bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationship between vasopressin and opioids in hypoxia induced pial artery vasodilation
Authors: Rossberg M. I. , Armstead W. M.
Published: December 2017

It has been observed that a vasopressin receptor antagonist attenuates hypoxic hyperemia in fetal sheep, whereas methionine enkephalin (Met) and leucine enkephalin (Leu) contribute to hypoxia-induced pial artery dilation in newborn pigs. This study was designed to investigate the relationship between vasopressin and opioids in hypoxia-induced pial artery dilation in the newborn pig by use of the closed cranial window technique. Hypoxia-induced pial artery dilation was attenuated during moderate [arterial Po2 (PaO2) approximately 35 mmHg] and severe hypoxia (PaO2 approximately 25 mmHg) by the vasopressin receptor antagonist, [beta-mercapto-beta beta-cyclopentamethylenepropionyl, 2-O-Me-Tyr2, Arg8]vasopressin (MeAVP, 5 micrograms/kg i.v.; 29 +/- 1 vs. 14 +/- 2 and 37 +/- 2 vs. 18 +/- 2% for moderate and severe hypoxia in absence vs. presence of MeAVP, respectively, n = 7). Hypoxia-induced dilation was accompanied by increased cerebrospinal fluid (CSF) vasopressin concentration (26 +/- 1 vs. 67 +/- 4 and 26 +/- 1 vs. 99 +/- 4 pg/ml for control vs. moderate and control vs. severe hypoxia, n = 5). Vasopressin increased CSF Met (895 +/- 28, 1,147 +/- 63, 1,327 +/- 48, and 1,600 +/- 75 pg/ml for control and 40, 400, and 4,000 pg/ml vasopressin, respectively, n = 7). CSF Leu concentration was similarly increased by vasopressin. Furthermore, MeAVP attenuated the release of Met during moderate hypoxia (910 +/- 38 and 2,682 +/- 49 vs. 911 +/- 38 and 2,110 +/- 84 pg/ml for control and moderate hypoxia in absence and presence of MeAVP, respectively, n = 5). MeAVP had similar effects on hypoxia-induced Leu release. These data show that vasopressin contributes to hypoxia-induced pial artery dilation and that vasopressin increases CSF Met and Leu concentrations. These data also suggest that elevated CSF vasopressin concentrations that occur during hypoxemia result in opioid release, which subsequently contributes to hypoxic pial artery dilation.
Nitric oxide synthase inhibition by L-NAME during repetitive focal cerebral ischemia in rabbits
Authors: Anderson R. E. , Meyer F. B.
Published: December 2017

The effects of nitric oxide synthase inhibition on brain acidosis, regional cortical blood flow (rCBF), and NADH redox state were examined using in vivo fluorescence imaging during four 15-min periods of moderate focal cerebral ischemia, each separated by three 5-min reperfusion periods followed by a final 3-h reperfusion period. Fasted rabbits under 1.5% halothane were divided into six groups of seven animals each: nonischemic controls, ischemic controls, and the following drug groups receiving NG-nitro-L-arginine methyl ester (L-NAME) intravenously 20 min before repetitive ischemia (as follows: 0.1 mg/kg, 1 mg/kg, 10 mg/kg, and 1 mg/kg + 5 mg/kg L-arginine). L-NAME at 0.1 and 1 mg/kg prevented the development of significant brain acidosis throughout the four ischemic insults. L-NAME at 10 mg/kg reduced preischemic rCBF by 21% (P < 0.05) and did not mitigate brain acidosis after the third and fourth ischemic insults. Brain intracellular pH returned toward baseline after the 3-h final reperfusion in all groups. NADH redox state was significantly (P < 0.05) elevated from baseline controls in all groups during the last three ischemic insults. During the final reperfusion period, NADH redox state returned toward baseline values only in the 0.1 mg/kg L-NAME and ischemic control group. In conclusion, low-dose L-NAME attenuated brain acidosis independent from rCBF changes during intermittent, moderate focal cerebral ischemia.
Inward rectifier K+ currents in smooth muscle cells from rat coronary arteries: block by Mg2+, Ca2+, and Ba2+
Authors: Robertson B. E. , Bonev A. D. , Nelson M. T.
Published: December 2017

Inward rectifier K+ channels have been implicated in the control of membrane potential and external K(+)-induced dilations of small coronary arteries. To identify and characterize inward rectifier K+ currents in coronary artery smooth muscle, whole cell K+ currents in smooth muscle cells enzymatically isolated from rat coronary (septal) arteries (diameters, 100-150 microns) were measured in the conventional and perforated configurations of the patch-clamp technique. Ba(2+)-sensitive, whole cell K+ current-voltage relationships exhibited inward rectification. Blockers of Ca(2+)-activated K+ channels (1 mM tetraethylammonium ion), ATP-sensitive K+ channels (10 microM glibenclamide), and voltage-dependent K+ channels (1 mM 4-aminopyridine) in smooth muscle did not affect inward rectifier K+ currents. The nonselective K+ channel inhibitor phencyclidine (100 microM) reduced inward rectifier K+ currents by approximately 50%. External Ba2+ reduced inward currents, with membrane potential hyperpolarization increasing inhibition. The half-inhibition constant for Ba2+ was 2.1 microM at -60 mV, decreasing e-fold for a 25-mV hyperpolarization. External Cs+ also blocked inward rectifier K+ currents, with the half-inhibition constant for Cs+ of 2.9 mM at -60 mV. External Ca2+ and Mg2+ reduced inward rectifier K+ currents. At -60 mV, Ca2+ and Mg2+ (1 mM) reduced inward currents by 33 and 21%, respectively. Inward rectification was not affected by dialysis of the cell's interior with a nominally Ca(2+)- and Mg(2+)-free solution. These findings indicate that inward rectifier K+ channels exist in coronary artery smooth muscle and that Ba2+ may be a useful probe for the functional role of inward rectifier K+ channels in coronary arteries.
Enhanced microvascular relaxations to VEGF and bFGF in chronically ischemic porcine myocardium
Authors: Sellke F. W. , Wang S. Y. , Stamler A. , Lopez J. J. , Li J. , Li J. , Simons M.
Published: December 2017

Changes in the vascular responses to vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) in chronically ischemic myocardium have not been investigated. Ameroid constrictors were placed on the proximal left circumflex (LCX) artery of seven Yorkshire pigs. Seven to nine weeks later, myocardial blood flow in the collateral-dependent LCX region was reduced, compared with that in the normally perfused left anterior descending (LAD) region. Both growth factors elicited significant relaxations of coronary microvessels. Relaxations to both VEGF and bFGF were inhibited in the presence of either NG-nitro-L-arginine or genistein, suggesting that the relaxations are through the tyrosine kinase-mediated release of endothelium-derived nitric oxide. Microvascular relaxations to both VEGF or bFGF were significantly greater in vessels harvested from the collateral-perfused LCX region, compared with those taken from the normally perfused LAD region. However, relaxation to the endothelium-dependent vasodilator ADP, which does not operate through a tyrosine kinase receptor, was reduced in the collateral-perfused region, compared with the normally perfused territory, suggesting a possible link of tyrosine kinase to the enhanced relaxations to VEGF and bFGF in collateral-perfused coronary microvessels. Northern analysis showed increased expression for both VEGF receptors (flk-1, flt-1) as well as the bFGF receptor 1 (FGFR-1) in the collateral-perfused region compared with that in the normally perfused region. This suggests that the increased relaxation responses to VEGF and bFGF in the ischemic myocardium may be related to increased gene expression of the respective tyrosine kinase receptors.
Increased activity of vascular ACE related to atherosclerotic lesions in hyperlipidemic rabbits
Authors: Mitani H. , Bandoh T. , Kimura M. , Totsuka T. , Hayashi S.
Published: December 2017

The relationship between vascular angiotensin-converting enzyme (ACE) activity in the aorta and atherosclerotic lesions was investigated in rabbits fed two atherogenic diets, 0.5 and 1.5% cholesterol, for 17 wk. Tissue ACE activity was assessed by the cleavage rate of hippuric acid from a synthetic substrate. Total cholesterol, triglycerides, and phospholipids in the serum were significantly increased by the diet. Vascular ACE activity in the femoral artery, abdominal aorta, and aortic arch was significantly increased (2-5 times) by the atherogenic diet in a high-cholesterol-related manner compared with the rabbits fed a normal diet. The increase was associated with vascular heterogeneity of regions. There was a significant correlation between plaque area and vascular ACE activity in the aortic arch isolated from rabbits fed the higher (1.5%)-cholesterol diet. Contractile responses of the femoral artery to angiotensin I and II in the atherogenic diet-fed rabbits did not differ from those in animals fed the normal diet. It is conceivable that increased ACE in the vascular walls is involved in hyperlipidemia-induced atherogenesis, presumably through production of growth or stimulating factor(s) contributing to plaque formation.
Regulation of endothelial NO synthase expression by cyclosporin A in bovine aortic endothelial cells
Authors: Lopez-Ongil S. , Saura M. , Rodriguez-Puyol D. , Rodriguez-Puyol M. , Lamas S.
Published: December 2017

The introduction of cyclosporin A (CsA) is considered a cornerstone advance in immunosuppression. However, serious side effects such as hypertension have fostered an important body of research regarding their pathophysiology. Although the participation of several vasoactive factors in the hypertensive response has been described, recent attention has focused on endothelium-derived vasoactive factors, and several reports describe an overproduction of endothelin-1 and a deficient endothelium-dependent vasodilation. In the case of the latter, no definitive clues for the precise molecular mechanisms have been provided. We demonstrate that endothelial cells in culture synthesize more NO in the presence of CsA for 24 h in a concentration-response manner. This augmentation is correlated with a threefold increase in the endothelial constitutive NO synthase (ecNOS) transcript, which is time dependent and maximal at 24 h. The CsA-induced increase in ecNOS mRNA expression was blocked by actinomycin D but unaltered by cycloheximide. Levels of ecNOS protein were also enhanced by CsA after 24 h. These data establish that NO synthesis is moderately enhanced in endothelial cells exposed to CsA for long periods of time and describe a new mode of regulating ecNOS gene expression.
Electrophysiological background of individual variability in electrical defibrillation efficacy
Authors: Murakawa Y. , Yamashita T. , Ajiki K. , Sezaki K. , Kanese Y. , Omata M.
Published: December 2017

This study was performed to test whether heart-to-heart variability of defibrillation efficacy is attributable to differences in postshock refractory state of nondepolarized myocardium. In 30 anesthetized dogs, a localized potential gradient was created using 1-16 V of stimulus across a pair of platinum plate electrodes on the right ventricle (5-mm interelectrode distance). The postshock recovery interval (PSRI) of the relatively refractory myocardium directly adjacent to the excited area was estimated by measuring the recovery interval after an appropriately timed field stimulus. The transcardiac defibrillation threshold (DFT) was also determined. The results showed that DFT normalized by the weight of the heart was inversely correlated with the PSRI measured with a field stimulus of 6 V (local shock intensity approximately 5 V/cm) or more (6 V: r = -0.502, P < 0.005; 16 V: r = -0.635, P < 0.0005). This observation suggests that variability of defibrillation efficacy in intact hearts is largely due to differences in the postshock refractory state of the nondepolarized myocardium.
Limitation of cardiac output by a coronary alpha 1-constrictor tone during exercise in dogs
Authors: Kim S. J. , Kline G. , Gwirtz P. A.
Published: December 2017

This study was performed to examine whether an alpha 1-constrictor tone, which limits coronary functional hyperemia during exercise, imposes a significant limitation on global cardiac performance as determined by cardiac output (CO). Seven dogs were chronically instrumented to measure left ventricular pressure (LVP), maximum rate of rise of LVP (dP/dtmax), heart rate (HR), mean aortic pressure (AoP), circumflex blood flow velocity (CFV), and CO at rest and during submaximal exercise. Either the selective alpha 1-adrenergic antagonist prazo (0.5 mg) or the vasodilator adenosine was administered into the circumflex artery during exercise at 6.4 kilometers per hour (kph)/16% treadmill incline. Exercise caused significant increase in mean AoP, HR, LVP, dP/dtmax, CFV, stroke volume (SV), and CO, whereas systemic vascular resistance (SVR) was significantly reduced. After intracoronary alpha 1-blockade with prazosin, CFV, dP/dtmax, SV, and CO increased further (17 +/- 2, 19 +/- 3, 16 +/- 2, and 17 +/- 2%, respectively) without changing mean AoP, HR, or SVR. Comparable increases were observed when CFV was increased by a similar degree using the direct vasodilator adenosine. These results indicate that increasing coronary flow by removing a coronary alpha 1-constrictor tone with prazosin or by direct vasodilation with adenosine during submaximal exercise leads to an increase in myocardial oxygen supply and, as a result, cardiac pump performance (SV and CO).
Acute transient coronary sinus hypertension impairs left ventricular function and induces myocardial edema
Authors: Pratt J. W. , Schertel E. R. , Schaefer S. L. , Esham K. E. , McClure D. E. , Heck C. F. , Myerowitz P. D.
Published: December 2017

This study was performed to evaluate the direct and indirect effects of acute coronary sinus hypertension (CSH) on systolic and diastolic left ventricular (LV) function. Coronary sinus pressure was elevated to 25 mmHg for 3 h in eight pentobarbital-anesthetized dogs and then relieved. LV contractility was assessed by preload recruitable stroke work (PRSW) and end-systolic elastance (Ees). Diastolic function was assessed by the time constant of isovolumic relaxation (tau) and the end-diastolic pressure volume relationship (EDPVR). PRSW and Ees decreased progressively, and tau and the slope of the EDPVR increased progressively with CSH. These changes persisted after relief of CSH. beta-Adrenergic and cholinergic receptor blockade, performed in six dogs, did not alter the effects of CSH on systolic or diastolic function. The LV wet-to-dry weight ratios of the groups with CSH were significantly greater than those of a control group without CSH. We conclude that CSH results in changes in the left ventricle that depress contractility, prolong active relaxation, and increase diastolic stiffness. The dysfunction was not the direct effect of CSH or autonomic reflex activation, but may have been induced by fluid accumulation within the interstitium.
Influence of apnea on cardiovascular responses to neck suction during exercise
Authors: Sundblad P. , Linnarsson D.
Published: December 2017

Short-lasting neck suction (NS) is a common method to assess the carotid-cardiac baroreflex, and NS is usually applied during apnea to avoid breath-synchronous variations of heart rate (HR) and blood pressure. We hypothesized that the apnea might provoke cardiovascular effects that could confound the HR and blood pressure responses to NS. HR and blood pressure responses to 10-s trains of 50-mmHg pulses of NS were studied in six male subjects during supine rest, upright rest, isometric arm exercise at 30% of maximal voluntary contraction, and dynamic leg exercise at 100 W in the sitting position. Repeated NS sequences were performed during apnea preceded by a relaxed expiration to functional residual capacity and during eupnea. Initial HR responses to NS were similar during eupnea and apnea in all conditions. However, during isometric and dynamic exercise, recordings made under eupneic and apneic conditions differed during the second half of the NS period. During apneic isometric arm contraction, the elevation of mean carotid distending pressure (MCDP) (arterial pressure at carotid level minus NS pressure) was maintained at a 25-35% higher level than during eupneic isometric exercise over the last half of the NS period. In dynamic exercise, mean arterial pressure and MCDP started to increase after 3-5 s of apneic NS, whereas they were maintained during eupnea. One to three seconds later, HR started to drop markedly in apneic subjects, reaching values 20 beats/min lower than those in eupneic subjects at the end of the NS. We conclude that cardiovascular effects of apnea may appear after only 8 s of apnea in dynamic exercise and therefore could confound responses to NS.
Frequency response characteristic of sympathetic-mediated vasomotor waves in conscious rats
Authors: Stauss H. M. , Kregel K. C.
Published: December 2017

Power spectrum analysis of arterial blood pressure (BP) and heart rate (HR) has been used to investigate autonomic nervous system activity. Sympathetic-mediated vasomotor tone has been attributed to the BP power at frequencies between 0.05 and 0.15 Hz in humans and dogs and between 0.2 and 0.8 Hz in rats. In contrast, it has been suggested that the sympathetic nervous system is too sluggish to transmit frequencies higher than 0.017 Hz in dogs. Thus we investigated the frequency-response characteristics of the transmission of peripheral sympathetic nerve discharge to peripheral vascular resistance and arterial blood pressure in conscious rats. Eleven rats were instrumented with arterial catheters, nerve electrodes on the sympathetic splanchnic nerve, and flow probes on the superior mesenteric artery. The splanchnic nerve was cut proximal to the electrode to avoid afferent nerve stimulation. The next day the nerve was stimulated at frequencies of 0.05, 0.1, 0.2, 0.5, 1.0, and 2.0 Hz while mesenteric blood flow, BP, and HR were recorded in conscious rats. Mesenteric resistance (MR) was calculated off-line. Nerve stimulation at 0.05, 0.1, 0.2, 0.5, and 1.0 Hz significantly increased the power in MR at these respective frequencies. The greatest response was found between 0.2 and 0.5 Hz. These oscillations in MR were translated to oscillations in BP, but not in HR. Nerve stimulation on the second day, when the nerve was degenerated, did not elicit oscillations in MR or BP. We conclude that the peripheral sympathetic nervous system in rats can transmit signals at frequencies higher than those traditionally assigned to sympathetic vasomotor activity in several species, including humans, and may even overlap with the respiration-related high-frequency range.
Alpha 1-adrenoceptor subtypes mediating inotropic and electrophysiological effects in mammalian myocardium
Authors: Nagashima M. , Hattori Y. , Akaishi Y. , Tohse N. , Sakuma I. , Kitabatake A. , Kanno M.
Published: December 2017

Stimulation of alpha 1-adrenoceptors produces a positive inotropic effect in rat and rabbit ventricular myocardium via different mechanisms, the prolongation of action potential duration (APD) exclusively in the former and an increase in myofibrillar Ca2+ sensitivity in large part in the latter. This study was designed to determine whether the two inotropic mechanisms are mediated by different alpha 1-adrenoceptor subtypes. In rat papillary muscles, the positive inotropic effect and APD prolongation induced by phenylephrine (in the presence of propranolol) were inhibited by WB-4101, but not affected by chlorethylclonidine (CEC). WB-4101, but not CEC, blocked the phenylephrine-induced inhibition of the transient outward current (Ito) in rat ventricular cells. On the other hand, WB-4101 and CEC each antagonized the positive inotropic effect of phenylephrine in rabbit papillary muscles. However, the phenylephrine-induced APD prolongation observed in rabbit papillary muscles was blocked only by WB-4101. These results indicate that the WB-4101 sensitive alpha 1-adrenoceptor subtype mediates the positive inotropism that is correlated with the APD prolongation resulting from Ito reduction, whereas the CEC-sensitive subtype mediates the positive inotropism that is probably associated with increased myofibrillar Ca2+ sensitivity. Radioligand binding studies with [3H] prazosin showed a similar ratio of alpha 1A-to alpha 1B-adrenoceptor subtypes in rat and rabbit ventricular myocardium, implying that the different degree of contribution of each action mechanism to the overall inotropic effect in the two species cannot be explained by distribution of the alpha 1-adrenoceptor subtypes.
Neural influences on renal responses to acute volume expansion in rats with heart failure
Authors: Patel K. P. , Zhang P. L. , Carmines P. K.
Published: December 2017

Experiments were performed to test the postulate that neural influences underlie the suppressed excretory response to acute volume expansion (VE) typically observed 3-4 wk after myocardial infarction to induce chronic heart failure (CHF). Responses to VE were assessed in innervated (intact) and denervated (DNX) kidneys of anesthetized CHF rats and sham-operated controls. CHF rats exhibited blunted natriuretic responses to VE in both intact kidneys (35% of sham response) and DNX kidneys (55% of sham DNX response). CHF rats also displayed suppressed excretory responses to atrial natriuretic factor (0.25 microgram.kg-1.min-1 iv) in both intact kidneys (74% of sham response) and DNX kidneys (63% of sham DNX response). Additional experiments confirmed that the compliance of the venoatrial junction did not differ between sham rats (52 +/- 2 mmHg/microliter) and CHF rats (54-2 mmHg/microliter). The observations support the contention that both tonic renal sympathetic renal nerve activity and suppressed renal atrial natriuretic factor responsiveness likely contribute to the blunted excretory response to VE during CHF.
Neurally mediated cardiac effects of forskolin in conscious dogs
Authors: Iwase M. , Ishikawa Y. , Shen Y. T. , Shannon R. P. , Sato N. , Ganguly P. K. , Eki T. , Vatner D. F. , Vatner S. F.
Published: December 2017

Because major cardiovascular disease states are characterized by defects in adenylyl cyclase regulation, it becomes important to understand the mechanisms by which adenylyl cyclase activators affect inotropy and chronotropy in intact conscious animals. Accordingly, we examined the inotropic and chronotropic responses to forskolin in 11 normal conscious, chronically instrumented dogs and 3 dogs with ventricular denervation (VD). Left ventricular first derivative of pressure (LV dP/dt) increased by 96 +/- 7%, P < 0.05, in response to forskolin (50 nmol.kg-1.min-1) in normal dogs and by significantly less, 52 +/- 14%, in VD dogs. Circulating norepinephrine (NE) levels increased similarly in both groups (from 226 +/- 18 to 389 +/- 33 pg/ml in normal dogs, from 177 +/- 23 to 329 +/- 71 pg/ml in VD dogs). In the presence of ganglionic blockade, the increase in LV dP/dt in response to forskolin was reduced (+62 +/- 4%) in normal dogs but was unchanged in VD dogs (+52 +/- 12%). Ganglionic blockade abolished the increase in circulating NE levels in both groups. Increases in heart rate in the presence of ganglionic blockade (+54 +/- 6 beats/min) were less than in the presence of atropine alone (+92 +/- 10 beats/min). Notably, the LV dP/dt and heart rate responses to forskolin were further attenuated by beta-adrenergic receptor blockade in the presence and absence of ganglionic blockade. Morphine also attenuated the increases in both LV dP/dt and plasma NE in response to forskolin. Increases in LV dP/dt in response to NKH-477 (30 micrograms/kg), a water-soluble forskolin derivative, were similar before and after ganglionic blockade (+63 +/- 8 and +51 +/- 10%, respectively). However, in vitro experiments in LV sarcolemmal membrane preparations demonstrated that stimulation of adenylyl cyclase by forskolin and NKH-477 was not affected by beta-adrenergic receptor blockade. These results indicate that in conscious dogs, inotropic and chronotropic effects of forskolin are not only due to direct activation of adenylyl cyclase, but the effects also are mediated by neural mechanisms and potentiated by the prevailing level of sympathetic tone.
Cardiac output mediates the antihypertensive effect of vasopressin in spontaneous hypertension
Authors: Balakrishnan S. , McNeill J. R.
Published: December 2017

The contribution of cardiac output and total peripheral resistance to the fall in arterial pressure that follows cessation of a 3-h intravenous infusion of arginine vasopressin (AVP; 20 ng.kg-1.min-1) was studied in conscious spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats instrumented with radiotelemetric probes for recording of blood pressure and ultrasonic transit-time flow probes for measuring cardiac output. Cessation of a 3-h infusion of AVP resulted in a significant decrease in arterial pressure in SHR (14-17 mmHg below preinfusion control levels) but not in WKY or in vehicle-treated controls. The fall in pressure persisted for several days. The fall in pressure was associated with a large decrease in cardiac output of 22 +/- 2 ml/min below control levels in SHR, and the time course of the cardiac output response over several days approximated the time course of the pressure response. By contrast, total peripheral resistance remained elevated for some time on withdrawal of the AVP infusion. We conclude that the withdrawal-induced antihypertensive phenomenon in SHR is mediated by a fall in cardiac output and not by a decline in total peripheral resistance.
Method for determining distribution of reflection sites in the arterial system
Authors: Pythoud F. , Stergiopulos N. , Westerhof N. , Meister J. J.
Published: December 2017

We developed a new method to determine the location and importance of reflection sites in the arterial system. The method is based on the decomposition of the aortic pressure wave into its forward and backward components, and it provides the reflection profile of the arterial system as a wave reflection site amplitude versus distance from the heart. The reflection profile can be seen as the response of the arterial system to a pressure delta pulse where reflections upstream from the measurement location have been eliminated. The method was successfully tested on a simple model loaded with a pure resistor, a two-element windkessel, and a bifurcating tube system. It was then applied to the aortic pressure and flow signals measured in six mongrel dogs whose aorta was occluded at different levels. The profiles obtained from measurements at control showed two main reflection regions, one located in the vicinity (0.1-0.2 m) of the heart and the other located in the region of the iliac bifurcation. All occlusions, even the most distant one at the iliac bifurcation, could be identified in both amplitude (amount of reflections) and distance from the heart. The spatial resolution of the profiles was approximately 0.1 m as a result of the limited power spectrum contained in the arterial pulse, and the identification of reflection sites decreased rapidly with the distance.
Effects of anion exchange on intracellular pH and tension in basilar artery of dogs
Authors: Yu J. , Ong B. Y. , Zheng J. , Cragoe E. J. , Bose D. , Bose R.
Published: December 2017

We simultaneously measured intracellular pH (pHi) and isometric tension in canine basilar arteries. pHi was calculated from the ratio of fluorescence intensities at 540 nm of exciting wavelengths of 500 and 440 nm in the presence of 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF). pHi was 7.33 +/- 0.02 in Krebs-Henseleit solution (pH of 7.4 at 37 degrees C). Application of the anion exchange blocker 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) decreased the resting pHi by 0.25 pH units. Increasing extracellular pH (pHo) [by decreasing CO2 tension (PCO2)] from 7.4 to 7.8 increased pHi by 0.38 pH units and increased tension by 2.28 +/- 0.21 mN. Decreasing pHo from 7.8 to 7.4 (by increasing PCO2) restored the pHi and muscle tension to their baseline levels. SITS inhibited the increase in pHi and isometric tension in response to the increase in pHo in an endothelium-independent fashion. The Na+/H+ exchange blockers, amiloride or 5-(N-methyl-N-guanidinocarbonylmethyl)-amiloride, did not affect the pHo or tension changes. The results suggest that in the range of pH tested, anion exchange is more important than Na+/H+ exchange in the regulation of pHi and mechanical tone in the basilar artery.
Arginase activity in endothelial cells: inhibition by NG-hydroxy-L-arginine during high-output NO production
Authors: Buga G. M. , Singh R. , Pervin S. , Rogers N. E. , Schmitz D. A. , Jenkinson C. P. , Cederbaum S. D. , Ignarro L. J.
Published: December 2017

Rat aortic endothelial cells were found to contain both constitutive and lipopolysaccharide (LPS)-inducible arginase activity. Studies were performed to determine whether induction of nitric oxide synthase (NOS) by LPS and cytokines is accompanied by sufficient arginase induction to render arginine concentrations rate limiting for high-output NO production. Unactivated cells contained abundant arginase activity accompanied by continuous urea formation. LPS induced the formation of both inducible NOS (iNOS) and arginase, and this was accompanied by increased production of NO, citrulline, and urea. Immunoprecipitation experiments revealed the constitutive presence of arginase-I in both unactivated and LPS-activated cells and arginase-II induction by LPS. Arginase-I and iNOS were verified by reverse transcriptase-polymerase chain reaction. Induction of large amounts of iNOS by LPS plus several cytokines resulted in large quantities of NO, citrulline, and NG-hydroxy-L-arginine (NOHA), but urea production was markedly diminished. Decreased urea production was attributed to increased formation of NOHA, the precursor to NO and citrulline and a potent inhibitor of arginase-I activity with an inhibitory constant of 10-12 microM. Inhibition of iNOS activity by NG-methyl-L-arginine decreased NO and NOHA production and increased urea production. This study reveals for the first time that substantial arginase activity is present constitutively in rat aortic endothelial cells, a different isoform of arginase is induced by LPS, and intracellular arginase activity can be markedly inhibited during cytokine induction of iNOS because of NOHA formation. The inhibition of arginase activity that occurs by NOHA during marked iNOS induction may be a mechanism to ensure sufficient arginine availability for high-output production of NO.
Hypoxia induces PECAM-1 phosphorylation and transendothelial migration of monocytes
Authors: Kalra V. K. , Shen Y. , Sultana C. , Rattan V.
Published: December 2017

Polymorphonuclear neutrophils (PMN) adhere to the vascular endothelium under hypoxic conditions, causing microvascular injury. The molecular mechanism of hypoxia-induced adhesion of PMN to and diapedesis through the vascular endothelium is poorly understood. We examined the effects of hypoxia on the transendothelial migration of monocytes. Exposure of human umbilical vein endothelial cells (HUVEC) cultured in Transwell chambers under low oxygen tension (3% O2 compared with 21% O2) resulted in an increased rate of migration of both monocyte-like HL-60 cells and human peripheral blood monocytes. Migration was inhibited by addition of an antibody to platelet endothelial cell adhesion molecule-1 (PECAM-1), a protein kinase C (PKC) inhibitor, or a platelet-activating factor (PAF)-receptor antagonist. In HUVEC, hypoxic conditions (1, 3, 5, and 14% O2) increased the phosphorylation of PECAM-1. The extent of phosphorylation of PECAM-1 was inversely related to the concentration of oxygen to which HUVEC were exposed. Hypoxia-induced phosphorylation of PECAM-1 was inhibited by either a PKC inhibitor or a PAF-receptor antagonist, indicating the involvement of hypoxia-induced release of PAF in both PKC activation and the concomitant phosphorylation of PECAM-1. These results were substantiated by the findings that treatment of HUVEC with 100 nM PAF under normoxic conditions augmented 11.8-fold the phosphorylation of PECAM-1 and twofold increase in the transendothelial migration of monocyte-like HL-60 cells. We conclude that PAF, produced by cultured endothelial cells in response to hypoxia, acts in an autocrine fashion to activate PKC, causing PECAM-1 phosphorylation and thus the transendothelial migration of monocytes.
Subcellular compartmentalization of Gs alpha in cardiac myocytes and its redistribution in heart failure
Authors: Nash J. A. , Hammond H. K. , Saffitz J. E.
Published: December 2017

Intracellular compartmentalization of G proteins may contribute to regulating signal transduction pathways in normal and failing myocardium. To test this hypothesis, we used postembedment immunogold electron microscopy to characterize the subcellular distribution of Gs alpha in normal canine and porcine left ventricular myocytes and in myocytes from a pacing-induced heart failure model in pigs in which beta-adrenergic signaling is impaired. Gs alpha was highly compartmentalized in normal canine myocytes and was localized specifically to the sarcolemma, intercalated disks, T-tubule and sarcoplasmic reticulum (SR) triads, and myoplasm. The highest Gs alpha concentration was observed in the intercalated disks. Only 20 +/- 5% of total cellular Gs alpha was localized to the sarcolemma. The triads and myoplasm compartments contained 45 +/- 13 and 27 +/- 8% of total cellular Gs alpha, respectively. The distribution of Gs alpha in normal porcine and canine myocytes was similar. However, in failing porcine myocytes Gs alpha was redistributed from the sarcolemma and T-tubule and SR triads to the myoplasm. The proportion of total cellular Gs alpha in the sarcolemma fell from 22 +/- 5 in normal to 11 +/- 4% in failing myocytes (P < 0.005), and the proportion in T-tubule and SR triads fell from 55 +/- 5 to 40 +/- 5% (P < 0.01), with a quantitatively corresponding increase in the proportion in the myoplasm from 19 +/- 3 to 43 +/- 4% (P < 0.0001). Thus redistribution of Gs alpha from the sarcolemma and the T-tubule and SR triads, where it may transduce beta-adrenergic signals, to internal sites where such actions may be precluded, might contribute to the pathophysiology of heart failure.
In vivo inhibition of transcellular water channels (aquaporin-1) during acute peritoneal dialysis in rats
Authors: Carlsson O. , Nielsen S. , Zakaria el-R. , Rippe B.
Published: December 2017

During peritoneal dialysis (PD), a major portion of the osmotically induced water transport to the peritoneum can be predicted to occur through endothelial water-selective channels. Aquaporin-1 (AQP-1) has recently been recognized as the molecular correlate to such channels. Aquaporins can be inhibited by mercurials. In the present study, HgCl2 was applied locally to the peritoneal cavity in rats after short-term tissue fixation, used to protect the tissues from HgCl2 damage. Dianeal (3.86%) was employed as dialysis fluid, 125I-albumin as an intraperitoneal volume marker, and 51Cr-EDTA (constantly infused intravenously) to assess peritoneal small-solute permeability characteristics. Immunocytochemistry and immunoelectron microscopy revealed abundant AQP-1 labeling in capillary endothelium in peritoneal tissues, representing sites for HgCl2 inhibition of water transport. HgCl2 treatment reduced water flow and inhibited the sieving of Na+ without causing any untoward changes in microvascular permeability, compared with that of fixed control rats, in which the peritoneal cavity was exposed to tissue fixation alone. In fixed control rats, the mean intraperitoneal volume (IPV) increased from 20.5 +/- 0.15 to 25.0 +/- 0.52 ml in 60 min, whereas in the HgCl2-treated rats, the increment was only from 20.7 +/- 0.23 to 23.5 +/- 0.4 ml. In fixed control rats, the dialysate Na+ fell from 135.3 +/- 0.97 to 131.3 +/- 1.72 mM, whereas in the HgCl2-treated rats the dialysate Na+ concentration remained unchanged between 0 and 40 min, further supporting that water channels had been blocked. Computer simulations of peritoneal transport were compatible with a 66% inhibition of water flow through aquaporins. The observed HgCl2 inhibition of transcellular water channels strongly indicates a critical role of aquaporins in PD and provides evidence that water channels are crucial in transendothelial water transport when driven by crystalloid osmosis.
Erythrocyte flux in capillary networks during maturation: implications for oxygen delivery
Authors: Berg B. R. , Sarelius I. H.
Published: December 2017

Erythrocyte (RBC) flow variables were measured with videomicroscopy in hamster cremaster muscle capillary networks. Capillary networks consist of subgroups, termed modules, with architectural characteristics that are invariant with maturation [B. R. Berg and I. H. Sarelius. Am. J. Physiol, 268 (Heart Circ. Physiol. 37): H1215-H1222, 1995]. RBC flux in modules decreased from 82.0 +/- 4.3 (SE) cells/s at 51 days of age to 59.5 +/- 7.5 and 27.5 +/- 2.8 cells/s at 65 and 79 days of age, respectively. Mean cell velocity at 51 days (385 +/- 10 microns/s) was higher than at 65 or 79 days (285 +/- 15 and 241 +/- 12 microns/s, respectively). Cell content (number of cells per unit length) decreased later, between 65 and 79 days (from 0.21 +/- 0.01 and 0.23 +/- 0.02 cells/micron at 51 and 65 days, respectively, to 0.12 +/- 0.01 cells/micron at 79 days). These temporal differences in the decrease in cell velocity and cell content suggest different regulatory mechanisms. The capacity of capillary networks to deliver oxygen was modeled by using the calculated mean PO2 at the capillary wall to indicate the capacity to delivery oxygen. During maturation, the mean capillary wall PO2 remained unchanged (15.5 +/- 1.2 and 11.4 +/- 2.7 Torr in maximal dilation and 24.5 +/- 1.4 and 22.8 +/- 2.4 Torr at rest at 51 and 79 days, respectively). Thus, despite changes in RBC flow variables with maturation, the capacity for networks to deliver oxygen remains constant.
Ca2+ entry through conductive pathway modulates receptor-mediated increase in microvessel permeability
Authors: He P. , Zhang X. , Curry F. E.
Published: December 2017

We investigated the relationship between receptor-mediated increases in cytoplasmic Ca2+ concentration ([Ca2+]i) and increased microvessel permeability. In individually perfused venular microvessels of frog mesentery exposed to 10 microM ATP, [Ca2+]i increased from 59 +/- 7 to 172 +/- 21 nM within 1 min and then fell back toward control values. The corresponding peak increase in the hydraulic conductivity (Lp) of the microvessel wall was 5.7 +/- 0.5-fold relative to control. After removal of extracellular Ca2+, there was no significant increase in Lp, and the initial increase in [Ca2+]i was attenuated but not abolished. Depolarization of the endothelial cell membrane with high-K+ Ringer solution reduced the peak increase in [Ca2+]i to 106 +/- 7 nM and attenuated the increase in Lp 1.8 +/- 0.4-fold. The results conform to the hypothesis that Ca2+ entry into endothelial cells is required for acute increase in venular microvessel permeability by inflammatory agents and that the pathway for Ca2+ entry has the properties of a passive conductance pathway. Similar conclusions were reached in previous experiments in frog microvessels exposed to Ca2+ ionophores and perfusates with no plasma proteins. In venular microvessels of hamster mesentery exposed to ATP and bradykinin, a similar pathway for Ca2+ entry was demonstrated in the present experiments. We did not measure permeability changes in hamster microvessels in this study, but these microvessels respond to histamine and ionophores with a transient increase in permeability to macromolecules similar to that measured in frog microvessels [Am. J. Physiol. 268 (Heart Circ. Physiol. 37): H1982-H1991, 1995].
Erythrocyte flow and elasticity of microvessels evaluated by marginal cell-free layer and flow resistance
Authors: Maeda N. , Suzuki Y. , Tanaka J. , Tateishi N.
Published: December 2017

Flow dynamics of human erythrocytes was compared in elastic (E) and hardened (H) microvessels with inner diameters of 10-40 microns. The thickness of the marginal cell-free layer and the overall flow resistance were measured with a vascular bed isolated from rabbit mesentery (E vascular bed) as well as with a 4% paraformaldehyde-fixed bed (H vascular bed). 1) In both E and H microvessels, the thickness of the cell-free layer increased with increasing inner diameter of the microvessels and with decreasing hematocrit accompanied by an overall decrease in the flow resistance. The hematocrit-dependent change of the cell-free layer thickness was greater in the E microvessels than in the H microvessels. The flow resistance was always greater in the H vascular beds than in the E vascular beds. 2) With decreasing erythrocyte deformability induced by treatment with 2 mM diazenedicar-boxylic acid bis(N,N-dimethylamide), the thickness of the cell-free layer decreased at a low hematocrit in the E microvessels and at a high hematocrit in the H microvessels, although the flow resistance was increased in both vascular beds. 3) Dextran of 70,400 average molecular weight accelerated the formation of the cell-free layer by inducing erythrocyte aggregation. A drastic increase in the cell-free layer thickness at 2-4 g/dl of dextran in the E microvessels and at 1-2 g/dl of dextran in the H microvessels was accompanied by a significantly lower increase in the flow resistance. This study concludes that the elasticity of microvessels may play an important role for reducing the overall flow resistance of a vascular bed, which is modulated by the marginal cell-free layer, itself a function of the rheological properties of the erythrocytes.
Permeability-related changes revealed at endothelial cell borders in inflamed venules by lectin binding
Authors: Thurston G. , Baluk P. , Hirata A. , McDonald D. M.
Published: December 2017

Plasma leakage in inflammation results from intercellular gaps that form in the endothelium of venules. These gaps and related morphological changes in endothelial cells are not readily seen by light microscopy. In this study we sought to visualize such changes by using the selective binding properties of plant lectins. Acute inflammation was induced in the trachea of pathogen-free F344 rats by injecting substance P intravenously, and 1, 3, or 10 min later the vasculature was perfused with fixative followed by a biotinylated lectin. Lectin binding was localized by avidinbiotin complex-peroxidase histochemistry and viewed in tracheal whole mounts by differential-interference contrast microscopy. The binding patterns of the 20 lectins tested fell into 4 groups. Most of the lectins either bound uniformly to the endothelium of normal and inflamed venules (group 1, e.g., Lycopersicon esculentum lectin) or bound weakly or not at all to venules (group 2, e.g., Maackia amurensis I lectin). The uniform binding of group 1 lectins not only revealed the overall vascular architecture but also made visible intercellular gaps and fingerlike processes at endothelial cell borders in inflamed venules. In postcapillary venules after substance P, the fingerlike processes were present along an average of 32% of the endothelial cell perimeter at 1 min, 25% at 3 min, and 7% at 10 min, compared with a baseline value of 2%. A third group of lectins (group 3, e.g., concanavalin A) bound selectively to focal patches of inflamed venules but bound weakly to normal venules. The fourth group (group 4, e.g., Ricinus communis I lectin) bound preferentially to focal patches in inflamed venules and also bound uniformly to normal venules. The focal binding of group 3 and 4 lectins coincided with sites of plasma leakage marked by extravasation of the particulate tracer monastral blue and was associated with subendothelial components of the vessel wall. We conclude that selected lectins reveal novel features of focal sites of plasma leakage, endothelial gaps, and fingerlike processes at endothelial cell borders in inflamed venules.
Captopril suppresses interstitial fibrin deposition in coxsackievirus B3 myocarditis
Authors: Takada H. , Kishimoto C. , Hiraoka Y. , Kurokawa M. , Shiraki K. , Sasayama S.
Published: December 2017

The effects of captopril on murine coxsackievirus B3 (CB3) myocarditis were investigated, with focus on interstitial fibrin deposition and changes in the connective tissue matrix. Captopril was administered intraperitoneally at a dose of 0.1 mg/g to CB3-infected mice daily on days 10–30 in experiment I (inflammatory phase) and on days 30-60 in experiment II (fibrotic phase). In experiment I, mouse survival was higher in the captopril-treated group than in the untreated group. Histological improvement, including prevention of extravasated fibrin deposition, maintenance of connective tissue architecture, suppression of myocyte hypertrophy, and prevention of myosin isoform shift from alpha to beta, was observed in captopril-treated mice in experiment I, but not in experiment II; in experiment II, captopril administration suppressed thickening of the interstitial reticulin fibers. Captopril inhibited inflammatory fibrin deposition, postmyocarditic myocyte hypertrophy, and ventricular remodeling during the inflammatory phase, but not during the fibrotic phase, of CB3 myocarditis in mice.
Assessment of cardiomyocyte DNA synthesis in normal and injured adult mouse hearts
Authors: Soonpaa M. H. , Field L. J.
Published: December 2017

Cardiomyocyte DNA synthesis was examined in normal and injured adult mouse hearts. In preliminary studied DNA synthesis was monitored by [3H]thymidine incorporation, followed by autoradiographic analysis of dispersed cell preparations. No synthetic cells were identified when 20,000 ventricular cardiomyocytes from normal adult hearts were examined. A high throughput assay was developed to establish the actual labeling index for the adult mouse heart. The assay utilized [3H]thymidine incorporation in transgenic mice which expressed a nuclear-localized beta-galactosidase (beta-Gal) reporter gene exclusively in cardiac myocytes. Cardiomyocyte DNA synthesis was evidenced by colocalization of beta-Gal activity and silver grains in autoradiograms of histological sections. Examination of 180,000 ventricular cardiomyocyte nuclei from normal adult transgenic mice identified a single synthetic nucleus, suggesting a maximum labeling index of 0.0005%. Cardiomyocyte DNA synthesis was next examined in hearts injured by focal cauterization of the left ventricular free wall. Only three synthetic nuclei were identified when 36,000 cardiomyocyte nuclei in the perinecrotic zone of the injured heart were examined. No additional synthetic nuclei were identified when 180,000 nuclei in regions distal to the necrotic zone were examined. These data confirm that cardiomyocyte DNA synthesis in the adult mouse heart is extremely rare and provide baseline data for analyses in genetically modified animals.