) baroreflex change in the arterial compliance, 2) baroreflex insensitivity of the resistance along large and conduit veins, and 3) spatially distinct location between the major site of reflex change in capacitance and the major site of compliance.
Heme oxygenase substrates acutely lower blood pressure in hypertensive rats
Authors: Johnson R. A. , Lavesa M. , DeSeyn K. , Scholer M. J. , Nasjletti A.
Published: December 2017

Heme oxygenase catalyzes the metabolism of heme to biliverdine, free iron, and carbon monoxide. The current study was designed to determine if treatment with the heme oxygenase substrates heme-L-arginate or heme-L-lysinate, to stimulate formation of heme oxygenase products, can lower blood pressure in the rat. Heme-L-arginate (45 mumol/kg ip) and heme-L-lysinate (45 mumol/kg ip) acutely lowered blood pressure in awake spontaneously hypertensive rats (SHR) by approximately 35 mmHg. For both heme oxygenase substrates, this effect was blunted by pretreatment with an inhibitor of heme oxygenase, zinc deuteroporphyrin 2,4-bis glycol. Heme-L-lysinate also lowered arterial pressure in deoxycorticosterone acetate-salt hypertensive rats and in rats with phenylephrine-induced hypertension, indicating that the vasodepressive actions of heme may be extended to other hypertensive models. However, neither heme-L-arginate nor heme-L-lysinate decreased blood pressure in normotensive controls. The heme oxygenase product biliverdine did not lower blood pressure in SHR, and the vasodepressive actions of heme-L-lysinate were unaffected by pretreatment with deferoxamine to chelate free iron. Carbon monoxide (12 ml/kg ip) lowered blood pressure in SHR and in rats made hypertensive by phenylephrine infusion, had no effect on blood pressure in Wistar-Kyoto rats, and elicited only a modest vasodepressive response in normotensive Sprague-Dawley rats. We conclude that heme-bearing preparations can lower blood pressure in hypertensive rats, presumably via heme oxygenase-mediated formation of carbon monoxide.
Influence of GABAergic mechanisms on baroreceptor inputs to nucleus tractus solitarii of rats
Authors: Ruggeri P. , Cogo C. E. , Picchio V. , Molinari C. , Ermirio R. , Calaresu F. R.
Published: December 2017

The firing frequency of baroreceptive neurons in the nucleus tractus solitarii (NTS) during microiontophoretic application of muscimol, a gamma-aminobutyric acid (GABA)A agonist, or baclofen, a GABAB agonist, was monitored in anesthetized rats. Muscimol decreased the spontaneous discharge of 69 of 73 (94.5%) NTS baroreceptive neurons without affecting the remaining four neurons (5.5%). The statistical comparison on a bin-by-bin basis of the peri-R wave interval histograms of the discharge of each NTS neuron showed that the inhibitory action of muscimol was always exerted on the whole neuronal discharge independently of its correlation to the cardiac cycle. Baclofen inhibited 60 of 73 (82.2%) NTS neurons without affecting the remaining 13 neurons (17.8%). In 31 of 60 (51.7%) neurons inhibited by baclofen, this substance significantly affected only pulse-synchronous peaks of neuronal discharge without significant inhibition of the neuronal firing between cardiac cycle-related peaks. Fifty-eight of 73 (79.5%) NTS neurons studied were inhibited by both muscimol and baclofen, 11 neurons (15%) only by muscimol, 2 neurons (2.7%) only by baclofen, and 2 neurons (2.7%) were unaffected by both substances. These results demonstrate that both GABAA and GABAB receptors mediate inhibition of the spontaneous discharge in the great majority of the NTS baroreceptive neurons studied and suggest different functions of the two types of GABA receptors in influencing baroreceptor inputs to the NTS.
Communication between tyrosine kinase pathway and myosin light chain kinase pathway in smooth muscle
Authors: Jin N. , Siddiqui R. A. , English D. , Rhoades R. A.
Published: December 2017

Two separate signal transduction pathways exist in vascular smooth muscle: one for cell growth, proliferation, and differentiation and the other for contraction. Although activation of protein tyrosine kinases is intimately involved in the signaling pathway that induces cell growth, proliferation, and differentiation, activation of myosin light chain kinase (MLCK) is an important step in the pathway leading to smooth muscle contraction. Indirect evidence suggests that “cross talk” exists between these two signaling pathways, but the common intermediates are not well defined. The purpose of this study was to determine whether a vasoconstrictor and a mitogen initiate crossover signaling between the tyrosine kinase pathway and the MLCK pathway in vascular smooth muscle. Rat aorta and pulmonary arteries were isolated and stimulated with either fetal calf serum (FCS) or phenylephrine in the presence or absence of a tyrosine kinase inhibitor (genistein) or tyrosine phosphatase inhibitor [sodium o-vanadate (Na3 VO4)]. Isometric force was recorded as a function of time; myosin light chain phosphorylation, protein tyrosine phosphorylation, and mitogen-activated protein kinase (MAPK) mobility were determined by immunoblotting. The results demonstrate that FCS, which contains a variety of growth factors known to activate tyrosine kinases, induced myosin light chain phosphorylation and contraction in vascular smooth muscle. Phenylephrine, a vasoconstrictor known to activate MLCK, induced tyrosine phosphorylation of a 42-kDa protein identified as MAPK. Tyrosine phosphorylation of this protein was inhibited by genistein and enhanced by vanadate. Genistein significantly inhibited both serum- and phenylephrine-induced myosin light chain phosphorylation as well as the serum- and phenylephrine-induced force generation, whereas vanadate enhanced these responses. These data demonstrate interrelationship between activation of the tyrosine kinase pathway and the MLCK pathway in vascular smooth muscle. These interactions may influence smooth muscle contraction and be important in the regulation of smooth muscle cell proliferation.
Impaired renin response to hemorrhage in hypertensive rabbits
Authors: Courneya C. A.
Published: December 2017

It is not known how the intrarenal mechanisms that control renin release, in particular the intrarenal receptor, respond to the structural changes in renal vasculature that are secondary to hypertension. It is also not known whether baroreflex control of renin release is affected by hypertension. We hypothesized impairment at both levels. Thus we compared plasma renin activity (PRA) during hemorrhage between conscious normotensive (NT) and renal-wrap hypertensive (HT) rabbits. Mean arterial pressure (MAP) and PRA were measured before and during hemorrhage at 4 ml/min. To look at intrarenal control of renin we hemorrhaged NT and HT rabbits after pharmacological autonomic nervous system (ANS) blockade, thus eliminating the influence of reflexes. The slope of the log PRA-MAP relationship was significantly (P < 0.002) reduced in ANS-blocked HT compared with NT rabbits, i.e., for a given fall in MAP, HT rabbits had lower plasma levels of PRA. To examine baroreflex control of renin we hemorrhaged rabbits with an intact ANS. The slope of the log PRA-MAP relationship was significantly attenuated (P < 0.0087) in ANS-intact HT compared with NT rabbits. Cardiac receptor denervation had no effect on the slope of this relationship for either NT or HT rabbits, indicating no appreciable role for cardiac receptors in the reflex control of renin under these circumstances. Although sinoaortic denervation significantly attenuated the slope of the log PRA-MAP relationship (suggesting an important role in reflex control of renin) it did so equally in NT (P < 0.0261) and HT (P < 0.0189) rabbits. We concluded that renin release was impaired in ANS-blocked HT rabbits and that the impairment may be due to dysfunction of intrarenal mechanisms (e.g., the intrarenal receptor). These results also support the hypothesis that reflex control of PRA was impaired in HT rabbits; however, no particular role could be ascribed to either cardiac or arterial baroreceptors in contributing to this impairment.
Adenosine inhibits leukocyte-induced vasoconstriction
Authors: Minamino T. , Kitakaze M. , Node K. , Funaya H. , Inoue M. , Hori M. , Kamada T.
Published: December 2017

Polymorphonuclear leukocytes (PMNs) can induce endothelium-dependent constriction of vascular rings. Because adenosine inhibits the function of PMNs, we examined the effects of adenosine on the PMN-induced coronary vasoconstriction. We measured changes in the isometric tension of isolated rings of canine coronary arteries suspended in an organ chamber filled with Krebs-Henseleit solution after the addition of autologous PMNs. N-formyl-L-methionyl-leucyl-phenylalanine (FMLP)-stimulated PMNs increased the tension of the coronary artery with the endothelium in a concentration-dependent manner. Treatment of FMLP-stimulated PMNs with adenosine inhibited both the adhesion of PMNs to the endothelium and the PMN-induced vasoconstriction. Stimulation of PMNs with CGS-21680C, but not with cyclohexyladenosine, inhibited both the adhesion of PMNs to the endothelium and the PMN-induced vasoconstriction. However, treatment of coronary arteries with adenosine had no effect on the adherence of PMNs to the endothelium and the PMN-induced constriction. These results suggest that stimulation of adenosine A2a receptors on PMNs may inhibit the PMN-induced vasoconstriction by inhibiting the adhesion of PMNs to the endothelium.
Hydraulic and diffusional permeabilities of isolated outer medullary descending vasa recta from the rat
Authors: Turner M. R. , Pallone T. L.
Published: December 2017

Water permeates many microvessel walls via a pathway shared with small hydrophilic solutes and also via an exclusive water pathway. In outer medullary descending vasa recta (OMDVR), the relationship between diffusional permeabilities to water and sodium indicates the existence of an exclusive water pathway and suggests that of a shared pathway. We investigated the latter possibility by estimating hydraulic permeability (Lp) and diffusional permeability to [3H]raffinose (P(raf)) in isolated, perfused OMDVR. The product of hydraulic permeability and osmotic reflexion coefficient of albumin (Lp sigma a) was 1.56 +/- 0.19 x 10(-6) cm.s-1.mmHg-1 (n = 28), calculated from transmural volume fluxes induced by perfusate-to-bath differences in albumin oncotic pressure (delta IIa). P(raf) in the same vessels was 40.1 +/- 7.5 x 10(-5) cm/s when delta IIa was zero. In separate experiments, sigma a was at least 0.89 +/- 0.10 (n = 17). Lp sigma a correlates with P(raf), indicating that OMDVR contain a shared pathway for convection driven by delta IIa and for diffusion of small hydrophilic solutes.
Regional vascular mechanical properties by 3-D intravascular ultrasound with finite-element analysis
Authors: Vonesh M. J. , Cho C. H. , Pinto J. V. , Kane B. J. , Lee D. S. , Roth S. I. , Chandran K. B. , McPherson D. D.
Published: December 2017

A method employing intravascular ultrasound (IVUS) and simultaneous hemodynamic measurements, with resultant finite element analysis (FEA) of accurate three-dimensional IVUS reconstructions (3-DR), was developed to estimate the regional distribution of arterial elasticity. Human peripheral arterial specimens (iliac and femoral, n = 7) were collected postmortem and perfused at three static transmural pressures: 80, 120, and 160 mmHg. At each pressure, IVUS data were collected at 2.0-mm increments through a 20.0-mm segment and used to create an accurate 3-DR. Mechanical properties were determined over normotensive and hypertensive ranges. An FEA and optimization procedure was implemented in which the elemental elastic modulus was scaled to minimize the displacement error between the computer-predicted and actual deformations. The “optimized” elastic modulus (Eopt) represents an estimate of the component element material stiffness. A dimensionless variable (beta), quantifying structural stiffness, was computed. Eopt of nodiseased tissue regions (n = 80) was greater than atherosclerotic regions (n = 88) for both normotensive (Norm) and hypertensive (Hyp) pressurization: Norm, 9.3 +/- 0.98 vs. 3.5 +/- 0.30; Hyp, 11.3 +/- 0.72 vs. 8.5 +/- 0.47, respectively (mean +/- SE x 10(6) dyn/cm2; P < 0.01 vs. nondiseased). No differences in beta between nondiseased and atherosclerotic tissue were noted at Norm pressurization. With Hyp pressurization, beta of atherosclerotic regions were greater than nondiseased regions: 21.5 +/- 2.21 vs. 14.0 +/- 2.11, respectively (P < 0.03). This method provides a means to identify regional in vivo variations in mechanical properties of arterial tissue.
Magnesium is a cerebrovasodilator in newborn piglets
Authors: Kim C. R. , Oh W. , Stonestreet B. S.
Published: December 2017

We tested the hypothesis that, in newborn piglets, magnesium results in a dose-dependent prostanoid-mediated cerebrovasodilation. Pial arterioles (50-200 microns in diameter) were serially measured, and cortical subarachnoid cerebrospinal fluid (CSF) was collected for radioimmunoassay of 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha, hydrolysis product of prostacyclin) and thromboxane B2 (TxB2, metabolite of thromboxane A2) before and after CSF containing 1.2, 2.4, 4.8, and 9.6 mM MgCl2 was suffused over the parietal cortex under a closed cranial window in twelve 2- to 4-day-old piglets. Magnesium suffusion resulted (P < 0.05) in a dose-dependent pial arteriolar vasodilation. The increase in vessel diameter was greater (P < 0.001) with 2.4, 4.8, and 9.6 mM than with 1.2 mM concentration of magnesium. The increase in vessel diameter with 9.6 mM was also greater (P < 0.001) than with the 2.4 mM concentration of magnesium. Magnesium suffusion did not result in changes in cortical CSF prostanoid concentrations. The effect of intravenous indomethacin (5 mg/kg) on cyclooxygenase inhibition in the pial arterioles was confirmed by a 24 +/- 3% decrease in vessel diameter at the baseline (1.2 mM) magnesium concentration. In contrast, cyclooxygenase inhibition with intravenous indomethacin did not attenuate the magnesium-induced cerebrovasodilation. We conclude that in new born piglets magnesium suffusion over the parietal cortex results in a dose-dependent cerebrovasodilation that is most likely not mediated by prostanoids.
Effects of 2,5-di-tert-butylhydroquinone on rat cardiac muscle contractility
Authors: Kabbara A. A. , Stephenson D. G.
Published: December 2017

The effects of 2,5-di-tert-butylhydroquinone (TBQ) on cardiac muscle contractility were investigated using cardiac preparations from the right ventricle of the rat. In saponin-skinned preparations, TBQ (50 and 100 microM) did not significantly affect the maximal isometric Ca2+-activated force or the steady-state force-Ca2+ concentration relation but significantly reduced the Ca2+ content of the sarcoplasmic reticulum (SR) in both the absence and the presence of 50 microM of the SR Ca2+-release channel blocker ruthenium red. The effect of TBQ on SR Ca2+ content was not due to an increased passive Ca2+ leak or Ca2+-induced Ca2+ release from the SR but to the specific inhibition of the SR Ca2+ pump. In electrically stimulated (0.2 Hz, 23 degrees C) intact cardiac preparations loaded with the Ca2+-sensitive fluorescent dye fura 2, TBQ (50 and 100 microM) caused the decrease in the rates of rise and fall of the fura 2 signal (ratio of fluorescence intensities at 360- and 380-nm excitation) and isometric force. In the presence of 50 and 100 microM TBQ, the twitch height of the isometric force response was significantly decreased, whereas the peak of the fura 2 signal was not significantly affected. At 2-Hz stimulation frequency, both parameters were reduced in the presence of 50 and 100 microM TBQ. Taken together, the results obtained in this study show that TBQ inhibits rather specifically the SR Ca2+ uptake in the rat ventricle and that it can be used as a tool to determine the function of the SR under different conditions.
Relationship between "extension of refractoriness" and probability of successful defibrillation
Authors: Tovar O. H. , Jones J. L.
Published: December 2017

The "extension of refractoriness" hypothesis, which suggests that the shock halts fibrillation by extending the refractory period, has not been directly tested. Defibrillation (5 isolated rabbit hearts; 111 episodes) was attempted by 8-ms pulses (65% tilt) delivered through epicardial patches. Monophasic action potentials were recorded in a low current density region (6.3 V/cm at 90% success). Fifty shocks failed to convert; 61 shocks successfully defibrillated. Postshock response duration (from shock to repolarization) was significantly longer for successful type A (with no postshock activations) defibrillation (102.3 +/- 7.5 ms) than for unsuccessful defibrillation (47.6 +/- 4.3 ms; P < 0.0001) for shocks occurring during the last 40% of the fibrillation action potential. Probability of success and postshock response duration both increased with current intensity. However, at each intensity, response durations for successful defibrillation were significantly longer than those for unsuccessful defibrillation. A minimum prolongation of 75 ms was associated with type A defibrillation. These results suggest that shock-induced response duration correlates with successful defibrillation and that a response of 75 ms is required to completely block fibrillation wavefronts.
K(ATP)-channel inhibition improves hemodynamics and cellular energetics in hemorrhagic shock
Authors: Salzman A. L. , Vromen A. , Denenberg A. , Szabo C.
Published: December 2017

We tested whether activation of K(ATP) channels contributes to vasodilatation and end-organ hypoperfusion in severe hemorrhagic shock (HS). Anesthetized juvenile pigs were hemorrhaged to a portal blood flow of 45% of baseline for 45 min and then resuscitated with Ringer lactate (RL; 100% volume of shed blood; n = 10) or RL in combination with the K(ATP)-channel antagonist glibenclamide (10 mg/kg iv bolus injection; n = 10). Addition of glibenclamide to the resuscitation fluid caused a sustained recovery of systemic blood pressure, cardiac index, portal blood flow, renal blood flow, renal cortical ATP concentration, and ileal mucosal P(CO2). Treatment with RL alone caused only a partial and transient hemodynamic and metabolic benefit. Glibenclamide treatment of sham-shocked control pigs (n = 6) transiently increased mesenteric and systemic vascular resistance. Inhibition of K(ATP)-channel activity in HS, which effectively and safely restores systemic hemodynamics, regional perfusion, and tissue metabolism, is a potentially novel therapeutic approach to the management of severe HS.
Estimation of cardiorespiratory transfer under spontaneous breathing conditions: a theoretical study
Authors: Kim T. S. , Khoo M. C.
Published: December 2017

Using simulated noisy sequences of respiration and heart rate, we assessed the accuracy of the respiratory sinus arrhythmia transfer function (RSATF) estimation under three kinds of spontaneous breathing patterns: regular or tidal breathing, periodic breathing with apnea, and broadband breathing. Estimation employing the cross-power and autopower spectra of the simulated data produced RSATF estimates that were generally more variable than those computed with an autoregressive modeling approach. Variability and bias errors in the RSATF estimates became larger as respiratory bandwidth decreased when the breathing pattern changed from broadband to periodic to regular breathing. However, between frequencies of 0.1 and 0.3 Hz, these errors fell within 12% in all breathing patterns. Error in the RSATF estimates was only slightly increased, with reductions in data length to as low as 90 s. The results suggest the feasibility of obtaining accurate estimates of RSATF between 0.1 and 0.8 Hz from a wide variety of conditions, such as in different sleep-wake states where voluntary control of breathing is not possible and the ventilatory pattern may vary substantially.
Evidence of functional beta-adrenoceptors in the cutaneous vasculature
Authors: Crandall C. G. , Etzel R. A. , Johnson J. M.
Published: December 2017

During a hyperthermic challenge, skin blood flow (SkBF) increases primarily through activation of the cutaneous active vasodilator system. However, mechanisms through which activation of this system elevates SkBF remain unknown. In this project, we sought to identify whether functional beta-adrenoceptors exist on cutaneous vessels and, if present, whether these receptors play an important role in elevating SkBF during a hyperthermic challenge. In protocol 1, SkBF was assessed over two intradermal microdialysis probes. Initially, both probes were perfused with lactated Ringer solution. Probe A was then perfused with a 200 microM solution of the beta-adrenoceptor agonist isoproterenol while probe B was perfused with a 1.7 mM solution of the beta-adrenoceptor antagonist propranolol. Isoproterenol perfusion significantly increased SkBF from 17.7 +/- 2.4 to 70.8 +/- 13.2 perfusion units (PU; P < 0.05), whereas propranolol perfusion did not significantly affect SkBF (23.4 +/- 6.5 to 27.0 +/- 6.8 PU; P > 0.05). After this period, the solutions perfusing the probes were switched. Isoproterenol did not significantly change SkBF at the propranolol-treated site (27.0 +/- 6.8 to 26.4 +/- 7.5 PU; P < 0.05). In protocol 2, SkBF was assessed over two microdialysis probes during indirect whole body heating. One probe was perfused with Ringer solution while the other probe was perfused with 1.7 mM propranolol. The degree of elevation in SkBF during heat stress at the propranolol-treated site (10.4 +/- 1.5 to 35.8 +/- 3.1 PU) was similar to the elevation in SkBF at the Ringer solution site (11.6 +/- 1.0 to 35.0 +/- 1.2 PU). These data demonstrate the presence of functional beta-adrenoceptors in the skin; however, these receptors play no significant role in mediating cutaneous vasodilation during indirect whole body heating.
Vagal stimulation decreases left ventricular contractility mainly through negative chronotropic effect
Authors: Matsuura W. , Sugimachi M. , Kawada T. , Sato T. , Shishido T. , Miyano H. , Nakahara T. , Ikeda Y. , Alexander J. , Sunagawa K.
Published: December 2017

Although an increase in vagal tone is known to slow heart rate (HR), whether it also depresses left ventricular contractility through mechanisms independent of the bradycardic effect remains unknown. The chief aim of this investigation, therefore, was the separation of the observed vagally mediated depression of ventricular contractility into direct and indirect vagal effects, the latter resulting via negative chronotropism. In 12 anesthetized, sympathectomized open-chest rabbits, we measured left ventricular contractility through determination of the end-systolic elastance (Ees). We found that tonic vagal stimulation administered at 0, 5, and 10 Hz decreased both HR (226.9 +/- 39.7, 201.9 +/- 25.7, and 171.3 +/- 18.5 beats/min, respectively; P = 0.0003) and Ees (109.5 +/- 25.7, 85.1 +/- 34.1, and 71.9 +/- 33.1 mmHg/ml, respectively; P = 5 x 10(-6)) in a frequency-dependent fashion. However, we observed that as long as HR was kept constant through fixed-rate atrial pacing, vagal stimulation resulted in little or no change in Ees. Thus we conclude that the negative inotropic effect of vagal stimulation is attributable primarily to its negative chronotropic effect when sympathetic tone is minimal.
Cardiovascular responses to glutamate stimulation of diagonal band of Broca
Authors: Kirouac G. J. , Ciriello J.
Published: December 2017

Experiments were done in alpha-chloralose-anesthetized, paralyzed, and artificially ventilated rats to investigate the effect of L-glutamate stimulation of the diagonal band of Broca (DBB) on arterial pressure (AP) and heart rate (HR). Stimulation of the horizontal limb of the DBB (hDB) elicited decreases in both mean AP (MAP; -32.3 +/- 2.5 mmHg; n = 37) and HR (-32.5 +/- 3.8 beats/min; n = 33) at 84% of the sites stimulated. Stimulation of the vertical limb of the DBB (vDB) elicited significantly smaller decreases in MAP (-9.7 +/- 1.0 mmHg; n = 19) and HR (-13.5 +/- 1.8 beats/min; n = 7) at approximately 13% of the sites stimulated. Intravenous administration of the muscarinic receptor blocker atropine methylbromide had no effect on the magnitude of the MAP and HR responses to stimulation of the hDB. In contrast, administration of the nicotinic receptor blocker hexamethonium bromide abolished both the depressor and the bradycardic responses elicited by stimulation of the hDB. These data indicate that the hDB contains neurons that exert cardiovascular depressor effects and that these circulatory effects are mediated by the inhibition of sympathetic vasoconstrictor fibers to the vasculature, and cardioacceleratory fibers to the heart.
Severe diastolic dysfunction with preserved energy conversion efficiency after countershock
Authors: Yasuda S. , Shishido T. , Goto Y.
Published: December 2017

The left ventricular (LV) mechanical performance and the LV myocardial oxygen consumption (VO2)-to-pressure-volume area (PVA; LV total mechanical energy index) relationship were measured in isovolumic contraction of isolated blood-perfused dog hearts before and after direct current (DC) countershocks. At a constant LV volume, DC shocks increased LV end-diastolic pressure progressively and strikingly with the progression of myocardial edema and a marked prolongation of the time constant of LV pressure decay. In contrast, DC shocks changed neither the slope of the LV end-systolic pressure-volume relationship nor the contractile efficiency (the slope of the Vo2-PVA relationship). The oxygen cost of contractility (the slope of the relationship between PVA-independent VO2 and LV contractility) increased 27% after DC shocks. However, the magnitude of this change was considerably smaller than that previously reported in postischemic stunned myocardium (123%), suggesting that the adverse effect of DC shocks on the energy cost of excitation-contraction coupling is relatively minor. Thus, despite the severe diastolic dysfunction, DC shocks do not substantially impair either the efficiency of cross-bridge cycling or calcium cycling. Myocardial interstitial edema is more likely a potential mechanism of diastolic dysfunction after DC shocks.
Characterization of energy metabolism and blood flow distribution in myocardial ischemia in hemorrhagic shock
Authors: Miyazaki K. , Hori S. , Inoue S. , Adachi T. , Bessho M. , Kuwahira I. , Mori H. , Nakazawa H. , Aikawa N. , Ogawa S.
Published: December 2017

To characterize the mechanisms for myocardial ischemia induced by hemorrhagic shock, 29 dogs were subjected to hemorrhage at a mean aortic pressure (MAoP) of 30-60 mmHg. After 10 min of hemorrhage, the beating hearts were rapidly cross sectioned and freeze clamped to visualize the two-dimensional distribution of myocardial ischemia with NADH fluorescence (NADH-F) in 22 dogs. NADH-F was developed at an MAoP of 40 mmHg or less and involved both the subendocardial half and the subepicardial half of the left ventricle [34 +/- 14 vs. 20 +/- 14% (P < 0.05) and 65 +/- 16 vs. 52 +/- 15% (not significant) of the cross-sectional area of the left ventricular slice at MAoP levels of 40 and 30 mmHg, respectively]. Magnified NADH-F photography demonstrated heterogeneously distributed microischemic lesions with a columnar shape (mode of short-axis length, 60-80 microns). NADH-F-guided microsamplings revealed higher NADH and lactate concentrations in a positive NADH-F area than those in a negative NADH-F area. The ratio of endocardial to epicardial blood flow was maintained at a relatively high level (1.07 +/- 0.07 and 0.88 +/- 0.07 at MAoP levels of 40 and 30 mmHg, respectively; n = 7 dogs), and the reactive hyperemia was preserved as well. In conclusion, myocardial ischemia in early hemorrhagic shock was characterized by minimal transmural heterogeneity and marked heterogeneity between contiguous small regions.
alpha-Tocopheryl succinate inhibits monocytic cell adhesion to endothelial cells by suppressing NF-kappa B mobilization
Authors: Erl W. , Weber C. , Wardemann C. , Weber P. C.
Published: December 2017

The adherence of monocytes to activated endothelium is an early event in atherogenesis. Because antioxidants have been considered to be of antiatherosclerotic potential, we investigated the effects of alpha-tocopherol (TCP) and its acetate and succinate esters on monocyte adhesion to cytokine-stimulated human umbilical vein endothelial cells (HUVEC). Endothelial cells were treated with TCP, alpha-tocopherol acetate (TCP acetate), or alpha-tocopheryl succinate (TCP succinate) before stimulation with tumor necrosis factor-alpha (TNF-alpha; 10 U/ml, 6 h) or interleukin-1 beta (IL-1 beta; 10 U/ml, 6 h). Cytokine-stimulated cell surface expression of vascular cell adhesion molecule-1 (VCAM-1, CD106) and E-selectin (ELAM-1, CD62E), but not of intercellular adhesion molecule-1 (ICAM-1, CD54), was time- and dose-dependently inhibited by TCP succinate but not by TCP or TCP acetate. TCP succinate (200 microM, 24 h) reduced TNF-induced VCAM-1 and E-selectin expression from a specific mean fluorescence intensity of 151 +/- 28 to 12 +/- 4 channels and from 225 +/- 38 to 79 +/- 21 channels, respectively. Succinate alone had no effect. Decreased adhesion molecule expression was associated with a reduction of monocytic cell adhesion. TCP succinate (20 microM, 72 h), but not TCP (200 microM, 72 h), reduced U-937 cell adhesion to TNF-alpha-stimulated (10 U/ml, 6 h) HUVEC by 30% (P < 0.025) and to IL-1 beta-stimulated HUVEC by 56% (P < 0.010). Electrophoretic mobility-shift assays of HUVEC nuclear proteins revealed a decrease in TNF-alpha-stimulated nuclear factor-kappa B (NF-kappa B) activation after pretreatment of HUVEC with TCP succinate but not with TCP, TCP acetate, or succinate alone. In conclusion, we demonstrate that the vitamin E derivative TCP succinate prevents monocytic cell adhesion to cytokine-stimulated endothelial cells by inhibiting the activation of NF-kappa B, further emphasizing the antiatherosclerotic potential of lipid soluble antioxidants.
Protein kinase C-dependent regulation of the human AT1 promoter in vascular smooth muscle cells
Authors: Holzmeister J. , Graf K. , Warnecke C. , Fleck E. , Regitz-Zagrosek V.
Published: December 2017

The expression level of angiotensin II (ANG II) type 1 receptors (AT1) determines the magnitude of ANG II signaling in vascular smooth muscle cells (VSMC). AT1 mRNA expression in cultured bovine VSMC increased twofold after 8 h of protein kinase C (PKC) activation with phorbol 12-myristate 13-acetate (PMA), whereas stimulation with forskolin did not alter the AT1 mRNA level. The expression of AT1 promoter/exon 1 [-513/+92 base pairs (bp)] luciferase constructs transfected into VSMC increased 2.4-fold with PMA stimulation. In-gel kinase assays demonstrated rapid phosphorylation of mitogen-activating protein kinases (MAPK) ERK1 and ERK2 by PMA. Electrophoretic gel mobility shift assays showed sequence-specific binding of nuclear proteins from PMA-activated VSMC, identified as activator protein 1 (AP-1) complex in competition assays, to a radiolabeled AT1-promoter fragment (-368/-399 bp). Recombinant AP-1 binds in a sequence-specific manner to the -386/-399-bp region. Site-specific mutagenesis destroying the AP-1 site, the adjacent polyoma enhancer activator 3 element, or both sites simultaneously indicated that both sites together are necessary and sufficient to control basal and PMA-induced activation of the human AT1 promoter in transfected VSMC. The capability of the phorbol ester PMA to activate the human AT1 promoter in VSMC via an AP-1 element suggests a prominent role for PKC/MAPK and Ets proteins in AT1 regulation.
Early and delayed preconditioning: differential mechanisms and additive protection
Authors: Meldrum D. R. , Cleveland J. C. , Rowland R. T. , Banerjee A. , Harken A. H. , Meng X.
Published: December 2017

The purposes of this study were to determine whether 1) 24-h endotoxin (ETX) pretreatment induces delayed ("second window") myocardial protection against ischemia-reperfusion (I/R), 2) acute adenosine (Ado) or phenylephrine (PE) pretreatment confers similar protection, 3) the mechanisms of Ado- and PE-induced early protection remain intact after endotoxemia, 4) Ado- and PE-induced protection may combine with ETX-induced delayed protection to optimize cardiac protection, and 5) these strategies of early and/or delayed myocardial protection require de novo protein synthesis. Rats (n = 6-8/group) were treated with ETX (0.5 mg/kg i.p.) or vehicle, with or without prior inhibition of protein synthesis. Twenty-four hours later, the hearts were isolated, perfused, and acutely pretreated with Ado or PE before I/R (20-min ischemia and 40-min reperfusion). Developed pressure, coronary flow, compliance (end-diastolic pressure), and reperfusion creatine kinase leak were measured. Results indicated that 1) Ado, PE, and ETX independently induced myocardial functional protection; 2) either Ado or PE acutely enhanced ETX induced protection; and 3) cycloheximide abolished delayed, but not acute, protection. We conclude that early and delayed forms of protection 1) may be combined to optimize protection and 2) differentially rely on de novo protein synthesis.
Protein kinase C-mediated preconditioning of cardiac myocytes: role of adenosine receptor and KATP channel
Authors: Liang B. T.
Published: December 2017

Activation of the adenosine receptor, protein kinase C (PKC), and the ATP-sensitive potassium (KATP) channel is known to induce preconditioning. The objective here was to determine the signaling role of the adenosine receptor, PKC, and the KATP channel and the temporal sequence of activation of these three mediators in preconditioning of cardiac myocytes. Chick embryo ventricular myocytes were used as a myocyte model of preconditioning. Brief hypoxic or adenosine exposure preconditioned the myocytes, and the PKC inhibitors chelerythrine or calphostin C blocked this preconditioning effect, suggesting that PKC is an effector distal to the adenosine receptor in initiating the hypoxia- or adenosine-induced preconditioning. The PKC activator phorbol 12-myristate 13-acetate (PMA), but not the inactive phorbol 4 alpha-phorbol [2,13-didecanoate or 4 alpha-phorbol 12-myristate 13-acetate, could precondition the myocyte; the PMA-induced preconditioning effect was blocked by chelerythrine or calphostin C. Glibenclamide or 5-hydroxydecanoate, when present during a 5-min exposure to PMA or a 90-min hypoxic period, blocked the PMA-induced preconditioning. However, the presence of 8-sulfophenyltheophylline during exposure to PMA failed to block the PMA-induced preconditioning, whereas 8-sulfophenyltheophylline was able to abolish this preconditioning effect when added during the 90-min hypoxic period. The data provide direct evidence that the KATP channel, not the adenosine receptor, is the effector down-stream from PKC in initiating PKC-mediated preconditioning. Both the adenosine receptor and KATP channel are required to exert the actual protective effect during the sustained hypoxia.
Effect of cocaine and methylecgonidine on intracellular Ca2+ and myocardial contraction in cardiac myocytes
Authors: Huang L. , Woolf J. H. , Ishiguro Y. , Morgan J. P.
Published: December 2017

We evaluated the cardiac effects of the principle pyrolysis product of crack cocaine smoking, methylecgonidine (MEG), in comparison with cocaine. Peak cell shortening and intracellular Ca2+, as detected by the Ca2+ indicator indo 1, were recorded in enzymatically isolated ferret myocytes. Both cocaine and MEG decreased peak cell shortening and peak intracellular Ca2+ concentration ([Ca2+]i) in a dose-dependent manner (10(-8)-10(-4) M). MEG shifted the peak [Ca2+]i-to-peak shortening relationship downward and was more potent than cocaine. Atropine (10(-6) M) upwardly shifted the dose-response curves of MEG, cocaine, and carbachol but not of procaine. The negative inotropic effects of MEG were inhibited by methoctramine, a selective M2 receptor blocker but not by M1 (pirenzepine) or M3 (4-diphenylacetoxy-N-methylpiperidine methiodide) blocking agents. In contrast to cocaine, the effects of large doses of MEG were irreversible over the time course of our experiments, raising the possibility of structural damage. We conclude that MEG acts primarily on M2 cholinergic receptors in the heart to produce acute cardiac intoxication and, in contrast to cocaine, may decrease the myofilament Ca2+ responseness and cause structural damage to myocytes by a direct toxic effect.
NO release and the opening of K+ATP channels mediate vasodilator responses to histamine in the cat
Authors: Champion H. C. , Kadowitz P. J.
Published: December 2017

Responses to histamine were investigated in the hindlimb vascular bed of the cat under constant-flow conditions. Injections of histamine, the H1 agonist HTMT, the H2 agonist dimaprit, and the H3 agonist R(-)-alpha-methylhistamine caused dose-related decreases in hindlimb perfusion pressure. Pyrilamine reduced the responses to histamine and HTMT by approximately 80%, whereas cimetidine reduced the responses to histamine by 20% and to dimaprit by approximately 50%. The H3-receptor antagonist thioperamide reduced the responses to R(-)-alpha-methylhistamine by approximately 60% but was without effect on the other histamine agonists. These data suggest the presence of H1, H2, and H3 receptors in the hindlimb vascular bed of the cat, that histamine acts, for the most part, by stimulating H1 receptors, and that H3-receptor activation is not involved in mediating the responses to histamine. The responses to histamine and the H1-, H2-, and H3-receptor agonists were significantly reduced by a nitric oxide synthase inhibitor and enhanced in duration by the guanosine 3', 5'-cyclic monophosphate (cGMP)-selective phosphodiesterase inhibitor zaprinast, suggesting that the responses are mediated, in part, by the release of nitric oxide and an increase in cGMP levels. The responses to histamine agonists but not to nitric oxide donors were significantly reduced by the nonselective K(+)-channel antagonist tetraethylammonium. The responses to histamine and the H1, H2, and H3 agonists were not affected by the cyclooxygenase inhibitor meclofenamate. The responses to histamine and HTMT are also reduced 30-50% by U-37883A, an ATP-sensitive K+ (K+ATP)-channel antagonist, at a time when the responses to the H2 and H3 agonists were unaltered. The present data suggest that vasodilation of the hindlimb vascular bed in response to H1-, H2-, and H3-receptor activation is mediated by a tetraethylammonium-sensitive mechanism that is associated with the release of nitric oxide and an increase in cGMP levels. These data further suggest that the response to H1-receptor activation is mediated by the complementary, yet independent, release of nitric oxide and the opening of a K+ATP channel.