bluuebunny/crossref_metadata_2025 huggingface dataset:
Hemodilution, cerebral O2delivery, and cerebral blood flow: a study using hyperbaric oxygenation
Authors: Tomiyama Yoshinobu , Jansen Kevin , Brian Johnny E. , Todd Michael M.
Published: December 2017

Hemodilution reduces blood viscosity and O2content ([Formula: see text]) and increases cerebral blood flow (CBF). Viscosity and [Formula: see text] may contribute to increasing CBF after hemodilution. However, because hematocrit is the major contributor to blood viscosity and[Formula: see text], it has been difficult to assess their relative importance. By varying blood viscosity without changing[Formula: see text], prior investigation in hemodiluted animals has suggested that both factors play roughly equal roles. To further investigate the relationship of hemodilution, blood viscosity,[Formula: see text], and CBF, we took the opposite approach in hemodiluted animals, i.e., we varied[Formula: see text] without changing blood viscosity. Hyperbaric O2 was used to restore[Formula: see text] to normal after hemodilution. Pentobarbital sodium-anesthetized rats underwent isovolumic hemodilution with 6% hetastarch, and forebrain CBF was measured with [3H]nicotine. One group of animals did not undergo hemodilution and served as controls (Con). In the three experimental groups, hematocrit was reduced from 44% to 17–19%. Con and hemodiluted (HDil) groups were ventilated with 40% O2 at 101 kPa (1 atmosphere absolute), which resulted in[Formula: see text] values of 19.7 ± 1.3 and 8.1 ± 0.7 (SD) ml O2/dl, respectively. A second group of hemodiluted animals (HBar) was ventilated with 100% O2 at 506 kPa (5 atmospheres absolute) in a hyperbaric chamber, which restored[Formula: see text] to an estimated 18.5 ± 0.5 ml O2/dl by increasing dissolved O2. A fourth group of hemodiluted animals (HCon) served as hyperbaric controls and were ventilated with 10% O2 at 506 kPa, resulting in[Formula: see text] of 9.1 ± 0.6 ml O2/dl. CBF was 79 ± 19 ml ⋅ 100 g−1 ⋅ min−1in the Con group and significantly increased to 123 ± 9 ml ⋅ 100 g−1 ⋅ min−1in the HDil group. When[Formula: see text] was restored to baseline with dissolved O2 in the HBar group, CBF decreased to 104 ± 20 ml ⋅ 100 g−1 ⋅ min−1. When normoxia was maintained during hyperbaric exposure in the HCon group, CBF was 125 ± 18 ml ⋅ 100 g−1 ⋅ min−1, a value indistinguishable from that in normobaric HDil animals. Our data demonstrate that the reduction in [Formula: see text] after hemodilution is responsible for 40–60% of the increase in CBF.
Hypoxic contraction of small pulmonary arteries from normal and endotoxemic rats: fundamental role of NO
Authors: Terraz Sylvain , Baechtold François , Renard Delphine , Barsi Attila , Rosselet Anne , Gnaegi Alex , Liaudet Lucas , Lazor Romain , Haefliger Jacques-A. , Schaad Nicolas , Perret Claude , Kucera Paul , Markert Michèle , Feihl Francois
Published: December 2017

The present study was aimed at examining the role of nitric oxide (NO) in the hypoxic contraction of isolated small pulmonary arteries (SPA) in the rat. Animals were treated with either saline (sham experiments) or Escherichia coli lipolysaccharide [LPS, to obtain expression of the inducible NO synthase (iNOS) in the lung] and killed 4 h later. SPA (300- to 600-μm outer diameter) were mounted as rings in organ chambers for the recording of isometric tension, precontracted with PGF2α, and exposed to either severe (bath [Formula: see text] 8 ± 3 mmHg) or milder (21 ± 3 mmHg) hypoxia. In SPA from sham-treated rats, contractions elicited by severe hypoxia were completely suppressed by either endothelium removal or preincubation with an NOS inhibitor [ N G-nitro-l-arginine methyl ester (l-NAME), 10−3 M]. In SPA from LPS-treated rats, contractions elicited by severe hypoxia occurred irrespective of the presence or absence of endothelium and were largely suppressed by l-NAME. The milder hypoxia elicited no increase in vascular tone. These results indicate an essential role of NO in the hypoxic contractions of precontracted rat SPA. The endothelium independence of HPV in arteries from LPS-treated animals appears related to the extraendothelial expression of iNOS. The severe degree of hypoxia required to elicit any contraction is consistent with a mechanism of reduced NO production caused by a limited availability of O2 as a substrate for NOS.
Inhibition of phospholipase A2attenuates functional hyperemia in the hamster cremaster muscle
Authors: Nuttle Louise C. , Ligon Alison L. , Farrell Kathryn R. , Hester Robert L.
Published: December 2017

Arachidonic acid (AA) is the common precursor for several vasodilatory factors involved in the local control of blood flow. This study was designed to determine the role of phospholipase A2(PLA2) and AA release in functional hyperemia in the hamster cremaster muscle. The muscle was prepared for in vivo microscopy and subjected to electrical field stimulation for 1 min. First- and second-order arterioles dilated in response from a mean diameter of 66 ± 5 to 88 ± 7 μm ( n = 6). PLA2was then inhibited with quinacrine (3 × 10−6M) for 60 min. PLA2inhibition was verified by an attenuation of thrombin-induced vasodilation (2 U/ml). Quinacrine had no effect on resting arteriolar diameter but completely abolished functional hyperemia. Quinacrine also had no effect on dilation induced by superfusion of the preparation with 3 × 10−6–10−5M AA, 10−6–10−4M adenosine, or 10−6–10−4M sodium nitroprusside, ruling out nonspecific effects of quinacrine on smooth muscle contractility. These results indicate that functional hyperemia in the hamster cremaster muscle is dependent on PLA2activation and the availability of AA.
Heterogeneity of 4-aminopyridine-sensitive current in rabbit sinoatrial node cells
Authors: Honjo Haruo , Lei Ming , Boyett Mark R. , Kodama Itsuo
Published: December 2017

The electrophysiological properties of sinoatrial (SA) node pacemaker cells vary in different regions of the node. In this study, we have investigated variation of the 4-aminopyridine (4-AP)-sensitive current as a function of the size (as measured by the cell capacitance) of SA node cells to elucidate the ionic mechanisms. The 10 mM 4-AP-sensitive current recorded from rabbit SA node cells was composed of transient and sustained components ( I trans and I sus, respectively). The activation and inactivation properties [activation: membrane potential at which conductance is half-maximally activated ( V h) = 19.3 mV, slope factor ( k) = 15.0 mV; inactivation: V h= −31.5 mV, k = 7.2 mV] as well as the density of I trans (9.0 pA/pF on average at +50 mV) were independent of cell capacitance. In contrast, the density of I sus (0.97 pA/pF on average at +50 mV) was greater in larger cells, giving rise to a significant correlation with cell capacitance. The greater density of I sus in larger cells (presumably from the periphery) can explain the shorter action potential in the periphery of the SA node compared with that in the center. Thus variation of the 4-AP-sensitive current may be involved in regional differences in repolarization within the SA node.
COX-2 and cytosolic PLA2mediate IL-1β-induced cAMP production in human vascular smooth muscle cells
Authors: Beasley Debbie
Published: December 2017

Interleukin (IL)-1 is a potent vasodilator that causes prolonged induction of prostacyclin (PGI2) and cAMP synthesis in human vascular smooth muscle cells (HVSMC). The present study investigated IL-1 induction of PG synthetic enzymes in HVSMC and tested their respective roles in PGI2and cAMP production. Cyclooxygenase (COX)-1 mRNA was not detectable in either control or IL-1-treated HVSMC, as assessed by RT-PCR. In contrast, COX-2 mRNA was detectable in control HVSMC, increased markedly (16-fold) after 1 h of IL-1 exposure, and increased further (52-fold) after 24 h. COX-2 protein levels, assessed by Western analysis, were increased concomitantly. HVSMC contained mRNA encoding both the secreted and cytosolic forms of phospholipase A2(sPLA2and cPLA2, respectively). IL-1 stimulation did not affect sPLA2mRNA levels, but cPLA2mRNA levels increased at 8 h, after the initial induction of PG synthesis. HVSMC constitutively expressed PGI2synthase mRNA, and its levels were not affected by IL-1. A selective COX-2 inhibitor, NS-398, reversed IL-1-induced PGI2and cAMP production, supporting a role of COX-2 in mediating increased PG synthesis. IL-1-induced cAMP was also reversed by a selective cPLA2inhibitor, AACOCF3, but not by thioetheramide phosphorylcholine, which inhibits sPLA2preferentially over cPLA2, supporting a requirement for cPLA2-derived arachidonic acid in IL-1-induced PG synthesis. The delayed induction of cPLA2mRNA was also attenuated by NS-398, suggesting that it was secondary to the initial COX-2-induced PG synthesis. Together, the results support the hypothesis that IL-1 induces intracellular PG synthesis in HVSMC via rapid upregulation of COX-2, which utilizes cPLA2-derived arachidonic acid to generate PG metabolites that regulate adenylate cyclase.
Linkage analysis of glucocorticoid and β2-adrenergic receptor genes with blood pressure and body mass index
Authors: Takami Seiju , Wong Zilla Y. H. , Stebbing Margaret , Harrap Stephen B.
Published: December 2017

Glucocorticoids and catecholamines exert important effects on cardiovascular physiology and metabolism. Variants of the glucocorticoid receptor gene ( GRL) and the β2-adrenergic receptor gene ( ADRB2) have been associated with high blood pressure and obesity. These genes are close on human chromosome 5q31–5q32, and we undertook a linkage analysis of this region in 264 families from the general population in relation to systolic and diastolic blood pressure, body mass index, weight, height, and pulse rate. All family members were genotyped at four microsatellite loci (D5S207, D5S210, D5S519, and D5S119) located on chromosome 5q31–5q33.3. Using quantitative identity-by-descent sibling pair linkage analysis, we found that at no loci was genetic similarity associated with phenotypic similarity for systolic and diastolic blood pressure, body mass index, weight, height, or pulse rate. Although it is not possible to exclude the influence of specific combinations of certain GRL and ADRB2 polymorphisms, the absence of significant linkage in our population argues against a role for GRL or ADRB2 in physiological variation of blood pressure and body mass index.
Muscle metaboreflex improves O2delivery to ischemic active skeletal muscle
Authors: O’Leary Donal S. , Augustyniak Robert A. , Ansorge Eric J. , Collins Heidi L.
Published: December 2017

Ischemia of active skeletal muscle elicits a powerful pressor response, termed the muscle metaboreflex. We recently reported that the muscle metaboreflex pressor response acts to partially restore blood flow to the ischemic active skeletal muscle. However, because this reflex is activated by reductions in O2 delivery rather than blood flow per se, gain of the muscle metaboreflex as analyzed on the basis of blood flow alone may underestimate its true strength if this reflex also acts to increase arterial O2content. In conscious dogs chronically instrumented to measure systemic arterial pressure, cardiac output, and hindlimb blood flow, we activated the muscle metaboreflex via graded, partial reductions in hindlimb blood flow during mild (3.2 km/h) and moderate (6.4 km/h, 10% grade) workloads. At rest, during free-flow exercise, and with metaboreflex activation, we analyzed arterial blood samples for Hb concentration and O2 content and compared muscle metaboreflex gain calculations based on the ability to partially restore flow with those based on the ability to partially restore O2 delivery (blood flow × arterial O2 content). During both mild and moderate exercise, metaboreflex activation caused significant increases in arterial Hb concentration and O2 content. Metaboreflex gain quantified on the ability to partially restore O2 delivery was significantly greater than that based on restoration of blood flow during both mild and moderate workloads (0.52 ± 0.10 vs. 0.39 ± 0.08, P < 0.05, and 0.61 ± 0.05 vs. 0.46 ± 0.04, P < 0.05, respectively). We conclude that the muscle metaboreflex acts to increase both arterial O2 content and blood flow to ischemic muscle such that when combined, O2 delivery is substantially increased and metaboreflex gain is greater when analyzed with a more integrative approach.
Human sympathetic and vagal baroreflex responses to sequential nitroprusside and phenylephrine
Authors: Rudas László , Crossman Alexandra A. , Morillo Carlos A. , Halliwill John R. , Tahvanainen Kari U. O. , Kuusela Tom A. , Eckberg Dwain L.
Published: December 2017

We evaluated a method of baroreflex testing involving sequential intravenous bolus injections of nitroprusside followed by phenylephrine and phenylephrine followed by nitroprusside in 18 healthy men and women, and we drew inferences regarding human sympathetic and vagal baroreflex mechanisms. We recorded the electrocardiogram, photoplethysmographic finger arterial pressure, and peroneal nerve muscle sympathetic activity. We then contrasted least squares linear regression slopes derived from the depressor (nitroprusside) and pressor (phenylephrine) phases with 1) slopes derived from spontaneous fluctuations of systolic arterial pressures and R-R intervals, and 2) baroreflex gain derived from cross-spectral analyses of systolic pressures and R-R intervals. We calculated sympathetic baroreflex gain from integrated muscle sympathetic nerve activity and diastolic pressures. We found that vagal baroreflex slopes are less when arterial pressures are falling than when they are rising and that this hysteresis exists over pressure ranges both below and above baseline levels. Although pharmacological and spontaneous vagal baroreflex responses correlate closely, pharmacological baroreflex slopes tend to be lower than those derived from spontaneous fluctuations. Sympathetic baroreflex slopes are similar when arterial pressure is falling and rising; however, small pressure elevations above baseline silence sympathetic motoneurons. Vagal, but not sympathetic baroreflex gains vary inversely with subjects’ ages and their baseline arterial pressures. There is no correlation between sympathetic and vagal baroreflex gains. We recommend repeated sequential nitroprusside followed by phenylephrine doses as a simple, efficientmeans to provoke and characterize human vagal and sympathetic baroreflex responses.
Comparison of putative cooperative mechanisms in cardiac muscle: length dependence and dynamic responses
Authors: Rice J. Jeremy , Winslow Raimond L. , Hunter William C.
Published: December 2017

Length-dependent steady-state and dynamic responses of five models of isometric force generation in cardiac myofilaments were compared with similar experimental data from the literature. The models were constructed by assuming different subsets of three putative cooperative mechanisms. Cooperative mechanism 1 holds that cross-bridge binding increases the affinity of troponin for Ca2+. In the models, cooperative mechanism 1can produce steep force-Ca2+(F-Ca) relations, but apparent cooperativity is highest at midlevel Ca2+concentrations. During twitches, cooperative mechanism 1 has the effect of increasing latency to peak as the magnitude of force increases, an effect not seen experimentally. Cooperative mechanism 2 holds that the binding of a cross bridge increases the rate of formation of neighboring cross bridges and that multiple cross bridges can maintain activation of the thin filament in the absence of Ca2+. Only cooperative mechanism 2 can produce sarcomere length (SL)-dependent prolongation of twitches, but this mechanism has little effect on steady-state F-Ca relations. Cooperativity mechanism 3 is designed to simulate end-to-end interactions between adjacent troponin and tropomyosin. This mechanism can produce steep F-Ca relations with appropriate SL-dependent changes in Ca2+sensitivity. With the assumption that tropomyosin shifting is faster than cross-bridge cycling, cooperative mechanism 3produces twitches where latency to peak is independent of the magnitude of force, as seen experimentally.
Adventitia-dependent relaxations of canine basilar arteries transduced with recombinant eNOS gene
Authors: Tsutsui Masato , Onoue Hisashi , Iida Yasuhiko , Smith Leslie , O’Brien Timothy , Katusic Zvonimir S.
Published: December 2017

We recently reported that expression of recombinant endothelial nitric oxide (NO) synthase (eNOS) gene in adventitial fibroblasts restores NO formation in canine cerebral arteries without endothelium in response to bradykinin ex vivo and in vivo. The present study was designed to further characterize the stimuli that can activate recombinant eNOS enzyme expressed in the adventitia of cerebral arteries. To stimulate recombinant eNOS, we used serum (0.1–10%), substance P (10−11–3 × 10−9M), and ANG II (10−7–10−5M) because they increase intracellular calcium concentrations in fibroblasts. Endothelium-denuded segments of canine basilar arteries were incubated with an adenoviral vector encoding β-galactosidase gene or eNOS gene for 30 min at 37°C. After 24 h, vasomotor activity and cGMP formation in eNOS or β-galactosidase arteries were examined by isometric force recording and by radioimmunoassay, respectively. In control arteries and β-galactosidase gene-transduced arteries, serum caused concentration-dependent contractions, whereas in recombinant eNOS gene-transduced arteries, serum produced concentration-dependent relaxations. Substance P and ANG II had no effect on vascular tone in control and β-galactosidase arteries but caused concentration-dependent relaxations as well as a significant increase in cGMP levels in eNOS arteries. These relaxations were blocked by the NOS inhibitor NG-nitro-l-arginine methyl ester. Chemical treatment or mechanical inactivation of adventitial function significantly attenuated substance P-induced relaxations and ANG II-induced relaxations. These findings demonstrate that serum, substance P, and ANG II cause adventitia-dependent relaxations in cerebral arteries expressing the recombinant eNOS gene. This mechanism of vasodilatation may have beneficial effects in the prevention and treatment of vascular disorders characterized by the diminished bioavailability of NO, such as cerebral vasospasm.
Cationic amino acid transporter gene expression in cultured vascular smooth muscle cells and in rats
Authors: Hattori Yoshiyuki , Kasai Kikuo , Gross Steven S.
Published: December 2017

Immunostimulants trigger vascular smooth muscle cells (VSMC) to express the inducible isoform of NO synthase (iNOS) and increased arginine transport activity. Although arginine transport in VSMC is considered to be mediated via the y+system, we show here that rat VSMC in culture express the cat-1 gene transcript as well as an alternatively spliced transcript of the cat-2 gene. An RT-PCR cloning sequence strategy was used to identify a 141-base nucleotide sequence encoding the low-affinity domain of alternatively spliced CAT-2A and a 138-base nucleotide sequence encoding the high-affinity domain of CAT-2B in VSMC activated with lipopolysaccharide (LPS) in combination with interferon-γ (IFN). With this sequence as a probe, Northern analyses showed that CAT-1 mRNA and CAT-2B mRNA are constitutively present in VSMC, and the expression of both mRNAs was rapidly stimulated by treatment with LPS-IFN, peaked within 4 h, and decayed to basal levels within 6 h after LPS-IFN. CAT-2A mRNA was not detectable in unstimulated or stimulated VSMC. Arginine transporter activity significantly increased 4–10 h after LPS-IFN. iNOS activity was reduced to almost zero in the absence of extracellular arginine uptake via system y+. Induction of arginine transport seems to be a prerequisite to the enhanced synthesis of NO in VSMC. Moreover, this work demonstrates tissue expression of CAT mRNAs with use of a model of LPS injection in rats. RT-PCR shows that the expression of CAT-1 and CAT-2B mRNA in the lung, heart, and kidney is increased by LPS administration to rats, whereas CAT-2A mRNA is abundantly expressed in the liver independent of LPS treatment. These findings suggest that together CAT-1 and CAT-2B play an important role in providing substrate for high-output NO synthesis in vitro as well as in vivo and implicate a coordinated regulation of intracellular iNOS enzyme activity with membrane arginine transport.
Brain O2 consumption and glutamate release during hypoglycemic coma in piglets are temperature sensitive
Authors: Ichord R. N. , Northington F. J. , van Wylen D. , Johnston M. V. , Kwon C. , Traystman R. J.
Published: December 2017

Hypoglycemic injury in the mature brain is mediated by excitotoxicity, which is worsened by disordered cellular energy metabolism. The role of excitotoxicity in relation to brain energy metabolism during hypoglycemia has not been studied in the immature brain. Brain oxygen consumption ([Formula: see text]) increases during hypoglycemia in piglets, whereas [Formula: see text] decreases in adult pig models. We tested the hypothesis that increased[Formula: see text] during hypoglycemic coma is temperature dependent and coincides with increased excitatory amino acids (EAA). We measured cerebral blood flow (CBF),[Formula: see text], and cortical microdiaysate EAA in pentobarbital-anesthetized piglets during hypoglycemic coma and during 2 h of recovery and in normoglycemic controls. In warmed animals brain temperature was kept normothermic (38.5°C). In unwarmed animals brain temperature was allowed to fall (37.6°C). During hypoglycemia CBF increased similarly in warmed animals and unwarmed animals;[Formula: see text] increased in warmed animals but not unwarmed animals. Glutamate increased during coma and increased more in warmed animals than unwarmed animals but normalized quickly during recovery. EEG recovered earlier in unwarmed animals. We conclude that during a hypoglycemic coma in the immature brain,[Formula: see text] and glutamate are increased in a temperature-dependent manner.
Lipoxygenase metabolism of arachidonic acid in ischemic preconditioning and PKC-induced protection in heart
Authors: Chen Weina , Glasgow Wayne , Murphy Elizabeth , Steenbergen Charles
Published: December 2017

We tested the hypothesis that activation of the 12-lipoxygenase (12-LO) pathway of arachidonic acid metabolism contributes to the protective effect of protein kinase C (PKC) activation and ischemic preconditioning (PC), and we report, in perfused rat heart, that both PC and the PKC activator 1,2-dioctanoyl- sn-glycerol (DOG) confer a similar protective effect and stimulate a comparable accumulation of 12-LO metabolites. The 12-LO product, 12( S)-hydroxyeicosatetraenoic acid [12( S)-HETE], was increased in DOG-treated (22.8 ± 4.4 ng/g wet wt) and PC hearts (26.8 ± 5.5 ng/g wet wt) compared with control (13.8 ± 2.1 ng/g wet wt, P < 0.05), and this increase was blocked by 12-LO or PKC inhibitors. Both DOG pretreatment and PC improved recovery of left ventricular developed pressure (LVDP) nearly twofold after 20 min of ischemia; this improvement was blocked by 12-LO inhibitors and was mimicked by infusion of 12-hydroperoxyeicosatetraenoic acid [12( S)-HpETE; 67 ± 6% recovery of LVDP vs. 35 ± 3% for untreated hearts]. Also, the protection afforded by 12( S)-HpETE, as well as by PC, was attenuated by the K+-channel blocker 5-hydroxydecanoate, suggesting that the downstream mechanisms of 12( S)-HpETE-mediated protection are similar to PC. Furthermore, PC stimulates 12-LO metabolism in perfused rabbit heart, and 12-LO inhibition blocks PC-induced cardioprotection. Thus the data suggest that 12-LO metabolism plays an important role in cardioprotection.
Naloxone reverses inhibitory effect of electroacupuncture on sympathetic cardiovascular reflex responses
Authors: Chao Dong M. , Shen Lin L. , Tjen-A-Looi Stephanie , Pitsillides Koullis F. , Li Peng , Longhurst John C.
Published: December 2017

Acupuncture and electroacupuncture (EA) have been used in traditional Chinese medicine to treat a wide range of diseases and conditions, including angina pectoris and myocardial infarction. In a feline model of reflex-induced reversible myocardial ischemia, electrical stimulation of the median nerves to mimic EA (Neiguan acupoint) significantly improved ischemic dysfunction, secondary to an inhibitory effect of EA on reflex pressor effects evoked by bradykinin (BK). The central mechanism of EA’s inhibitory effect in this model is unknown. Accordingly, in α-chloralose-anesthetized cats, BK (10 μg/ml) was applied to the gallbladder to elicit a cardiovascular reflex response that significantly ( P < 0.05) increased arterial blood pressure and heart rate; normalized systolic wall thickening (%WTh) of the left ventricle, measured by ultrasonic single-crystal sonomicrometer, increased by 31 ± 11% ( P < 0.05). After ligation of a side branch of the left anterior descending coronary artery, the reflex pressor response to BK resulted in a significant decrease of %WTh (−32 ± 6%) in the ischemic region. When bilateral EA of the Neiguan acupoints was performed, the pressor response to BK was inhibited and regional myocardial function was significantly improved (+19 ± 20%). The inhibitory effects of EA on blood pressure and %WTh were reversed by intravenous injection of naloxone (0.4 mg/kg; n = 9) or microinjection of naloxone (10 nM in 0.1 μl/site; n= 14) into the rostral ventrolateral medulla (rVLM). Thus %WTh with intravenous naloxone was reduced to −13 ± 29% ( P<0.05) during stimulation of the gallbladder. Our results indicate that the inhibitory effect of EA on the BK-induced pressor response and the consequent improvement of ischemic dysfunction is dependent on the activation of opioid receptors, specifically receptors located in the rVLM.
Enhanced DNA fragmentation in the thymus of spontaneously hypertensive rats
Authors: Suzuki Hidekazu , Delano Frank A. , Jamshidi Neema , Katz Dan , Mori Mikiji , Kosaki Kenjiro , Gottlieb Roberta A. , Ishii Hiromasa , Schmid-Schönbein Geert W.
Published: December 2017

The mechanisms contributing to organ injury in hypertension have been incompletely defined. The thymus gland of the spontaneously hypertensive rat (SHR) shows significant atrophy at the age of 15 wk compared with its normotensive control, the Wistar-Kyoto rat (WKY). The aim of the present study was to examine the thymus of SHR for evidence of DNA nicking as one of the mechanisms for thymic atrophy. SHR and WKY were subjected to adrenalectomy or sham surgery at 12 wk and studied at 15 wk. Adrenalectomy served to normalize the blood pressure in the SHR. DNA nicking was detected by in situ nick-end labeling (ISEL) of fixed tissue sections. Tissue sections were treated with proteolysis, and terminal deoxyribonucleotidyl transferase was used to incorporate biotinylated deoxynucleotides into DNA nick end in situ. Separately, DNA fragmentation was evaluated by measuring the level of released mono- and oligonucleosomes to the cytoplasm. A higher number of thymic ISEL-positive cells and a higher level of cytoplasmic mono- and oligonucleosomes were observed in SHR than in WKY. After adrenalectomy the enhanced level of ISEL and cytoplasmic mono- and oligonucleosomes in SHR was reduced to the level in WKY. Dexamethasone treatment (0.05 mg ⋅ kg−1⋅ day−1) in WKY serves to decrease the thymus weight and significantly elevate the level of mono- and oligonucleosomes. Thus increased DNA fragmentation represents one of the mechanisms associated with thymic atrophy, a feature that reflects immune suppression in SHR.
Modulation of force-frequency relation by phospholamban in genetically engineered mice
Authors: Kadambi Vivek J. , Ball Nancy , Kranias Evangelia G. , Walsh Richard A. , Hoit Brian D.
Published: December 2017

Phospholamban levels regulate cardiac sarcoplasmic reticulum Ca2+ pump activity and myocardial contractility. To determine whether and to what extent phospholamban modulates the force-frequency relation and ventricular relaxation in vivo, we studied transgenic mice overexpressing phospholamban (PLBOE), gene-targeted mice without phospholamban (PLBKO), and isogenic wild-type controls. Contractility was assessed by the peak rate of left ventricular (LV) isovolumic contraction (+dP/d t max), and diastolic function was assessed by both the peak rate (−dP/d t max) and the time constant (τ) of isovolumic LV relaxation, using a high-fidelity LV catheter. Incremental atrial pacing was used to generate heart rate vs. −dP/d t max(force-frequency) relations. Biphasic force-frequency relations were produced in all animals, and the critical heart rate (HRcrit) was taken as the heart rate at which dP/d t max was maximal. The average LV +dP/d t maxincreased in both PLBKO and PLBOE compared with their isogenic controls (both P < 0.05). The HRcrit for LV +dP/d t max was significantly higher in PLBKO (427 ± 20 beats/min) compared with controls (360 ± 18 beats/min), whereas the HRcrit in PLBOE (340 ± 30 beats/min) was significantly lower compared with that in isogenic controls (440 ± 25 beats/min). The intrinsic heart rates were significantly lower, and the HRcrit and the ±dP/d t max at HRcrit were significantly greater in FVB/N than in SvJ control mice. We conclude that 1) the level of phospholamban is a critical negative determinant of the force-frequency relation and myocardial contractility in vivo, and 2) contractile parameters may differ significantly between strains of normal mice.
Four different components contribute to outward current in rat ventricular myocytes
Authors: Himmel Herbert M. , Wettwer Erich , Li Qi , Ravens Ursula
Published: December 2017

In rat ventricle, two Ca2+-insensitive components of K+ current have been distinguished kinetically and pharmacologically, the transient, 4-aminopyridine (4-AP)-sensitive I to and the sustained, tetraethylammonium (TEA)-sensitive I K. However, a much greater diversity of depolarization-activated K+ channels has been reported on the level of mRNA and protein. In the search for electrophysiological evidence of further current components, the whole cell voltage-clamp technique was used to analyze steady-state inactivation of outward currents by conditioning potentials in a wide voltage range. Peak ( I peak) and late ( I late) currents during the test pulse were analyzed by Boltzmann curve fitting, producing three fractions each. Fractions a and b had different potentials of half-maximum inactivation ( V 0.5); the third residual fraction, r, did not inactivate. Fractions a for I peak and I late had similar relative amplitudes and V 0.5 values, whereas size and V 0.5 of fractions b differed significantly between I peak and I late. Only b of I peak was transient, suggesting a relation with I to, whereas a, b, and r of I late appeared to be three different sustained currents. Therefore, four individual outward current components were distinguished: I to( b of I peak), I K( a), the steady-state current I ss( r), and the novel current I Kx( b of I late). This was further supported by differential sensitivity to TEA, 4-AP, clofilium, quinidine, dendrotoxin, heteropodatoxin, and hanatoxin. With the exception of I to, none of the currents exhibited a marked transmural gradient. Availability of I K was low at resting potential; nevertheless, I K contributed to action potential shortening in hyperpolarized subendocardial myocytes. In conclusion, on the basis of electrophysiological and pharmacological evidence, at least four components contribute to outward current in rat ventricular myocytes.
A CD18 monoclonal antibody reduces multiple organ injury in a model of ruptured abdominal aortic aneurysm
Authors: Boyd A. J. , Rubin B. B. , Walker P. M. , Romaschin A. , Issekutz T. B. , Lindsay T. F.
Published: December 2017

The role of CD18 antibody (anti-CD18) in remote and local injury in a model of ruptured abdominal aortic aneurysm repair was investigated. Rats were divided into sham, shock, clamp, and shock + clamp groups. Shock + clamp animals received anti-CD18 or a control monoclonal antibody. One hour of hemorrhagic shock was followed by 45 min of supramesenteric aortic clamping. Intestinal and pulmonary permeability to125I-labeled albumin was determined. Myeloperoxidase (MPO) activity, F2-isoprostane levels, and transaminases were also measured. Only shock + clamp resulted in statistically significant increases in pulmonary and intestinal permeability, which were associated with significant increases in MPO activity and F2-isoprostane levels. Treatment with anti-CD18 significantly decreased intestinal and pulmonary permeability in shock + clamp animals. These reductions were associated with significantly reduced intestinal and hepatic MPO activity and pulmonary F2-isoprostane levels and reduced alanine and aspartate aminotransferase levels; however, anti-CD18 had no effect on intestinal or hepatic F2-isoprostane levels or on pulmonary MPO activity. These results suggest CD18-dependent and -independent mechanisms of local and remote organ injury in this model of ruptured abdominal aortic aneurysm.
Effect of exogenous nitric oxide on baroreflex function in humans
Authors: Hogan N. , Kardos A. , Paterson D. J. , Casadei B.
Published: December 2017

Nitric oxide (NO) donors inhibit sympathetic neurotransmission and baroreceptor activity and can directly stimulate heart rate (HR) in vitro. To assess whether exogenous NO affects cardiovascular autonomic control in humans, we tested the baroreceptor-cardiac reflex [baroreflex sensitivity (BRS)] and the arterial blood pressure (BP) and HR variability during an infusion of the NO donor sodium nitroprusside (SNP, 2 μg ⋅ kg−1 ⋅ min−1) or 5% glucose in 16 healthy subjects. The hypotensive action of SNP was prevented by phenylephrine (PE, 0.9 ± 0.15 μg ⋅ kg−1 ⋅ min−1). The SNP + PE infusion did not affect BRS or HR variability, but it caused a significant reduction in the diastolic and systolic BP low-frequency power. In addition, SNP + PE caused a sustained 12% increase in HR in the absence of changes in brachial and aortic BP. In conclusion, SNP had no effect on the cardiac-vagal limb of the baroreflex in humans but caused a substantial reduction in BP low-frequency power consistent with a decreased baroreflex/sympathetic control of peripheral resistance. The increase in HR in the absence of baroreceptor downloading confirms our previous finding of a direct positive chronotropic effect of NO donors.
Cardiac performance and creatine kinase flux during inhibition of ATP synthesis in the perfused rat heart
Authors: Mateo P. , Stepanov V. , Gillet B. , Beloeil J.-C. , Hoerter J. A.
Published: December 2017

To study the relation among mitochondrial energy supply, cardiac performance, and energy transfer through creatine kinase (CK), two acute models of inhibition of ATP synthesis were compared in the isovolumic acetate-perfused rat heart. Similar impairments of mechanical performance (rate-pressure product, RPP) were achieved by various stepwise decreases in O2supply ([Formula: see text] down to 20% of control) or by infusing CN (0.15–0.25 mM). The forward CK flux measured by saturation-transfer31P NMR spectroscopy was 6.1 ± 0.4 mM/s in control hearts. Only after severe hypoxia ([Formula: see text] < 40% of control) did CK flux drop (to 1.9 ± 0.2 mM/s at[Formula: see text] = 25% of control) together with impaired systolic activity and a rise in end-diastolic pressure. In contrast, in mild hypoxia CK flux remained constant and similar to control (5.3 ± 0.5 mM/s, not significant) despite a twofold reduction in systolic activity. Similarly in all CN groups, constant CK flux was maintained for a threefold reduction in RPP, showing the absence of a relation between cardiac performance and global NMR-measured CK flux during mild ATP synthesis inhibition.
Cell density and contraction regulate p38 MAP kinasedependent responses in neonatal rat cardiac myocytes
Authors: Hines Wirt A. , Thorburn Jacqueline , Thorburn Andrew
Published: December 2017

In vitro cardiac myocyte hypertrophy is characterized by increased cell size, sarcomere organization, and induction of several genes including atrial natriuretic factor (ANF). The hypertrophic growth program has been associated with activation of various mitogen-activated protein kinase (MAP) kinase family members, one of which is a stress kinase, p38. In this study, we found that the p38-specific inhibitor SB-203580 failed to inhibit phenylephrine-induced ANF-driven gene expression in low-density myocyte cultures but did inhibit gene expression in higher density cultures. Dense myocyte cultures also had a higher metabolic activity and contraction rate than cells plated at low density. We found that mimicking this effect by rapid electrical pacing activated ANF-driven gene expression and that this expression was inhibited by inactivation of p38. However, addition of SB-203580 at time points ranging between 1 and 72 h suggests that the effect of p38 on the ANF promoter may be both direct and indirect. Electrical pacing induced a small, but consistent, increase in p38 phosphorylation (phospho-p38) at time points ranging from 30 min to 4 h, but at later times phospho-p38 levels were reduced. When myocytes were treated with phenylephrine or electrically paced in the presence of the p38 inhibitor, there was little discernible change in morphology or rates of protein synthesis from DMSO-treated cells at 48 or 72 h. These data indicate that cell density and myocyte contraction may modulate p38-dependent pathways for ANF gene expression, but these pathways may not be direct and have limited effects on hypertrophic morphology.
Nonuniform responses of transmembrane potential during electric field stimulation of single cardiac cells
Authors: Cheng David Ker-Liang , Tung Leslie , Sobie Eric A.
Published: December 2017

The response of cellular transmembrane potentials ( V m) to applied electric fields is a critical factor during electrical pacing, cardioversion, and defibrillation, yet the coupling relationship of the cellular response to field intensity and polarity is not well documented. Isolated guinea pig ventricular myocytes were stained with a voltage-sensitive fluorescent dye, di-8-ANEPPS (10 μM). A green helium-neon laser was used to excite the fluorescent dye with a 15-μm-diameter focused spot, and subcellular V m were recorded optically during field stimulation directed along the long axis of the cell. The membrane response was measured at the cell end with the use of a 30-ms S1-S2 coupling interval and a 10-ms S2 pulse with strength of up to ∼500-mV half-cell length potential (field strength × one-half the cell length). The general trends show that 1) the response of V m at the cell end occurs in two stages, the first being very rapid (<1 ms) and the second much slower in time scale, 2) the rapid response consists of hyperpolarization when the cell end faces the anode and depolarization when the cell end faces the cathode, 3) the rapid response varies nonlinearly with field strengths and polarity, being relatively larger for the hyperpolarizing responses, and 4) the slower, time-dependent response has a time course that varies in slope with field strength. Furthermore, the linearity of the dye response was confirmed over a voltage range of −280 to +140 mV by simultaneous measurements of optically and electrically recorded V m. These experimental findings could not be reproduced by the updated, Luo-Rudy dynamic model but could be explained with the addition of two currents that activate outside the physiological range of voltages: a hypothetical outward current that activates strongly at positive potentials and a second current that represents electroporation of the cell membrane.
Factors contributing to pressure overload-induced immediate early gene expression in adult rat hearts in vivo
Authors: Ogino Kazuhide , Cai Bolin , Gu Anguo , Kohmoto Takushi , Yamamoto Noriyoshi , Burkhoff Daniel
Published: December 2017

We determined the contributions of angiotensin II type 1 receptor (AT1) stimulation, adrenergic stimulation, and autonomic activation to pressure overload-induced c- fos expression in the adult rat heart in vivo. c- fos expression was increased in pressure-overloaded hearts created by aortic banding compared with sham-operated rats (458 ± 100% vs. sham, P < 0.05). GR-138950, a selective AT1antagonist, did not blunt this expression (banding vs. banding + GR-138950: 458 ± 100% vs. 500 ± 125%, not significant). Atropine and hexamethonium partially decreased c- fos expression (banding vs. banding + atropine/hexamethonium: 700 ± 67% vs. 400 ± 67%, P < 0.05). Phentolamine had no significant effect on c- fosexpression; however, propranolol inhibited the expression (banding vs. banding + propranolol: 492 ± 108% vs. 154 ± 15%, P < 0.05). The inhibition by propranolol was independent of the decreases in heart rate. Thus factors contributing to pressure overload-induced c- fos expression in adult rat hearts in vivo are different from those in neonatal myocytes in vitro undergoing stretch.
Changes in sarcolemmal PLC isoenzymes in postinfarct congestive heart failure: partial correction by imidapril
Authors: Tappia Paramjit S. , Liu Song-Yan , Shatadal Shalini , Takeda Nobuakira , Dhalla Naranjan S. , Panagia Vincenzo
Published: December 2017

We have examined the changes in quantity and activity of cardiac sarcolemmal (SL) phosphoinositide-phospholipase C (PLC)-β1, -γ1, and -δ1in a model of congestive heart failure (CHF) secondary to large transmural myocardial infarction (MI). We also instituted a late in vivo monotherapy with imidapril, an ANG-converting enzyme (ACE) inhibitor, to test the hypothesis that its therapeutic action is associated with the functional correction of PLC isoenzymes. SL membranes were purified from the surviving left ventricle of rats in a moderate stage of CHF at 8 wk after occlusion of the left anterior descending coronary artery. SL PLC isoenzymes were examined in terms of protein mass and hydrolytic activity. CHF resulted in a striking reduction (to 6–17% of controls) of the mass and activity of γ1- and δ1-isoforms in combination with a significant increase of both PLC β1parameters. In vivo treatment with imidapril (1 mg/kg body wt, daily, initiated 4 wk after coronary occlusion) improved the contractile function and induced a partial correction of PLCs. The mass of SL phosphatidylinositol 4,5-bisphosphate and the activities of the enzymes responsible for its synthesis were significantly reduced in post-MI CHF and partially corrected by imidapril. The results indicate that profound changes in the profile of heart SL PLC-β1, -γ1, and -δ1occur in CHF, which could alter the complex second messenger responses of these isoforms, whereas their partial correction by imidapril may be related to the mechanism of action of this ACE inhibitor.
Effect of early transient adherent leukocytes on venular permeability and endothelial actin cytoskeleton
Authors: Valeski J. Edward , Baldwin Ann L.
Published: December 2017

In a time course study of the development and recovery of venular leaks, it was shown that, after as early as 3 min of histamine application, venular leak formation was identified [Baldwin, A. L., and G. Thurston. Am. J. Physiol. 269 ( Heart Circ. Physiol. 38): H1528–H1537, 1995]. This was accompanied by changes in the endothelial actin cytoskeleton and the presence of adherent leukocytes. The venular leaks remained elevated for at least 30 min, whereas the adherent leukocytes were decreased by 20 min. The present study was performed to determine the role that 3 min (early), transient histamine-associated adherent leukocytes play in the formation of venular leaks and changes in the endothelial actin cytoskeleton. In anesthetized rats, the microvasculature of a mesenteric window was perfused with buffered saline or fucoidin. FITC-BSA or FITC-BSA and 10−4M histamine was added to the perfusate for the last 3 min. The vasculature was perfusion fixed, stained for filamentous actin, and viewed microscopically. Fucoidin pretreatment significantly reduced the number of early, transient histamine-associated adherent leukocytes ( P < 0.01). The number of adherent leukocytes in leaky venules was significantly greater than that seen in nonleaky venules ( P < 0.01); however, the reduction in the number of histamine-associated adherent leukocytes with fucoidin pretreatment had no significant effect on the number ( P > 0.05) or area ( P > 0.05) of FITC-BSA leaks or on the endothelial actin cytoskeleton.
Myocardial oxygenation in vivo: optical spectroscopy of cytoplasmic myoglobin and mitochondrial cytochromes
Authors: Arai Andrew E. , Kasserra Claudia E. , Territo Paul R. , Gandjbakhche Amir H. , Balaban Robert S.
Published: December 2017

The oxygenation state of myoglobin and the redox state of cytochrome c provide information on the[Formula: see text] in the cytosol and mitochondria, respectively. An optical “window” from ∼540 to 585 nm was found in the pig heart in vivo that permitted the monitoring of myoglobin and cytochrome c without interference from Hb oxygenation or blood volume. Scanning reflectance spectroscopy was performed on the surgically exposed left ventricle of pigs. Difference spectra between control and a total left anterior descending coronary artery occlusion revealed maxima and minima in this spectral region consistent with myoglobin deoxygenation and cytochrome c and b reduction. Comparison of in vivo data with in vitro fractions of the heart, including Hb-free tissue whole heart and homogenates, mitochondria, myoglobin, and pig red blood cells, reveals minimal contributions of Hb in vivo. This conclusion was confirmed by expanding the blood volume of the myocardium and increasing mean Hb O2saturation with an intracoronary infusion of adenosine (20 μg ⋅ kg−1⋅ min−1), which had no significant effect on the 540- to 585-nm region. These results also suggested that myoglobin O2saturation was not blood flow limited under these conditions in vivo. Work jump studies with phenylephrine also failed to change cytochrome c redox state or myoglobin oxygenation. Computer simulations using recent physical data are consistent with the notion that myoglobin O2saturation is >92% under basal conditions and does not change significantly with moderate workloads. These studies show that reflectance spectroscopy can assess myocardial oxygenation in vivo. Myoglobin O2saturation is very high and is not labile to moderate changes in cardiac workload in the open-chest pig model. These findings indicate that myoglobin does not contribute significantly to O2transport via facilitated diffusion under these conditions.
Sodium/calcium exchange contributes to contraction and relaxation in failed human ventricular myocytes
Authors: Gaughan John P. , Furukawa Satoshi , Jeevanandam Valluvan , Hefner Colleen A. , Kubo Hajime , Margulies Kenneth B. , McGowan Brian S. , Mattiello Julian A. , Dipla Konstantina , Piacentino Valentino , Li Siyun , Houser Steven R.
Published: December 2017

Defects in myocyte contraction and relaxation are key features of human heart failure. Sodium/calcium exchanger-mediated contribution to contraction and relaxation were separated from other mechanisms [L-type calcium current, sarco(endo)plasmic reticulum (SR) Ca2+-ATPase] based on voltage, temperature, and selective blockers. Rod-shaped left ventricular myocytes were isolated from failed human explants ( n = 29) via perfusion with collagenase-containing Krebs solution. Action potentials using perforated patch and contractions using an edge detector were recorded at 0.5–1.5 Hz in Tyrode solution at 25°C and 37°C. Contraction duration was dependent on action potential (AP) duration at 37°C but not at 25°C, suggesting the role of the exchanger in relaxation and linking myocyte relaxation to the repolarization phase of the AP. Voltage-clamp experiments from −50 to +10 mV for 1,500 ms in Tyrode or Na+- and K+-free solutions after conditioning pulses triggered biphasic contractions that included a rapid SR-mediated component and a slower voltage-dependent exchanger-mediated component. We used thapsigargin to block the SR, which eliminated the rapid component, and we used an exchanger blocker, Kanebo 7943, which eliminated the slow component. The exchanger was shown to contribute to contraction through reverse-mode exchange, as well as to play a key role in relaxation of human ventricular myocytes.