bluuebunny/crossref_metadata_2025 huggingface dataset:
Chronic effects of ANG II antagonist in heart failure: improvement of cGMP generation from ANP
Authors: Maeda Y. , Wada A. , Tsutamoto T. , Fukai D. , Kinoshita M.
Published: December 2017

To evaluate the effects of endogenous angiotensin II (ANG II) on the development of congestive heart failure (CHF), we examined cardiorenal and hormonal factors after chronic administration of the ANG II type 1 receptor antagonist TCV-116 in dogs with CHF induced by rapid right ventricular pacing. After 8 days of pacing, TCV-116 administration [1 (group 1) or 3 mg.kg-1.day-1 (group 2)] was started and continued until the 22nd day. TCV-116 was found to have protected the deterioration of cardiorenal functions and the activation of neurohormonal factors. Although there was no significant difference in the pulmonary capillary wedge pressure or plasma atrial natriuretic peptide (ANP) level between the TCV-116-treated groups (354 +/- 85 and 364 +/- 29 pg/ml for groups 1 and 2, respectively) and the vehicle group (385 +/- 20 pg/ml), the plasma guanosine 3',5'-cyclic monophosphate (cGMP) levels, a second messenger of ANP, were twofold higher in TCV-116-treated groups (49.4 +/- 10.2 and 50.6 +/- 7.7 pmol/ml for groups 1 and 2, respectively) than in the vehicle group (24 +/- 4.0 pmol/ml), with a high correlation between the plasma ANP and cGMP levels (r = 0.90; P < 0.05). These findings indicate that endogenous ANG II has important roles in hemodynamics and renal functions during the development of CHF, which may be due, in part, to a reduction in endogenous ANP activity, suggesting the usefulness of an ANG II-receptor antagonist against the development of CHF.
Role of nitric oxide in vasodilator response induced by salbutamol in rat diaphragmatic microcirculation
Authors: Chang H. Y.
Published: December 2017

To determine the contribution of nitric oxide (NO) to the vasodilator response induced by salbutamol in diaphragmatic microcirculation, we studied a diaphragmatic preparation in anesthetized rats. With bicarbonate-buffered Ringer solution continuously suffusing the diaphragm, laser-Doppler flowmetry was used to record microvascular blood flow (QLDF). The drugs were applied to the surface of the diaphragm. Salbutamol (3.2 x 10(-7)-10(-4) M), isoproterenol (3.2 x 10(-8)-3.2 x 10(-6) M), and forskolin (3.2 x 10(-7)-10(-5) M) each elicited a concentration-dependent increase in QLDF. The vasodilator response induced by salbutamol (3.2 x 10(-7), 10(-6), and 3.2 x 10(-6) M) was attenuated by a 15-min suffusion of N omega-nitro-L-arginine (L-NNA, 10(-4) M), and pretreatment with L-arginine (10(-2) M) could restore salbutamol-induced vasodilator responses. Salbutamol-induced vasodilation was also abolished by propranolol (10(-5) M). Similarly, the vasodilator response elicited by isoproterenol (3.2 x 10(-8), 10(-7), and 3.2 x 10(-7) M) and forskolin (3.2 x 10(-7), 10(-6), and 3.2 x 10(-6) M) was inhibited by L-NNA (10(-4) M). In contrast, the vasodilator response induced by adenosine (10(-6), 10(-5), and 10(-4) M) was not affected by L-NNA (10(-4) M). These data indicate that in rat diaphragmatic microcirculation salbutamol-induced vasodilation may be partly mediated by beta-adrenoceptors on the endothelium. Moreover, these data suggest that an elevation of cyclic AMP in the endothelium may cause release of NO.
Involvement of AT2 receptors at NRVL in tonic baroreflex suppression by endogenous angiotensins
Authors: Lin K. S. , Chan J. Y. , Chan S. H.
Published: December 2017

We evaluated the role of endogenous angiotensin II and III (ANG II and ANG III) at the rostral nucleus reticularis ventrolateralis (NRVL) in the modulation of baroreceptor reflex (BRR) response and the subtype of angiotensin receptors involved in this process. Adult male Sprague-Dawley rats anesthetized and maintained with pentobarbital sodium were used. Exogenous application of ANG II or ANG III (10, 20, or 40 pmol) by bilateral microinjection into the NRVL significantly suppressed the BRR response to transient hypertension induced by phenylephrine (5 micrograms/kg i.v.). The suppressive effect of ANG II (20 pmol) was reversed by an equimolar dose (1.6 nmol) of its peptide antagonist, [Sar1, Ile8]ANG II, and the nonpeptide antagonists for AT1 and AT2 receptors, losartan and PD-123319, respectively. On the other hand, the inhibitory action of ANG III (20 pmol) was blunted by its peptide antagonist. [Ile7]ANG III or PD-123319, but not by losartan. Blocking the endogenous activity of the angiotensins by microinjection into the bilateral NRVL of [Sar1, Ile8]ANG II, [Ile7]ANG III, or PD-123319 elicited an appreciable enhancement of the BRR response, whereas losartan produced minimal effect. These results suggest that, under physiological conditions, both endogenous ANG II and ANG III may exert a tonic inhibitory modulation on the BRR response by acting selectively on the AT2 receptors at the NRVL.
Oxygen tension gradients and heterogeneity in venous microcirculation: a phosphorescence quenching study
Authors: Shonat R. D. , Johnson P. C.
Published: December 2017

Localized measurements of intravascular oxygen tension (PO2) at multiple locations in the microvascular network of the rat spinotrapezius muscle were used to study the spatial distribution of PO2 in venular structures. By use of a newly developed phosphorescence system to rapidly and repeatedly measure PO2, 538 individual measurements were made in 18 different networks during rest. Average intravascular PO2 was (in mmHg +/- SD) 33 +/- 9, 21 +/- 9, 26 +/- 10, and 33 +/- 8 in small arcade arterioles, postcapillary venules (PV), 3 degrees venules (3V), and arcade venules, respectively. The coefficient of variation (CV), a descriptive indicator of spatial heterogeneity, was correspondingly 0.28, 0.45, 0.37, and 0.23 for the different vessel groups. PO2 was found to increase significantly (P < 0.001) from PV to 3V, rising 0.009 +/- 0.002 mmHg/microns along the vessel. By linear regression, the slope of PO2 for the vessel difference group, PV-3V as a function of mean systemic blood pressure (BPm; in mmHg) was -0.09 +/- 0.04 (P < 0.05), indicating that the measured longitudinal oxygen gradients and CV are only weakly dependent on BPm. The results support the hypothesis that oxygen can diffuse across the walls of postcapillary vessels and suggest that the venular structures are not merely passive conduits for removing oxygen and waste products but may play an important role in regulating oxygen delivery.
KCa-channel blockade prevents sustained pressure-induced depolarization in rat mesenteric small arteries
Authors: Wesselman J. P. , Schubert R. , VanBavel E. D. , Nilsson H. , Mulvany M. J.
Published: December 2017

In small blood vessels, elevation of transmural pressure induces myogenic constrictions and smooth muscle depolarization. The role of calcium-activated K+ channels (KCa channels) in these responses was examined in cannulated rat mesenteric small arteries. Inner and outer diameter were continuously monitored with a video technique. Smooth muscle membrane potential was recorded simultaneously using microelectrodes. To test for myogenic responsiveness, the transmural pressure was changed stepwise in the range between 10 and 120 mmHg. Pressure elevation induced moderate myogenic responses and significant depolarization, from -54.5 +/- 0.4 (SE) mV (n = 56) at 10 mmHg to -47.3 +/- 1.8 mV (n = 12) at 120 mmHg. Norepinephrine (NE, 0.67 and 10 microM) induced constriction and vasomotion, augmented myogenic responsiveness, and shifted the pressure-membrane potential relation to more depolarized values. Blockade of the Kca channels with charybdotoxin (ChTX) suppressed the responsiveness to pressure. In the absence of ChTX, with 0.67 microM NE, pressure elevation from 10 to 120 mmHg induced depolarization from -46.9 +/- 1.0 (n = 16) to -35.8 +/- 0.7 (n = 12) mV, whereas because of the myogenic response, the diameter increased only by 7%. In the presence of ChTX, with 0.3 microM NE, pressure changed the membrane potential from -41.0 +/- 1.1 (n = 12) to -37.8 +/- 0.7 mV (n = 4), which was not significant, and the diameter increased by 28%. These results demonstrate that blockade of KCa channels reduces responsiveness to pressure elevation. This suggests that pressure may induce depolarization and concomitant myogenic responsiveness by closure of KCa channels.
Effect of K(+)-channel blockers on ACh-induced hyperpolarization and relaxation in mesenteric arteries
Authors: Chen G. , Cheung D. W.
Published: December 2017

Acetylcholine (ACh) induces endothelium-dependent hyperpolarization in the rat mesenteric artery in the presence of the nitric oxide synthase inhibitor N omega-nitro-L-arginine. We have now studied the effects of K(+)-channel blockers on the hyperpolarization responses to ACh in resting and norepinephrine-contracted rat mesenteric arteries. We also measured tension simultaneously to determine whether the inhibitory effects of these agents on relaxation could be correlated to their effects on hyperpolarization. Glibenclamide had no significant effect on the hyperpolarization or relaxation. Tetraethylammonium (TEA, 5 mM) inhibited the hyperpolarization to ACh significantly to a similar extent in both the resting and norepinephrine-stimulated arteries. Charybdotoxin (100–150 nM) caused only a small but significant inhibition. Apamin (0.3 microM) was the most effective in inhibiting the hyperpolarization in resting arteries. It was less effective in the norepinephrine-contracted arteries. A combination of apamin and charybdotoxin completely abolished the hyperpolarization responses in both conditions. The relaxation to ACh was correlated to hyperpolarization. In all cases, the inhibition of the relaxation by the K(+)-channel blockers could be accounted for by their effects on the hyperpolarization. These results indicate that Ca(2+)-activated K(+)-channels, especially those sensitive to apamin, may be the major ion channels mediating endothelium-dependent hyperpolarization to ACh.
Response of native and stimulated collateral vessels to serotonin
Authors: Lamping K. G.
Published: December 2017

Previous studies suggest that collateral vessels constrict in response to serotonin. The objective of these studies was to directly measure responses of native and stimulated collateral vessels 30-400 microns in diameter to serotonin and to determine the mechanisms involved in responses to serotonin. Serotonin was suffused onto the left ventricle of dogs, and microvascular diameters were measured with computer-controlled stroboscopic illumination coupled to a microscope-video system. Stimulated collateral vessels and arterioles in collateral-dependent myocardium were measured after Ameroid constriction of the left circumflex artery. Noncollateral and native collateral vessels were examined in dogs without a constrictor. Serotonin produced dose-dependent dilation of noncollateral vessels that was decreased in native collateral vessels, stimulated collateral vessels, and vessels in collateral-dependent myocardium. Dilation in response to nitroprusside was similar in all groups. Dilation in response to serotonin was enhanced by inhibition of 5-hydroxytryptamine (5-HT)2 receptors with ketanserin and blocked by nonselective 5-HT1 and 5-HT2 receptors with methiothepin. Inhibition of nitric oxide (NO) synthase with NG-nitro-L-arginine decreased dilation in response to serotonin. Thus collaterals and arterioles in collateral-dependent myocardium are less sensitive to the dilating effect of serotonin. Responses to serotonin involve a balance between dilation mediated by 5-HT1 receptors and constriction mediated by 5-HT2 receptors.
Use of oxygen-15 to measure oxygen-carrying capacity of blood substitutes in vivo
Authors: Phillips W. T. , Lemen L. , Goins B. , Rudolph A. S. , Klipper R. , Fresne D. , Jerabek P. A. , Emch M. E. , Martin C. , Fox P. T. , McMahan C. A.
Published: December 2017

A method for determining oxygen-carrying capacity of blood substitutes has been developed using the short-lived cyclotron-produced positron-emitting isotope 15O. This method measures the oxygen-carrying capacity of the blood substitutes in vivo in the presence of red blood cells and allows determination of changes in the oxygen-carrying capacity over time after exchange transfusion. This method is applied to the blood substitutes of liposome-encapsulated hemoglobin (LEH) and cell-free hemoglobin (Hb). We have used 15O (half-life of 2 min) to quantitate the lung uptake and tissue delivery of [15O2]LEH. Lung uptake studies were performed in intubated, catheterized rats after a 40% exchange transfusion of bovine LEH (LEBH; 0.68 g Hb/kg body wt), human hemolysate LEH (LEHH; 1.0 g Hb/kg body wt), or free bovine hemoglobin (SFHS; 0.56 g Hb/kg body wt). A bolus inhalation of 15O2 (3-5 mCi) was given at 15 min, 3 h, and 24 h post-transfusion. Arterial blood samples were collected, spun, and separated into LEH, red blood cell, and plasma fractions. 15O activity and hemoglobin content were determined for each fraction. Oxygen-carrying capacity was calculated as a percentage of the original red blood cell fraction removed. For LEBH, the carrying capacity was 15% at 15 min, 13% at 3 h, and 1% at 24 h. For LEHH, the carrying capacity was 30% at 15 min, 26% at 3 h, and 19% at 24 h. The marked decrease in carrying capacity at 24 h for LEBH compared with LEHH was attributable to the increased formation of methemoglobin in the circulating LEBH rather than increased removal from circulation, because total hemoglobin concentrations measured for both LEH samples decreased at a similar rate during the 24 h. The presence of methemoglobin reductase and other naturally occurring antioxidants in the LEHH may be responsible for maintaining the higher levels of oxyhemoglobin. Oxygen-carrying capacity for SFHS also decreased over time but at a much sharper rate compared with both LEH formulations. The carrying capacity for SFHS of 8% measured at 15 min decreased to 0.3% at 3 h and undetectable levels at 24 h. This sharper decrease in carrying capacity for SFHS is attributable to the rapid removal of the hemoglobin from circulation.d
Absence of age-related decline in total blood volume in physically active females
Authors: Jones P. P. , Davy K. P. , DeSouza C. A. , van Pelt R. E. , Seals D. R.
Published: December 2017

Total blood volume (TBV) is an important determinant of cardiovascular functional capacity and the ability to maintain homeostasis during acute thermal and orthostatic stress. The primary aim of the present study was to test the hypotheses that TBV is 1) decreased with age in healthy, sedentary females, 2) not decreased with age in physically active females, and 3) directly related to maximal aerobic activity [maximal O2 consumption (VO2max)] in women of different ages and physical activity levels. An additional aim was to determine whether the use of hormone-replacement therapy in postmenopausal women is associated with altered TBV. Resting supine plasma volume (modified Evans blue dye technique) was measured in 25 postmenopausal women [12 sedentary (post-S), 13 physically active (post-PA; mean values, respectively, age 60 and 58 yr, and VO2max = 23 and 40 ml.kg-1.min-1)] and 27 premenopausal women [12 sedentary (pre-S), 15 physically active (pre-PA; mean values, respectively, age 29 and 31 yr, and VO2max = 35 and 54 ml.kg-1.min-1)]. TBV was lower in post-S (61 ml/kg) compared with pre-S (73 ml/kg) but not in post-PA (82 ml/kg) compared with pre-PA (87 ml/kg). It was also lower in post-S compared with post-PA. The lower TBV in post-S relative to pre-S and post-PA was related to lower plasma and estimated red blood cell volumes. Volumes did not differ between users and nonusers of hormone replacement. TBV was directly related to VO2max among all subjects (r = 0.65). It is concluded that 1) aging is associated with a decrease in TBV due to reductions in both plasma and erythrocyte cell volumes in healthy, sedentary females; 2) total blood, plasma, and red blood cell volumes are maintained with age in physically active females; 3) TBV is directly related to maximal aerobic capacity in females; and 4) TBV is not different in postmenopausal women using versus not using hormone-replacement therapy.
Influence of gender on vasomotor effects of oxidized low-density lipoprotein in porcine coronary arteries
Authors: Cox D. A. , Cohen M. L.
Published: December 2017

This study compared 5-hydroxytryptamine (5-HT)-induced contraction and relaxation in coronary arteries from male and female pigs and compared the vasomotor effects of the atherosclerotic lipoprotein, oxidized low-density lipoprotein (LDL), in these tissues. 5-HT-induced contraction and endothelium-dependent relaxation were similar, as was sodium nitroprusside-induced relaxation, in coronary arteries from male and female pigs. These data suggest that there were no gender-related differences in 5-HT-induced contraction or 5-HT-mediated nitric oxide (NO) release from the coronary endothelium. In contrast, oxidized LDL (100 micrograms/ml) enhanced 5-HT-induced contraction to a greater extent in coronary arteries from male versus female pigs. Because oxidized LDL inhibited 5-HT-induced relaxation similarly in arteries from male and female animals, a greater effect of oxidized LDL on agonist-induced NO release in tissues from male pigs cannot explain the greater effect on 5-HT-induced contraction. Oxidized LDL contracted coronary arteries from males with a greater force than arteries from females when measured from baseline tone, suggesting that oxidized LDL inhibited basal NO release to a greater extent in coronary arteries from male pigs compared with females, an effect that may have participated in the greater enhancement of 5-HT-induced contraction that occurred in arteries from male pigs. These gender-related differences in the vasomotor effects of oxidized LDL may play an important role in the lesser incidence of cardiovascular disease in premenopausal females than in males and may provide insight into the cardioprotective effect of estrogen.
Ca2+ release mechanism of primate drug-induced coronary vasospasm
Authors: Miyagawa K. , Vidgoff J. , Hermsmeyer K.
Published: December 2017

Cellular mechanisms of protection against drug-stimulated coronary vasospasm were studied by multiweek estrogen plus progesterone (P) vs. medroxy-progesterone acetate (MPA) treatments by measuring intracellular Ca2+ and protein kinase C (PKC) signals. Ovariectomized monkeys (OVX) were treated by slow-release implants with either P or MPA for 4 wk added to estradiol-17 beta (E2) begun 2 wk earlier. A third group received E2 for 2 wk and withdrawal of E2 (W; no steroid treatment) during the last 4 wk. OVX coronary artery vascular muscle cells (VMC) in primary culture conditions were labeled by the fluorescent indicators, fluo 3 and hypericin, respectively, to study intracellular Ca2+ and PKC mechanisms of coronary artery hyperre-activity, using digital analysis of single VMC by photon-counting camera. Stimulation by 10 microM serotonin and 100 nM U-46619 (thromboxane A2 mimetic) caused Ca2+ increases (2-5 min) and no PKC activation in VMC from five P-treated monkeys but prolonged (> or = 30 min) increases in both Ca2+ and PKC signals in VMC from six MPA-treated monkeys or seven W-treated monkeys; these P vs. MPA (or W) differences were maintained > or = 14 days. We hypothesize that hyperreactivity in VMC from MPA- or W-treated monkeys results from accelerated prolonged Ca2+ release, with concomitant PKC activation, and that MPA (but not P) negates the coronary vasospasm protective effect of E2.
Interactions between sympathetic and vagal cardiac afferents in nucleus tractus solitarii
Authors: Tjen-A-Looi S. , Bonham A. , Longhurst J.
Published: December 2017

Epicardial application of hydrogen peroxide (H2O2) reflexly elicits a sympathetically mediated pressor response. This pressor response is augmented by vagotomy and abolished by sympathectomy, suggesting an occlusive interaction between the afferents in the central nervous system (CNS). To support this observation we recorded sympathetic efferent responses from the sympathetic chain (T1-T2) before and after epicardial application of H2O2 in six cats before and after vagotomy. Cardiac sympathetic efferent responses to H2O2 were increased by vagotomy. Thus there exists an occlusive interaction between the two afferent pathways in the CNS. Because cardiopulmonary vagal afferents make their first central synapse in the nucleus tractus solitarii (NTS), we further hypothesized that cells in the NTS receive convergent inputs from sympathetic and vagal afferents and that the inputs would interact in an occlusive manner. In alpha-chloralose-anesthetized sinoaortic-denervated cats, cardiac sympathetic and vagal branches were stimulated electrically at 1 Hz, either separately or in combination. Extracellular single-unit activity was recorded in the NTS. Vagal stimuli most frequently (38%) diminished sympathetically evoked unit activity (-46.6 +/- 6.0%) versus control (1.4 +/- 1.5%). However, a few (21%) vagal and sympathetic afferent inputs were found to be additive or facilitative. We conclude that interactions occur between cardiac sympathetic and vagal afferents in the NTS. It is possible that this occlusive interaction explains the alteration in cardiac sympathetic outflow after epicardial stimulation with H2O2.
Increased cardiac ppENK mRNA in cardiac hypertrophy and effects on blood pressure of its peptide products
Authors: Hao J. M. , Rabkin S. W.
Published: December 2017

The objective of this study was to examine the expression of preproenkephalin (ppENK) in the heart in cardiac hypertrophy and the effects on cardiac contractility and blood pressure regulation of its peptide products. The ppENK-derived peptides Leu5-enkephalin (LE), Met5-enkephalin (ME), Met5-enkephalin-Arg6-Gly7-Leu8 (MEAGL), and Met5-enkephalin-Arg6-Phe7 (MEAP) were administered intravenously to unanesthetized Sprague-Dawley rats and to an isolated heart preparation from the same species. LE, ME, MEAGL, or MEAP (360 nmol iv) produced an immediate decrease in heart rate, reaching its maximum within 10 s and returning to baseline by 30 s. The blood pressure response for each enkephalin was a small initial decrease followed by a marked and significant increase (P < 0.05 for MEAP). In the isolated heart preparation, neither LE, ME, MEAGL, nor MEAP altered left ventricular contractility. Cardiac hypertrophy was produced in the Dahl salt-dependent model of hypertension with a significantly greater heart weight-to-body weight ratio in the Dahl salt-sensitive (S) compared with the Dahl salt-resistant (R) rat on a high-salt diet (P < 0.05). Tissue RNA was extracted, and Northern blot analysis identified and quantitated mRNA with a 0.93-kilobase cDNA of ppENK A. There was more ppENK mRNA in the left than in the right ventricle and much less in the atria than in the ventricles. The amount of ppENK mRNA was markedly and significantly increased in the left ventricle of the Dahl S compared with the Dahl R rat (P < 0.05). In contrast, there were no differences in ppENK mRNA levels in different brain regions between the R and S rats on a high-salt diet. Interestingly, a larger ppENK mRNA of 1.75 kilobases was abundantly expressed in testicular tissue. These data showing increased ppENK expression raise the possibilities of 1) an autocrine/paracrine role for enkephalins in cardiac hypertrophy and 2) an endocrine role for the hypertrophic heart, with an increased production of enkephalins, especially MEAP, that produces vasoconstriction and further increases in blood pressure.
Open channel block of human heart hKv1.5 by the beta-subunit hKv beta 1.2
Authors: De Biasi M. , Wang Z. , Accili E. , Wible B. , Fedida D.
Published: December 2017

Voltage-gated K+ currents in human heart are likely to derive from multisubunit complexes of pore-forming alpha-subunits with one or more auxiliary beta-subunits. We recently cloned a novel beta-subunit from human atrium, hKv beta 1.2 (K. Majumder, M. De Biasi, Z. Wang, and B. A. Wible. FEBS Lett. 361: 13-16, 1995), and showed that it interacts with channels in the Kv1 family. Here we characterize the interaction of hKv beta 1.2 with hKv1.5 in terms of a two-closed-state and one-open-state open channel block model. After coexpression in Xenopus oocytes, hKv1.5 currents were reduced in the presence of hKv beta 1.2, and at positive potentials an inactivation process was introduced. Deactivation kinetics of hKv1.5 were slowed, and there was an increased steepness with a -14-mV hyperpolarizing shift in the midpoint of steady-state activation. The model was able to predict all the above features of the interaction of hKv1.5 and hKv beta 1.2 as a result of rapid open channel block of activated channels. Understanding the mechanism of hKv beta 1.2 action on heart K+ channels will further aid the development of the functional and pharmacological characterization of native cardiac K+ currents.
Influence of aging on protein import into cardiac mitochondria
Authors: Craig E. E. , Hood D. A.
Published: December 2017

This study was undertaken to determine whether age-related changes in the content and composition of cardiac mitochondria could be due, in part, to alterations in mitochondrial protein import. Precursor proteins malate dehydrogenase and ornithine carbamoyltransferase were synthesized by in vitro transcription and translation and were incubated with mitochondria isolated from the hearts of young (4-mo), old (22-mo), and senescent (28-mo) rats. Mitochondria from senescent animals exhibited a twofold higher import rate of both precursors into the matrix compartment compared with mitochondria from young and old animals. The expression of glucose regulated protein 75 and heat shock protein 60, two matrix chaperonins that are essential for import, was elevated in the mitochondria of both old and senescent animals before the observed changes in import. Import was equally affected in senescent and young heart mitochondria by inhibition of cardiolipin, a mitochondrial phospholipid involved in protein translocation. The results indicate that the altered mitochondrial phenotype evident in the aging myocardium cannot be accounted for by reduced rates of protein import. Furthermore, levels of cardiolipin and matrix chaperonins do not appear to be rate-limiting steps in the import process. These data suggest that the protein import step of mitochondrial assembly is subject to adaptations under pathophysiological conditions.
Negative chronotropic and inotropic effects of endothelin isopeptides in mammalian cardiac muscle
Authors: Zhu Y. , Yang H. T. , Endoh M.
Published: December 2017

In isolated rabbit right atria, endothelin (ET) isopeptides ET-1 and ET-3 elicited a concentration-dependent negative chronotropic effect (NCE) in the presence of isoproterenol (Iso): ET-1 was approximately 10 times more potent than ET-3. The NCE of ET-1 was abolished by the ETA- and ETB-receptor antagonist TAK-044 (1 microM) or the ETA-receptor antagonist BQ-123 (10 microM), but it was not affected by the ETB-receptor antagonist RES-701-1 or BQ-788. ET-1 decreased the adenosine 3',5'-cyclic monophosphate (cAMP) level in the presence of Iso in rabbit atria. Pretreatment with pertussis toxin (PTX) markedly attenuated the NCE of ET-1 and abolished the decrease in the cAMP level induced by ET-1. In isolated dog ventricular trabeculae, ET-1 elicited a pronounced negative inotropic effect (NIE), whereas ET-3 induced a small but significant positive inotropic effect in the presence of Iso. The NIE was abolished by the ETA-receptor antagonist BQ-123 (1 microM) and partially attenuated by the ETB-receptor antagonist RES-701-1. The positive inotropic effect of ET-3 was abolished by RES-701-1. Although pretreatment with PTX markedly attenuated the NIE of ET-1, cAMP levels in dog ventricular muscle were not decreased by ET-1. These results indicate that activation of an ETA receptor that is coupled to the PTX-sensitive G protein plays a dominant role in the NCE and NIE of ET-1. The NCE of ET-1 may, in part, be due to a decrease in cAMP level. By contrast, the NIE of ET-1 does not involve an alteration of cAMP accumulation. The present findings imply that ET isopeptides might antagonize the cardiostimulatory action of catecholamines mediated by beta-adrenoceptors when the blood level of both endogenous regulators are increased under cardiovascular pathophysiological situations.
Relationship between external load and isolated myocyte contractile function with CHF in pigs
Authors: Wang Z. , Lam C. F. , Mukherjee R. , Hebbar L. , Wang Y. , Spinale F. G.
Published: December 2017

Past studies have demonstrated that the negative relationship between afterload and contractile performance of papillary muscles is shifted downward and to the left with the development of hypertrophy. However, it remained unclear whether a similar load-contractility relationship could be constructed for isolated myocytes, particularly with the development of congestive heart failure (CHF). Accordingly, the effect of incrementally increased external loads on the contractile performance of left ventricular (LV) myocytes isolated from pigs in the normal state (n = 5) and after the development of chronic supraventricular tachycardia (SVT)-induced CHF (SVT-CHF; 240 beats/min, 3 wk; n = 5) was examined. This study used precalibrated microspheres to impose a quantifiable load on isolated myocytes, and myocyte contractility was assessed by videomicroscopy. Steady-state unloaded extent of shortening was 5.4 +/- 0.2 microns in control myocytes (n = 80) and was significantly reduced in the myocytes with the development of SVT-CHF (4.4 +/- 0.2 microns, n = 93; P <0.05). Inverse relationships between relative resistive load and myocyte contractile function were observed at both normal and CHF states (r2 > 0.85). For myocyte velocity of shortening, the slope of this relationship was significantly reduced in the SVT-CHF state compared with controls (-46.3 x 10(-6) and -34.6 x 10(-6) microns3.microN-1.s-1, respectively; P < 0.05). At higher relative resistive loads (> 0.18 x 10(-6) microN/microns2), the reduction in myocyte shortening extent under an equivalent relative resistive load was significantly greater in the SVT-CHF myocytes compared with controls (62.8 +/- 3.9 vs. 45.6 +/- 4.7%, respectively, P < 0.05). The present study demonstrated for the first time that a load-dependent relationship can be derived for intact isolated LV myocytes in both normal and CHF states. The defect in the capacity of SVT-CHF myocytes to respond to an increased relative resistive load is a likely contributory mechanism for the LV pump dysfunction that occurs in this model of CHF.
Plasma renin activity in heart failure-prone SHHF/Mcc-facp rats
Authors: Holycross B. J. , Summers B. M. , Dunn R. B. , McCune S. A.
Published: December 2017

Plasma renin activity (PRA) increases during heart failure; however, PRA is altered by drug therapy, and it is difficult to study the natural progression of elevated PRA in humans and the possible factors that contribute to its rise. This study evaluated PRA in a drug-naive hypertensive rat model (SHHF/Mcc-facp) that has a genetic program resulting in heart failure (HF). Mean arterial blood pressure and PRA were determined and correlated to heart weight index in conscious normotensive, spontaneously hypertensive rats and HF rats of various ages. PRA, atrial natriuretic peptide, and aldosterone levels progressively increase with age in male HF rats. PRA and blood pressure are independently correlated to cardiac hypertrophy in male HF rats. Atrial natriuretic peptide was elevated in spontaneously hypertensive compared with normotensive rats. Female HF rats have elevated PRA, but the increase is temporally delayed compared with that in male HF rats. Hypertension, PRA, and male gender are independent factors contributing to cardiac hypertrophy and heart failure in the HF model. The HF rat model may prove useful in determining the contribution of these factors in the progression from cardiac hypertrophy to heart failure.
Role of ATP-sensitive K+ channels in ischemic preconditioning of skeletal muscle against infarction
Authors: Pang C. Y. , Neligan P. , Xu H. , He W. , Zhong A. , Hopper R. , Forrest C. R.
Published: December 2017

We studied the role and mechanism of ATP-sensitive K+ (KATP) channels in ischemic preconditioning (IPC) of skeletal muscle against infarction in vivo. Surgically denervated, noncontractile latissimus dorsi muscle flaps in pentobarbitone-anesthetized pigs were assigned to nine groups: control; IPC (3 cycles of 10-min ischemia/reperfusion); preischemic lemakalim (LMK, 0.18 mg/muscle); postischemic LMK; sodium 5-hydroxydecanoate (5-HD, 27 mg/muscle) before IPC; glibenclamide (Glib 0.3 mg/kg iv) before IPC; 5-HD before preischemic LMK; 5-HD before ischemia; and Glib before ischemia. Except for Glib, all drugs were delivered to each muscle by 10-min local intraarterial infusion to avoid systemic effects. All muscle flaps underwent 4 h of global ischemia. Infarction was assessed at 48 h of reperfusion. In a separate study, muscle biopsies were taken before, during, and after ischemia for assay of high-energy phosphate and lactate contents and myeloperoxidase (MPO) activity. It was observed that muscle infarction in the IPC (24 +/- 2%) and preischemic LMK (21 +/- 2%) groups were smaller (P < 0.05) than that in the control (42 +/- 2%). The anti-infarction effect of IPC and LMK was blocked by 5-HD or Glib. IPC and preischemic LMK caused a higher (P < 0.05) muscle content of ATP and energy charge potential, a lower (P < 0.05) muscle content of lactate during ischemia, and a lower (P < 0.05) muscle MPO activity throughout 16 h of reperfusion compared with the control. These observations indicated for the first time that KATP channels are also involved in the anti-infarction effect of IPC in noncontractile skeletal muscle in vivo. Presently, the cause and importance of energy-sparing and neutrophil-inhibitory effects of IPC and LMK are not known.
Molecular analysis of blood vessel formation and disease
Authors: Carmeliet Peter , Collen Désiré
Published: December 2017

Blood vessels affect the quality of life in many ways. They provide an essential nutritive function during growth and repair of tissues but, on the other hand, can become affected by disorders or trauma, resulting in bleeding, thrombosis, arterial stenosis, and atherosclerosis. Three molecular systems, the vascular endothelial growth factor (VEGF) system, the plasminogen system, and the coagulation system, have been implicated in the formation and pathobiology of blood vessels. This review focuses on the role of these systems in these processes. Recent gene-targeting studies have identified VEGF as a potent modulator of the formation of endothelial cell-lined channels. Somewhat unanticipated, the initiator of coagulation is not only involved in the control of hemostasis but also in the maturation of a muscular wall around the endothelium. With different murine models of cardiovascular disease, a pleiotropic role of the plasminogen system was elucidated in thrombosis, in arterial neointima formation after vascular wound healing and allograft transplantation, in atherosclerosis, and in the formation of atherosclerotic aneurysms. Surprisingly, tissue-type plasminogen activator is also involved in brain damage after ischemic or neurotoxic insults. The insights from these gene-targeting studies have formed the basis for designing gene therapy strategies for restenosis and thrombosis, which have been successfully tested in these knockout models.
Molecular remodeling of cardiac contractile function
Authors: James Jeanne , Robbins Jeffrey
Published: December 2017

A number of techniques are now available that allow the contractile apparatus of the heart to be altered in a defined manner. This review focuses on those approaches that result in germ-line transmission of the remodeling event(s). Thus the desired modifications can be propagated stably throughout multiple generations and result in the creation of stable, new animal models. Necessarily, such stable changes need to be performed at the level of the genome, and two distinct but complementary approaches have been developed: transgenesis and gene targeting. Each results in the stable modification of the mammalian genome. Via gene targeting or gene ablation of sequences encoding various components of the sarcomere, the contractile apparatus of the heart can be altered dramatically. Ablating a gene may lead to a loss in function, which can help establish a function of the candidate sequence. Gene targeting can also be used to effect changes in the sequences encoding a functional domain of the contractile protein or at a single-amino acid residue, resulting in the establishment of precise structure-function relationships. With the use of transgenesis, the contractile apparatus of the heart can also be significantly remodeled. These approaches are rapidly creating a group of animals in which altered contractile protein complements will lead to a fundamental understanding of the structure-function relationships that underlie the function of the heart at the molecular, biochemical, whole organ, and whole animal levels.
A role for neuropeptide Y in rat iridial arterioles
Authors: Newhouse Matthew J. , Hill Caryl E.
Published: December 2017

A role for neuropeptide Y (NPY) in neurotransmission in rat iridial arterioles has been investigated. Reverse transcription-polymerase chain reaction analysis has demonstrated mRNA expression for both Y1and Y2receptors in the superior cervical ganglion and iris. The Y1agonist [Leu31,Pro34]NPY caused a dose-dependent constriction of iris arterioles (50% effective concentration of 10−8M), but, at low concentrations (10−9and 10−10M), it failed to potentiate either submaximal responses to norepinephrine (10−6M) or submaximal, noradrenergic responses to nerve stimulation. In contrast, 10−7M [Leu31,Pro34]NPY potentiated submaximal, noradrenergic responses to nerve stimulation (10 Hz, ≤1 s) and to a concentration of norepinephrine (10−7M) which produced only small contractions. The Y1antagonist 1229U91 blocked contractions induced by [Leu31,Pro34]NPY. Stimulation of the nerves for longer periods (10 or 20 Hz; 5, 30, or 60 s) revealed a component of the response which was reduced by 1229U91. This component was not apparent after brief stimuli (10 Hz, ≤1 s), even when opposing receptor pathways were blocked. The Y2agonist N-acetyl-[Leu28,Leu31]NPY24–36had little effect on arterioles preconstricted with either high potassium or an α2-adrenoceptor agonist, or on nerve-mediated contractions. Results suggest that NPY, released from sympathetic nerves during long-duration, high-frequency stimulation, activates Y1receptors on iris arterioles to produce vasoconstriction and to potentiate responses to low concentrations of norepinephrine.
Effects of insulin on glucose uptake by rat hearts during and after coronary flow reduction
Authors: Chen T. Minsue , Goodwin Gary W. , Guthrie Patrick H. , Taegtmeyer Heinrich
Published: December 2017

We tested the hypothesis that low-flow ischemia increases glucose uptake and reduces insulin responsiveness. Working hearts from fasted rats were perfused with buffer containing glucose alone or glucose plus a second substrate (lactate, octanoate, or β-hydroxybutyrate). Rates of glucose uptake were measured by3H2O production from [2-3H]glucose. After 15 min of perfusion at a physiological workload, hearts were subjected to low-flow ischemia for 45 min, after which they were returned to control conditions for another 30 min. Insulin (1 mU/ml) was added before, during, or after the ischemic period. Cardiac power decreased by 70% with ischemia and returned to preischemic values on reperfusion in all groups. Low-flow ischemia increased lactate production, but the rate of glucose uptake during ischemia increased only when a second substrate was present. Hearts remained insulin responsive under all conditions. Insulin doubled glucose uptake when added under control conditions, during low-flow ischemia, and at the onset of the postischemic period. Insulin also increased net glycogen synthesis in postischemic hearts perfused with glucose and a second substrate. Thus insulin stimulates glucose uptake in normal and ischemic hearts of fasted rats, whereas ischemia stimulates glucose uptake only in the presence of a cosubstrate. The results are consistent with two separate intracellular signaling pathways for hexose transport, one that is sensitive to the metabolic requirements of the heart and another that is sensitive to insulin.
Dynamics of cardiovascular responses to repeated partial umbilical cord compression in late-gestation sheep fetus
Authors: Giussani Dino A. , Unno Nobuya , Jenkins Susan L. , Wentworth Richard A. , Derks Jan B. , Collins Jason H. , Nathanielsz Peter W.
Published: December 2017

We characterized the detailed hemodynamics of fetal blood pressure, heart rate, common umbilical blood flow, and femoral blood flow responses to partial compression of the umbilical cord and tested the hypothesis that repeated cord compression modulates fetal cardiovascular responses in 10 chronically instrumented fetal sheep at ∼130 days of gestation. In five fetuses ( group I), partial compression of the umbilical cord was induced 12 times, each for 5 min at 15-min intervals. Each cord compression reduced common umbilical blood flow by 50% and produced modest falls in fetal pH (7.33 ± 0 to 7.29 ± 0) and arterial [Formula: see text] (21.1 ± 0.2 to 16.8 ± 0.2 mmHg) and a mild increase in arterial[Formula: see text] (49.9 ± 0.5 to 54.9 ± 0.4 mmHg). Sham experiments were performed in five other fetuses ( group II). Second-by-second analysis of group I fetal cardiovascular data revealed a clear biphasic response to partial cord compression. Phase I (1st min of cord compression) was characterized by a rapid bradycardia and a rapid femoral vasoconstriction (primary response); phase II ( minutes 2–5of cord compression) was characterized by a delayed bradycardia and a return of femoral vascular resistance toward baseline (secondary response). Repeated cord compression abolished the primary, but not the secondary, cardiovascular responses. These results demonstrate that fetal cardiovascular responses to stress may be modified by preexposure to repeated intrauterine challenges.
Effect of chronic volume overload on baroreflex control of heart rate and sympathetic nerve activity
Authors: Willenbrock Roland , Stauss Harald , Scheuermann Michaela , Osterziel Karl Josef , Unger Thomas , Dietz Rainer
Published: December 2017

Baroreceptor-heart rate reflex sensitivity is decreased in congestive heart failure. The reflex control of heart rate and sympathetic nerve activity in rats with chronic volume overload, an established model for moderate heart failure, is still unknown. Therefore, we investigated the regulation of humoral and neuronal sympathetic activity and the baroreflex control of heart rate and sympathetic nerve activity in conscious, unrestrained rats with aortocaval shunt. Rats with aortocaval shunts had larger hearts (388 ± 11 vs. 277 ± 4 mg/100 g body wt), elevated central venous pressures (14 ± 4 vs. 4 ± 3 mmHg), and higher atrial natriuretic peptide plasma levels (87 ± 16 vs. 25 ± 3 pmol/l) than controls but had similar systemic blood pressure and heart rate values. Plasma epinephrine (0.63 ± 0.16 vs. 0.21 ± 0.08 pmol/l, P < 0.05) and norepinephrine concentrations (0.27 ± 0.03 vs. 0.16 ± 0.02 pmol/l, P < 0.05) were elevated in shunted rats compared with controls. Nitroprusside-induced hypotension led to a significantly greater increase in efferent splanchnic sympathetic nerve activity in shunted rats than in controls (0.9 ± 0.1 vs. 2.6 ± 0.6 μV, P < 0.05), whereas the heart rate responses were not different between the groups. These results indicate that the regulation of the autonomic nervous system is altered in chronically volume-overloaded rats. The arterial baroreflex control of efferent splanchnic sympathetic nerve activity was dissociated from the control of heart rate. Therefore, analysis of the activation of sympathetic nervous system assessed by direct measurements of efferent sympathetic nerve activity appears to be more sensitive for the detection of altered autonomic nervous system function than the analysis of baroreflex control of heart rate.
Separation of peripheral and central cardiovascular actions of angiotensin II
Authors: Kooner Jaspal S. , May Clive N. , Peart Stanley , Mathias Christopher J.
Published: December 2017

The pressor and vasoconstrictor action of angiotensin II (ANG II) is considered to be caused by a combination of its direct and indirect vascular effects, the latter mediated by the sympathetic nervous system. The purpose of this study was to determine the extent to which the direct and indirect actions of ANG II contribute to its pressor and vascular effects. Blood pressure, cutaneous vascular, and plasma norepinephrine responses to intravenous ANG II were measured in conscious rabbits before and after inhibition of central sympathetic outflow with intravenous and intracisternal clonidine and after ganglionic blockade with intravenous pentolinium. Intravenous ANG II caused a similar dose-related rise in blood pressure before and after sympathetic blockade with intravenous clonidine, intracisternal clonidine, and intravenous pentolinium. In contrast, the dose-related fall in cutaneous ear blood flow and cutaneous ear temperature and rise in cutaneous ear vascular resistance induced by intravenous ANG II were abolished after intravenous clonidine, intracisternal clonidine, and intravenous pentolinium. Heart rate was unchanged after ANG II. There were no changes in back skin or rectal temperature. There was a nonsignificant fall in plasma norepinephrine and no change in epinephrine after ANG II. These results demonstrate that the acute pressor response to intravenous ANG II is mediated by its direct vascular effects and is not dependent on central or ganglionic stimulation of the sympathetic nervous system, in contrast to the effect of ANG II on cutaneous ear vasoconstriction, which is predominantly caused by a centrally mediated increase in sympathetic nervous activity. Our results separate, in conscious rabbits, the direct vascular effects of ANG II from its indirect vascular actions, which are mediated by central sympathetic stimulation in the brain.
Troponin I phosphorylation and myofilament calcium sensitivity during decompensated cardiac hypertrophy
Authors: McConnell Bradley K. , Moravec Christine Schomisch , Bond Meredith
Published: December 2017

We have measured myocyte cell shortening, troponin-I (Tn-I) phosphorylation, Ca2+dependence of actomyosin adenosinetriphosphatase (ATPase) activity, adenosine 3′,5′-cyclic monophosphate (cAMP) levels, and myofibrillar isoform expression in the spontaneously hypertensive rat (SHR) during decompensated cardiac hypertrophy (76 wk old) and in age-matched Wistar-Kyoto rat (WKY) controls. The decreased inotropic response to β-adrenergic stimulation previously observed in myocytes from 26-wk-old SHR was further reduced at 76 wk of age. In response to β-adrenergic stimulation, Tn-I phosphorylation was greater in the 76-wk-old SHR than in the WKY, although cAMP-dependent protein kinase A (PKA)-dependent Tn-I phosphorylation in the SHR did not increase with progression from compensated (26 wk) to decompensated (76 wk) hypertrophy. We also observed a dissociation between the increased PKA-dependent Tn-I phosphorylation and decreased cAMP levels in the 76-wk-old SHR versus WKY during β-adrenergic stimulation. Baseline Tn-I phosphorylation was significantly reduced in 76-wk-old SHR versus WKY and was associated with decreased basal cAMP levels and increased Ca2+sensitivity of actomyosin ATPase activity. The change in myofilament Ca2+sensitivity during β-adrenergic stimulation in the 76-wk-old SHR (0.65 pCa units) was over twofold greater than in the 76-wk-old WKY (0.30 pCa units). We also determined whether embryonic troponin T isoforms were reexpressed in decompensated hypertrophy and observed significant reexpression of the embryonic cardiac troponin T isoforms in the 76-wk-old SHR. The significant decrease in Ca2+sensitivity with β-adrenergic stimulation in 76-wk-old SHR may contribute to the severely impaired inotropic response during decompensated hypertrophy in the SHR.