bluuebunny/crossref_metadata_2025 huggingface dataset:
L-NNA suppresses cerebrovascular response and evoked potentials during somatosensory stimulation in rats
Authors: Ngai A. C. , Meno J. R. , Winn H. R.
Published: December 2017

We studied the local cerebrovascular response and somatosensory-evoked potentials (SEPs) to stimulation of the sciatic nerve during both short- (< 30 min) and long-term (90-150 min) exposure to topically applied NG-nitro-L-arginine (L-NNA). The pial circulation was visualized through a cranial window in alpha-chloralose-anesthetized rats. The diameter of pial arterioles (25-45 microns) and laser-Doppler flow (LDF) in the hindlimb sensory cortex were simultaneously measured during sciatic nerve stimulation. Short-term (< 30 min) treatment with L-NNA (1 mM) abolished the dilation of pial arterioles induced by acetylcholine, whereas the response to sciatic nerve stimulation was not affected. When applied for > 30 min, L-NNA induced severe vasomotion and attenuated the vascular responses to sciatic nerve stimulation. Long-term exposure to topically (1 mM) or systemically (10 mg/kg i.v.) applied L-NNA also attenuated cortical SEPs to sciatic nerve stimulation. Thus L-NNA-induced inhibition of vascular responses may be secondary to suppression of neuronal activity and an L-arginine metabolite, such as nitric oxide, may be involved in neurotransmission in the cerebral cortex during somatosensory activity.
Local cholinergic mechanisms mediate nitric oxide-dependent flow-induced vasorelaxation in vitro
Authors: Martin C. M. , Beltran-Del-Rio A. , Albrecht A. , Lorenz R. R. , Joyner M. J.
Published: December 2017

To determine whether local cholinergic mechanisms evoke nitric oxide (NO)-mediated flow-induced vasorelaxation, canine coronary artery rings without endothelium were suspended beneath an organ chamber that contained a stainless steel tube and a femoral artery segment with endothelium. The rings were superfused at a basal rate of 1 ml/min with physiological salt solution that was bubbled with 95% O2-5% CO2 and maintained at 37 degrees C. They were stretched to optimal length and contracted with prostaglandin F 2 alpha (2 x 10(-6) M). When flow through the stainless steel tube (direct superfusion) was increased from the basal rate of 1 to 4 ml/min, coronary force did not change. Superfusion of the rings (n = 8) with effluent from the femoral segment (endothelial superfusion) at 4 ml/min to study flow-induced vasodilation caused a 67.3 +/- 10.8% relaxation. Treatment of the segment with the NO synthase blocker NG-monomethyl-L-arginine (10(-4) M) eliminated the relaxation seen during endothelial superfusion (P < 0.05 vs. control). Application of atropine (10(-6) M) to additional femoral segments (n = 8) abolished the coronary relaxation observed during endothelial superfusion at 1 ml/ min, and the flow-induced relaxation observed at 4 ml/min was reduced from 64 +/- 8.3 to 27 +/- 5.6% (P < 0.05 vs. control). In studies on additional segments and rings (n = 6), the flow-induced relaxations at 4 ml/min of endothelial superfusion were blunted from 86 +/- 10 to 28 +/- 13% after the segments were treated with acetylcholinesterase (0.00028 U/min for 20 min). These data indicate that basal- and flow-induced release of NO from the vascular endothelium can be mediated by local cholinergic mechanisms. It is possible that flow causes acetylcholine release from certain endothelial cells, which stimulates NO release from these cells or from neighboring endothelial cells.
Auto- and cross-spectral analysis of cardiovascular fluctuations during pentobarbital anesthesia in the rat
Authors: Yang C. C. , Kuo T. B. , Chan S. H.
Published: December 2017

We applied auto- and cross-spectral analysis of systemic arterial pressure (SAP) and heart rate (HR) signals to quantify the effects of pentobarbital sodium on short-term cardiovascular fluctuations in adult, male Sprague-Dawley rats. Intravenous administration of pentobarbital, delivered as a bolus injection (5, 10, or 20 mg/kg) or continuous infusion (10, 20, or 40 mg.kg-1.h-1), elicited only mild hypotension and tachycardia. This was accompanied by a dose-related depression of the very low (0-0.25 Hz) and low (0.25-0.8 Hz)-frequency components of both SAP and HR signals and high (0.8-2.4 Hz)-frequency component of HR signals. Cross-spectral analysis of SAP and HR signals during intravenous infusion of pentobarbital revealed a maintained coherence in the high-frequency range, together with a gradual and dose-related decrease in magnitude of transfer function and baro-receptor reflex sensitivity. Stable plasma concentration and all hemodynamic parameters were observed during 120 min of infusion at 20 mg.kg-1.h-1. Under this dosing condition, autonomic blockade by phentolamine, propranolol, or atropine still evoked discernible but differential reductions in the SAP and HR spectral components. Our data suggest that continuous intravenous administration of pentobarbital at 20 mg.kg-1.h-1 offers maintained anesthesia while preserving the capacity of cardiovascular regulation.
Inhaled nitric oxide: diameter response patterns in feline small pulmonary arteries and veins
Authors: Shirai M. , Shimouchi A. , Kawaguchi A. T. , Sunagawa K. , Ninomiya I.
Published: December 2017

Using an X-ray television system on the in vivo cat lung, we directly measured internal diameter (ID) changes in the small pulmonary arteries and veins (100-1,100 microns ID) in response to 5, 15, and 40 ppm nitric oxide (NO) inhalations. We also measured to what extent 40 ppm NO inhalation can attenuate large ID constrictions at the different serial segments of the small vessels due to unilobar anoxic (0% O2) exposure. Under normoxic conditions, 5-40 ppm NO inhalations significantly increased the ID of both arteries and veins less than approximately 900 microns dose dependently but caused no significant, or only slight, ID increases in the vessels larger than this, if any at all. The ID increase in the serially connected arteries was nonuniform (4-18, 8-28, and 7-35% with 5, 15, and 40 ppm NO inhalations, respectively), whereas that for the veins was relatively uniform (4-9, 6-17, and 7-18% with 5, 15, and 40 ppm NO, respectively). The maximum ID increase occurred in the 200- to 500- and 200- to 700-microns arteries in response to 5-15 and 40 ppm NO, respectively. Unilobar anoxic exposure significantly decreased the ID of the 100- to 700-microns arteries and veins, but not the ID of the other-sized vessels. The ID decrease in the serially connected arteries was nonuniform (13-29%) but relatively uniform in the veins (8-12%). The maximum ID decrease occurred in the 200- to 300-microns arteries. However, adding 40 ppm NO to the lobe completely eradicated the ID decreases at all segments of the arteries and veins and, instead, caused significant ID increase (11-21%) in the arteries and (10-12%) in the veins. The data indicate that, according to dosage, 5-40 ppm NO inhalations cause selective dilation of approximately 100- to 900-microns pulmonary arteries and veins, particularly the 200- to 700-microns arteries. During anoxic exposure, the vasodilator effect of NO is preserved and can completely reverse the marked pulmonary vasoconstriction.
Differences in myocardial stunning following coronary artery occlusion in conscious dogs, pigs, and baboons
Authors: Shen Y. T. , Vatner S. F.
Published: December 2017

To determine whether myocardial stunning differs among dogs, pigs, and baboons and is reproducible within species, we examined the effects of 10-min coronary artery (CA) occlusion (CAO) on 9 conscious dogs, 12 minipigs, and 6 baboons. During 10-min CAO, systolic wall thickening in the ischemic zone fell similarly in dogs (-108 +/- 5.6%), pigs (-102 +/- 1.8%), and baboons (-107 +/- 5.7%), but blood flow fell more (P < 0.05) in the subepicardium in pigs (0.07 +/- 0.01 ml.min-1.g-1) and baboons (0.07 +/- 0.02 ml.min-1.g-1) than in dogs (0.18 +/- 0.03 ml.min-1.g-1). At 1 h after CA reperfusion (CAR), wall thickening was reduced more (P < 0.05) in dogs (-40 +/- 4.2%) than in pigs (-22 +/- 2.1%) and baboons (-4 +/- 2.4%). In five dogs and five pigs, three separate 10-min CAO, each 2 days apart, were also examined. In dogs, reductions in wall thickening after CAR were significantly less following the second (-26 +/- 4.2%) or third (-30 +/- 3.2%) CAO, compared with the first CAO (-47 +/- 4.9%). In contrast, repetitive CAO did not induce differences in recovery of wall thickening in pigs. These results indicate that myocardial stunning is less severe in conscious pigs and baboons, compared with conscious dogs, despite more intense transmural ischemia. The dogs demonstrated a "preconditioning-like effect" with serial brief CAO, which was not exhibited in pigs.
Deriving respiration from pulse wave: a new signal-processing technique
Authors: De Meersman R. E. , Zion A. S. , Teitelbaum S. , Weir J. P. , Lieberman J. , Downey J.
Published: December 2017

Investigations of autonomic nervous system activity using spectral analysis of heart rate (HR) and blood pressure (BP) variability is very popular in many scientific disciplines, and yet only half of all studies involving spectral analysis control for respiration. Because respiration modulates HR and BP variability, knowledge of the respiratory rate is necessary for the proper interpretation of HR and BP power spectra. We devised and validated a new signal-processing technique to derive respiration from the blood pressure wave. This technique is based on the relationship between oscillations in the area under the dicrotic notch of the pulse wave and respiration. The results of our view signal-processing technique yielded significant correlations between protocols of the actual number of respiratory cycles and our blood pressure-derived respiratory cycles and their respective spectra for a number of standard autonomic tests (P < 0.05). Our method will allow retrospective extraction of the respiratory wave and as such afford a more precise interpretation of HR and BP spectra.
Nitric oxide regulates endothelium-dependent vasodilator responses in rabbit hindquarters vascular bed in vivo
Authors: Cohen G. A. , Hobbs A. J. , Fitch R. M. , Zinner M. J. , Chaudhuri G. , Ignarro L. J.
Published: December 2017

The objective of this study was to determine whether nitric oxide (NO) could function as a negative feedback modulator of endothelium-dependent vasodilation in vivo. To this end, the influence of exogenous NO on vasodilator responses in the rabbit hindquarters vascular bed was determined. Previous in vitro studies have demonstrated that NO inhibits both neuronal NO synthase from rat cerebellum as well as NO synthase derived from bovine aortic endothelial cells. The present study was conducted in the rabbit hindquarters vascular bed under conditions of constant blood flow so that changes in pressure directly reflected changes in vascular resistance. Under these in vivo conditions, the NO donor agent S-nitroso-N-acetylpenicillamine (SNAP) reversibly attenuated responses to the endothelium-dependent vasodilators, acetylcholine and bradykinin. In contrast, SNAP did not influence the endothelium-independent vasodilator response to SNAP itself or to 8-bromoguanosine 3',5'-cyclic monophosphate. These observations indicate clearly that NO interferes with endothelium-dependent vasodilator action and support the view that endogenous NO may actually play a physiological role in regulating vascular tone.
KATP channels in rat heart: blockade of ischemic and acetylcholine-mediated preconditioning by glibenclamide
Authors: Qian Y. Z. , Levasseur J. E. , Yoshida K. , Kukreja R. C.
Published: December 2017

The objective of this study was to examine if the opening of ATP-sensitive K+ (KATP) channels play an important role in ischemic preconditioning (PC) in the rat heart. A second goal was to test the role of acetylcholine (ACh) in mimicking PC and test if it could be blocked by KATP antagonist. Glibenclamide, a specific antagonist of the KATP channel, was given as two doses of 0.3 mg/kg each at 60 and 30 min before PC. Six groups of rats were subjected to ischemia and reperfusion (I/R) using these protocols: 1) control (I/R), 30-min ischemia followed by 90-min reperfusion (n = 6 rats); 2) preconditioned hearts given 5-min ischemia 10 min before I/R (n = 9 rats); 3) glibenclamide (0.3 mg/kg) treatment 60 and 30 min before PC (n = 13 rats); 4) glibenclamide treatment before I/R (n = 15 rats); 5) ACh infusion for 5 min (18 micrograms/ml) at a rate of 0.15 ml/min followed by equilibration for 10 min before I/R, n = 13 rats; and 6) glibenclamide treatment before ACh infusion followed by I/R (n = 11 rats). Preconditioning reduced the infarcted area (expressed as percent area at risk) from 42.0 +/- 4.4% in control to 8.7 +/- 6% (mean +/- SE, P < 0.05). Glibenclamide blocked the protection conferred by PC (39.1 +/- 4.5%, P < 0.05) without having a significant effect on control nonpreconditioned hearts. ACh infusion in lieu of PC also reduced infarct size to 25.0 +/- 5.63% (P < 0.05 compared with control), which was again blocked by glibenclamide (44.2 +/- 5.0%, P < 0.05). The data suggest that opening of KATP channels for ischemic and ACh-mediated preconditioning is also important in the rat heart.
Muscarine-gated K+ channel: subunit stoichiometry and structural domains essential for G protein stimulation
Authors: Tucker S. J. , Pessia M. , Adelman J. P.
Published: December 2017

Coexpression in Xenopus oocytes of the cloned cardiac inward rectifier subunits Kir 3.1 and Kir 3.4 results in G protein-stimulated channel activity closely resembling the muscarinic channel underlying the inwardly rectifying K+ current in atrial myocytes. To determine the stoichiometry and relative subunit positions within the channel, Kir 3.1 and Kir 3.4 were coexpressed in varying ratios with cloned G beta 1 gamma 2 subunits and also as tandemly linked tetramers with different relative subunit positions. The results reveal that the most efficient channel comprises two subunits of each type in an alternating array within the tetramer. To localize regions important for subunit coassembly and G protein sensitivity, chimeric subunits containing domains from either Kir 3.1, Kir 3.4, or the G protein-insensitive subunit Kir 4.1 were expressed. The results demonstrate that the transmembrane domains dictate the potentiation of the coassembled channels and that, although the NH4- or COOH-termini of both subunits alone can confer G protein sensitivity, both termini are required for maximal stimulation by G beta 1 gamma 2.
Phosphatidic acid increases intracellular free Ca2+ and cardiac contractile force
Authors: Xu Y. J. , Panagia V. , Shao Q. , Wang X. , Dhalla N. S.
Published: December 2017

Although phosphatidic acid (PA) is mainly formed due to the hydrolysis of phosphatidylcholine by myocardial phospholipase D, its functional significance in the heart is not fully understood. The present study was designed to determine the effects of PA on intracellular free Ca2+ level ([Ca2+]i) in freshly isolated adult rat cardiomyocytes by using fura 2-acextoxmethylester and free fura 2 technique. Addition of PA at concentrations of 1–200 microM produced a concentration-dependent increase in [Ca2+]i from the basal level of 117 +/- 8 nM; maximal increase in [Ca2+]i was 233 +/- 50 nM, whereas median effective concentration (EC50) for PA was 45 +/- 1.2 microM. This increase in [Ca2+]i was abolished by the removal of extracellular Ca2+ with ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid and was partially attenuated by Ca2+ channel blockers, verapamil or diltiazem. Preincubation of cardiomyocytes with cyclopiazonic acid and thapsigargin or with ryanodine [to deplete sarcoplasmic reticulum (SR) Ca2+] attenuated the PA-induced increase in [Ca2+]i by 66, 37, and 43%, respectively. Furthermore, the response of [Ca2+]i to PA was blunted by 2-nitro-4 carboxyphenylcarbonate, an inhibitor of phospholipase C, but was unaffected by staurosporine, a protein kinase C inhibitor. PA was also observed to induce Ca2+ efflux from the myocytes. In addition, an injection of PA (0.34 microgram/100 g body wt i.v.) in rats produced a significant increase of the left ventricular developed pressure as well as the maximum rates of cardiac contraction and relaxation within 5 min. These data suggest that the PA-induced increase in [Ca2+]i in cardiomyocytes is a consequence of both Ca2+ influx from the extracellular source and Ca2+ release from the intracellular SR stores. Furthermore, these in vitro data suggest the possibility that PA may regulate [Ca2+]i and contractile parameters in the heart.
Age-related differences in beta-adrenergic regulation of repolarization in canine epicardial myocytes
Authors: Charpentier F. , Liu Q. Y. , Rosen M. R. , Robinson R. B.
Published: December 2017

Developmental changes occur in beta-adrenergic modulation of repolarization in canine. Purkinje fibers that may have important implications for rhythm and arrhythmias. No comparable data exist for ventricular myocardium. Therefore, we studied developmental changes in beta-adrenergic regulation of repolarization and delayed rectifier potassium current (IK) in canine ventricular epicardium. We first investigated the effects of isoproterenol (Iso) on action potentials (AP) recorded from epicardial slices with standard microelectrodes, and then we further determined the mechanisms of Iso action using the nystatin-perforated patch technique on isolated epicardial myocytes. In microelectrode studies Iso (10(-7) M) induced a shortening of the AP in preparations from adult dogs but not in those from dogs < 30 days old. These results were confirmed on AP recorded from single myocytes. Although the plateau was increased by Iso at all ages, the AP at 90% of repolarization was shortened (P < 0.05, n = 6) in adult but unchanged in < 30-day-old myocytes (NS, n = 6). Voltage-clamp studies showed that IK of adult cells was increased from a control value of 10.23 +/- 1.87 to 13.43 +/- 1.92 pA/pF with Iso (step to +50 mV, P < 0.05, n = 6), but IK was not modified in cells from young animals (6.49 +/- 2.72 pA/pF in control and 6.56 +/- 2.62 pA/pF with Iso, n = 4). Increasing the Iso concentration to 10(-5) M failed to increase IK significantly (n = 4). However, 10(-7) M Iso did increase L-type Ca2+ current from 172 +/- 31 to 262 +/- 42 pA (P < 0.05, n = 4), consistent with the effect to increase the AP plateau. These results show that there are developmental changes in beta-adrenergic regulation of repolarization in canine epicardium and that the control site of developmental changes is in the IK channel rather than the beta-adrenergic receptor cascade.
Valsalva's maneuver revisited: a quantitative method yielding insights into human autonomic control
Authors: Smith M. L. , Beightol L. A. , Fritsch-Yelle J. M. , Ellenbogen K. A. , Porter T. R. , Eckberg D. L.
Published: December 2017

Seventeen healthy supine subjects performed graded Valsalva maneuvers. In four subjects, transesophageal echographic aortic cross-sectional areas decreased during and increased after straining. During the first seconds of straining, when aortic cross-sectional area was declining and peripheral arterial pressure was rising, peroneal sympathetic muscle neurons were nearly silent. Then, as aortic cross-sectional area and peripheral pressure both declined, sympathetic muscle nerve activity increased, in proportion to the intensity of straining. Poststraining arterial pressure elevations were proportional to preceding increases of sympathetic activity. Sympathetic inhibition after straining persisted much longer than arterial and right atrial pressure elevations. Similarly, R-R intervals changed in parallel with peripheral arterial pressure, until approximately 45 s after the onset of straining, when R-R intervals were greater and arterial pressures were smaller than prestraining levels. Our conclusions are as follows: opposing changes of carotid and aortic baroreceptor inputs reduce sympathetic muscle and increase vagal cardiac motor neuronal firing; parallel changes of barorsensory inputs provoke reciprocal changes of sympathetic and direct changes of vagal firing; and pressure transients lasting only seconds reset arterial pressure-sympathetic and -vagal response relations.
Mechanisms of cerebral vasodilation by superoxide, hydrogen peroxide, and peroxynitrite
Authors: Wei E. P. , Kontos H. A. , Beckman J. S.
Published: December 2017

We investigated the role of potassium channels in the vasodilator action of hydrogen peroxide, peroxynitrite, and superoxide on cerebral arterioles. We studied the effect of topical application of these agents in anesthetized cats equipped with cranial windows. Hydrogen peroxide and peroxynitrite induced dose-dependent dilation that was inhibited by glyburide, an inhibitor of ATP-sensitive potassium channels. Superoxide, generated by xanthine oxidase acting on xanthine in the presence of catalase, also induced dose-dependent dilation of cerebral arterioles that was unaffected by glyburide but inhibited completely by tetraethylammonium chloride, an inhibitor of calcium-activated potassium channels. The vasodilations from hydrogen peroxide, peroxynitrite, or superoxide were unaffected by inhibition of soluble guanylate cyclase with LY-83583. The findings provide pharmacological evidence that hydrogen peroxide and peroxynitrite reversibly dilate cerebral arterioles by activating ATP-sensitive potassium channels, probably through an oxidant mechanism, whereas superoxide dilates cerebral arterioles by opening calcium-activated potassium channels. Activation of soluble guanylate cyclase is not a mediator of the vasodilator action of these agents in cerebral arterioles.
Modeling regional myocardial flows from residue functions of an intravascular indicator
Authors: Kroll K. , Wilke N. , Jerosch-Herold M. , Wang Y. , Zhang Y. , Bache R. J. , Bassingthwaighte J. B.
Published: December 2017

The purpose of the present study was to determine the accuracy and the sources of error in estimating regional myocardial blood flow and vascular volume from experimental residue functions obtained by external imaging of an intravascular indicator. For the analysis, a spatially distributed mathematical model was used that describes transport through a multiple-pathway vascular system. Reliability of the parameter estimates was tested by using sensitivity function analysis and by analyzing “pseudodata”: realistic model solutions to which random noise was added. Increased uncertainty in the estimates of flow in the pseudodata was observed when flow was near maximal physiological values, when dispersion of the vascular input was more than twice the dispersion of the microvascular system for an impulse input, and when the sampling frequency was < 2 samples/s. Estimates of regional blood volume were more reliable than estimates of flow. Failure to account for normal flow heterogeneity caused systematic underestimates of flow. To illustrate the method used for estimating regional flow, magnetic resonance imaging was used to obtain myocardial residue functions after left atrial injections of polylysine-Gd-diethylenetriaminepentaacetic acid, an intravascular contrast agent, in anesthetized chronically instrumental dogs. To test the increase in dispersion of the vascular input after central venous injections, magnetic resonance imaging data obtained in human subjects were compared with left ventricular blood pool curves obtained in dogs. It is concluded that if coronary flow is in the normal range, when the vascular input is a short bolus, and the heart is imaged at least once per cardiac cycle, then regional myocardial blood flow and vascular volume may be reliably estimated by analyzing residue functions of an intravascular indicator, providing a noninvasive approach with potential clinical application.
Cardiac inducible nitric oxide synthase negatively modulates myocardial function in cultured rat myocytes
Authors: Kinugawa K. I. , Kohmoto O. , Yao A. , Serizawa T. , Takahashi T.
Published: December 2017

Recent work has demonstrated that endotoxin or cytokines induce nitric oxide synthase in heart or cardiac myocytes. We investigated the functional significance of inducible nitric oxide synthase (iNOS) in indo 1-loaded beating myocytes with regard to intracellular Ca2+ concentration ([Ca2+]i) and cell contraction. Lipopolysaccharide (LPS; 10 micrograms/ml) time dependently induced iNOS mRNA and protein in cultured neonatal rat cardiac myocytes. Nitrite concentration in the medium and intracellular guanosine 3',5'-cyclic monophosphate (cGMP) contents after 24-h exposure to LPS increased in proportion to the levels of iNOS induction in these cells. Myocytes treated with both NG-monomethyl-L-arginine and LPS for 24 h expressed iNOS protein, but nitrite production was significantly inhibited. Subsequent perfusion with 100-fold molar excess L-arginine of these myocytes elicited decreases in peak systolic [Ca2+]i (790 +/- 42 to 551 +/- 27 nM, P < 0.05), relative amplitude of cell contraction (100 to 72.4 +/- 5.5%, P < 0.05), and spontaneous beating rate (146 +/- 13 to 85 +/- 22 beats/min, P < 0.05). Pretreatment with methylene blue or KT-5823 inhibited these negative myocardial effects. These results suggest that LPS induces iNOS in cardiac myocytes and that the increased nitric oxide produced by iNOS has cardiac depressant effects through the activation of cGMP-dependent protein kinase
c-Fos expression in the medulla induced by static muscle contraction in cats
Authors: Li J. , Hand G. A. , Potts J. T. , Wilson L. B. , Mitchell J. H.
Published: December 2017

In this study, we examined Fos-like immunoreactivity (FLI) in the medulla after static muscle contraction induced by stimulation of L7 and S1 ventral roots of the spinal cord in anesthetized cats. The results show that FLI increases in the lateral reticular nucleus, nucleus of the solitary tract, lateral tegmental field, vestibular nucleus, subretrofacial nucleus, and A1 region of the medulla in comparison with these same areas in sham-operated animals (P < 0.05 in each region). In the rostral ventrolateral medulla, FLI distribution in neurons containing phenylethanolamine-N-methyltransferase (PNMT, the synthetic enzyme for epinephrine) was also observed utilizing double-labeling methods. The majority of neurons with PNMT also expressed FLI (66 +/- 4%). These data are in contrast to the results from sham-operated animals showing that 24 +/- 3% of the neurons costained with PNMT (P < 0.05). Our findings indicate that expression of FLI can be used to identify neurons activated during static muscle contraction and support previous studies implicating the ventrolateral medulla as a critical region for expression of the exercise pressor reflex. Furthermore, neurons in the rostral ventrolateral medulla containing PNMT were activated during static muscle contraction.
Exercise training enhances cardiac function in response to an afterload stress in older men
Authors: Spina R. J. , Turner M. J. , Ehsani A. A.
Published: December 2017

This study was designed to characterize cardiac adaptations to endurance exercise training in older healthy men by evaluation of changes in left ventricular function in response to an afterload stress in the presence of cardiac muscarinic receptor blockade. Eight men 65 +/- 2 (SE) yr old underwent 9 mo of endurance exercise training. Maximal O2 uptake (V(O2 max)) was determined during treadmill exercise. Left ventricular function was assessed with two-dimensional echocardiography and pulsed Doppler transmitral flow velocity profile at baseline, after an intravenous bolus of atropine and during infusion of graded doses of phenylephrine. V(O2 max) was increased by 29% in response to training (28.9 +/- 1 to 37.3 +/- 1 ml x kg(-1) x min(-1)). Baseline end-diastolic diameter (EDD) was increased, with no change in left ventricular wall thickness-to-radius ratio, after training, suggestive of eccentric left ventricular hypertrophy. EDD, end-systolic dimension, and end-systolic wall stress (sigma(es)) increased similarly in response to phenylephrine before and after training. Fractional shortening (FS) decreased in response to phenylephrine before but not after training. When the changes in FS (delta FS) during phenylephrine infusion were plotted as a function of changes in sigma(es), delta FS were significantly higher after than before training (P = 0.003) at comparable increases in sigma(es), indicative of improved contractile function. This adaptive response was preload independent, because EDD did not differ between the trained and untrained states during phenylephrine infusion. Heart rate responses to phenylephrine were similar before and after training. Exercise training resulted in a higher (P = 0.028) early-to-late transmitral diastolic flow velocity ratio at virtually identical heart rates, suggestive of improved diastolic filling. The results suggest that endurance exercise training induces an enhancement of left ventricular systolic function in response to an afterload stress in older healthy men.
ACE inhibitors and cardiac ACE mRNA in volume overload-induced cardiac hypertrophy
Authors: Lear W. , Ruzicka M. , Leenen F. H.
Published: December 2017

Quinapril, an angiotensin-converting enzyme (ACE) inhibitor with high affinity for cardiac ACE, prevents increases in both plasma and cardiac angiotensin II (ANG II) and development of cardiac hypertrophy after aortocaval shunt in rats. In contrast, enalapril, an ACE inhibitor with low affinity for cardiac ACE, only prevents the increase in plasma ANG II. In the present study, we assessed whether these differences between enalapril and quinapril reflect different inhibition of cardiac tissue ACE and local ANG II by measuring their effects on cardiac ACE mRNA. Treatment with enalapril (250 mg/l) and quinapril (200 mg/l in drinking water) was started 3 days before the shunt and sham surgery. After 1 wk of aortocaval shunt, the hearts were excised and the left ventricle and right ventricle were weighed and used for reverse transcriptase-polymerase chain reaction (RT-PCR) assays for ACE and phosphoglycerate kinase-1 (internal standard). Quinapril, but not enalapril, inhibited the development of cardiac hypertrophy by aortocaval shunt. The shunt increased ACE mRNA in both left and right ventricles about twofold. In animals with aortocaval shunt, quinapril markedly further upregulated ACE mRNA in both ventricles, whereas enalapril did not cause significant changes. In sham rats, both ACE inhibitors increased ACE mRNA, but the increase was more pronounced by treatment with quinapril. These studies show that in vivo ACE inhibitors with low (enalapril) vs. high (quinapril) affinity for cardiac ACE differ in their effects on cardiac ACE mRNA. This difference is more pronounced in volume overload-induced cardiac hypertrophy, presumably reflecting their different effects on cardiac ANG II.
Rate-dependent abbreviation of Ca2+ transient in rat heart is independent of phospholamban phosphorylation
Authors: Hussain M. , Drago G. A. , Colyer J. , Orchard C. H.
Published: December 2017

The mechanisms underlying the accelerated decline of the intracellular Ca2+ transient that occurs in cardiac muscle when stimulation rate is increased have been investigated in ventricular myocytes from rat hearts. Increasing stimulation rate from 0.1 to 0.5 and 1 Hz decreased the time taken for the Ca2+ transient to decline from its peak to 50% of its peak value in cells generating action potentials, when the duration of depolarization was held constant by voltage clamp, and when Na/Ca exchange was inhibited. The sarcoplasmic reticulum Ca2+ adenosinetriphosphatase inhibitor thapsigargin inhibited rate-dependent abbreviation of the Ca2+ transient. However, neither a chemical inhibitor of Ca(2+)-calmodulin-dependent protein kinase II (KN62) nor a peptide inhibitor of this enzyme (calmodulin-binding domain peptide) had a significant effect on rate-dependent abbreviation of the Ca2+ transient. Analysis of the phosphorylation of the regulatory sites Ser16 and Thr17 of phospholamban showed no significant change in phosphorylation with changes of stimulation rate. These data suggest that rate-dependent shortening of the Ca2+ transient is due predominantly to enhanced Ca2+ uptake by the sarcoplasmic reticulum without changes in phospholamban phosphorylation.
Frequency-response characteristics of autonomic nervous system function in conscious rats
Authors: Stauss H. M. , Persson P. B. , Johnson A. K. , Kregel K. C.
Published: December 2017

To characterize the efferent pathway from the hypothalamic paraventricular nucleus (PVN) to peripheral autonomic neurons and finally to selected effector organs, we stimulated the PVN in 10 conscious rats at frequencies ranging from 0.05 to 2.0 Hz. Simultaneously, blood pressure, heart rate, splanchnic sympathetic nerve activity, and mesenteric artery blood flow were measured. The sinus node of the heart responded to PVN stimulation via the parasympathetic pathway (during beta 1-adrenergic blockade) up to a stimulation frequency of 2.0 Hz, whereas the sympathetically mediated response (during muscarinic blockade) was limited to stimulation frequencies < 0.5 Hz. The splanchnic nerve responded to PVN stimulation with synchronous discharges up to stimulation frequencies of 2.0 Hz, whereas the oscillatory component of the vasoconstrictor response of the mesenteric artery was negligible beyond stimulation frequencies of 1.0 Hz. We conclude that sympathetic transmission to the heart is at least four times slower than parasympathetic transmission. In addition, the time-limiting step in sympathetic transmission from the hypothalamus to vascular smooth muscle contraction and pacemaker activity of the sinus node may be located at the site of synaptic transmission to the adrenergic receptors.
Reperfusion-induced leukocyte adhesion and vascular protein leakage in normal and hypercholesterolemic rats
Authors: Kurose I. , Argenbright L. W. , Anderson D. C. , Tolley J. , Miyasaka M. , Harris N. , Granger D. N.
Published: December 2017

The objective of this study was to define the influence of hypercholesterolemia on ischemia-reperfusion (I/R)-induced leukocyte-endothelial cell adhesion and albumin leakage in rat mesenteric venules. The microvascular alterations normally elicited by I/R (leukocyte adherence and emigration, albumin leakage, and platelet aggregation) were more pronounced in hypercholesterolemic rats (compared with control rats). Monoclonal antibodies against the adhesion glycoproteins CD11/CD18 and intercellular adhesion molecule-1 attenuated the I/R-induced leukocyte adherence and emigration and albumin leakage. Leukocyte adherence, but not albumin leakage, was diminished in animals pretreated with a P-selectin-specific antibody. Platelet aggregation was reduced by antibodies directed against either P-selectin, CD18, or intercellular adhesion molecule-1, as well as a GPIIb-IIIa antagonist. These results indicate that the enhanced reperfusion-induced albumin leakage in hypercholesterolemic rats is dependent on leukocyte-endothelial cell adhesion. Furthermore, P-selectin- and CD11/CD18-dependent heterotypic and GPIIb-IIIa-mediated homotypic platelet aggregation appear to influence the extravasation of both leukocytes and albumin in postischemic venules of hypercholesterolemic rats.
Adenylyl cyclase isoforms and vasopressin enhancement of agonist-stimulated cAMP in vascular smooth muscle cells
Authors: Zhang J. , Sato M. , Duzic E. , Kubalak S. W. , Lanier S. M. , Webb J. G.
Published: December 2017

The influence of arginine vasopressin (AVP) on agonist-stimulated adenosine 3',5'-cyclic monophosphate (cAMP) accumulation was investigated in vascular smooth muscle cells (VSMC) cultured from rat thoracic aorta. Incubation of VSMC with AVP for 60 s produced a 2- to 2.5-fold enhancement of isoproterenol-induced cAMP formation. AVP also increased cAMP stimulation by the prostaglandin I2 analogue iloprost. The effect of AVP to enhance agonist-stimulated cAMP formation was completely inhibited in cells pretreated with a selective antagonist of V1 vasopressin receptors but was not affected by blockade of V2 receptors. Inhibition of protein kinase C activation failed to alter the action of AVP to potentiate cAMP stimulation, but treatment of cells with calmodulin antagonists significantly attenuated this effect of the peptide. Moreover, depletion of Ca2+ stores with thapsigargin decreased AVP enhancement of isoproterenol-stimulated cAMP by > 70%. The action of AVP to increase cAMP stimulation was also demonstrated in freshly isolated strips of rat aorta where treatment with peptide produced a twofold increase in isoproterenol-stimulated cAMP formation. RNA blot analysis indicated expression in VSMC of mRNA encoding type III adenylyl cyclase, a Ca(2+)-calmodulin-sensitive isoform of the effector. Furthermore, when detergent-solubilized membrane extract was subjected to calmodulin affinity chromatography, a peak of adenylyl cyclase activity was identified which had affinity for calmodulin matrix in the presence of Ca2+. The results indicate that AVP activates V1 receptors in VSMC to enhance agonist-stimulated cAMP formation by a Ca(2+)-calmodulin-dependent mechanism and suggest that type III adenylyl cyclase may provide a focal point in the VSMC for cross talk between constrictor and dilator pathways.
Assessment of protein permeability in normal human systemic circulation
Authors: Shanholtz C. , White P. , Permutt S. , Sylvester J. T. , Brower R.
Published: December 2017

Vascular permeability to oncotic agents is an important determinant of transvascular fluid flux (J) and systemic fluid balance. In this study, a technique was developed to measure protein reflection coefficients (omega) for albumin (Alb), immunoglobulin (Ig) G, and IgM in the intact human systemic circulation to evaluate the role of vascular protein permeability in health and disease. A mathematical model was developed to calculate omega in the forearm circulation from changes in venous hematocrit and protein concentration that occur during edema formation. Assumptions required for the model were validated in an initial set of experiments in normal subjects when edema was induced by inflating a pneumatic cuff on the upper arm. A second series of experiments assessed omega for Alb, IgG, and IgM in men (n = 7) and in women in the follicular (n = 5) and luteal (n = 4) phases of the menstrual cycle. There was an increasing trend in omega with molecular size in aggregated subjects [omega Alb = 0.81 +/- 0.12 (SE), omega IgG = 0.88 +/- 0.12, omega IgM = 0.92 +/- 0.18; P = 0.088]. These values were consistent with those obtained with in vitro preparations. omega values were lower in women in the luteal than in the follicular phase (P = 0.047). We conclude that the assumptions required for this model can be achieved in the intact forearm circulation and that there are menstrual phase-related differences in vascular protein permeability in normal women.
Role of Ca(2+)-independent PKC in alpha 1-adrenoceptor-mediated inotropic responses of neonatal rat hearts
Authors: Deng X. F. , Mulay S. , Varma D. R.
Published: December 2017

We investigated the role of protein kinase C (PKC) in alpha 1-adrenoceptor (alpha 1-AR)-mediated positive inotropic responses of neonatal rat myocardium. Bisindolylmaleimide (BIM), an inhibitor of all PKC isoforms, reduced the positive inotropic responses to phenylephrine and methoxamine but not to isoproterenol. The positive inotropic effect of phenylephrine was not attenuated by Go-6976, a selective inhibitor of Ca(2+)-dependent isoforms; it was potentiated by the 1,2-diacylglycerol kinase inhibitor R-59949. Phorbol 12,13-dibutyrate, an activator of both Ca(2+)-dependent and-independent PKC isoforms, as well as thymeleatoxin, a selective activator of Ca(2+)-dependent PKC isoforms, inhibited myocardial contractions, which were prevented by BIM and Go-6976. BIM inhibited the phenylephrine-induced increase in particulate PKC activity but not the increase in phosphatidylinositide turnover. Phenylephrine induced translocation of only Ca(2+)-independent PKC-epsilon and -delta. These results suggest that activation of Ca(2+)-independent PKC isoforms by alpha 1-AR agonists plays a key role in alpha 1-AR-mediated positive inotropic effect on neonatal myocardium.
Time course of the human pulmonary vascular response to 8 hours of isocapnic hypoxia
Authors: Dorrington K. L. , Clar C. , Young J. D. , Jonas M. , Tansley J. G. , Robbins P. A.
Published: December 2017

To examine the hypothesis that the human pulmonary vascular response to hypoxia has a component with a slow time course, we measured pulmonary vascular resistance (PVR) in six healthy adult males during 8 h of isocapnic hypoxia. A balloon-tipped pulmonary artery catheter with thermistor was introduced via a forearm vein and used to derive PVR. The subjects were seated in a chamber in which the oxygen and carbon dioxide concentrations were adjusted to maintain an end-tidal Po2 of 50 Torr and an end-tidal Pco2 equal to the subject's normal prehypoxic value. PVR was measured before and at 0.5-h intervals during 8 h of hypoxia, the following 3 h of isocapnic euoxia (end-tidal Po2 100 Torr), and a subsequent 1-h reexposure to hypoxia. PVR rose from 1.23 +/- 0.26 (SE) Torr-min.1(-1) under euoxia [time (t) = 0] to 1.77 +/- 0.21 Torr.min.1(-1) at t = 0.5 h, reached a maximum at 2 h (2.91 +/- 0.33 Torr.min.1(-1)), and remained fairly constant between 2 and 8 h. Restoration of euoxia at 8 h led to a reduction in PVR with a slow component. Reexposure to hypoxia at 11 h resulted in a greater increase in PVR than at 1 h. Systemic vascular resistance had a similar slow component to its response, falling from 18.6 +/- 1.3 Torr.min.1(-1) at t = 0 to 17.3 +/- 1.4 Torr.min.1(-1) at t = 0.5 h, 14.4 +/- 0.6 Torr.min.1(-1) at t = 4 h, and 13.8 +/- 0.8 Torr.min.1(-1) at t = 8 h. The human pulmonary and systemic vascular responses to hypoxia extend over at least several hours.
Angiogenesis but not collateral growth is associated with ischemia after femoral artery occlusion
Authors: Ito W. D. , Arras M. , Scholz D. , Winkler B. , Htun P. , Schaper W.
Published: December 2017

It remains unclear whether capillary sprouting (angiogenesis) and in situ growth of muscular collateral arteries share the same or different molecular mechanisms. To study the role of ischemia in these two forms of vascular proliferation, we measured tissue flows and maximum collateral conductances in hindlimbs of 22 rabbits previously subjected to either acute, 7-day, 21-day, or no femoral artery occlusion. After 1 wk of femoral artery occlusion, corkscrew collaterals were observed radiographically in the thigh. These collaterals showed histochemical evidence for active proliferation of endothelial and smooth muscle cells. Maximum collateral conductance increased sixfold in the 1st wk. Perfusion deficits, however, were only observed in the distal adductor muscles (region of collateral reentry). In the lower leg, which suffered from a profound perfusion deficit, conductance increased in the absence of any visible collateral arteries but with evidence for capillary proliferation. This study therefore demonstrates that upon femoral artery occlusion angiogenesis occurs in regions of profound ischemia, whereas no direct correlation can be drawn between ischemia and collateral artery development.
Role of spinal NMDA and AMPA receptors in episodic hypertension in conscious spinal rats
Authors: Maiorov D. N. , Krenz N. R. , Krassioukov A. V. , Weaver L. C.
Published: December 2017

The neurotransmitters mediating the spinal sympathetic reflexes that initiate episodic hypertension after spinal cord injury are unknown. We examined the role of glutamatergic transmission in these reflexes by testing effects of the N-methyl-D-aspartate (NMDA)-receptor antagonist 2-amino-5-phosphonopentanoic acid (AP-5) and of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfamoylbenzoquinone (NBQX) on the reflex hypertension caused by colon distension. Antagonists were administered intrathecally in conscious rats 1-2 days (acute, n = 10) or 15-16 days (chronic, n = 14) after cord transection at the fifth thoracic segment under barbiturate anesthesia. AP-5 blocked pressor responses to intrathecal NMDA but had no effect on responses to AMPA; similarly, NBQX blocked responses to AMPA but had no effect on responses to NMDA. Before antagonist injection, colon distension increased mean arterial pressure by 24 +/- 1 mmHg (from 100 +/- 3 mmHg) and by 37 +/- 2 mmHg (from 116 +/- 3 mmHg) in the acute and chronic groups, respectively. Pretreatment with AP-5 attenuated the pressor responses by 36 and 37% in these respective groups; pretreatment with NBQX attenuated them by 34 and 31%. These data suggest that both NMDA and AMPA receptors contribute to spinal viscerosympathetic transmission and initiation of episodic hypertension in conscious spinal rats.
Synergistic vascular effects of dietary sodium supplementation and angiotensin II administration
Authors: Csiky B. , Simon G.
Published: December 2017

The hypertensinogenic action of dietary sodium supplementation was investigated in angiotensin II (ANG II)-treated rats. We hypothesized that high-sodium diet would potentiate ANG II-induced vasoconstriction and hypertension, including the development of structural vascular changes, through synergistic action with ANG II in stimulating sympathetic activity and vascular growth. Mesenteric vasoconstrictor responses to ANG II, norepinephrine (NE), arginine vasopressin (AVP), and periarterial nerve stimulation were measured in Sprague-Dawley rats after 7-10 days of the following treatments: 200 ng.kg-1.min-1 ip ANG II (n = 12), 4% NaCl diet (n = 11), ANG II + 4% NaCl diet (n = 7), and 0.7% NaCl diet (controls) (n = 15). Additional rats received 50 ng.kg-1.min-1 sc ANG II (n = 8), 2% NaCl diet (n = 9), ANG II + 2% NaCl diet (n = 6), or 0.7% NaCl diet (controls) (n = 10) for 12 wk. Systolic blood pressure (SBP) values were measured weekly for 4 wk and then every other week for 8 wk. Then, the wall-to-lumen ratio (W/L) of mesenteric resistance arteries (< 150 microns OD) was measured after in situ perfusion-fixation. After 7-10 days of treatment, there were no significant changes in SBP in any of the groups. High-sodium diet increased vasoconstrictor responses to ANG II (P < 0.01) and nerve stimulation (P < 0.02), but not to NE or AVP, and in combination with ANG II treatment further potentiated vasoconstrictor responses to ANG II (synergism). After 12 wk of treatment, ANG II increased W/L of small resistance arteries by 11% (P < 0.05) without a significant rise in SBP. ANG II and 2% NaCl diet in combination raised SBP by 36 mmHg (P < 0.01) and increased small artery W/L by 28% (P < 0.001) compared with values obtained in control rats. To test the specificity of the interaction between ANG II and high-sodium diet, all the experiments were repeated during phenylephrine (PE, 10 micrograms.kg-1.min-1 sc) treatment of rats. PE by itself or in combination with high-sodium diet had no effect on the measured parameters. Thus short-term administration of high-sodium diet appears to potentiate vasoconstrictor responses to ANG II by facilitating sympathetic neurotransmission, and long-term administration of high-sodium diet raises SBP by potentiating the trophic vascular effects of ANG II. The interaction appears to be specific to ANG II and is occurring on the vascular level.