[A summary on surveillance system of occupational disease under the framework of National Health Insurance Informatization Project]

The surveillance of occupational disease has entered a new stage ofdevelopment, with the implementation of the national health informatization project. To improve the efficiency and quality of occupational disease monitoring information reporting in this paper, the system architecture and related management regulations, as long as the major changes and achievement of "surveillance system of occupational disease and health hazards information" under the framework of National Health Insurance Informatization Project were elaborated. The deficiencies existing in the system were analyzed, and expectation for the construction of the occupational disease surveillance system was addressed.

Fatigue device driven by a three degree of freedom tripodal piezoelectric actuator

A miniature piezoelectric-driven fatigue device with three degrees of freedom is developed. The device integrates two fatigue testing functions, including uniaxial tensile fatigue and tensile-bending combined loading modes. The synchronous tensile-bending loading principle is described, which is applicable for calculating the vector displacements along two orthogonal directions and investigating the anisotropic fatigue properties. Regarding the combined loading mode, maximum load/displacement amplitudes for tensile and bending vector components that could be achieved are 16.9 N/22.8 µm and 3.3 N/5.6 µm, respectively. Based on tensile and tensile-bending combined fatigue loading modes, the displacement responses and fatigue lives at loading frequencies ranging from 1 Hz to 100 Hz are valuated experimentally to indicate the validation.

Note: Motor-piezoelectricity coupling driven high temperature fatigue device

The design and performance evaluation of a novel high temperature fatigue device simultaneously driven by servo motor and piezoelectric actuator is our focus. The device integrates monotonic and cyclic loading functions with a maximum tensile load of 1800 N, driving frequency of 50 Hz, alternating load of 95 N, and maximum service temperature of 1200 °C. Multimodal fatigue tests with arbitrary combinations of static and dynamic loads are achieved. At temperatures that range from RT to 1100 °C, the tensile and tensile-fatigue coupling mechanical behaviors of UM Co50 alloys are investigated to verify the feasibility of the device.

[Clinical effect of vacuum sealing drainage in the treatment of complex fracture and dislocation of foot with severe soft tissue injury]

Objective: To observe the clinical effect of vacuum sealing drainage (VSD) in the treatment of complex fracture and dislocation of foot with severe soft tissue injury. Methods: From March 2012 to January 2015, a retrospective analysis of 108 cases of the foot closed complex fracture dislocation with severe soft tissue injury in Department of Foot and Ankle, the Second Hospital of Tangshan City, Tangshan.Injury mechanisms included press and crush injury, traffic accident.According to the operation the cases were divided into the VSD group (56 cases) and the control group (52 cases). The injury foot swelling after treated by open reduction and internal fixation or fusion joint fracture and dislocation. VSD technique was used to cover the wound and wound in group VSD. The wound was sutured, the sterile dressing was covered and the dressing was changed regularly in the control group. Results: Preoperative hospitalization time: 16 days in group VSD, 28 days in the control group; the total hospitalization time: 33 days in group VSD, 53 days in the control group; wound healing: 29 cases in VSD group, 12 cases in the control group; prolonged healing after dressing: 16 cases in VSD group, 13 cases in the control group; after skin grafting healing: 9 cases in VSD group, 17 cases in the control group; healed after flap transposition: 2 cases in VSD group and 10 cases in thecontrol group.The difference of the data of the two groups was statistically significant, P<0.05.Maryland foot score: 55-98 (average: 88.8, median: 91.5) points in VSD group, 38-97 (average: 84.85, median: 91) points in control group, compared with median by rank sum test, Z value: -2.755, the difference was statistically significant, P< 0.05.The late recovery effect rating: 39 casesexcellent, good 12 cases, can be 5 cases, no poor in VSD group, excellent 29 cases, good 8 cases, can be 11 cases, poor 4 cases in the the control group, the difference was statistically significant, P<0.05. Conclusion: VSD can shorten the preoperative waiting time and total hospitalization time, improve the wound healing rate directly, reduce the skin grafting and flap transfer replacement rate, reduce the secondary injury, increased fracture risk reduction and internal fixation, reduce joint fusion rate in the treatment of foot closed complex fracture and dislocation with severe soft tissue injury.

[Clinical effect of double layer vacuum sealing drainage in the treatment of delayed severe infection after calcaneal fracture operation]

Objective: To observe the clinical effect of vacuum sealing drainage (VSD) technique and simple dressing change in the treatment of delayed severe infection after calcaneal fracture surgery. Methods: From August 2008 to July 2015 , 73 patients with delayed severe infection were treated after calcaneal fractures 3 months in Department of Foot and Ankle, the Second Hospital of Tangshan City, according to the treatment methods are divided into vacuum sealing drainage group of 38 cases, 35 cases of simple dressing group.Two groups of patients after regular wound debridement debridement and sterilization after vacuum sealing drainage group received double wound VSD dressing group received postoperative dressing, two groups of patients with sensitive antibiotics for treatment.Two groups of patients according to the frequency of dressing change, wound healing time, bacterial clearance time and healing time were compared in stage Ⅱ during the perioperative period. Results: Vacuum sealing drainage group: dressing: 7 times, the wound healing time was 27 days, bacterial culture negative for 8 days, the healing time of 13.5 days of perioperative period; treatment group: 34 times the number of dressing, wound healing time was 44 days, bacterial culture negative for 18 days, the healing time of 17 days of surgery period. Two groups of data were compared with the median, after the rank sum test, the difference was statistically significant (Z values were -6.670, -5.529, -5.011, -3.227, P<0.05). The vacuum sealing drainage group compared with conventional dressing group significantly reduced the number of dressing, wound healing time, healing time was significantly shortened bacterial clearance time and perioperative period Ⅱ. Conclusion: Double VSD is easy , safe and quick, short cure time, less pain, higher quality of late life advantages, compared with the traditional dressing treatment of calcaneal fractures of postoperative delayed severe infection, is a safe and effective method.

Reperfusion-induced Ins(1,4,5)P(3) generation and arrhythmogenesis require activation of the Na(+)/Ca(2+) exchanger

Reperfusion of globally ischemic rat hearts causes rapid generation of inositol(1,4,5) trisphosphate [Ins(1,4,5)P(3)] and the development of arrhythmias, following stimulation of alpha(1)-adrenergic receptors by norepinephrine released from the cardiac sympathetic nerves. The heightened inositol phosphate response in reperfusion depends on the activation of the Na(+)/H(+) exchanger, which might reflect a central role for increased Ca(2+)following reverse mode activation of the Na(+)/Ca(2+) exchanger (NCX). Isolated, perfused rat hearts were subjected to 20 min ischemia followed by 2 min reperfusion and the content of Ins(1,4,5)P(3) measured by mass analysis or by anion-exchange high performance liquid chromatography (HPLC) following [(3)H]inositol labeling. Reperfusion caused generation of Ins(1,4,5)P(3) (1266+/-401 to 3387+/-256 cpm/g tissue, mean+/-s.e.m., n=6, P<0.01) and the development of arrhythmias. Inhibition of NCX either by reperfusion at low Ca(2+) (1133+/-173 cpm/g tissue, mean+/-s.e.m., n=6, P<0.01 relative to reperfusion control) or by adding 10 microm KB-R7943, an inhibitor of reverse mode Na(+)/Ca(2+) exchange, prevented the Ins(1,4,5)P(3) response (1151+/-243 cpm/g tissue, mean+/-s.e.m., n=6, P<0.01 relative to reperfusion control) and the development of ventricular fibrillation. Lower concentrations of KB-R7943 were less effective. Reverse mode activation of NCX is therefore required for the enhanced Ins(1,4,5)P(3) response in early reperfusion, and inhibitors of this transporter may be useful in the prevention of arrhythmias under such conditions.

Cardiac output in mice overexpressing beta2-adrenoceptors or with myocardial infarct

1. The aims of the present study were to characterize cardiac output (CO) in transgenic mice that overexpress the beta2-adrenoceptor and to evaluate ultrasonic flowmetery for continuous CO measurement in the mouse in vivo. 2. Under conditions of anaesthesia, open chest and positive ventilation, CO was determined with a transonic flowmeter at baseline and during dobutamine administration and intravenous volume loading in wild-type mice (n = 17) and beta2-adrenoceptor transgenic (n = 9) and wild-type mice with chronic myocardial infarct (n = 16). 3. Compared with wild-type mice, beta2-adrenoceptor transgenic mice with markedly enhanced ventricular contractility had a significantly higher CO, heart rate (HR) and maximal acceleration of aortic flow. Both dobutamine and volume loading increased CO in the two groups and higher levels of CO were measured in transgenic mice during the interventions. At baseline or during interventions, stroke volume was similar between beta2-adrenoceptor transgenic and wild-type mice. Infarcted mice with impaired cardiac function had a significantly lower CO under basal and stress conditions. 4. Thus, beta2-adrenoceptor transgenic mice revealed higher CO that was largely attributable to a significantly higher HR but not to an increase in stroke volume. Transonic flowmetery can detect differences in CO among mice in various functional states and is suitable for evaluation of cardiac functional reserve in mice in vivo by continuous monitoring of CO responses to different interventions.

Age-dependent cardiomyopathy and heart failure phenotype in mice overexpressing beta(2)-adrenergic receptors in the heart

OBJECTIVE

To explore long-term cardiac phenotype in transgenic (TG) mice with 300-fold overexpression of beta(2)-adrenergic receptors (AR).

METHODS

Echocardiography was performed serially on a cohort of wild-type and TG mice (n=26 each) between 4 and 15 months of age. Survival was monitored and autopsy and histological examinations were performed.

RESULTS

Heart rate was higher in TG than in wild-type mice throughout the study period. The left ventricular dimensions and fractional shortening were similar between TG and wild-type groups during 4-6 months. Starting at 9 months, however, TG mice showed progressive reduction in fractional shortening and systolic wall thickening, and increase in left ventricular dimensions and left ventricular mass, indicating onset of heart failure, left ventricular hypertrophy and remodeling. Abnormal waveforms in the electrocardiogram and episodes of ventricular ectopic beats were also observed in TG mice. Death of TG mice started at 8.5 months, and the cumulative mortality was 81% by 15 months (P<0.0001 vs. 4% in wild-type mice). The majority of deaths were due to severe heart failure, indicated by cardiac dilatation, lung congestion, pleural effusion and atrial thrombus. Left ventricular sections showed widespread interstitial fibrosis, loss of myocytes and myocyte hypertrophy in TG mice.

CONCLUSIONS

A high level of beta(2)AR overexpression results in cardiomyopathy and heart failure. The onset was slower and the expression levels of receptors required are much higher than previously described for the beta(1)AR overexpression.

Preserved ventricular contractility in infarcted mouse heart overexpressing beta(2)-adrenergic receptors

Effects of cardiac specific overexpression of beta(2)-adrenergic receptors (beta(2)-AR) on the development of heart failure (HF) were studied in wild-type (WT) and transgenic (TG) mice following myocardial infarction (MI) by coronary artery occlusion. Animals were studied by echocardiography at weeks 7 to 8 and by catheterization at week 9 after surgery. Post-infarct mortality, due to HF or cardiac rupture, was not different among WT mice, and there was no difference in infarct size (IS). Compared with the sham-operated group (all P < 0.01), WT mice with moderate (<36%) and large (>36%) IS developed lung congestion, cardiac hypertrophy, left ventricular (LV) dilatation, elevated LV end-diastolic pressure (LVEDP), and suppressed maximal rate of increase of LV pressure (LV dP/dt(max)) and fractional shortening (FS). Whereas changes in organ weights and echo parameters were similar to those in infarcted WT groups, TG mice had significantly higher levels of LV contractility in both moderate (dP/dt(max) 4,862 +/- 133 vs. 3,694 +/- 191 mmHg/s) and large IS groups (dP/dt(max) 4,556 +/- 252 vs. 3,145 +/- 312 mmHg/s, both P < 0.01). Incidence of pleural effusion (36% vs. 85%, P < 0.05) and LVEDP levels (6 +/- 0.3 vs. 9 +/- 0.8 mmHg, P < 0.05) were also lower in TG than in WT mice with large IS. Thus beta(2)-AR overexpression preserved LV contractility following MI without adverse consequence.

Activation of the Na(+)/H(+) exchanger is required for reperfusion-induced Ins(1,4,5)P(3) generation

Post-ischemic reperfusion causes a change in inositol phosphate responses to norepinephrine from primary generation of inositol(1,4) bis phosphate (Ins(1,4)P(2)) to generation of inositol(1,4,5) tris phosphate (Ins(1,4,5)P(3)) that is required for the initiation of reperfusion arrhythmias. The current study was undertaken to investigate the role of Na(+)/H(+)exchange in facilitating this transient change in inositol phosphate response. Rat hearts were subjected to 20 min ischemia followed by 2 min reperfusion and Ins(1, 4,5)P(3)content was measured by mass analysis or by anion-exchange HPLC following [(3)H]inositol labeling. Reperfusion caused generation of [(3)H]Ins(1,4,5)P(3)(1732+/-398 to 3103+/-214, cpm/g tissue, mean+/-S.E.M., n=5, P<0.01) and the development of arrhythmias. Inhibition of Na(+)/H(+)exchange, by reperfusing at pH 6.3 or by pretreating with HOE-694 (10 n M-3 microM) or HOE-642 (3 microM) prevented the [(3)H]Ins(1,4,5)P(3)generation, without causing any suppression of norepinephrine release. Increases in Ins(1,4,5)P(3)mass were similarly reduced by inhibition of Na(+)/H(+)exchange. Thus, activation of Na(+)/H(+)exchange is required for the enhanced Ins(1,4,5)P(3)response observed under reperfusion conditions, and prevention of Ins(1,4,5)P(3)generation may be an important contributor to the anti-arrhythmic actions of inhibitors of Na(+)/H(+)exchange.

Adverse effects of constitutively active alpha(1B)-adrenergic receptors after pressure overload in mouse hearts

Cardiac hypertrophy and function were studied 6 wk after constriction of the thoracic aorta (TAC) in transgenic (TG) mice expressing constitutively active mutant alpha(1B)-adrenergic receptors (ARs) in the heart. Hearts from sham-operated TG animals and nontransgenic littermates (WT) were similar in size, but hearts from TAC/TG mice were larger than those from TAC/WT mice, and atrial natriuretic peptide mRNA expression was also higher. Lung weight was markedly increased in TAC/TG animals, and the incidence of left atrial thrombus formation was significantly higher. Ventricular contractility in anesthetized animals, although it was increased in TAC/WT hearts, was unchanged in TAC/TG hearts, implying cardiac decompensation and progression to failure in TG mice. There was no increase in alpha(1A)-AR mRNA expression in TAC/WT hearts, and expression was significantly reduced in TAC/TG hearts. These findings show that cardiac expression of constitutively actively mutant alpha(1B)-ARs is detrimental in terms of hypertrophy and cardiac function after pressure overload and that increased alpha(1A)-AR mRNA expression is not a feature of the hypertrophic response in this murine model.

Expression of active alpha(1B)-adrenergic receptors in the heart does not alleviate ischemic reperfusion injury

Ischemic preconditioning reduces infarct size and improves cardiac function in various species, including mice. The mechanism for ischemic preconditioning protection is not entirely clear and activation of alpha(1B)-adrenergic receptors (AR) is believed to be involved. Transgenic mice expressing constitutively active mutant alpha(1B)-AR in the heart have enhanced alpha(1B)-AR activity and therefore can be used to test the role of alpha(1B)-AR in ischemic preconditioning. Wild-type and transgenic mice were subjected to 30- or 40-min periods of left coronary artery occlusion followed by 60-min reperfusion, or ischemic preconditioning prior to sustained ischemia-reperfusion. Risk and infarct zones were determined by staining with Evans blue and triphenyltetrazolium, respectively, and quantitated digitally. Infarct zone and infarct size were not different between wild-type and transgenic mice, nor was the extent of reduction in infarct size by preconditioning ischemia (wild-type mice: 45+/-3 to 18+/-3%, transgenic mice: 46+/-3 to 19+/-2% of the left ventricle, both P<0.01). Ventricular function was similar between wild-type and transgenic mice with or without ischemia-reperfusion injury. In conclusion, enhanced alpha(1B)-AR activity by cardiac-specific expression of constitutively active mutant alpha(1B)-AR in mice does not mimic ischemic preconditioning to protect against ischemia-reperfusion injury.

Beta(2)-adrenergic receptor overexpression driven by alpha-MHC promoter is downregulated in hypertrophied and failing myocardium

OBJECTIVE

The alpha-myosin heavy chain (alpha-MHC) promoter is frequently used to direct cardiac specific transgene expression. We studied whether transgene expression controlled by this promoter was altered under conditions of cardiac hypertrophy and failure.

METHODS

Transgenic (TG) mice overexpressing human beta(2)-adrenergic receptors (beta(2)AR) and wild type (WT) controls were subjected to thoracic aortic constriction (TAC) or sham operation and studied at 1, 3 and 8 weeks after surgery.

RESULTS

Sham operated TG mice had higher heart rates and left ventricular (LV) contractility than WT (all P<0.01), demonstrating enhanced betaAR activation. TAC at 1, 3 and 8 weeks produced progressive LV hypertrophy which was similar between WT and TG mice. Evidence of heart failure was more marked in TG mice with a greater increase in weights of the right ventricle and lungs and a higher prevalence of atrial thrombus (P<0.05 in each case). In hypertrophied TG hearts, endogenous alpha-MHC mRNA transcripts in LV were maintained at 1 and 3 weeks, but were reduced by approximately 40% relative to the sham-operated group at 8 weeks after TAC. Transgene expression, measured as human beta(2)AR mRNA, was reduced by 45% at 1 and 3 weeks and by 70% at 8 weeks after TAC. beta(2)AR binding sites were reduced by 35, 47 and 65%, respectively, at 1, 3 and 8 weeks.

CONCLUSION

Cardiac hypertrophy and failure cause downregulation of the endogenous alpha-MHC as well as cardiac specific overexpression of the transgene directed by an alpha-MHC promoter.

Reduced myocardial nerve growth factor expression in human and experimental heart failure

Maintenance of cardiac performance is tightly controlled by the autonomic nervous system. In congestive heart failure (CHF), although the adverse pathophysiological effects of cardiac sympathetic overactivity are increasingly recognized, the paradoxical finding of reduced sympathetic innervation density in the failing heart remains unexplained. Given these observations, we tested the hypothesis that a reduction in the myocardial production of nerve growth factor (NGF), which is important for the maintenance of sympathetic neuronal survival, could explain the conflicting neurochemical and neuroanatomical profile of CHF. In healthy humans (n=11), there was a significantly greater transcardiac venoarterial plasma NGF gradient than in CHF patients (n=11, P<0.05). In a rat model of CHF, a 40% reduction (P<0.05) NGF mRNA expression was apparent in association with a 24% reduction in tissue NGF content (P<0.05). In conjunction, evidence of reduced sympathetic innervation in the failing heart was apparent, as measured histologically by catecholamine fluorescence and by expression of the neuronal NGF receptor trkA. Norepinephrine (10 micromol/L) exposure reduced both NGF mRNA and protein expression in isolated cardiomyocytes, suggesting that myocardial NGF downregulation may represent an adaptive response to sympathetic overactivity. These data indicate that NGF expression in the heart is dynamic and may be altered in cardiovascular disease states. In CHF, reduced NGF expression may account for alterations in sympathetic neuronal function and neuroanatomy. The full text of this article is available at http://www.circresaha.org.

Enhanced negative chronotropy by inhibitory receptors in transgenic heart overexpressing beta(2)-adrenoceptors

Transgenic (TG) mice overexpressing beta(2)-adrenoceptors (AR) in the heart have enhanced beta-adrenergic activity. Since the degree of beta-adrenergic activation influences the negative chronotropic control of heart rate (HR), we studied the inhibitory effect of cholinergic and purinergic stimulation on HR in TG and wild-type (WT) control mice. Bradycardia in response to vagal nerve stimulation and administration of acetylcholine or adenosine was studied in anesthetised animals and perfused hearts. Basal HR was significantly higher in TG than WT mice (P<0.01). Electrical stimulation of vagal nerves (1-32 Hz) induced a Hz-dependent reduction in HR and the response was more pronounced in TG than WT groups (P<0.01). In perfused hearts, HR reduction by acetylcholine (ACh) was more pronounced with EC(50) 110-fold lower in TG than WT hearts. Adenosine-induced bradycardia, which was abolished by a P(1) antagonist, was more pronounced in TG hearts. After pre-treatment with pertussis toxin (PT, 100 microg/kg), bradycardia by vagal nerve stimulation or ACh remained unchanged in WT, but markedly inhibited in TG hearts (both P<0.01). Conversely, inhibiting guanylyl cyclase with LY83583 (30 microM) or nitric oxide synthase with L-NMMA (100 microM) attenuated HR reduction by vagal nerve stimulation in WT but not in TG hearts. Immunobloting assay showed similar G(ialpha2) abundance in TG and WT hearts. Thus, cardiac overexpression of beta(2)AR with high beta-adrenergic activity leads to hypersensitivity of inhibitory receptors controlling HR due to increase in activity of PT-sensitive G-proteins.

Serial echocardiographic assessment of left ventricular dimensions and function after myocardial infarction in mice

OBJECTIVE

To test the usage of serial echocardiography in mice with induced myocardial infarct (MI) and to characterize the mouse model of MI.

METHODS

C57 mice underwent open-chest surgery to induce left coronary artery occlusion or sham-operation (SH). Echocardiography was performed before and at 1, 2.5, 6 and 9 weeks after surgery. Left ventricular end diastolic and end systolic dimensions (LVEDd, LVESd) and fractional shortening (FS) were measured. Haemodynamics was determined at week 9 by LV catheterization and hearts were examined morphologically.

RESULTS

Post-infarct mortality was 46% (10/22), of which, 70% died of acute heart failure or LV rupture within the first week. LV dimensions and FS remained stable in SH group (n = 10) during the study period. In surviving MI mice (n = 12), there was modest LV dilatation and fall in FS at week 1. Compared with week 0 values, there were progressive increase in LVEDd (+50(-)+66%) and LVESd (+124(-)+171%), and decline in FS (-53(-)-73%) during the 2.5-9 week period. Infarcted mice also had lower LV systolic pressure (LVSP), dP/dtmax and dP/dtmin (all P < 0.01 vs. SH group). Infarct size, LVSP and dP/dt significantly correlated with FS and LV dimensions (r = 0.61-0.80, all P < 0.01).

CONCLUSIONS

LV remodeling and dysfunction in mice with MI are time-dependent processes and early remodeling seems associated with high risk of rupture and acute pump failure. Our findings provide a baseline description of this murine model and confirm echocardiography as a reliable means to serially assess changes of cardiac structure and function after MI.

beta(2)-adrenergic receptor overexpression exacerbates development of heart failure after aortic stenosis

BACKGROUND

Beta-adrenergic signaling is downregulated in the failing heart, and the significance of such change remains unclear.

METHODS AND RESULTS

To address the role of beta-adrenergic dysfunction in heart failure (HF), aortic stenosis (AS) was induced in wild-type (WT) and transgenic (TG) mice with cardiac targeted overexpression of beta(2)-adrenergic receptors (ARs), and animals were studied 9 weeks later. The extents of increase in systolic arterial pressure (P<0.01 versus controls), left ventricular (LV) hypertrophy (TG, 94+/-6 to 175+/-7 mg; WT, 110+/-6 to 168+/-10 mg; both P<0.01), and expression of ANP mRNA were similar between TG and WT mice with AS. TG mice had higher incidences of premature death and critical illness due to heart failure (75% versus 23%), pleural effusion (81% versus 45%), and left atrial thrombosis (81% versus 36%, all P<0.05). A more extensive focal fibrosis was found in the hypertrophied LV of TG mice (P<0.05). These findings indicate a more severe LV dysfunction in TG mice. In sham-operated mice, LV dP/dt(max) and heart rate were markedly higher in TG than WT mice (both P<0.01). dP/dt(max) was lower in both AS groups than in sham-operated controls, and this tended to be more pronounced in TG than WT mice (-32+/-5% versus -16+/-6%, P=0.059), although dP/dt(max) remained higher in TG than WT groups (P<0.05).

CONCLUSIONS

Elevated cardiac beta-adrenergic activity by beta(2)-AR overexpression leads to functional deterioration after pressure overload.

Sympathetic activation triggers ventricular arrhythmias in rat heart with chronic infarction and failure

OBJECTIVE

To seek direct evidence for a cause-effect relation between sympathetic activation and arrhythmogenesis.

METHODS

Rats underwent open-chest surgery with either coronary artery occlusion or sham operation, and were studied 8 weeks later using in situ heart perfusion and nerve stimulation methods.

RESULTS

Infarcted rats showed cardiac functional impairment and increased heart and lung weight. The extent of these changes correlated well with infarct size (IS). In in situ perfused hearts, sympathetic nerve stimulation (2 and 4 Hz, 45 s duration) induced a frequency-dependent release of norepinephrine (NE). NE release was lower in MI than that in control groups. In hearts with large IS (> or = 40%, n = 19) ventricular arrhythmias were rare at baseline, but nerve stimulation evoked the onset of ventricular premature beats (95%), tachycardia (37%) and fibrillation (26%), IS and stimulation frequency were key determinants for the inducibility of arrhythmias. Lower K- concentration enhanced arrhythmia inducibility. beta-blockade inhibited the frequency of arrhythmias produced by nerve stimulation.

CONCLUSION

In infarcted rat hearts sympathetic activation is a potent trigger for the onset of ventricular tachyarrhythmias.

Effects of heart rate on arterial compliance in men

1. Arterial compliance is a major determinant of left ventricular afterload. In keeping with earlier experimental data obtained in isolated arterial segments, it has recently been shown in the rat that arterial compliance decreases with an increase in heart rate (HR) induced by atrial pacing. 2. To elucidate the potential relevance of this effect in humans, we investigated nine male volunteers (age 20-30 years; mean 26 years). Systemic arterial compliance (SAC) was measured with the diastolic area method and carotid-to-femoral and femoral-to-dorsalis pedis pulse wave velocities (PWV) were measured to determine regional changes in compliance. Heart rate was first lowered with intravenous metoprolol to 56 +/- 2 b.p.m. and then increased by transoesophageal atrial pacing to 80 and 100 b.p.m. 3. Increasing HR from 56 +/- 2 to 80 b.p.m. by pacing increased mean arterial pressure (MAP) from 78 +/- 2 to 98 +/- 1 mmHg (P < 0.001) and then to 102 +/- 2 mmHg (P = NS). Systemic arterial compliance fell from 0.48 +/- 0.06 to 0.33 +/- 0.04 arbitrary compliance units (ACU; P < 0.01), carotid-to-femoral PWV increased from 6.1 +/- 0.3 to 6.8 +/- 0.4 m/s (P < 0.001) and femoral-to-dorsalis pedis PWV increased from 8.9 +/- 0.4 to 10.1 +/- 0.5 m/s (P < 0.001). Pacing at 100 b.p.m did not change MAP, but did lead to a further decrease in SAC (to 0.24 +/- 0.03 ACU; P < 0.05) and further increases in carotid-to-femoral (7.3 +/- 0.4 m/s; P = NS) and femoral-to-dorsalis pedis PWV (11.3 +/- 0.4 m/s; P < 0.001). 4. We conclude that systemic, central and peripheral compliances decrease in vivo with an increase in HR induced by atrial pacing.

Inhibition of inositol(1,4,5)Trisphosphate generation by endothelin-1 during postischemic reperfusion: A novel antiarrhythmic mechanism

BACKGROUND

Reperfusion of ischemic rat hearts in the presence of thrombin or norepinephrine but not endothelin-1 causes the generation of inositol 1,4,5-trisphosphate (Ins 1,4,5P3) and arrhythmias. The present study investigates the effect of endothelin-1 on these responses.

METHODS AND RESULTS

Ins 1,4,5P3 generation was quantified by use of [3H] labeling and high-performance liquid chromatography as well as by mass analysis. Twenty minutes of global ischemia followed by 2 minutes of reperfusion increased [3H]Ins 1,4,5P3 from 2828+/-265 to 5033+/-650 cpm/g tissue in the presence of thrombin 2.5 IU/mL and to 4561+/-286 cpm/g tissue in response to release of norepinephrine (n=4, P<0.01) in both cases. Reperfusion in the presence of endothelin-1 alone caused no change in Ins 1,4,5P3 (2762+/-240 cpm/g tissue), but when added together with thrombin or norepinephrine, endothelin-1 reduced the Ins 1,4,5P3 responses to 2313+/-197 and 1764+/-168 cpm/g tissue, respectively (n=4, P<0.01 in both cases). Similar inhibitory interactions between endothelin-1 10 nmol/L and thrombin 2.5 IU/mL were observed under normoxic conditions in nonperfused ventricle, eliminating the possibility that excessive vasoconstriction was responsible. In parallel studies, endothelin-1 suppressed the development of reperfusion arrhythmias initiated by either thrombin (ventricular fibrillation, 75% to 39%, n=16 to 18) or norepinephrine (83% to 8%, n=12 to 22) (P<0.01 in both cases).

CONCLUSIONS

Inhibition of Ins 1,4,5P3 generation during myocardial reperfusion by endothelin-1 represents a novel antiarrhythmic mechanism.

Presynaptic antisympathetic action of amiodarone and its metabolite desethylamiodarone

Amiodarone has a "reserpine-like" sympatholytic action in the heart. The aims of this study were to test whether desethylamiodarone (DEA), the in vivo bioactive metabolite of amiodarone, has this action and whether this action could be demonstrated in a neuronal preparation. Experiments were performed in intact rats, perfused hearts, or brain synaptosomes treated with DEA and amiodarone, and concentrations of norepinephrine (NE) and dihydroxyphenylglycol (DHPG), the intraneuronal metabolite of NE, were assayed in plasma, coronary effluent, and synaptosomes. In perfused hearts, DEA at 1, 3, and 10 microM increased DHPG overflow by threefold, sixfold, and ninefold, respectively (all p < 0.01 vs. control). DEA at 1 microM was more potent than amiodarone in increasing DHPG overflow. DEA at 1 and 3 microM also inhibited NE release evoked by sympathetic nerve stimulation (p < 0.05). In intact rats, intravenous DEA at 15 mg/kg elicited onefold increase in plasma DHPG level, and oral pretreatment with amiodarone did not interfere with the sympatholytic action of intravenous amiodarone. In synaptosomes, 40-min incubation with amiodarone, DEA (both 10 microM), and reserpine reduced synaptosomal NE content by 42, 45, and 60%, respectively. Thus similar to its parent drug, DEA exerts a presynaptic sympatholytic action in rat hearts in vivo and in vitro. This action of amiodarone and DEA also was observed in synaptosomes.

Reduced reperfusion-induced Ins(1,4,5)P3 generation and arrhythmias in hearts expressing constitutively active alpha1B-adrenergic receptors

Reperfusion of globally ischemic rat hearts causes the generation of inositol(1,4,5)trisphosphate [Ins(1,4,5)P3] and the initiation of arrhythmias. These responses are mediated by alpha1-adrenergic receptors (ARs), but the subtype of receptor involved has not been identified. Under normoxic conditions, hearts from transgenic animals expressing constitutively active alpha1B-ARs in heart (alpha1B-constitutively active mutant [CAM]) showed higher [3H] inositol phosphate responses to norepinephrine (2.3-fold) than hearts from nontransgenic animals (alpha1B-WT) (1.6-fold). alpha1B-WT hearts responded to 2 minutes of reperfusion after 20 minutes of global ischemia by generation of Ins(1,4,5)P3 (5301+/-1310 to 11 413+/-1597 CPM/g tissue; mean+/-SEM; n=6; P<0.01 in [3H] labeling studies and 3.8+/-0.2 to 6.3+/-0.6 nmol/g by mass analysis, n=6; P<0.05). In contrast to findings in normoxia, hearts from alpha1B-CAM animals showed no Ins(1,4,5)P3 response in early reperfusion. In parallel studies, alpha1B-WT hearts developed ventricular tachycardia and ventricular premature beats (VPB) during 5 minutes of reperfusion after 20 minutes of ischemia. The incidence of these arrhythmias was reduced in the alpha1B-CAM hearts (95% to 62% for VPB and 47% to 12% for ventricular tachycardia; both P<0.05). The resistance of the alpha1B-CAM hearts was not due to alpha1B-AR-mediated preconditioning, as the Ins(1,4,5)P3 response to thrombin receptor activation during reperfusion was not different between the 2 groups. To investigate the possibility of reduced alpha1A-receptor activity in the alpha1B-CAM hearts, expression of the mRNA for alpha1A- and alpha1B-receptors was measured. alpha1B-WT hearts contained mRNA for both receptor subtypes, but the levels of alpha1B-receptor mRNA were 5-fold higher than alpha1A-receptor mRNA. alpha1B-CAM hearts contained very high levels of alpha1B-receptor mRNA (26-fold increase), but the expression of mRNA for the alpha1A-receptors (0.141+/-0.035 amol/ microg RNA; mean+/-SEM; n=6) was reduced by 50% relative to alpha1B-WT controls (0.276+/-0.046 amol/ microg RNA; n=6; P<0.01). The reduction in arrhythmogenic and Ins(1,4,5)P3 responses in alpha1B-CAM hearts provides evidence that these response are not mediated by alpha1B-receptors.

Effect of fish oil supplementation on aortic compliance in rats: role of the endothelium

Arterial compliance improves with dietary fish oils in patients with high cardiovascular risk. Since fish oils alter prostaglandin metabolism and the L-arginine-nitric oxide pathway, and since compliance may be modified by vasoactive substances, the effect of the endothelium and some of its derivatives on aortic complaince were examined. Rats were randomly allocated to four groups, the first of which fed only the regular chow. The remaining three groups were fed the chow supplemented by daily gavage with either coconut, fish or safflower oil for 8 weeks. The thoracic aorta was removed and six 2 mm rings obtained. Rings were paired and one from each pair treated with either N(W)-nitro-L-arginine, indomethacin or de-endothelialized. A diameter-tension curve was initiated from wire touch position using incremental increases in wire distance until no further response observed. The data was transformed to a diameter-pressure relationship and fitted with a linear equation, the slope of which related directly to compliance. De-endothelialization (slopes: control vs de-endothelialized: 9.05+/-0.15 vs 8.31+/-0.24; P< 0.05) and indomethacin (slopes: control vs indomethacin: 9.11+/-0.15 vs 7.76+/-0.37; P< 0.05) significantly decreased arterial compliance as did dietary fish oils (slopes: control vs n-3: 9.16+/-0.11 vs 7.84+/-0.39; P< 0.05). No further effect was seen with indomethacin in the fish oil treated group. It is concluded that the endothelium and in particular, endothelium derived prostanoids, contribute to vessel compliance. We also conclude that fish oils have a similar action to indomethacin, leading to the increase in aortic stiffness observed.