bluuebunny/crossref_metadata_2025 huggingface dataset:
Aortic distensibility and compliance in conscious pregnant rats
Authors: Slangen B. F. , van Ingen Schenau D. S. , van Gorp A. W. , De Mey J. G. , Peeters L. L.
Published: December 2017

In pregnancy, complex hormonal and hemodynamic changes develop. In this study, we tested the hypothesis that these pregnancy-associated changes are accompanied by an alteration of the compliance of central conduit vessels. To this end, we determined in awake, restrained pregnant rats the distensibility (DC) and compliance (CC) coefficients of the descending thoracic aorta. End diastolic aortic diameter (d) and changes in aortic diameter during the cardiac cycle (delta d) were measured noninvasively by ultrasound, simultaneously with diastolic aortic blood pressure (Pdia) and pulse pressure (delta P) through a chronically implanted catheter. From these parameters, DC and CC (expressed as the relative and the absolute increase, respectively, in lumen cross-sectional area for a given increase in P) were calculated. Nine rats were studied before pregnancy and, on days 4, 8, 10, and 18 of pregnancy, were matched for age and days postsurgery with eight nonpregnant rats. On day 20, the animals were killed and the thoracic aorta was isolated for morphometric analysis. In the pregnant group, Pdia decreased from 109 +/- 5 mmHg on day 4 to 98 +/- 9 mmHg on day 18 (means +/- SD), whereas d did not change. delta d increased from 242 +/- 20 microm on day 4 to 271 +/- 29 microm on day 18. delta P did not change. Both DC and CC increased in early pregnancy to a plateau reached by day 10. The increase in DC and CC preceded the fall in Pdia. On day 20, neither cross-sectional area nor thickness of the aortic media had changed significantly, when compared with the nonpregnant group. In the nonpregnant group, none of the variables changed consistently during the study period. On the basis of these results, we conclude that CC of the thoracic aorta increases in early pregnancy. We speculate that the increased aortic CC and DC and the decreased total peripheral resistance develop in early pregnancy in response to the increase in stroke volume, thus preventing a concomitant rise in arterial wall stress.
Modulation of K channels by coexpressed human alpha1C-adrenoceptor in Xenopus oocytes
Authors: Tseng G. N. , Yao J. A. , Tseng-Crank J.
Published: December 2017

alpha1-Adrenoceptors participate in the regulation of inotropy and chronotropy in the heart. Modulation of cardiac K-channel function plays an important role in these alpha1-adrenergic functions. Studies of the mechanisms of K-channel modulation by alpha1-adrenoceptors are hampered by the coexistence of multiple receptor and channel subtypes in the heart. We therefore used a model system of coexpressing a specific receptor (human alpha1c-adrenoceptor) and a K-channel clone (hIsK, rKv1.2, or rKv1.4) in oocytes. alpha1c-Adrenoceptor stimulation caused a rapid upregulation of hIsK by elevating the intracellular Ca concentration. At least part of this effect was due to an activation of calmodulin and Ca/calmodulin-dependent protein kinase II. On the other hand, alpha1c-adrenoceptor stimulation caused a slow downregulation of rKv1.2 and rKvl.4 by activating protein kinase C. The differential modulation of K channels by alpha1c-adrenoceptors demonstrated in our experiments corroborates the complexity of alpha1-adrenergic functions in the heart. Our results indicate that the oocyte model system can be a useful approach in studying alpha1-adrenergic modulation of ion-channel function and signal transduction.
Effect of hypoxia on steady-state arachidonic acid metabolism in bovine aortic endothelial cells
Authors: Patton G. M. , Kadowaki H. , Albadawi H. , Soler H. M. , Watkins M. T.
Published: December 2017

At the onset of acute hypoxia, eicosanoid synthesis by bovine aortic endothelial cells (BAEC) markedly decreases, reflecting a decreased release of arachidonic acid from endogenous stores. To determine the cause of decreased arachidonic acid release, we pulse-labeled BAEC with [14C]arachidonic acid for 5 min under normoxic conditions and chased cells for 1 h under normoxic or hypoxic conditions. The 14C incorporation and specific activity (disintegrations per minute per nanomole) of three major arachidonyl molecular species (16:0-20:4, 18:1-20:4, and 18:0-20:4) of each phospholipid class were determined in cells chased under either of the two conditions. There was no relevant difference between normoxic and hypoxic cells in the metabolism of any of the arachidonyl molecular species of diacyl lipids. However, there was a marked decrease (approximately 40%) in the turnover of arachidonyl alkenylacyl phosphatidylethanolamine in the hypoxic cells. From these results, it appears that the source of arachidonic acid supporting constitutive eicosanoid synthesis in BAEC is alkenylacyl phosphatidylethanolamine and that the limiting enzyme activity determining the rate of eicosanoid synthesis is a plasmalogen-specific phospholipase A2.
Decreased active vasodilator sensitivity in aged skin
Authors: Kenney W. L. , Morgan A. L. , Farquhar W. B. , Brooks E. M. , Pierzga J. M. , Derr J. A.
Published: December 2017

Older men and women respond to local and reflex-mediated heat stress with an attenuated increase in cutaneous vascular conductance (CVC). This study was performed to test the hypothesis that an augmented or sustained noradrenergic vasoconstriction (VC) may play a role in this age-related difference. Fifteen young (22 +/- 1 yr) and 15 older (66 +/- 1 yr) men exercised at 50% peak oxygen uptake in a 36 degrees C environment. Skin perfusion was monitored at two sites on the right forearm by laser-Doppler flowmetry: one site pretreated with bretylium tosylate (BT) to block the local release of norepinephrine and thus VC and an adjacent control site. Blockade of reflex VC was verified during whole body cooling using a water-perfused suit. CVC (perfusion divided by mean arterial pressure) at each site was reported as a percentage of the maximal CVC (%CVCmax) induced at the end of each experiment by prolonged local heating at 42 degrees C. Neither age nor BT affected the %CVCmax (75-86%) attained at high core temperatures. During the early rise phase of CVC, the %CVCmax-change in esophageal temperature (delta T(es)) curve was shifted to the right in the older men (effective delta T(es) associated with 50% CVC response for young, 0.22 +/- 0.04 and 0.39 +/- 0.04 degrees C and for older, 0.73 +/- 0.04 and 0.85 +/- 0.04 degrees C at control and BT sites, respectively). BT had no interactive effect on this age difference, suggesting a lack of involvement of the VC system in the attenuated CVC response of individuals over the age of 60 yr. Additionally, increases in skin vascular conductance were quantitatively compared by measuring increases in total forearm vascular conductance (FVC, restricted to the forearm skin under these conditions). After the initial approximately 0.2 degrees C increase in T(es), FVC was 40-50% lower in the older men (P < 0.01) for the remainder of the exercise. Decreased active vasodilator sensitivity to increasing core temperature, coupled with structural limitations to vasodilation, appears to limit the cutaneous vascular response to exertional heat stress in older subjects.
1,25-Dihydroxyvitamin D3 regulation of cardiac myocyte proliferation and hypertrophy
Authors: O'Connell T. D. , Berry J. E. , Jarvis A. K. , Somerman M. J. , Simpson R. U.
Published: December 2017

We previously demonstrated that 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] inhibits myocyte maturation (T. D. O'Connell, D. A. Giacherio, A. K. Jarvis, and R. U. Simpson. Endocrinology 136: 482-488, 1995). To define further the role of 1,25(OH)2D3 in regulating myocardial development, we examined the effects of 1,25(OH)2D3 on proliferation and growth of primary cultures of ventricular myocytes isolated from neonatal rat hearts. When neonatal myocytes were grown in a serum-supplemented medium, cell number approximately doubled, and treating these myocytes with 1,25(OH)2D3 inhibited their proliferation by 56.56% after 4 days. Flow cytometry revealed that 1,25(OH)2D3 reduced the percentage of cells in the S phase of the cell cycle by 31.39% after 4 days. We show for the first time that proliferating cell nuclear antigen protein levels were specifically reduced by 1,25(OH)2D3. Protooncogene c-myc protein levels were also reduced by this hormone. Interestingly, a phorbol ester had a similar effect on myocyte proliferation. Furthermore, 1,25(OH)2D3 increased myocyte protein levels and increased cell size, suggesting that it induces cardiac myocyte hypertrophy. Our findings indicate that 1,25(OH)2D3 and phorbol esters directly regulate myocyte proliferation and induce myocyte hypertrophy. Finally, the data demonstrate that the mechanism by which 1,25(OH)2D3 regulates myocyte proliferation involves blocking entry into the S phase of the cell cycle.
Effects of relaxin on rat atrial myocytes. I. Inhibition of I(to) via PKA-dependent phosphorylation
Authors: Piedras-Renteria E. S. , Sherwood O. D. , Best P. M.
Published: December 2017

The peptide hormone relaxin has direct, positive inotropic and chronotropic effects on rat hearts in vivo and in vitro. Relaxin's effects on the electrophysiological properties of single quiescent atrial cells from normal rats were investigated with a whole cell patch clamp. Relaxin had a significant inhibitory effect on outward potassium currents. The outward potassium current consisted of a transient component (I(to)) and a sustained component (I(S)). The addition of 100 ng/ml of relaxin inhibited the peak I(to) in a voltage-dependent manner (74% inhibition at a membrane potential of -10 mV to 30% inhibition at +70 mV). The time to reach peak I(to) and the apparent time constant of inactivation of I(to) were increased by relaxin. Dialysis with the protein kinase A inhibitor 5-24 amide (2 microM) prevented relaxin's effects, suggesting an obligatory role for this kinase in the relaxin-dependent regulation of the potassium current.
Myogenic contribution to agonist-induced renal vasoconstriction during normoxia and hypoxia
Authors: Eichinger M. R. , Resta J. M. , Walker B. R.
Published: December 2017

Acute hypoxia attenuates agonist-induced constrictor and pressor responses in conscious rats, and a recent report suggests that hypoxia may also diminish myogenic reactivity in isolated, perfused rat kidneys. Thus we hypothesized that the diminished responsiveness to pressor agents during hypoxia is caused by an impairment of myogenic reactivity. Male Sprague-Dawley rats were instrumented with a pulsed Doppler flow probe on the left renal artery, an aortic vascular occluder cuff immediately above the left renal artery to control renal perfusion pressure, and catheters were inserted to measure systemic arterial blood pressure and renal arterial pressure (RAP) and for administration of agents. Animals were studied under normoxic or acute hypoxic (fractional concentration of O2 in inspired gials = 0.12) conditions and were administered phenylephrine, arginine vasopressin, or angiotensin II. To determine the myogenic (pressure-dependent) component of agonist-induced vasoconstriction, renal vascular resistance was calculated during agonist infusion with RAP uncontrolled and with RAP controlled to preinfusion levels. Significant myogenic components of agonist-induced renal vasoconstriction were evident with all pressor agents used. However, hypoxia did not attenuate agonist-induced, pressure-dependent increases in renal vascular resistance. We conclude that the reduced vasoreactivity associated with acute hypoxia is not caused by diminished myogenic reactivity.
Phase dependencies of the human baroreceptor reflex
Authors: Seidel H. , Herzel H. , Eckberg D. L.
Published: December 2017

We studied the influence of respiratory and cardiac phase on responses of the cardiac pacemaker to brief (0.35-s) increases of carotid baroreceptor afferent traffic provoked by neck suction in seven healthy young adult subjects. Cardiac responses to neck suction were measured indirectly from electrocardiographic changes of heart period. Our results show that it is possible to separate the influences of respiratory and cardiac phases at the onset of a neck suction impulse by a product of two factors: one depending only on the respiratory phase and one depending only on the cardiac phase. This result is consistent with the hypothesis that efferent vagal activity is a function of afferent baroreceptor activity, whereas respiratory neurons modulate that medullary throughput independent of the cardiac phase. Furthermore, we have shown that stimulus broadening and stimulus cropping influence the outcome of neck suction experiments in a way that makes it virtually impossible to obtain information on the phase dependency of the cardiac pacemaker's sensitivity to vagal stimulation without accurate knowledge of the functional shape of stimulus broadening.
Cardiac sympathetic activity in response to acute myocardial ischemia
Authors: Newton G. E. , Adelman A. G. , Lima V. C. , Seidelin P. H. , Schampaert E. , Parker J. D.
Published: December 2017

Although experimental evidence has demonstrated that brief periods of myocardial ischemia are not associated with norepinephrine overflow from the heart, cardiac sympathetic responses to myocardial ischemia in humans remain unclear. Eleven patients undergoing angioplasty of the left anterior descending coronary artery had cardiac norepinephrine spillover measured immediately before inflation, during the final minute of a 5-min balloon inflation, and 1 min after deflation. Angioplasty caused significant S-T segment elevation and a reduction in the transcardiac lactate extraction ratio. Cardiac norepinephrine spillover was reduced from a mean value of 58 +/- 14 pmol/min at control to 41 +/- 15 pmol/min during balloon inflation and 38 +/- 14 pmol/min after deflation (P < 0.05 vs. control for both inflation and deflation values). In contrast, during balloon inflation, there were significant increases in arterial norepinephrine and epinephrine concentrations. Therefore, a brief period of myocardial ischemia caused by angioplasty of the left anterior descending coronary artery does not result in cardiac sympathetic activation, despite evidence of generalized sympathoadrenal activation.
Pressure-independent effects of AT1-receptor antagonism on cardiovascular remodeling in aortic-banded rats
Authors: Regan C. P. , Anderson P. G. , Bishop S. P. , Berecek K. H.
Published: December 2017

To determine the role of angiotensin II-receptor blockade on cardiovascular remodeling in a pressure-overload model of cardiac hypertrophy, a subdiaphragmatic aortic band was placed in adult male Sprague-Dawley rats. Aortic-banded (AB) rats were left untreated or were losartan (Los; 250 mg/l) treated (AB-Los). Sham-operated (S) controls were either left untreated or treated with Los (S-Los). After 4 wk, rats were catheterized for measurement of mean arterial pressures [carotid (CMAP) and femoral (FMAP), in mmHg]. Hearts were perfused on a modified Langendorff system, and minimal coronary resistance (MCR) was determined. Hearts were then perfusion fixed, total and regional heart weights were recorded, and sections were processed for morphology. Changes in coronary artery medial thickness and perivascular fibrosis were assessed by quantitative image analysis. CMAP was significantly higher in AB and AB-Los than in S or S-Los (P < 0.05). There was no difference in FMAP in AB vs. S, but AB-Los and S-Los had lower FMAPs than S. Total heart weight and left ventricular weight-to-body weight ratios were increased in AB and AB-Los compared with S and S-Los (P < 0.05). MCR of AB was greater than S and S-Los. MCR of AB-Los was significantly lower than AB and was not significantly different from S and S-Los. In coronary vessels, medial thickness was greatest in AB, whereas there was no difference among AB-Los, S, and S-Los. Similarly, the increase in perivascular fibrosis was greatest in AB, and there was no difference among AB-Los, S, and S-Los. These data suggest that angiotensin II, independent of increased arterial pressure, is critical for the development of the vascular and fibrotic changes that occur in this model of pressure-overload hypertrophy.
Cardiac function in a rat model of chronic aortic stiffness
Authors: Lartaud-Idjouadiene I. , Niederhoffer N. , Debets J. J. , Struyker-Boudier H. A. , Atkinson J. , Smits J. F.
Published: December 2017

Cardiac function was investigated in conscious normotensive rats in which increased aortic stiffness was produced as a result of vascular calcium overload after treatment with vitamin D3 plus nicotine (VDN rats, n = 16; controls, n = 17). Baseline stroke volume, cardiac output, and cardiac response to a venous volume overload were unchanged after 1 mo of exposure to increased aortic stiffness, as were baseline venous return and total vascular capacitance. The latter was estimated from the change in mean circulatory filling pressure after modification of circulatory volume. Cardiovascular reflexes were modified in VDN rats. Bradycardia evoked by an increase in arterial PCO2 (PaCO2) or hypotensive hemorrhage was more pronounced. The PaCO2-induced bradycardia was accompanied by a fall in cardiac output in VDN rats but not in controls. In VDN rats, the attenuation of sympathetic reflexes may explain the slower recovery of blood pressure after hypotensive hemorrhage. In conclusion, a chronic increase in aortic stiffness does not compromise cardiac performance, but cardiovascular reflexes are impaired in VDN rats. Whether this is because of the increase in aortic stiffness or the effect of VDN treatment on the baroreceptors or other components of the reflex arc remains to be elucidated.
Role of endogenous centrally released NO in cardiovascular adaptation to hypovolemia in WKY and SHR
Authors: Paczwa P. , Budzikowski A. S. , Szczepanska-Sadowska E.
Published: December 2017

The role of endogenous centrally released nitric oxide (NO) during hypovolemia was investigated in normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Bleeding of the rats (1.3% of blood volume) was performed after intracerebroventricular (ICV) administration of: 1) artificial cerebrospinal fluid (series 1, time control, 8 WKY and 8 SHR); 2) 0.5 mg NG-nitro-L-arginine (L-NNA, 2.3 nmol), an inhibitor of NO synthesis (series 2, 8 WKY and 7 SHR); and 3) 0.5 mg L-NNA followed by 1 mg (5.8 nmol) of L-arginine (L-Arg) (6 WKY and 5 SHR). In WKY, hypotension was associated with significant bradycardia (P < 0.001), whereas in SHR slight acceleration of heart rate was observed. In series 2 hemorrhage resulted in a small but significant increase of mean arterial pressure (MAP; P < 0.05) and considerable tachycardia (P < 0.001). In SHR, L-NNA did not modify the decrease of MAP during hypovolomia, and bleeding resulted in a significant bradycardia (P < 0.001). Pretreatment with L-Arg in series 3 was able to reverse the effects of L-NNA on changes of MAP and heart rate during hypovolemia. The results indicate that the central nitroxidergic system plays a significant role in eliciting hypotension and bradycardia in normotensive WKY during hemorrhage. Function of the central nitroxidergic system is significantly altered in SHR in which NO appears to prevent hemorrhagic bradycardia and to reduce the hypotensive effect.
Increased cardiomyocyte apoptosis during the transition to heart failure in the spontaneously hypertensive rat
Authors: Li Z. , Bing O. H. , Long X. , Robinson K. G. , Lakatta E. G.
Published: December 2017

The transition from compensated hypertrophy to failure in spontaneously hypertensive rats (SHR) of advanced age is associated with a marked increase in collagen, a reduction in myocyte mass, and a reduction in maximum Ca(2+)-activated myofibrillar force. We hypothesized that the reduction in myocyte mass and associated functional loss may be due to increased cell death by apoptosis. To test this hypothesis, we studied hearts from failing (SHR-F) and nonfailing SHR (SHR-NF) and age-matched Wistar-Kyoto rats (WKY). In addition, hearts from SHR-F that had been treated with an angiotensin-converting enzyme inhibitor (captopril) for an average of 27 days were also studied. Apoptotic cells were quantified in cross sections of myocardium by the terminal deoxynucleotidyltransferase- mediated 2'-deoxyuridine 5'-triphosphate nick end labeling technique. To identify the type of the cells undergoing apoptosis, sections were also stained for alpha-sarcomeric actin. Apoptotic cells were significantly increased in the SHR-F (38.92 +/- 12.79 vs. 8.05 +/- 3.98 cells/100,000 nuclei in SHR-NF; P < 0.05 and vs. 2.21 +/- 1.4 cells/100,000 nuclei in WKY; P < 0.01). Captopril treatment of SHR-F reduced the number of apoptotic cells to the level in SHR-NF (9.17 +/- 1.53 cells/100,000 nuclei; P < 0.01 vs. SHR-F). Most apoptotic cells were of cardiac myocyte origin. There was no significant difference in Bcl-2 protein expressed by hearts among the three groups. WAF-1 mRNA levels were increased in both SHR groups vs. WKY; in SHR-F, the density of WAF-1 mRNA was higher than in SHR-NF. Thus increased numbers of apoptotic cells are present in failing SHR hearts, suggesting that apoptosis might be a mechanism involved in the reduction of myocyte mass that accompanies the transition from stable compensation to heart failure in this model. Administration of the angiotensin-converting enzyme inhibitor captopril, which ameliorates heart failure in this model, is associated with a reduction in the exaggerated apoptosis that accompanies heart failure.
Formation of nitric oxide, superoxide, and peroxynitrite in myocardial ischemia-reperfusion injury in rats
Authors: Liu P. , Hock C. E. , Nagele R. , Wong P. Y.
Published: December 2017

In the present study, the contribution of nitric oxide (NO), superoxide, and peroxynitrite to the inflammatory response induced by myocardial ischemia-reperfusion (MI/R) was investigated. Male Sprague-Dawley rats were anesthetized, and the left main coronary artery was ligated for 20 min and reperfused for 5 h. MI/R induced severe arrhythmias, indicated by a significantly elevated arrhythmia score in the MI/R group compared with that in the sham control group. Creatine kinase activity in the left ventricular free wall of the MI/R group was significantly reduced by 38%. In contrast, myeloperoxidase activity in the left ventricular free wall of the MI/R group was increased by 140%. Similarly, superoxide and tissue NO levels in the ischemic region of the heurt were increased by 140 and 90%, respectively. Superoxide and NO values in the nonischemic regions were similar to the sham control group. Total NO synthase (NOS) activity was elevated by 212%; moreover, inducible NOS (iNOS) activity increased 6.7-fold in the ischemic vs. nonischemic regions. MI/R also induced both systemic and remote organ (lung) inflammatory responses. Circulating neutrophils and plasma NO levels were increased by 163 and 138%, respectively, in MI/R rats compared with sham control animals. NO levels and superoxide generation were increased by 90 and 176%, respectively, in the lung tissues. The expression of iNOS and peroxynitrite generation were demonstrated by immunohistochemical staining with polyclonal anti-iNOS and monoclonal anti-nitrotyrosine antibodies, respectively. Sections of both the ischemic area of the ventricular wall and the lung tissue of MI/R animals exhibited a marked immunoreactivity with anti-iNOS and anti-nitrotyrosine antibodies, indicating the presence of iNOS and nitrotyrosine. Our data indicate that NO, superoxide, and peroxynitrite formation are elevated after reperfusion of the ischemic heart, suggesting that these inflammatory mediators may be involved in MI/R injury.
Purine nucleotides contribute to pulmonary vasodilation caused by birth-related stimuli in the ovine fetus
Authors: Konduri G. G. , Mital S. , Gervasio C. T. , Rotta A. T. , Forman K.
Published: December 2017

We investigated the hypothesis that the purine nucleotides ATP and adenosine mediate the pulmonary vasodilation that occurs at birth in fetal lambs. We instrumented 44 fetal lambs to measure left pulmonary arterial pressure and flow. In control studies, we investigated the effects of sequential ventilation with 10, 50, and 100% O2 on fetal pulmonary arterial pressure and flow and pulmonary vascular resistance (PVR). We also measured the blood and plasma ATP levels in the pulmonary artery and left atrium in the control studies. In three separate groups of studies, we investigated the effects of 8-phenyltheophylline, an adenosine-receptor antagonist, and cibacron blue, an inhibitor of ATP-sensitive P2y receptors, given alone or in combination, on the response of PVR to sequential ventilation. Fetal arterial PO2 increased during ventilation with 50 and 100% O2 but not with 10% O2. Ventilation with 10% O2 caused a 4-fold increase in pulmonary blood flow and a 10-fold decrease in PVR. Ventilation with 50 and 100% O2 caused a 7-fold increase in pulmonary blood flow and a 20-fold decrease in PVR. Blood and plasma ATP levels in the pulmonary artery and blood ATP levels in the left atrium increased significantly during ventilation with 50 and 100% O2 but not with 10% O2. Pretreatment of animals with 8-phenyltheophylline attenuated the increase in pulmonary flow and decrease in PVR caused by ventilation at all fractions of inspired O2 (FIO2 levels). Pretreatment of animals with cibacron blue attenuated pulmonary vasodilation at 50 and 100% FIO2. Combined treatment with 8-phenyltheophylline and cibacron blue caused complete inhibition of the decrease in PVR in response to ventilation at the three FIO2 levels. Incubation of fetal red blood cells in vitro with 100% O2 caused an increase in ATP production. An increase in arterial PO2 in the fetus causes an increase in blood ATP levels, and an inhibition of ATP receptors attenuates the O2-induced decrease in PVR. Adenosine-receptor inhibition attenuates both ventilation- and O2-induced changes in PVR. Increased synthesis and release of ATP plays a major role in causing pulmonary vasodilation in response to birth-related stimuli in the ovine fetus.
Possible role of T-type Ca2+ channels in L-NNA vasoconstriction of hypertensive rat lungs
Authors: Muramatsu M. , Tyler R. C. , Rodman D. M. , McMurtry I. F.
Published: December 2017

Acute inhibition of endothelium-derived nitric oxide (NO) synthesis by L-arginine analogs such as N omega-nitro-L-arginine (L-NNA) has little effect on basal vascular tone in normal rat lungs but elicits marked vasoconstriction in hypertensive lungs. The NO-suppressible vasoconstriction is dependent on extracellular Ca2+ but is not mediated by L-type Ca2+ channels. This study tested whether the response was mediated by Ca2+ influx through receptor-operated channels, reverse Na+/Ca2+ exchange, or low-threshold voltage-gated (T-type) Ca2+ channels. We first examined whether SKF-96365, a blocker of receptor-operated Ca2+ channels, inhibited L-NNA-induced vasoconstriction in salt solution-perfused hypertensive lungs isolated from chronically hypoxic male rats (exposed to hypobaria of 410 mmHg for 3-5 wk). Whereas 50 microM SKF-96365 inhibited pressor responses to angiotensin II and acute hypoxia, it did not reduce vasoconstriction in response to 100 microM L-NNA. We next examined effects of pretreatment with Na+/Ca2+ exchange blockers and observed that L-NNA vasoconstriction was reduced by both 100 microM amiloride and 50 microM ethylisopropyl amiloride (EIPA). The third experiment showed that each of two different blockers of T-type Ca2+ channels, 10 microM Ro-40-5967 and 300 microM nordihydroguariaretic acid, inhibited L-NNA vasoconstriction and that the combination of EIPA and Ro-40-5967 did not cause more inhibition than did Ro-40-5967 alone. These results suggest that, whereas receptor-operated Ca2+ channels are not significantly involved in the mechanism of NO-suppressible vasoconstriction in hypertensive rat lungs, Ca2+ influx through reverse Na+/Ca2+ exchange and/or T-type Ca2+ channels may play a role. Because both amiloride and EIPA also inhibit T-type Ca2+ channels, we speculate that Ca2+ influx through these channels rather than through reverse Na+/Ca2+ exchange is an important mediator of the vasoconstriction.
Autonomic reactivity and hormonal secretion in lactate-induced panic attacks
Authors: Seier F. E. , Kellner M. , Yassouridis A. , Heese R. , Strian F. , Wiedemann K.
Published: December 2017

To compare autonomic and neuroendocrine responses during lactate-induced panic attacks, heart rate variability and cortisol and atrial natriuretic hormone (ANH) levels were measured in patients with panic attacks and in healthy control subjects. In a randomized double-blind design, all subjects received either 10 ml/kg body weight of 0.5 M racemic sodium lactate or normal saline from 1100 to 1120. Spectral analysis of the R-R interval of analog electrocardiograms was performed, and total (0.001-0.45 Hz), low-frequency (0.01-0.05 Hz), midfrequency (0.05-0.15 Hz), and high-frequency power (0.15-0.45 Hz) were computed. Cortisol was measured 12 times in the period from 0900 to 1300, and ANH was measured at 1100, 1120, and 1200 by radioimmunoassay. In both panickers (n = 6) and nonpanickers (n = 8), an infusion of lactate resulted in an acceleration of heart rate, a reduction in total spectral power, and a decrease in the high- and low-frequency components of spectral power. Panickers showed a significant enhancement of the high-frequency power, whereas in nonpanickers, a shift from the mid- and high-frequency toward the low-frequency power emerged. ANH plasma concentrations during lactate infusion in panickers showed a significant increase (115 and 131% at 1120 and 1200, respectively, over concentrations at 1100) in contrast to nonpanickers (20 and 74%, respectively). No group or treatment effects on cortisol secretion emerged, which is in line with former reports. Our study supports preliminary observations that lactate-induced panic attacks enhance the release of ANH, a vasodilatator and inhibitor of sympathetic activity. Hence this hormone not only could inhibit the secretion of the stress hormone cortisol but, in parallel, could also attenuate the sympathetic stimulation to the heart. These inhibitory effects of ANH could explain the so-far-unresolved dissociation between psychopathological alterations and autonomic and endocrine responses of panic attacks.
Activation of tyrosine kinases in H2O2-induced contraction in pulmonary artery
Authors: Jin N. , Rhoades R. A.
Published: December 2017

Hydrogen peroxide (H2O2) is an important reactive oxygen species implicated in lung vascular constriction and injury. The purpose of this study was to investigate the role of tyrosine kinases in H2O2-induced vascular contraction and dysfunction. In our study, H2O2 (200 microM) caused an initial transient contraction followed by a strong, sustained contraction in isolated rat pulmonary arteries. Genistein, a tyrosine kinase inhibitor, attenuated both the initial and the sustained contractions. Aminogenistein and tyrphostin 51, specific inhibitors of tyrosine kinases, had the same effects as genistein. Exposure of pulmonary arteries to H2O2 for 1 h caused a significant reduction in the contractile response to KCl or phenylephrine and in the vasodilatory response to acetylcholine (smooth muscle dysfunction). Although tyrosine kinase inhibitors significantly blocked contractions induced by H2O2, pretreatment of pulmonary arteries with these inhibitors before H2O2 exposure did not prevent the decreases in responses to KCl, phenylephrine, or acetylcholine. Removal of extracellular Ca2+ and depletion of intracellular Ca2+ pools by ryanodine or thapsigargin did not inhibit the initial and sustained contractions in response to H2O2. W-7, a calmodulin antagonist, or ML-9, a myosin light chain kinase inhibitor, significantly inhibited the sustained contractions but did not prevent smooth muscle dysfunction induced by H2O2. These data show that 1) exposure to H2O2 causes smooth muscle contractions and dysfunction in isolated pulmonary arteries and 2) activation of tyrosine kinases mediates H2O2-induced contractions; however, tyrosine kinases do not appear to be involved in H2O2-induced inhibition of arterial responses to vasoactive substances. These data suggest that different signaling pathways and mechanisms are involved in H2O2-induced smooth muscle contraction and dysfunction.
Hypercholesterolemia is associated with enhanced angiotensin AT1-receptor expression
Authors: Nickenig G. , Jung O. , Strehlow K. , Zolk O. , Linz W. , Scholkens B. A. , Bohm M.
Published: December 2017

Low-density lipoprotein increases the AT1-receptor gene expression in vascular smooth muscle cells. To elucidate whether elevated cholesterol serum levels upregulate the AT1 receptor and its functional response to angiotensin II in vivo, we compared 1) the vasoconstrictive effect of angiotensin II and 2) the level of expression of the vascular AT1 receptor in aortas of normocholesterolemic and hypercholesterolemic rabbits. Contraction experiments on isolated aortic rings showed that the angiotensin II-induced vasoconstriction was increased in hypercholesterolemic New Zealand White rabbits compared with normocholesterolemic New Zealand White rabbits. This difference in the angiotensin II-induced vasoconstriction was caused by a twofold increase in the density of cell surface AT1 receptors in hypercholesterolemic rabbits, as assessed by radioligand binding assays. The enhanced expression of AT1 receptors on the surface of these vascular cells was caused by elevated steady-state levels of the AT1-receptor mRNA to 220 +/- 35% in aortas excised from hypercholesterolemic rabbits compared with levels in aortas from normocholesterolemic rabbits, as measured by Northern blot analysis. These data indicate that hypercholesterolemia is associated with upregulation of expression and function of vascular AT1 receptors in vivo. This suggests a novel mechanism by which hypercholesterolemia could be involved in the onset and progression of chronic vascular diseases such as hypertension and arteriosclerosis if the phenomenon is confirmed in humans.
Diameter variability and microvascular flow resistance
Authors: Pries A. R. , Schonfeld D. , Gaehtgens P. , Kiani M. F. , Cokelet G. R.
Published: December 2017

Microvessels are known to exhibit irregular shapes, deviating substantially from an idealized cylindrical tube geometry. Such irregularities must be taken into account in calculating microvascular flow resistance and may add to the observation that flow resistance in living microvessels in vivo is about twice that predicted on the basis of tube flow studies in vitro. The present study was aimed at providing a comprehensive database describing the apparent diameter variability for all segments of a complete microvascular network in the rat mesentery and assessing the impact of this variability on segmental flow resistance and the pressure drop across the network. Diameters were estimated by intravital microscopy at axial intervals of 20 microns along the 546 vessel segments of a mesenteric microvessel network, resulting in 6,319 separate diameter measurements. The amplitude of diameter variations in individual vessel segments decreased from approximately 15% of the mean vessel diameter in the smallest segments (approximately 5 microns diam) to approximately 5% in the largest segments (approximately 60 microns diam). Segmental hindrance was estimated to be 10-23% higher than calculated from arithmetic mean diameter, depending on the model used to estimate the hydrodynamically effective segment diameter. The overall pressure drop across the network calculated using a mathematical flow simulation was increased by 7-13.5%. This increase in flow resistance can explain approximately 10% of the observed discrepancy between flow resistance in vivo and in vitro.
Components of methacholine-initiated conducted vasodilation are unaffected by arteriolar pressure
Authors: Rivers R. J.
Published: December 2017

Conducted vasodilation occurs remotely from a site of microapplication of a drug. Intravascular pressure is required for a conducted response in vivo, yet in vitro studies in unpressurized arterioles show pressure is not essential. To determine how pressure affects conducted vasodilation, intra-arteriolar pressure was controlled within an in situ isolated segment (average length 950 +/- 96 microns, average baseline diameter 28 +/- 2.1 microns) of arterioles in the hamster cheek pouch. Methacholine (10(-4) M, 5 s) was microapplied either onto the isolated segment or remotely, with local and conducted vasodilation measured at both locations. Increasing pressure in the lumen of the segment (0-80 cmH2O) increased the segment local dilation to methacholine, and the segment-conducted dilation plateaued (at 4.1 +/- 0.8 micron) when segment pressure reached 20 cmH2O. Any local (16 +/- 1.5 microns) and conducted (4.4 +/- 1.3 microns) dilations viewed outside the segment were unaffected by segment pressure and persisted in its absence. Thus segment pressure affected only electromechanical transduction of the conducted response. Thus vasomotor signals move throughout the vasculature regardless of tone, but tone is essential to transduce the response.
Humoral factor(s) produced by pressure overload enhance cardiac hypertrophy and natriuretic peptide expression
Authors: Iso T. , Arai M. , Wada A. , Kogure K. , Suzuki T. , Nagai R.
Published: December 2017

Chronic pressure overload is known to increase cardiac mass and expression levels of both atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) mRNAs. Although mechanical stretching of cardiac myocytes could cause these changes, humoral factor(s) secondary to pressure overload may also be involved. To dissociate humoral effects from the effects of mechanical loading on cardiac hypertrophic responses, we examined expression of ANP and BNP at both mRNA and protein levels and proportions of myosin isoforms in transplanted cervical hearts that were mechanically unloaded under conditions with or without hypertension by aortic coarctation. Seven days after transplantation, cardiac atrophy that usually occurs in transplanted hearts without hypertension by coarctation was prevented in the transplanted hearts with hypertension by coarctation. The levels of expression of ANP and BNP mRNAs were increased in the transplanted hearts with relative to those without hypertension by coarctation. The plasma level of angiotensin II was higher in rats with than without hypertension by coarctation. Plasma endothelin-1 levels were not significantly different between the two groups. In addition, levels of expression of ANP and BNP mRNAs were increased in the transplanted hearts without hypertension relative to those in the in situ hearts. The proportion of the V3 myosin isoform was also increased in the transplanted hearts without hypertension relative to the in situ hearts. These results indicate that humoral factor(s) secondary to the pressure overload produced by aortic coarctation enhanced the cardiac hypertrophic response and elevated the levels of mRNAs encoding these embryonic markers. Moreover, our findings regarding ANP and BNP expression in the transplanted hearts provide additional evidence that the fetal genes are reexpressed during the process of cardiac atrophy as well as in cardiac hypertrophy.
SR Ca(2+)-ATPase activity and expression in ventricular myocardium of dogs with heart failure
Authors: Gupta R. C. , Shimoyama H. , Tanimura M. , Nair R. , Lesch M. , Sabbah H. N.
Published: December 2017

The purpose of this study was to examine the activity and expression of sarcoplasmic reticulum (SR) Ca(2+)-ATPase in left ventricular (LV) myocardium of dogs with chronic heart failure (HF). LV and right ventricular (RV) tissue specimens were obtained from six normal (NL) control dogs and six dogs with chronic HF (LV ejection fraction, 23 +/- 2%) produced by multiple sequential intracoronary microembolizations. Thapsigargin-sensitive Ca(2+)-ATPase activity was measured in isolated SR membrane fractions prepared from LV and RV myocardium. Ca(2+)-ATPase expression, using a specific dog myocardium monoclonal antibody, was measured in sodium dodecyl sulfate (SDS) extract prepared from LV and RV myocardium. Ca(2+)-ATPase activity in both ventricles of NL or HF dogs increased with increasing Ca2+ concentration and reached a plateau at 3 microM Ca2+. The maximal velocity (Vmax, mumol Pi released.min-1.mg-1) of Ca(2+)-ATPase activity was significantly lower in LV of HF dogs compared with NL (0.15 +/- 0.01 vs. 0.23 +/- 0.01, P < 0.05), whereas the affinity of the Ca2+ pump for Ca2+ was unchanged. LV tissue levels of Ca(2+)-ATPase (densitometric units/5 micrograms noncollagen protein) were also significantly lower in LV myocardium of HF dogs compared with NL (3.52 +/- 0.43 vs. 5.53 +/- 0.47, P < 0.05). No significant differences in Ca(2+)-ATPase activity or expression were observed in RV myocardium of HF dogs compared with NL. We conclude that SR Ca(2+)-ATPase activity and protein levels are reduced in LV myocardium of dogs with chronic HF. This abnormality of the SR Ca2+ pump of the failed LV can result in impaired Ca2+ uptake and ultimately to Ca2+ overload and global LV dysfunction.
Dissociation of TNF-alpha from endotoxin-induced nitric oxide and acute-phase hypotension
Authors: Xie J. , Joseph K. O. , Bagby G. J. , Giles T. D. , Greenberg S. S.
Published: December 2017

We tested the concept that tumor necrosis factor-alpha (TNF-alpha) or platelet-activating factor (PAF) mediated Escherichia coli endotoxin lipopolysaccharide (LPS)-induced upregulation of nitric oxide (NO) and acute-phase hypotension (APH) in the rat. LPS (0.5 mg/kg i.v.) given to rats treated with saline or nonimmune goat-derived gamma-globulin (immunoglobulin G, 22 mg/kg i.m.) produced APH and increased plasma concentrations of TNF-alpha and nitrate and nitrite anions (reactive nitrogen intermediates; RNI) and NO in ex vivo incubates of polymorphonuclear neutrophils (PMN) and inducible NO synthase (iNOS) mRNA in PMN. Pretreatment of rats with a polyclonal TNF-alpha antibody (TNF-Ab, 22 mg/kg i.m.) abolished LPS-mediated increases in plasma TNF-alpha but failed to inhibit APH or the NO system. TNF-alpha (8.2 micrograms/kg i.v.) produced transient hypertension and sustained tachycardia and increased plasma TNF-alpha and PMN iNOS mRNA but not RNI. LPS and TNF-alpha decreased spontaneous and calcimycin (Ca2+ ionophore, 1 microM)- and PAF (1 microM)-mediated increases in head-space NO production by rings of mesenteric artery incubated ex vivo. TNF-Ab abolished all effects of TNF-alpha. PAF (25, 50, and 100 ng/kg) produced APH without increasing plasma TNF-alpha, RNI, or PMN iNOS mRNA. The PAF receptor antagonist BN-50730 (80 micrograms/kg i.v.) abolished PAF-induced APH and attenuated LPS-induced increases in RNI. We conclude that 1) LPS produces parallel but unrelated changes in TNF-alpha and RNI in plasma and PMN during the APH of endotoxemia; and 2) endogenous TNF-alpha is not required for LPS-mediated induction of iNOS mRNA, and PAF mediates LPS-induced APH.
Low-dose prostacyclin has potent capillary permeability-reducing effect in cat skeletal muscle in vivo
Authors: Moller A. D. , Grande P. O.
Published: December 2017

The dose-response effects of intravenous infusion of prostacyclin on capillary permeability (the capillary filtration coefficient technique), hydrostatic capillary pressure, transcapillary filtration, and vascular tone were analyzed in vivo on cat skeletal muscle from a normal and an increased permeability level. Increased permeability was accomplished by intra-arterial infusion of tumor necrosis factor-alpha or histamine. Permeability effects of bradykinin were also analyzed. Prostacyclin decreased capillary permeability by 8% at a dose of 0.1 ng.kg-1.min-1 and at most by 30% below control attained at 2 ng.kg-1.min-1, also with no effect on vascular tone and hydrostatic capillary pressure. The permeability increase by tumor necrosis factor-alpha and histamine (by 54 and 73%) was more than counteracted by the simultaneous infusion of prostacyclin at 2 ng.kg-1.min-1. The vasodilator effect of tumor necrosis factor-alpha was also restituted. Indomethacin (prostacyclin inhibitor)-induced increase in capillary permeability (25%) was more than restituted by prostacyclin at 2 ng.kg-1.min-1. Surprisingly, bradykinin decreased capillary permeability. We conclude that endogenous prostacyclin may be a physiological regulator of capillary permeability and that low-dose prostacyclin infusion may have clinical relevance in states of increased permeability.
ANP protects against reoxygenation-induced hypercontracture in adult cardiomyocytes
Authors: Hempel A. , Friedrich M. , Schluter K. D. , Forssmann W. G. , Kuhn M. , Piper H. M.
Published: December 2017

It was investigated whether atrial natriuretic peptide (ANP) or the related peptide urodilatin can be used for protecting cardiomyocytes against reoxygenation-induced hypercontracture. Isolated ventricular cardiomyocytes (from adult rats) were used as the experimental model. When the cells were submitted to substrate-free anoxia (135 min) and subsequent reoxygenation (30 min), the onset of reoxygenation provoked their hypercontracture. It was studied whether the temporary presence of ANP or urodilatin (1 nM to 1 microM) or 8-bromo-guanosine 3',5'-cyclic monophosphate (8-BrcGMP; 1 microM to 1 mM) during the last 15 min of anoxia and the first 15 min of reoxygenation prevented hypercontracture. It was found that ANP (1 microM) prevented hypercontracture in 82 +/- 8% (SD), urodilatin (1 microM) in 80 +/- 9%, and 8-BrcGMP (1 mM) in 72 +/- 10% of the cells (n = 40 cells). When ANP (1 microM) was added during the last 15 min of anoxia and the first 15 min of reoxygenation, the cellular concentration of cGMP increased from 0.41 +/- 0.04 to 2.80 +/- 0.81 pmol/mg protein (n = 6 cultures). The results show that the reoxygenation-induced hypercontracture in cardiomyocytes can be attenuated by the temporary presence of the stimulators of particulate guanylate cyclase, ANP or urodilatin.
Myogenic constriction of human coronary arterioles
Authors: Miller F. J. , Dellsperger K. C. , Gutterman D. D.
Published: December 2017

Myogenic constriction is an important mechanism of blood flow regulation; however, it has never been demonstrated in the human coronary circulation. We examined responses of human coronary resistance vessels in vitro to changes in intraluminal pressure and evaluated the role of protein kinase C (PKC). Microvessels (passive diameter 44-227 microns) were dissected from atrial appendages obtained during cardiac surgery and studied under conditions of zero flow. In response to stepped increases in pressure, there was a graded response such that at 100 mmHg, vessels constricted to 55 +/- 4% of their passive diameter. There was an inverse relationship between vessel diameter and myogenic responsiveness. Basal tone was attenuated by inhibition of voltage-dependent calcium channels (VDCC) with diltiazem and by inhibition of PKC with calphostin C. Activation of PKC with phorbol 12-myristate 13-acetate (PMA) enhanced basal tone. Active myogenic constriction was also impaired by calphostin C and augmented by PMA. Arterioles from patients with hypertension demonstrated enhanced myogenic constriction compared with vessels from normotensive patients (0.55 +/- 0.04 vs. 0.74 +/- 0.03; P < 0.01). These results demonstrate myogenic constriction in the human coronary microcirculation. Regulation of extracellular calcium by VDCC and intracellular calcium by PKC are important in mediating the magnitude of basal tone and myogenic responsiveness of these vessels.