bluuebunny/crossref_metadata_2025 huggingface dataset:
Starling resistor vs. distensible vessel models for embolic pulmonary hypertension
Authors: Melot C. , Delcroix M. , Closset J. , Vanderhoeft P. , Lejeune P. , Leeman M. , Naeije R.
Published: December 2017

We investigated whether the Starling resistor model (Mitzner et al. J. Appl. Physiol. 51: 1065–1071, 1981) or a distensible vessel model (Haworth et al. J. Appl. Physiol. 70: 15–26, 1991) best describes pulmonary vascular pressure-flow (Q) relationships in embolic pulmonary hypertension. Mean pulmonary arterial pressure (Ppa)-Q plots at constant left atrial pressure (Pla) and Ppa-Pla plots at constant Q were investigated in seven dogs before and after 500-micron glass bead pulmonary embolism. Embolization to a mean angiographic obstruction of 78% increased the slope and extrapolated pressure intercept (P(i)) of Ppa-Q plots and increased the inflection point of Ppa-Pla plots, above which an increase in Pla is transmitted to Ppa in a ratio of approximately 1:1. The Starling resistor and the distensible vessel model provided a reasonably good fit to the Ppa-Q and Ppa-Pla coordinates before and after embolism. However, contrary to the prediction of the Starling resistor model, no correlation was found between the inflection point of Ppa-Pla plots and P(i). We therefore conclude that an increased closing pressure is unlikely to contribute to embolic pulmonary hypertension.
LV and myocyte structure and function after early recovery from tachycardia-induced cardiomyopathy
Authors: Spinale F. G. , Holzgrefe H. H. , Mukherjee R. , Arthur S. R. , Child M. J. , Powell J. R. , Koster W. H.
Published: December 2017

Left ventricular (LV) function and mass were measured in six conscious dogs at weekly intervals during the progression of tachycardia-induced dilated cardiomyopathy (DCM) and during a 1-mo recovery period from DCM (post-DCM). LV end-diastolic volume and LV wall stress increased and LV ejection fraction decreased with each week of pacing. Despite the increased LV wall stress, LV mass did not change during the progression of tachycardia DCM. One week post-DCM resulted in an improved LV ejection fraction and normalization of neurohormonal profiles. However, 1 wk post-DCM was accompanied by a 26% increase in LV mass and persistent LV chamber dilation. Isolated myocyte function was examined and compared with that in six normal control dogs. Myocyte percent and myocyte velocity of shortening were 19 and 32% lower, respectively, in the post-DCM group compared with controls. Thus termination of the tachycardia subsequent to the development of DCM resulted in persistent LV chamber dilation and abnormalities in myocyte contractile function. The improved LV pump function with early recovery from tachycardia-induced DCM was mediated by LV hypertrophy and a subsequent reduction in LV wall stress rather than a normalization of LV geometry and myocyte contractile function.
cGMP mediates the desensitization to bradykinin in isolated canine coronary arteries
Authors: Olmos L. , Mombouli J. V. , Illiano S. , Vanhoutte P. M.
Published: December 2017

The relaxation to bradykinin in canine coronary arteries is mediated by endothelium-derived nitric oxide (NO) and hyperpolarizing factor (EDHF). Desensitization to the kinin was induced by incubation of canine coronary arteries with endothelium with 10(-8) M bradykinin for 30 min. After washout, tissues were contracted with prostaglandin F2 alpha, and concentration-relaxation curves to bradykinin were obtained in control and desensitized arteries treated with indomethacin. After desensitization, there was a shift to the right of the concentration-relaxation curves to bradykinin. However, the elevation in guanosine 3',5'-cyclic monophosphate (cGMP) levels evoked by bradykinin was similar in both groups of tissues. The curves to bradykinin obtained in the presence of NG-nitro-L-arginine (an NO synthase inhibitor) were depressed, whereas those obtained in arteries contracted with potassium (to eliminate the EDHF-mediated relaxation) were not affected by the desensitization. Addition of NG-nitro-L-arginine, oxyhemoglobin, or methylene blue before the desensitization procedure preserved, whereas 3-morpholinosydnonimine (SIN-1, a donor of NO) and 8-bromoguanosine 3',5'-cyclic monophosphate impaired, the EDHF-mediated relaxation to bradykinin. Thus the selective impairment of the EDHF-dependent relaxation to bradykinin may be mediated by NO, acting mainly through increased production of cGMP.
In vivo differentiation of leukocytes rolling in mesenteric postcapillary venules
Authors: Tangelder G. J. , Janssens C. J. , Slaaf D. W. , oude Egbrink M. G. , Reneman R. S.
Published: December 2017

A method is presented to assess in vivo in transparent tissues the leukocyte subtypes that roll in microvessels. In nine rabbits anesthetized with ketamine-xylazine, leukocyte nuclei were stained in situ with acridine yellow (3 mg/kg i.v. for 5 min). Intravital fluorescence video microscopy in 24 mesenteric venules (17–29 microns, median 21) indicated labeling of all rolling leukocytes. On the basis of the shape of their nucleus, 67–100% (median 89) could be classified unequivocally (13366 cells analyzed, median 77) as polymorphonuclear (PMN, i.e., granulocytes) or monomorphonuclear (lymphocytes and monocytes). Of these classified cells, 94–100% were PMNs (median 100, including 1 stray value of 69%). This PMN percentage was independent of the level of leukocyte rolling (2–36/min, median 14), vessel diameter, flow velocity (0.5–2.5 mm/s), or duration of the experiment (< 6 h). The dye had no significant influence on hemodynamic parameters, systemic leukocyte counts (1.5–7.8 x 10(9)/l), or in vitro differentiation pattern (27–38% granulocytes, 0–2% monocytes, 61–71% lymphocytes). In conclusion, our method demonstrated that the leukocytes that roll in postcapillary venules of the exteriorized rabbit mesentery are almost exclusively granulocytes.
ANP increases capillary permeability to protein independent of perfusate protein composition
Authors: McKay M. K. , Huxley V. H.
Published: December 2017

In further studying hormonal regulation of microvascular exchange, we tested two hypotheses: 1) atrial natriuretic peptide (ANP) would increase capillary permeability to protein and 2) the actions of ANP on capillary permeability would be independent of the perfusate protein composition. These hypotheses were tested by assessing in situ capillary transport coefficients: hydraulic conductivity (Lp), apparent and diffusive permeabilities (Ps and Psd, respectively) to the protein alpha-lactalbumine, and convective coupling [Lp(1-sigma)] in mesenteric capillaries in cerebrally pithed frogs (Rana pipiens). The transport coefficients were determined in the absence and presence of frog ANP (fANP) during perfusion with either frog plasma or bovine serum albumin (BSA). Control Lp was 1.8-fold greater in vessels perfused with BSA compared with plasma. In the presence of 10 or 100 nM fANP, Lp was increased by approximately 3.5-fold in plasma-perfused vessels and approximately 2-fold in BSA-perfused vessels from their respective controls. Control Ps was 4.2-fold higher in vessels perfused with BSA compared with plasma. Despite the differences in control permeability, the increase in Ps by fANP was of similar magnitude (2- to 3-fold) for both protein perfusates. Analysis of the pressure-dependent alpha-lactalbumin flux suggested that the increase in capillary permeability induced by fANP is consistent with fANP increasing permeability without altering the selectivity of the capillary barrier.
Tolerance of the developing heart to ischemia: impact of hypoxemia from birth
Authors: Baker E. J. , Boerboom L. E. , Olinger G. N. , Baker J. E.
Published: December 2017

Many infants who require cardiac surgery have cyanotic heart disease. We assessed the relative tolerances to ischemia of hearts from immature normoxemic rabbits versus hearts from immature rabbits subjected to hypoxemia since birth. Normoxemic animals were raised from birth in an environment where the inspired fractional concentration of oxygen (FIO2) was 0.21; for the hypoxemic studies FIO2 was reduced to 0.09. Hearts (n = 6/group) from normoxemic and chronically hypoxemic rabbits at 7–12, 21–28, 35–44, and 51–56 days of age underwent aerobic “working” perfusion with Krebs bicarbonate buffer, and cardiac function was measured. Hearts were then arrested by a 3-min infusion with either cold (14 degrees C) Krebs buffer (hypothermia alone group) or St. Thomas' Hospital II solution (hypothermia plus cardioplegia group) before 6 h of hypothermic (14 degrees C) global ischemia. Hearts were reperfused, and postischemic creatine kinase leakage and recovery of function were measured. For hearts protected with hypothermia alone, recovery of aortic flow was better in hearts hypoxemic from birth compared with normoxemic controls at 7–12 days (78 +/- 7 vs. 60 +/- 6%, P < 0.05) and 21–28 days old (81 +/- 12 vs. 26 +/- 28%, P < 0.05). Protection with hypothermia plus cardioplegia was also better in hearts hypoxemic from birth compared with normoxemic controls at 7-12 days (74 +/- 8 vs. 63 +/- 10%, P < 0.05) and 21–28 days old (84 +/- 3 vs. 71 +/- 5%, P < 0.05). Protection with hypothermia alone and hypothermia plus cardioplegia was no different within chronically hypoxemic age groups.(ABSTRACT TRUNCATED AT 250 WORDS)
Reduced effect of phenylephrine on regional myocardial function and O2 consumption in experimental LVH
Authors: Roitstein A. , Cheinberg B. V. , Kedem J. , Tse J. , Weiss H. R. , Scholz P. M.
Published: December 2017

In a dog model of left ventricular hypertrophy (LVH) created by aortic valve plication, we examined the hypothesis that regional myocardial inotropic and metabolic responses to alpha-adrenergic stimulation would be diminished due to decreased alpha-adrenoceptor number. After systemic beta-adrenergic blockade, phenylephrine (PE, 5 micrograms.kg-1.min-1) was infused into the left anterior descending artery in eight LVH and nine control open-chest anesthetized dogs. The circumflex region served as control. In both regions, local segment work was calculated as the integrated products of force (miniature transducer) and segment shortening (ultrasonic crystals). Local myocardial O2 consumption was calculated from regional blood flow (microspheres) and O2 saturation (microspectrophotometry). A saturation radioligand binding assay was used to determine adrenoceptor number and affinity. In control animals in the treated region, PE increased work from 815 +/- 140 to 1,493 +/- 149 g.mm.min-1. In LVH, work was not significantly altered (688 +/- 142 vs. 730 +/- 149 g.mm.min-1). Regional blood flow was elevated in controls (81 +/- 10 to 141 +/- 24 ml.min-1.100 g-1) but was not changed in LVH (105 +/- 12 vs. 123 +/- 18 ml.min-1.100 g-1). In controls, but not in LVH, myocardial O2 consumption was almost doubled during PE infusion (6.2 +/- 0.9 vs. 12.0 +/- 2.1 ml O2.min-1.100 g-1). alpha-Adrenoceptor number and dissociation constants values were not different between control and LVH (15.7 +/- 2.8 vs. 16.4 +/- 2.7 fmol/mg protein; 13.2 +/- 3.4 vs. 16.9 +/- 4.3 nm, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)
An ultrasonic system for measurement of absolute myocardial thickness using a single transducer
Authors: Pitsillides K. F. , Longhurst J. C.
Published: December 2017

We have developed an ultrasonic instrument that can measure absolute regional myocardial wall motion throughout the cardiac cycle using a single epicardial piezoelectric transducer. The methods in place currently that utilize ultrasound to measure myocardial wall thickness are the transit-time sonomicrometer (TTS) and, more recently, the Doppler echo displacement method. Both methods have inherent disadvantages. To address the need for an instrument that can measure absolute dimensions of myocardial wall at any depth, an ultrasonic single-crystal sonomicrometer (SCS) system was developed. This system can identify and track the boundary of the endocardial muscle-blood interface. With this instrument, it is possible to obtain, from a single epicardial transducer, measurement of myocardial wall motion that is calibrated in absolute dimensional units. The operating principles of the proposed myocardial dimension measurement system are as follows. A short duration ultrasonic burst having a frequency of 10 MHz is transmitted from the piezoelectric transducer. Reflected echoes are sampled at two distinct time intervals to generate reference and interface sample volumes. During steady state, the two sample volumes are adjusted so that the reference volume remains entirely within the myocardium, whereas half of the interface sampled volume is located within the myocardium. After amplification and filtering, the true root mean square values of both signals are compared and an error signal is generated. A closed-loop circuit uses the integrated error signal to continuously adjust the position of the two sample volumes. We have compared our system in vitro against a known signal and in vivo against the two-crystal TTS system during control, suppression (ischemia), and enhancement (isoproterenol) of myocardial function. Results were obtained in vitro for accuracy (> 99%), signal linearity (r = 0.99), and frequency response to heart rates > 450 beats/min, and in vivo data were acquired for end-systolic dimension (r = 0.99), end-diastolic dimension (r = 0.99), and percent wall thickness (r = 0.99). Both in vitro and in vivo tests indicate that the SCS functions identically to the two-crystal TTS. Use of the SCS allows measurement of absolute wall thickness and hence myocardial function, for both acute and chronically instrumented animal studies, with minimal or no trauma to myocardium.
Effects of glycogen depletion on ischemic injury in isolated rat hearts: insights into preconditioning
Authors: Schaefer S. , Carr L. J. , Prussel E. , Ramasamy R.
Published: December 2017

Limitation of myocardial injury and infarction has been demonstrated by interventions such as ischemic preconditioning or the use of pyruvate as a substrate, which reduces glycogen content before, and acidosis during, ischemia. An isolated perfused rat heart model of global ischemia was employed to test the hypothesis that glycogen depletion reduces ischemic injury as measured by creatine kinase release. 31P-nuclear magnetic resonance spectroscopy was used to measure high-energy phosphates (ATP and phosphocreatine), phosphomonoesters (PME), and intracellular pH. Compared with control glucose-perfused hearts with normal glycogen content (1.49 +/- 0.13 mg Glc/g wet wt), glycogen-depleted pyruvate, ischemic preconditioned, and glycogen-depleted glucose hearts all had reduced glycogen content before ischemia (0.62 +/- 0.16, 0.81 +/- 0.10, and 0.67 +/- 0.12 mg Glc/g wet wt, respectively; P = 0.003) and significantly higher pH at the end of ischemia (5.85 +/- 0.02, 6.33 +/- 0.06, 6.24 +/- 0.04, and 6.12 +/- 0.02 in control, glycogen-depleted pyruvate, preconditioned, and glycogen-depleted glucose-perfused hearts, respectively; P < 0.01), although acidification during the initial phase of ischemia was differentially affected by the three interventions. Glycogen-depleted pyruvate and preconditioned hearts had reduced PME accumulation, greater recovery of function and phosphocreatine, and lower creatine kinase release on reperfusion, whereas glycogen-depleted glucose-perfused hearts were similar to control hearts. In summary, glycogen depletion by these three methods limits the fall in pH during global ischemia, although glycogen depletion in the absence of preconditioning does not limit ischemic injury.(ABSTRACT TRUNCATED AT 250 WORDS)
Viscoelastic properties of cross bridges in cardiac muscle
Authors: De Winkel M. E. , Blange T. , Treijtel B. W.
Published: December 2017

Tension responses of rat right ventricular trabeculae to fast length changes are measured with microsecond resolution to obtain information about elastic properties of ventricular myocardium. Responses of these isometrically mounted trabeculae at 22 degrees C to fast length changes completed within 30 microseconds at 22 degrees C to fast length changes completed within 30 microseconds were similar in shape to those of skeletal muscle fibers. Results of quantitative evaluation of responses are interpreted in terms of cross-bridge properties. An upper bound for the elastic range of cross bridges in trabeculae, derived from the maximal developed force during Ca2+ activation and from stiffness in rigor, has been estimated as 8.4 +/- 2.2 nm. Their working stroke, estimated from the tension loss in the rigor state due to a shortening and from tension remaining after (partial) recovery, was 20 +/- 4 nm. The estimated working stroke of cross bridges is about three times larger in trabeculae than in freeze-dried skeletal muscle fibers of the frog at 4 degrees C, which points to important differences between cross-bridge mechanisms of contraction in cardiac and skeletal muscle.
Sites of inhaled NO-induced vasodilation during hypoxia and U-46619 infusion in isolated lamb lungs
Authors: Tod M. L. , O'Donnel D. C. , Gordon J. B.
Published: December 2017

The sites of relaxation in response to inhaled nitric oxide (NO) were investigated using the vascular occlusion technique in isolated blood-perfused lungs from 1- to 3-mo-old lambs. In one group of 10 lungs, inhaled NO (45 ppm) was administered during hypoxia- and U-46619-induced pulmonary vasoconstriction. In a second group of 5 lungs, responses to inhaled NO and infused sodium nitroprusside (SNP, 3 micrograms.kg-1.min-1) during U-46619-induced hypertension were compared. Hypoxia caused significant pulmonary vasoconstriction, with increases in the pressure gradients of large and small arteries and small veins, as defined by vascular occlusion. Inhaled NO significantly reduced the total pulmonary pressure gradient by 67% and relaxed both large and small arteries. Infusion of U-46619 caused significant increases in all segmental pressure gradients. While inhaled NO was effective in relaxing the large and small arteries and the small veins, it had no effect on the large veins. Infusions of SNP, a nitrosovasodilator thought to act like endogenous NO, caused a similar degree of total relaxation as NO (81 vs. 77%, respectively). However, in contrast to inhaled NO, SNP was effective in reducing the pressure gradient of the large pulmonary veins. These results suggest that rapid binding to and thus inactivation of inhaled NO by hemoglobin limit its efficacy as a pulmonary venous dilator.
Exercise training alters aortic vascular reactivity in hypothyroid rats
Authors: Delp M. D. , McAllister R. M. , Laughlin M. H.
Published: December 2017

Hypothyroidism induces a number of cardiovascular adaptations in rats, including decreases in blood flow to high-oxidative skeletal muscle and increases in total peripheral resistance. Conversely, exercise training results in elevations in blood flow to high-oxidative skeletal muscle and decreases in vascular resistance. The purpose of this study was to determine whether hypothyroidism induces changes in the vasomotor responses of arterial vessels and whether exercise training modifies these responses. Rats were divided into three groups, sedentary euthyroid (S-Eut), sedentary hypothyroid (S-Hypo), and exercise-trained hypothyroid (ET-Hypo). Responses to vasoactive compounds were examined in vitro using abdominal aortic rings. Maximal isometric contractile tension (g/mm2) evoked by KCl and norepinephrine (NE) were not different among groups. However, sensitivity to KCl [agonist concentration producing 50% of maximal vasoconstrictor response (EC50; in mM): S-Eut, 21.1 +/- 1.1; S-Hypo, 35.7 +/- 2.7; ET-Hypo, 43.8 +/- 2.0] and to NE [EC50 (in M): S-Eut, 4.0 x 10(-8) +/- 2.3 x 10(-8); S-Hypo, 8.3 x 10(-8) +/- 3.4 x 10(-8); ET-Hypo, 3.6 x 10(-7) +/- 1.1 x 10(-7)] was different among groups, and in the order S-Eut > S-Hypo > ET-Hypo. Maximal vasodilator responses induced by acetylcholine (10(-7) M NE preconstriction) were lower in rings from S-Hypo animals than those from S-Eut and ET-Hypo rats. Dilatory responses induced by sodium nitroprusside (SNP) with the same NE preconstriction were not different among groups. However, with a 10(-4) M NE preconstriction, maximal dilatory responses induced by SNP were lower in vessels from hypothyroid animals. Dilatory responses to forskolin (10(-4) M NE preconstriction) were not different among groups.(ABSTRACT TRUNCATED AT 250 WORDS)
Disruption of cGMP production in pulmonary arteries isolated from fetal lambs with pulmonary hypertension
Authors: Steinhorn R. H. , Russell J. A. , Morin F. C.
Published: December 2017

Ligation of the ductus arteriosus of the fetal sheep produces severe pulmonary hypertension at birth. Standard tissue bath techniques were used to study third- and fourth-generation pulmonary arteries and veins isolated from fetal sheep with pulmonary hypertension created by ligation of the ductus arteriosus 11–12 days before birth as well as from age-matched control sheep. Vessels pretreated with indomethacin and propranolol were submaximally preconstricted with norepinephrine before exposure to A-23187 (10(-8) to 3 x 10(-7) M), sodium nitroprusside (SNP; 10(-9) to 10(-5) M), and nitric oxide (NO) gas (1-973 ppm). Pulmonary veins in both control and ligated animals relaxed similarly and completely to A-23187, SNP, and NO. Control pulmonary arteries relaxed by 16 +/- 2% to A-23187 and relaxed completely to SNP and NO, with concentration-response curves shifted rightward of those observed in pulmonary veins. Pulmonary arteries from ligated animals did not relax at all to A-23187. SNP relaxations in ligated arteries were shifted rightward of control. Ligated arteries relaxed by only 11 +/- 5% to the highest dose of NO. However, control and ligated pulmonary arteries relaxed similarly to 8-bromoguanosine 3',5'-cyclic monophosphate (8-bromo-cGMP; 10(-5) to 10(-3) M) and atrial natriuretic peptide (10(-9) to 10(-7) M). These data are most simply explained by decreased arterial vascular smooth muscle sensitivity to NO at the level of soluble guanylate cyclase.
Evaluation of methods for estimation of total arterial compliance
Authors: Stergiopulos N. , Meister J. J. , Westerhof N.
Published: December 2017

Seven classic and recently proposed methods used for the estimation of total arterial compliance have been evaluated for their accuracy and applicability in different physiological conditions. The pressure and flow data are taken from a computer model that provides realistic simulations of the nonlinear-distributed systemic arterial tree. Besides the great flexibility in simulating different physiological or pathological cases, the major advantage of the computer model is that it allows precise knowledge of the pressure-dependent total arterial compliance, which is the variable of interest. The results show that the methods based on the two-element windkessel (WK) model are more accurate than those based on the three-element WK model. The classic exponential decay and the diastolic area method yield essentially similar results, and their compliance estimates are accurate within 10% except at high heart rates. The later part of diastole, i.e., from the time that the systolic pressure wave has reached all peripheral beds, gives the best results. The newly proposed two-area and pulse pressure methods, both based on the two-element WK model, are accurate (errors in general < 10%) and can be applied to other locations in the arterial tree where the decay time and area method cannot. Methods based on the three-element WK model consistently overestimate total arterial compliance (> or = 25%). The errors in the methods based on the three-element WK model arise from the fact that the input impedance in that model deviates significantly from the true input impedance at low frequencies. The strong dependence of compliance on pressure (elastic nonlinearity) does not invalidate the compliance estimates.(ABSTRACT TRUNCATED AT 250 WORDS)
Method for isolation of human ventricular myocytes from single endocardial and epicardial biopsies
Authors: Peeters G. A. , Sanguinetti M. C. , Eki Y. , Konarzewska H. , Renlund D. G. , Karwande S. V. , Barry W. H.
Published: December 2017

The study of adult human ventricular cells has been limited by tissue availability. In this study we describe techniques for the isolation of Ca(2+)-tolerant adult human ventricular cells from both transvenous endomyocardial and epicardial biopsies. Ca(2+)-tolerant cells were obtained from 80% of the biopsies processed. Although the yield of Ca(2+)-tolerant myocytes from either type of biopsy was low (1–5%), myocytes with normal resting potentials and action potentials can be obtained from single biopsy specimens, providing a source of normal human myocytes for electrophysiological study. Resting potentials (Vrest) were recorded in 41 isolated right ventricular endomyocardial cells at 37 degrees C. Sixteen cells were depolarized (Vrest = -26 +/- 13 mV), and 25 cells had normal resting potentials (Vrest = -84 +/- 6 mV). Action potentials were recorded in 16 cells. At a pacing cycle length of 1 s, 4 cells had prolonged action potential duration at 90% (APD90, 718 +/- 26 ms) and 10 cells had normal APD90 (381 +/- 94 ms) compared with those recorded from intact right ventricular septal trabeculae from explanted hearts. Voltage-clamp studies of isolated human ventricular myocytes obtained from these biopsies document the presence of currents previously reported from cells isolated from explanted hearts.
Calcium- and sodium-dependent modulation of stretch-induced arrhythmias in isolated canine ventricles
Authors: Hansen D. E. , Stacy G. P. , Taylor L. K. , Jobe R. L. , Wang Z. , Denton P. K. , Alexander J.
Published: December 2017

Gadolinium-sensitive stretch-activated channels have been implicated in the process of mechanotransduction signaling of ventricular myocardium. Such channels nonspecifically transport Na+ and Ca2+ in the inward direction. We tested the hypothesis that Na+ and Ca2+ influx are important in the genesis of stretch-induced arrhythmias (SIAs) in an isolated, blood-perfused canine ventricle. To elicit SIAs, left ventricular volume was transiently increased in early diastole using a computerized servo-pump system. Monophasic action potential recordings revealed stretch-induced depolarizations (SIDs) that preceded the arrhythmias. In five ventricles, raising the perfusate Ca2+ concentration from 1 to 3 mM increased ventricular sensitivity to SIAs, manifested by a decrease in the volume change required to precipitate an arrhythmia 50% of the time (delta V50) from 19.5 +/- 2.7 to 15.2 +/- 1.9 ml (P < 0.05). When the perfusate Na+ concentration was decreased from 150 to 90 mM in seven ventricles, delta V50 greatly increased (31.1 +/- 14.4 vs. 17.7 +/- 5.3 ml, P < 0.05), and SID amplitude decreased by 47% (P = 0.002). The suppression of SIAs with low extracellular Na+ is unlikely to be mediated by voltage-gated Na+ channels because lidocaine (5 mg/dl) did not alter SID amplitude. Thus the transsarcolemmal Na+ gradient (and probably that of Ca2+) modulates the amplitude of SIDs, which, in turn, initiate SIAs. These data provide initial evidence that Na+ and Ca2+ help mediate the mechanotransduction processes that underly the genesis of SIAs.
Adenosine-induced vasodilation: receptor characterization in pulmonary circulation
Authors: Haynes J. , Obiako B. , Thompson W. J. , Downey J.
Published: December 2017

Adenosine mediates vascular smooth muscle relaxation in the pulmonary circulation. The A2 receptor has been suggested to mediate adenosine-induced vasodilation (AIV). In this study, the effect(s) of selective adenosine agonist and antagonist on the hypoxic pressor response (HPR) was assessed in the isolated blood-perfused rat lung. Adenosine (0.075-7.5 mM) infusion (0.125 ml/min) into the pulmonary artery dose dependently attenuated the HPR. AIV was mimicked by 10 microM 5'-(N-ethylcarboxamido)adenosine (NECA), a nonselective adenosine agonist. Adenosine- and NECA-induced vasodilation were attenuated by 67 microM 8-(p-sulfophenyl)theophylline. In contrast, NECA-induced vasodilation was not attenuated by the A1 antagonist 8-cyclopentyl-1,3-dipropylxanthine (1 microM). At 10 microM, a minimal vasodilatory effect was seen with the nonselective adenosine agonists CV-1808 and N6-(2-phenylisopropyl)adenosine (R-PIA) compared with NECA. The highly selective A2a agonist 2-[p-(2-carboxyethyl)phenyl amino]-5'-N-ethyl carboxamido adenosine (CGS-21680C, 10 microM) and A1 agonist 2-chloro-N6-cyclopentyladenosine (CCPA, 10 microM) had no vasodilatory effect. Neither the K+ channel blockers tetraethylammonium chloride (10 mM) and glibenclamide (100 microM) nor the NO synthase inhibitor N omega-nitro-L-arginine methyl ester attenuated NECA-induced vasodilation. These findings suggest that AIV is mediated via the A2b receptor and that AIV occurs via an NO-independent mechanism.
Adult cardiomyocytes express functional high-affinity receptors for basic fibroblast growth factor
Authors: Liu L. , Pasumarthi K. B. , Padua R. R. , Massaeli H. , Fandrich R. R. , Pierce G. N. , Cattini P. A. , Kardami E.
Published: December 2017

As a first step in addressing the question of function for basic fibroblast growth factor (bFGF) in the adult myocardium, expression of bFGF receptors by adult rat myocytes was investigated. Cross-linking of 125I-labeled bFGF to purified sarcolemmal vesicles from adult hearts indicated specific binding to 90- to 104-kDa proteins, whereas equilibrium binding studies revealed the presence of "low"-affinity (1 nM) and "high"-affinity (115 pM) sites. Adult myocytes were found to express short and long variants of bFGF receptor 1 (FGFR-1, tyrosine kinase) mRNA. Adult heart overall levels of FGFR-1 mRNA were decreased by about one-third of corresponding fetal values. Several lines of evidence indicated that bFGF receptors in adult cardiomyocytes in situ and/or in isolation are functional. Isolated adult myocytes were found to be capable of heparin-resistant internalization of 125I-labeled bFGF, to lose their viability after interaction with bFGF-saporin (a mitotoxin known to kill cells after entry via the bFGF receptor), and to respond to bFGF by activation of mitogen-activated protein kinase. In addition, introduction of exogenous bFGF into the myocardium by Langendorff perfusion resulted in stimulation of tyrosine phosphorylation in association with cardiomyocyte intercalated disks, as assessed by immunofluorescence. It is concluded that adult cardiomyocytes express functionally coupled high-affinity bFGF receptors and that they are capable of a biologic response to bFGF in vivo.
Whole cell membrane currents in cultured pig endocardial endothelial cells
Authors: Fransen P. F. , Demolder M. J. , Brutsaert D. L.
Published: December 2017

The whole cell mode of the patch-clamp technique was applied to cultured endocardial endothelial cells from the porcine right ventricle to study their electrophysiological properties. With isotonic pipette and bathing solutions (300-310 mosmol/kgH2O), single endocardial endothelial cells had resting membrane potentials ranging from -20 to -90 mV (mean = -55 +/- 20 mV, n = 48). In voltage-clamp experiments, the main membrane current was an inwardly rectifying K+ current with all characteristics described for the inwardly rectifying K+ current in vascular endothelium. Outward currents at positive clamp potentials were small, but when cell swelling was induced by means of a hypertonic pipette or hypotonic bathing solution and ATP (5 mM) was present in the pipette solution, a large outwardly rectifying current developed. This volume-activated current was insensitive to extracellular K+ or Na+ concentration variations but sensitive to changes in extracellular Cl- concentrations. It was inhibited in the presence of 4,4'-diisothiocyanostilbene-2,2 disulfonic acid (100-300 microM) and flufenamic acid (50-100 microM). Volume-activated Cl- channels are different from the stretch-activated cationic channels described in vascular endothelium and might be involved in the regulation of cell volume or the response to mechanical stretch.
Neutrophil lipoxygenase activation and leukosequestration in postischemic myocutaneous flaps: role of LTB4
Authors: Kirschner R. E. , Chiao J. J. , Fyfe B. S. , Hoffman L. A. , Davis J. M. , Fantini G. A.
Published: December 2017

Reperfusion of ischemic tissues leads to eicosanoid- and polymorphonuclear leukocyte (PMN)-dependent injury. The present experiments were undertaken to examine the effect of myocutaneous flap ischemia-reperfusion on neutrophil 5-lipoxygenase activity and to define the role of leukotriene B4 (LTB4) in postischemic PMN infiltration into such composite tissue grafts. Anesthetized Yorkshire pigs underwent 6 h of rectus abdominis myocutaneous flap ischemia or sham ischemia, and LTB4 generation was measured in calcium ionophore-stimulated neutrophils isolated from the circulation. At 30 min of reperfusion, neutrophil generation of LTB4 increased from a baseline value of 31.0 +/- 6.8 to 98.5 +/- 5.1 ng/5 x 10(6) PMN (P < 0.01) and was significantly greater than those neutrophils isolated from animals subjected to sham ischemia and reperfusion (54.3 +/- 4.1 ng/5 x 10(6) PMN; P < 0.01). Pretreatment of animals with the LTB4-receptor antagonist, SC-41930 (n = 5), significantly attenuated reperfusion-associated 5-lipoxygenase activation (60.3 +/- 11.6 ng LTB4/5 x 10(6) PMN; P < 0.01), suggesting the presence of a positive feedback mechanism for eicosanoid biosynthesis.(ABSTRACT TRUNCATED AT 250 WORDS)
Endothelial-dependent vasodilation is preserved in non-insulin-dependent Zucker fatty diabetic rats
Authors: Bohlen H. G. , Lash J. M.
Published: December 2017

Alterations in the structural properties of the microvasculature and in vasodilation mediated by endothelial- and, to some extent, nonendothelial-dependent mechanisms occurs in insulin-dependent diabetic humans and animals. Less severe problems of this type appear to occur during non-insulin-dependent diabetes mellitus (NIDDM) in humans, but data based on animal models of NIDDM are not available. The endothelial- and nonendothelial-mediated dilation of intestinal arterioles was studied in insulin-resistant male Zucker fatty diabetic (DB) rats and their lean normal male littermates (LM) at ages 22-25 and 35-40 wk. DB become hyperglycemic (450-550 mg/100 ml) at age 9-10 wk. Microiontophoretic release of acetylcholine, ADP, and nitroprusside onto arterioles caused equivalent dilation in LM and DB for both large and intermediate diameter arterioles. Administration of streptozotocin (STZ) to DB at age 18-19 wk lowered their insulin concentration approximately 25% but did not significantly effect the resting plasma glucose concentration. However, endothelial-dependent vasodilation was attenuated by 70-80% within 8-10 wk. The overall results indicate that prolonged hyperglycemia in insulin-resistant but hyperinsulinemic rats does not impair the endothelial- and nonendothelial-dependent dilation of the intestinal microvasculature. However, compromising beta-cell function with STZ, as indicated by lowering the insulin concentration by one-fourth, substantially compromises endothelial-dependent dilation similar to that found in insulin-dependent diabetic rats and humans.
A method to assess endocardial regional longitudinal curvature of the left ventricle
Authors: DeAnda A. , Moon M. R. , Nikolic S. D. , Castro L. J. , Fann J. I. , Daughters G. T. , Ingels N. B. , Miller D. C.
Published: December 2017

Knowledge of the instantaneous geometry of the left ventricular (LV) chamber is necessary to calculate LV function and wall stresses. We describe a method utilizing myocardial markers that does not rely on any a priori assumptions of global LV geometry. Five dogs underwent placement of 25 endocardial and 3 epicardial miniature LV markers. Six weeks later, the animals were studied during conscious closed-chest conditions. The three-dimensional coordinates of the LV markers were used to compute longitudinal fitted curves for LV walls and septum during steady-state conditions; endocardial radii of curvature (rcurv) were then computed for each region at the midequatorial (rcurv-eq) and apical levels. There was a uniform decrease in rcurv in each LV wall during systole (compared with diastole, P < 0.01); at end systole, rcurv was regionally heterogeneous between opposing walls, e.g., anterior and posterior rcurv-eq values were 17.2 +/- 2.0 and 17.7 +/- 1.8 (SD) cm, respectively (P < 0.05). At end diastole, only septal-lateral rcurv-eq was different (16.9 +/- 2.1 vs. 18.7 +/- 1.3 cm: P < 0.05). Normalization of rcurv (to instantaneous LV volume) removed the systolic-diastolic differences, but a similar pattern of regional heterogeneity persisted. The data presented pertain to the LV endocardial surface, but the method described can be applied to the epicardial surface as well; this new method offers promise in assessing dynamic changes in longitudinal LV endocardial curvature.
Lack of a role of adenosine in activation of ischemically sensitive cardiac sympathetic afferents
Authors: Pan H. L. , Longhurst J. C.
Published: December 2017

Adenosine has been implicated in the pathogenesis of cardiac pain through activation of cardiac sympathetic afferents. The present study was performed to assess directly the contribution of adenosine in activating ischemically sensitive cardiac sympathetic afferents. Single-unit activity of ischemically sensitive afferents located in both ventricles was recorded from the left thoracic sympathetic chain or rami communicantes of anesthetized cats during 5 min of myocardial ischemia. Intracardiac injection (5 mg) or epicardial application (1–5 mg/ml) of adenosine onto the receptive fields failed to activate 31 ischemically sensitive A delta- and C fiber afferents, which were responsive to topical application of bradykinin (10 micrograms/ml). Intracardiac injection (5 mg) or topical application (1–5 mg/ml) of an adenosine A1 receptor agonist, N6-cyclopentyladenosine, also did not increase the discharge activity of 13 other ischemically sensitive C fiber afferents. Treatment with dipyridamole (1 mg/kg iv) to inhibit the cellular uptake of adenosine did not significantly potentiate the response of 10 separate C fiber afferents to 5 min of myocardial ischemia. Furthermore, blockade of adenosine receptors with aminophylline (5 mg/kg iv) did not significantly attenuate the response of 10 other C fiber afferents to 5 min of myocardial ischemia. The results of the present study demonstrate that exogenous and endogenous adenosine do not contribute to activation of ischemically sensitive cardiac sympathetic afferents. The findings of the present study fail to support a substantial role for adenosine and its A1 receptors in activation of cardiac sympathetic afferents during myocardial ischemia.
Effects of renal denervation on cardiovascular response to furosemide in conscious lambs
Authors: Smith F. G. , Strack A. M.
Published: December 2017

The cardiovascular response to furosemide in the newborn and the role of renal sympathetic nerves in influencing this response have not been investigated. We hypothesized that in conscious lambs, furosemide would decrease blood pressure, the response being accentuated in the absence of renal sympathetic nerves. Pulsatile pressures and heart rates were measured before and after furosemide (2 mg/kg) administration to chronically instrumented lambs with either bilateral renal denervation (denervated, n = 8) or renal nerves intact (intact, n = 6). In intact lambs, mean arterial pressure remained constant after furosemide; in denervated lambs there was an increase in arterial pressure 20 min after furosemide (P < 0.001), and control levels were reached by 100 min. Basal heart rate was higher in denervated than in intact lambs (P = 0.009). In both groups of lambs, heart rate increased 40 min after furosemide and remained elevated. These data provide new information that, in conscious newborn animals, renal sympathetic nerves influence the blood pressure response to furosemide, as well as basal control of heart rate.
Cardiac responses to induced lactate oxidation: NMR analysis of metabolic equilibria
Authors: Lewandowski E. D. , Damico L. A. , White L. T. , Yu X.
Published: December 2017

The role of lactate as a source of pyruvate oxidation in supporting cardiac work, energetics, and formation of oxidative metabolites was examined in normal myocardium. 13C- and 31P-nuclear magnetic resonance (NMR) spectra were acquired from isolated rabbit hearts supplied 2.5 mM [3-13C]lactate or [3-13C]pyruvate with or without stimulation of pyruvate dehydrogenase (PDH) by dichloroacetate (DCA). Similar workloads determined by rate-pressure products were noted with pyruvate (21,700 +/- 2,400; mean +/- SE) and lactate (18,970 +/- 1,510). Oxygen consumption was similar in all four groups with means between 19.0 and 22.2 mumol.min-1.g dry weight-1 (SE = 1.6-2.0) as was the ratio of phosphocreatine to ATP with means between 1.8 and 2.1 (SE = 0.1-0.6). Intracellular pH, determined from 31P-NMR spectra, was essentially the same with pyruvate (7.06 +/- 0.02) and lactate (7.05 +/- 0.04). 13C enrichment of glutamate was higher with lactate (92%) than with pyruvate (70%). Pyruvate plus DCA induced no change in glutamate content at 9-10 mumol/g, but 13C enrichment increased to 83%, while lactate plus DCA maintained enrichment at 90%. Levels of alpha-ketoglutarate were lower with lactate (1.81 mumol/g) than with pyruvate (2.36 mumol/g). Lactate plus DCA elevated glutamate by 60% with a proportional increase in alpha-ketoglutarate. Thus the balance between glutamate and alpha-ketoglutarate was affected by substrate supply only and not by PDH activation. The results suggest that the equilibrium between alpha-ketoglutarate and glutamate is sensitive to cytosolic redox state, an important consideration for 13C-NMR analyses that rely on glutamate.(ABSTRACT TRUNCATED AT 250 WORDS)
Dissociation of endothelial cell dysfunction and blood pressure in SHR
Authors: Tesfamariam B. , Ogletree M. L.
Published: December 2017

This study was designed to examine the impairment of endothelium-dependent relaxation in spontaneously hypertensive rats (SHR), to determine whether endothelial cell function is normalized by in vivo treatment with a thromboxane A2-prostaglandin endoperoxide (TP)-receptor blocker, and to establish whether endothelial dysfunction contributes to the elevated blood pressure. In isolated aortic rings from SHR, endothelium-dependent relaxations caused by acetylcholine, adenosine diphosphate, and alpha-thrombin were markedly impaired compared with those from Wistar-Kyoto (WKY) normotensive rats. Arachidonic acid-induced contractions were significantly enhanced in aorta from SHR. In contrast, relaxations caused by direct smooth muscle vasodilators, nitroprusside and cromakalim, and contractions caused by U-46619 were not different between SHR and WKY rats. Treatment of SHR with the oral TP-receptor antagonist, ifetroban, at 20 and 50 mg.kg-1.day-1 fully restored endothelium-dependent relaxation toward normal. However, ifetroban produced no effect on blood pressure in SHR. In vitro incubation of aortic rings from SHR with ifetroban also normalized relaxations to acetylcholine but had no effect in aorta from WKY. In contrast, the thromboxane A synthase inhibitor, dazoxiben, only partially improved abnormal acetylcholine-induced relaxations in aorta from SHR. The results demonstrate that endothelial cell dysfunction in hypertension can be restored to normal by selective TP-receptor blockade. Furthermore, endothelial cell dysfunction and TP-receptor activation may not significantly contribute to elevated systemic blood pressure in SHR.
In vivo production of nitric oxide correlates with NMDA-induced cerebral hyperemia in newborn sheep
Authors: Northington F. J. , Tobin J. R. , Koehler R. C. , Traystman R. J.
Published: December 2017

Stimulation of N-methyl-D-aspartate (NMDA) receptors in brain increases nitric oxide production in vitro. We tested the hypothesis that nitric oxide participates in the increase in local cerebral blood flow (CBF) caused by infusion of NMDA in anesthetized newborn sheep. We used the combined hydrogen clearance and microdialysis technique for simultaneous measurement of local CBF, infusion of drugs, and measurement of interstitial levels of L-[14C]citrulline in the parietal cortex. Release of L-[14C]citrulline into the dialysate during continuous infusion of L-[14C]arginine was used as a marker of nitric oxide production in vivo. Citrulline recovery and CBF were measured hourly during a 4-h infusion of cerebrospinal fluid containing either 1) no additional drugs, 2) 1 mM NMDA, 3) 1 mM NG-nitro-L-arginine methyl ester (L-NAME, a nitric oxide synthase inhibitor), 4) 1 mM NMDA + 1 mM L-NAME, 5) 0.1 mM 2-chloroadenosine (adenosine receptor agonist), or 6) 0.1 mM 2-chloroadenosine + 1 mM L-NAME. At 240 min of perfusion, CBF (ml.min-1.100 g-1; means +/- SE) was as follows: control 52 +/- 3, NMDA 116 +/- 11, L-NAME 32 +/- 5, NMDA+L-NAME 40 +/- 4,2-chloroadenosine 201 +/- 63, and 2-chloroadenosine+L-NAME 129 +/- 18. Citrulline recovery (fmol/min) at 240 min of perfusion was as follows: control 38 +/- 12, NMDA 149 +/- 21, L-NAME 9 +/- 1, NMDA+L-NAME 39 +/- 5, 2-chloroadenosine 13 +/- 5, and 2-chloroadenosine+L-NAME 17 +/- 1.(ABSTRACT TRUNCATED AT 250 WORDS)
Noninvasive measurements of albumin flux into lung interstitium with increased microvascular pressure
Authors: Abernathy V. J. , Pou N. A. , Wilson T. L. , Roselli R. J.
Published: December 2017

The purpose of this study was to determine the effect of increasing left atrial pressure on noninvasive measurements of radiolabeled albumin normalized slope index (NSI). Using portable gamma scintillation detectors, we monitored radioactivities of 131I-labeled albumin and 51Cr-labeled red blood cells in the blood and over the lung of six anesthetized sheep before and 2 h after a 9- to 14-Torr increase in left atrial pressure. Measurements of NSI for 131I-albumin decreased > 50% after a step increase in left atrial pressure. We interpreted the data using a model that has been used to successfully describe unsteady-state lymph flow and protein concentrations after vascular pressure increases in sheep. Model predictions strongly suggest that the reduction in NSI is due to rapid fluid and solute removal from the interstitium via the lymphatics. The theoretical model was able to predict external scan data and lung lymph protein concentrations only when a change in lymphatic conductance (LI) or initial lymphatic pressure (P0) was imposed at the time of increased pressure. On average, model-predicted increases in LI were sevenfold, whereas predicted decreases in P0 were four- to fivefold. Imposed changes in LI and P0 opposed increases in interstitial fluid volume after increased pressure. This was consistent with normal-to-low postmortem measurements of bloodless wet-to-dry lung weight ratios. In summary, these results indicate that changes in the rate of fluid removal from the interstitium can significantly alter NSI, and in this case, NSI does not reflect pulmonary microvascular permeability. In sheep, increases in the lymphatics' ability to remove interstitial fluid may occur with relatively small increases in microvascular pressure.