Reduced LVEDD following a 12 week exercise training program in patients with symptomatic chronic heart failure is associated with reduction in serum levels of Troponin I

Funding Acknowledgements

Type of funding sources: Public Institution(s). Main funding source(s): Norwegian University of Science and Technology Danish Research Council

Background

Exercise training (ET) exerts many beneficial effects on the cardiovascular system, and longitudinal observational data from epidemiological studies suggest that higher physical activity is associated with lower concentrations of cardiac troponins. We have previously shown that ET can reduce Left Ventricle End-diastolic diameter (LVEDD), and improve exercise capacity.

Purpose

Our aim was to explore the relationship between changes in LVEDD and changes in high-sensitive plasma troponin I (hs-TnI) levels in patients with symptomatic heart failure undergoing a 12 week structured exercise training program in the randomized multicenter SMARTEX trial.

Methods

This was a post hoc analysis in 199 patients with symptomatic HF with LVEF <35% and NYHA II-III that were randomly assigned to High Intensity Interval Training (HIIT, n = 73), Moderate Continuous Training (MCT, n = 59) or Recommendation of Regular Exercise, (RRT, n = 67) for 12 weeks. Log-transformed Hs-TnI measurements and clinical data acquired before (BL) and after a 12 week exercise training intervention (12 weeks) and at 1 year follow-up (1 year) were analysed using a linear mixed model. For Troponin analysis the STAT Troponin-I from Abbott Diagnostics was used.

Nakagawa’s marginal R2 and conditional R2 were used to evaluate variance explained by fixed effects only and by fixed and random effects together, respectively.

Changes of LVEDD between baseline and 12 weeks and baseline and 52 weeks were evaluated using linear mixed model. The outcome variable were measures of LVEDD, while age, sex, visit and training group and their interaction [visit × training group]  were included as fixed effects. Patient id and training center were random effects. Covariance structure was compound symmetry.

Linear association between log-transformed TnI and LVEDD baseline was evaluated using Pearson correlation coefficient (R).

Results

Serum was available for hs-TnI analyses in 199 patients. In the HIIT group there was a sustained significant reduction in LVEDD at both 12 and 52 weeks.

In the MCT group this reduction was statistically significant at 52 weeks only.

Mixed model analysis predicts that each 1 mm decrease in LVEDD is associated with 1.2% decrease in TnI levels (95% CI: 0.6 – 1.9%, p <0.001). Neither time nor training group were associated with changes of TnI (overall test p = 0.739 and p = 0.987, respectively).

Dynamics of TnI is highly patient-specific with Intraclass correlation coefficient (ICC) = 0.86. Mixed model explains 87% variation of the data (conditional R2), however, only 7% is attributed to the fixed effects (marginal R2).

At baseline, TnI and LVEDD have modest but statistically significant correlation (R = 0.2, p= 0.004).

Conclusions

A reduction of LVEDD following a 12-week exercise-training program is associated with a reduction in plasma troponin levels, in patients with mild to moderate chronic heart failure. Abstract Figure.

Trans‐sodium crocetinate does not affect oxygen uptake in rats during treadmill running

Trans-sodium crocetinate (TSC), the isomer of the carotenoid compound crocetin, is found markedly to increase survival in hemorrhagic shock subsequent to 50-60% blood loss, mainly via restored resting oxygen consumption (VO(2)), blood pressure and heart rate. The proposed mechanism is that TSC increases oxygen diffusivity, and thus availability, in plasma. If this were found to be a prominent feature in the oxygen transfer from blood to skeletal muscle fiber mitochondria, increased VO(2) during exercise would be expected because of reduced partial pressure of venous oxygen (increased utilization), which we aimed to elucidate in this study. Male Sprague-Dawley rats were intravenously injected with 0.3 mL kg(-1) TSC (40 microg mL(-1)) or placebo and immediately thereafter tested on a ramped treadmill test protocol. Rats were introduced to the experimental protocols beforehand. Administration of TSC had a neutral effect on submaximal and maximal VO(2) (VO(2max)) as well as running performance measured as maximal running time and maximal aerobic running velocity. Thus, in this study we cannot report any effects of TSC on steady-state submaximal VO(2) or VO(2max) at exhaustive exercise.

Chronic exposure to carbon monoxide and nicotine: endothelin ET(A) receptor antagonism attenuates carbon monoxide-induced myocardial hypertrophy in rat

The aims of the present study were to determine the effects of endothelin ET(A) receptor antagonism on carbon monoxide (CO)-induced cardiac hypertrophy and endothelin-1 (ET-1) expression and to compare myocardial effects of chronic nicotine with CO exposure. Female Sprague-Dawley rats (n = 84) were randomized to three groups exposed 20 h/day to CO (200 ppm), nicotine (500 microg/m3), or air for 14 consecutive days. In each exposure group, animals were randomized to ET(A) receptor antagonist LU 135252 in drinking water (0.5 mg/ml) or placebo. Myocardial ET-1 and atrial natriuretic peptide (ANP) expression was measured by competitive RT-PCR and plasma ET-1 by immunoassay. Carboxyhemoglobin was 22.1 +/- 0.3% in CO-exposed animals and 2.8 +/- 0.3% in controls. Plasma nicotine was 57 +/- 7 ng/ml and plasma cotinine was 590 +/- 23 ng/ml in nicotine-exposed animals and below detection levels in controls. CO exposure induced a 21% increase in right ventricular hypertrophy (p < 0.01), a 7% increase in left ventricular hypertrophy (p < 0.01), a 25% increase in right ventricular ET-1 expression (p < 0.05), and an eightfold increase in ANP expression (p = 0.08). ET(A) receptor antagonism reduced right ventricular hypertrophy by 60% (p < 0.05) with no significant effect on left ventricular hypertrophy or myocardial ET-1 expression. Chronic nicotine exposure did not significantly affect cardiac weights or ANP and ET-1 expression. We conclude that ET(A) receptor antagonism reduces right ventricular hypertrophy induced by chronic CO exposure, whereas CO-induced myocardial ET-1 expression remains unchanged.

Increased contractility and calcium sensitivity in cardiac myocytes isolated from endurance trained rats

OBJECTIVE

Regular exercise enhances cardiac function and modulates myocyte growth in healthy individuals. The purpose of the present study was to assess contractile function and expression of selected genes associated with intracellular Ca2+ regulation after intensity controlled aerobic endurance training in the rat.

METHODS

Female Sprague-Dawley rats were randomly assigned to sedentary control (SED) or treadmill running (TR) 2 h per day, 5 days per week for 2, 4 or 13 weeks. Rats ran 8-min intervals at 85-90% of VO2max separated by 2 min at 50-60%. Myocyte length, intracellular Ca2+ (Fura-2), and intracellular pH (BCECF) were measured in dissociated cells in response to electrical stimulation at a range of stimulation rates.

RESULTS

The increase in VO2max plateaued after 6-8 weeks, 60% above SED. After 13 weeks, left and right ventricular weights were 39 and 36% higher than in SED. Left ventricular myocytes were 13% longer, whereas width remained unchanged. After 4 weeks training, myocyte contractility was approximately 20% higher in TR. Peak systolic intracellular Ca2+ and time for the decay from systole were 20-35 and 12-17% lower, respectively. These results suggest that increased myofilament Ca2+ sensitivity is the dominant effect responsible for enhanced myocyte contractility in TR. Intracellular pH progressively decreased as stimulation frequency was increased in the SED group. This decrease was markedly attenuated in TR and the intracellular pH was significantly higher in the TR group at a stimulation rate of 5-10 Hz. This effect may contribute to the increased contractility observed at the higher stimulation frequencies in TR. A higher intrinsic myofilament Ca2+ sensitivity was observed in permeabilised myocytes from the TR group under conditions of constant pH and [Ca2+]. Western blot analysis indicated 21 and 46% higher myocardial SERCA-2 and phospholamban, but unaltered Na+/Ca(2+)-exchanger levels. Competitive RT-PCR revealed that TR significantly increased Na+/H(+)-exchanger mRNA.

CONCLUSION

Intensity controlled interval training increases cardiomyocyte contractility. Higher myofilament Ca(2+)-sensitivity, and enhanced Ca(2+)-handling and pH-regulation are putative mechanisms. Our results suggest that physical exercise induces adaptive hypertrophy in cardiac myocytes with improved contractile function.

Attenuated endothelin- mRNA expression with endothelin- receptor blockade during hypoxaemia and reoxygenation in newborn piglets

We investigated the cause of decreased plasma endothelin-1 (ET-1) during hypoxaemia and reoxygenation in newborn piglets subjected to simultaneous blocking of the ET-1 receptors. Changes in plasma ET-1 and prepro-ET-1 mRNA expression in the main pulmonary artery and the left lower lobe in the lung were studied in 1-2-d-old piglets. Ten minutes prior to hypoxaemia, the hypoxaemia group (n = 10) was given saline, two groups (both n = 9) were given 1 and 5 mg/kg i.v. SB 217242 (an ET-1 receptor antagonist). Two groups served as normoxic controls, with and without SB 217242 5 mg/kg i.v. Hypoxaemia was induced by ventilating with 8% O2 until base excess was <-20 mmol/l or mean arterial blood pressure was <20 mmHg. Reoxygenation was performed for 2 h with room air. During hypoxaemia, plasma ET-1 decreased in the hypoxaemia group, remained unchanged in the 1-mg group and increased in the 5-mg group. At the end of reoxygenation, plasma ET-1 was above baseline in the 1-mg and 5-mg groups. In the pulmonary artery, the hypoxaemia group showed 2- to 5-fold higher prepro-ET- 1 mRNA expression compared to all the other groups (p < 0.05). There were trends for higher prepro-ET-1 mRNA expression in pulmonary tissue in the hypoxaemia group compared to the two receptor-blocking groups (p < 0.07).

CONCLUSIONS

We conclude that hypoxaemia and reoxygenation increase prepro-ET-1 mRNA expression in the pulmonary artery in newborn piglets. These observations suggest that the half-life of ET-1 is decreased during hypoxaemia and reoxygenation in newborn piglets.

Chronic carbon monoxide exposure in vivo induces myocardial endothelin-1 expression and hypertrophy in rat

Smoking is associated with endothelial dysfunction and increased plasma levels of endothelin-1. The component of tobacco smoke inducing these effects is unknown. Carbon monoxide induces hypoxia, and there is evidence of carbon monoxide acting as a local mediator in both endothelial and smooth muscle cells. The purpose of this study was to determine whether chronic carbon monoxide exposure similar to that experienced by smokers affects myocardial endothelin-1 expression. Sprague-Dawley female rats were exposed to carbon monoxide 100 ppm for one week or to 100 ppm for one week and 200 ppm for a second week. Carboxyhaemoglobin was 12+/-0.9% in the low and 23+/-1.1% in the high carbon monoxide exposure group. Endothelin-1 expression was measured by competitive reverse transcriptase polymerase chain reaction. High carbon monoxide exposure increased endothelin-1 mRNA by 54+/-12% (P<0.001) in the left ventricle and by 53+/-12% (P<0.001) in the right ventricle. In the low carbon monoxide exposure group corresponding changes were 43+/-14% (P=0.06) and 12+/-16%(P=0.29). Right ventricular weight increased by 18+/-7% (P=0.02) after high and by 16+/-5% (P=0.02) after low exposure. Left ventricular weight was elevated by 5+/-2% (P=0.05) when both exposure groups were compared to controls. We conclude that chronic carbon monoxide exposure leading to carboxyhaemoglobin levels similar to those observed in smokers increases endothelin-1 gene expression and induces myocardial hypertrophy in the rat.

Expression of calcium channels in adult cardiac myocytes is regulated by calcium

In addition to playing a significant role in cardiac excitation-contraction coupling, intracellular Ca2+ ([Ca2+]i) can regulate gene expression. While the mechanisms regulating expression of Ca2+ channels are not entirely defined, some evidence exists for Ca2+-dependent regulation. Using an adult ventricular myocyte culture system, we determined the effects of Ca2+ on: (1) abundance of mRNA for L-type Ca2+ channel alpha1 subunit (DHP receptor); (2) amount of DHP receptors; and (3) whole-cell Ca2+ current (ICa). Rat ventricular myocytes were cultured for 1-3 days in serum-free medium containing either normal (1.8 mM) or high (4.8 mM) Ca2+. Exposing myocytes to high Ca2+ rapidly elevated [Ca2+]i as determined by fura-2. Northern blot analysis revealed that culturing cells in high Ca2+ produced 1.5-fold increase in mRNA levels for the DHP receptor. The abundance of DHP receptors, determined by ligand binding, was two-fold greater in myocytes after 3 days in high Ca2+. Moreover, peak ICa was larger in myocytes cultured for 3 days in high Ca2+ (-17.8+/-1.5 pA/pF, n=26) than in control cells (-11.0+/-1.0 pA/pF, n=23). Voltage-dependent activation and inactivation, rates of current decay, as well as percent increases in ICa elicited by Bay K8644 were similar in all groups. Therefore, larger ICa is likely to represent a greater number of functional channels with unchanged kinetics. Our data support the conclusion that transient changes in [Ca2+]i can modulate DHP receptor mRNA and protein abundance, producing a corresponding change in functional Ca2+ channels in adult ventricular myocytes.

Na,K-pump concentration in hypertrophied human hearts

Several studies have associated myocardial dysfunction with reduced myocardial Na,K-pump concentration, but whether impaired Na,K-pump capacity is a pathogenetic factor or an epiphenomenon related to accompanying cardiac hypertrophy is not established. We measured Na,K-pump concentrations in 10 hypertrophied and 11 normal weighted hearts obtained at autopsy using [3H]ouabain as ligand. Specific [3H] ouabain binding site concentration (OBC) in the left ventricle (LV) averaged 449 +/- 40 (pmol.g-1 wet weight; mean +/- SEM) in hypertrophied and 598 +/- 36 in normal weighted ventricles (P = 0.02). A trend towards lower LV OBC (-19%; P = 0.25) was found in hypertrophied hearts from patients with congestive heart failure as compared with non-failing hypertrophied hearts. In multivariate analysis with 18 variables including age and heart failure, only LV weight correlated independently with LV OBC (r = -0.61; P = 0.003). When OBC was related to either dry weight or to protein content, a 25-35% reduction was consistently found in hypertrophied LV, whereas RV OBC was similar in both groups. In conclusion, myocardial Na,K-pump concentration and thus the capacity to maintain homeostasis is reduced in LV, but not in RV, of hypertrophied hearts. Whether the moderately reduced myocardial Na,K-pump concentration is a pathogenetic factor in LV dysfunction remains to be determined.

Mortality and causes of death in a 10-year follow-up of patients treated for self-poisonings in Oslo

The present 10-year follow-up study includes all patients (N = 926; 50% females) treated in the medical departments in Oslo for self-poisonings during one year (1980). Seventeen percent were considered suicidal attempts upon admission, 25% among the non-substance abusers and 8% among the abusers. At follow-up, 207 patients (22%) were dead (62% males). The mortality rate was highest among the abusers. The most common causes of death were suicide (21%), heart disease (17%), opiate abuse (15%), and accidents/wounds (13%). Forty-one percent of the suicides occurred during the first two years of the follow-up period. The suicides were by poisoning (57%), hanging (20%), and other methods (23%). The female mortality rate decreased in the second half of the follow-up period whereas the male rate did not change. The risk of death within 10 years after discharge increased with age and was higher in men and in abusers, whereas social group and motive for suicide were not predictive factors. The females had an excess suicide rate of 182 (36-327, 95% CI) in the first year after the self-poisoning and 61 (36-87, 95% CI) in the total period. The corresponding figures for males were 70 (19-122) and 21 (12-30). The only factor associated with an increased suicide rate was a suicidal motive upon the admission for self-poisoning with a 3.1 (1.7-5.8, 95% CI) times increased risk of suicide in the 10-year follow-up period.

Continual electric field stimulation preserves contractile function of adult ventricular myocytes in primary culture

To model with greater fidelity the electromechanical function of freshly isolated heart muscle cells in primary culture, we describe a technique for the continual electrical stimulation of adult myocytes at physiological frequencies for several days. A reusable plastic cover was constructed to fit standard, disposable 175-cm2 tissue culture flasks and to hold parallel graphite electrodes along the long axis of each flask, which treated a uniform electric field that resulted in a capture efficiency of ventricular myocytes of 75-80%. Computer-controlled amplifiers were designed to be capable of driving a number of flasks concurrently, each containing up to 4 x 10(6) myocytes, over a range of stimulation frequencies (from 0.1 to 7.0 Hz) with reversal of electrode polarity after each stimulus to prevent the development of pH gradients around each electrode. Unlike quiescent, unstimulated myocytes, the amplitude of contraction, and velocities of shortening and relaxation did not change in myocytes paced at 3-5 Hz for up to 72 h. The maintenance of normal contractile function in paced myocytes required mechanical contraction per se, since paced myocytes that remained quiescent due to the inclusion of 2.5 microM verapamil in the culture medium for 48 h also exhibited a decline in contractility when paced after verapamil removal. Similarly, pacing increased peak calcium current compared with quiescent cells that had not been paced. Thus myocyte contraction at physiological frequencies induced by continual uniform electric field stimulation in short-term primary culture in defining medium maintains some biophysical parameters of myocyte phenotype that are similar to those observed in freshly isolated adult ventricular myocytes.

Adult rat ventricular myocytes cultured in defined medium: phenotype and electromechanical function

We studied primary short-term cultures of adult rat ventricular myocytes in defined medium to determine whether phenotype and electromechanical function are maintained in rod-shaped, quiescent cells. Although > 80% of the myocytes retained their rod-shaped in vivo morphology for up to 72 h, contractile function as measured by cell edge motion declined 30-50% from 6 to 24 h, paralleling a 68% shortening of action potential duration. From 24 to 72 h, contractility remained unchanged. Ca2+ channel current density increased 55% after 24-48 h and then returned to the level of freshly isolated cells (9 +/- 1 pA/pF, mean +/- SE). Resting membrane potential (-71 +/- 1 mV) and action potential overshoot (34 +/- 3 mV) did not change. The ratio of alpha- to beta-myosin heavy chain mRNA and the level of cardiac alpha-actin mRNA were maintained for 8 days. Thus quiescent adult rat ventricular myocytes in defined medium undergo extensive phenotypic adaptation within 72 h of isolation, despite maintenance of a rod-shaped morphology and stable levels of contractile protein mRNA, which may limit their suitability for electrophysiological and contractile function studies.

Isolation and characterization of human and rat cardiac microvascular endothelial cells

Although reciprocal intercellular signaling may occur between endocardial or microvascular endothelium and cardiac myocytes, suitable in vitro models have not been well characterized. In this report, we describe the isolation and primary culture of cardiac microvascular endothelial cells (CMEC) from both adult rat and human ventricular tissue. Differential uptake of fluorescently labeled acetylated low-density lipoprotein (Ac-LDL) indicated that primary isolates of rat CMEC were quite homogeneous, unlike primary isolates of human ventricular tissue, which required cell sorting based on Ac-LDL uptake to create endothelial cell-enriched primary cultures. The endothelial phenotype of both primary isolates and postsort subcultured CMEC and their microvascular origin were determined by characteristic histochemical staining for a number of endothelial cell-specific markers, by the absence of cells with fibroblast or pericyte-specific cell surface antigens, and by rapid tube formation on purified basement membrane preparations. Importantly, [3H]-thymidine uptake was increased 2.3-fold in subconfluent rat microvascular endothelial cells 3 days after coculture with adult rat ventricular myocytes because of release of an endothelial cell mitogen(s) into the extracellular matrix, resulting in a 68% increase in cell number compared with CMEC in monoculture. Thus biologically relevant cell-to-cell interactions can be modeled with this in vitro system.

Transcriptional regulation in cardiac muscle. Coordinate expression of Id with a neonatal phenotype during development and following a hypertrophic stimulus in adult rat ventricular myocytes in vitro

The transcriptional regulatory mechanisms in heart muscle that direct cardiac development and allow for a flexible, adaptive response to physiologic stress are not well understood. We demonstrate that a negative regulator of gene transcription termed Id that has been described predominantly in proliferating cell lines and in undifferentiated tissue during growth, is expressed in freshly isolated terminally differentiated adult rat ventricular myocytes, in contrast to most other tissues in the adult rat. Id mRNA expression is regulated in ventricular myocytes during post-natal development, peaking at the transition from hyperplastic to hypertrophic growth at day 17 in the rat, declining subsequently to lower, stable levels in adult myocytes. Although Id mRNA becomes undetectable in adult ventricular myocytes 48 h following isolation in the absence of serum, it can be rapidly reinduced by an alpha-adrenergic agonist, accompanied by increased protein synthesis and the reexpression, in defined media, of the neonatal genes prepro-ANP and skeletal muscle alpha-actin. Thus, the differential regulation of Id during cardiac development, the presence of Id mRNA in normal cardiac myocytes, and its increased expression following a hypertrophic stimulus all suggest a role for this transcriptional regulator in the control of cardiac muscle cell phenotype.

Calcium-induced net potassium uptake of pig hearts in vivo

To determine whether the catecholamine-induced myocardial potassium uptake could be mimicked by increasing extracellular and intracellular calcium concentrations in vivo, we measured changes in myocardial potassium balance in nine anaesthetized open-chest pigs with PVC-valinomycin electrodes in arterial and coronary sinus blood. CaCl2 infusion (200-400 mumol min-1) into the left coronary artery increased coronary sinus blood calcium concentration from 2.29 (2.19-2.42) to 4.63 (3.76-5.67) mmol l-1 (median, 95% confidence interval, P = 0.01) indicating a similar increment in myocardial extracellular calcium concentration. The contractility measure LV dP/dt increased 95 (76-147) %, indicating a substantial increment in intracellular calcium concentration. During the CaCl2 infusion coronary sinus potassium concentration declined to a nadir 0.12 (0.09-0.17) mmol l-1 below baseline (P = 0.008) whereas arterial concentration remained unchanged. Peak myocardial potassium uptake was 18 (7-32) mumol min-1 100 g-1 and occurred 150 (110-195) s after start of infusion. The response remained unaltered after adrenoceptor blockade by prazosin and propranolol. Prolonged CaCl2 infusion caused a net myocardial potassium loss which was accompanied by metabolic and haemodynamic indications of myocardial ischaemia. These findings are consistent with enhanced Na-K pump activity in the intact beating pig heart in response to increased extracellular and intracellular calcium concentrations.

Suicide and other causes of death in a five-year follow-up of patients treated for self-poisoning in Oslo

This 5-year follow-up study includes all patients (n = 934; 50% females) treated for self-poisoning in Oslo during 1 year. Seventeen percent were considered suicide attempts upon admission, 25% among the nonabusers and 8% among the abusers. At follow-up, 122 patients were dead (61% males). The mortality rate was highest among the abusers. The mortality rate was similar (13%) among those who were considered to be suicidal on admittance and those who were not. The causes of death were suicide (28%), opiate abuse (16%), heart disease (14%), accidents or wounds (11%), alcoholism (9%) and others (22%). The standard mortality rate was highly increased in all groups (8 times on average), highest among the female opiate abusers, whose rate was 63 times higher than expected. The increased suicide rates (87 times for females, 27 times for males), however, may be a more relevant measure of mental morbidity than the standard mortality rate. Logistic regression analysis demonstrated that male sex, age above 50 years and the lowest social group were factors on admission associated with death in the follow-up period. Age above 50 years and suicidal attempt on admission were associated with subsequent suicide. The study strongly supports the idea of self-destructiveness and slow suicide in substance abuse.

Frequency dependent myocardial potassium fluxes during beta adrenergic stimulation of intact pig hearts

STUDY OBJECTIVE

The aim was to determine the frequency dependent myocardial potassium fluxes of intact pig hearts at control inotropy and during beta adrenergic stimulation. DESIGN - Atrial pacing rate was suddenly raised and decreased by 50 beats.min-1 at control inotropy and during infusion of isoprenaline, 2.5 nmol.min-1, into the left coronary artery.

EXPERIMENTAL MATERIAL

Nine anaesthetised pigs (21-33 kg) were instrumented for electric pacing of the right atrium and metabolic and haemodynamic recordings.

MEASUREMENTS AND MAIN RESULTS

Myocardial potassium balance was measured by PVC-valinomycin electrodes in the left atrial cavity and in a shunt (with flow meter) diverting blood from the coronary sinus to the right atrium. Isoprenaline raised net myocardial potassium flux following the change in pacing rate from 19(14-23) to 38(32-46) mumol.100 g-1.min-1 (median, 95% confidence interval, difference: p = 0.03). The corresponding myocardial potassium flux per beat increased from 0.38(0.29-0.45) to 0.80(0.63-0.97) mumol.100 g-1 (p = 0.03). Accumulated potassium flux increased from 9(8-11) to 17(11-27) mumol.100 g-1, respectively (p = 0.03).

CONCLUSIONS

In intact hearts beta adrenergic stimulation doubles the frequency dependent myocardial potassium flux. This component constitutes 22-25% of the ouabain inhibitable potassium flux at both levels of inotropy.

Inotropic effect of meperidine: influence of receptor and ion channel blockers in the rat atrium

Meperidine increases developed force in isolated rat atria. We initiated this study to determine if this positive inotropic effect was attenuated by commonly used receptor- and ion channel blockers. Neither naloxone (opioid blocker), phentolamine (alpha-adrenoceptor blocker), propranolol (beta-adrenoceptor blocker), polaramine (H1-receptor blocker), ranitidine (H2-receptor blocker), verapamil (calcium-channel blocker), nor lidocaine (fast sodium-channel blocker) attenuated the positive inotropic effect of meperidine. However, after lidocaine pretreatment meperidine increased contractile force by 57% (27%-80%) (median and 95% confidence interval), which is significantly more (P less than 0.001) than the 21% (13%-35%) increase seen after pretreatment with saline. After Na,K-pump inhibition by ouabain, meperidine caused no further increase in contractility, but the atria still responded to isoproterenol with an increase in developed force. Conversely, meperidine prevented the positive inotropic effect of ouabain. These findings suggest that the positive inotropic effect of meperidine is mediated by an increase in intracellular sodium activity and not by regulation of the slow inward calcium channel.

Effects of hemodynamic variables on myocardial K+ balance during and after shortlasting ischemia

Ischemia-induced myocardial potassium loss and post-ischemic potassium reuptake was quantitated in 8 open chest pigs during control conditions and during hemodynamic alterations which have been shown to increase steady state sarcolemmal potassium fluxes. Myocardial K+ balance was continuously computed before, during and after a 90 s occlusion of a branch of the circumflex artery during control (CTR), during pacing tachycardia (PACE: 34% increase in heart rate), during proximal aortic constriction (AC; 28% increase in LVSP), and during isoprenaline infusion (ISO; 135% increase in LVdP/dt and 35% increase in heart rate). Ischemia-induced potassium loss increased significantly (40%) during ISO only. Higher basal metabolic rate, increased sarcolemmal K+ conductance, or ischemia-induced depression of a more active Na/K-pump during ISO are possible explanations to why increased K+ loss appeared in this situation. The maximal rate of post-ischemic potassium reuptake was not different from CTR during PACE and ISO, but it was reduced during AC, which might be due to persisting subendocardial ischemia in early reperfusion when ventricular wall stress is high. The extent of potassium restoration was not different from CTR during AC, PACE and ISO.

Myocardial K+ repletion and rise in contractility after brief ischemic periods in the pig

Potassium loss from the myocardium during brief ischemic periods is well documented, but whether intrinsic myocardial mechanisms restore this loss during reperfusion is unclear. To address this question, we established a shunt from the coronary sinus to the right atrium in seven open-chest pigs. Shunt flow and arterial and coronary sinus potassium concentrations were measured continuously in order to determine myocardial potassium balance. Thirty, 60 and 120 s occlusions of the mid-LAD coronary artery were repeated four times each at 10 min intervals with reproducible metabolic and hemodynamic responses. A myocardial K+ reuptake amounting to 51 to 77% of K+ release during ischemia occurred between 20 and 140 s of reperfusion. The maximal rate of K+ reuptake was 1.4 (0.7 to 3.6), (median and 95% confidence interval), 4.3 (2.5 to 9.6) and 7.3 (4.9 to 13.4) mumol/100 g min after occlusion periods of 30, 60 and 120 s, respectively. Concomitant with the K+ reuptake a progressive rise in LV dP/dt occurred. Adrenoceptor stimulation could not explain these findings since catecholamine release declined during occlusion and reperfusion. We suggest that increased intracellular Na+ concentration in early reperfusion stimulates the Na,K-pump and favours Ca++ entry through Na+/Ca++ exchange, thereby mediating K+ reuptake and the rise in contractility.

Different oxygenators for cardiopulmonary bypass lead to varying degrees of human complement activation in vitro

Complement activation was studied in vitro with six different membrane and bubble oxygenators for cardiopulmonary bypass. There was a similar increase in terminal (C5 to C9) activation with all oxygenators (p less than 0.001), ranging from 281% (117% to 444%) to 453% (225% to 680%) after 60 minutes (median and 95% confidence intervals). C3 activation was not observed with a hollow fiber membrane and a soft shell bubble oxygenator. On the other hand, a capillary membrane, a sheet membrane, a nonporous membrane, and a hard shell bubble oxygenator all induced a similar increase in C3 activation (p less than 0.01), ranging from 107% (23% to 346%) to 272% (88% to 395%) after 60 minutes. The differences in C3 activation could not be explained by the blood contact materials or any other single factor known to induce activation, which suggests that overall complement activation during cardiopulmonary bypass is a multifactorial effect. The tubing set per se induced only minor C3 activation but contributed to the overall formation of terminal complement complex. The study further indicates that an arterial line blood filter prevents activated neutrophils from being reinfused to the patient and should be used regardless of type of oxygenator.

In-vivo quantification of myocardial Na-K pump rate during beta-adrenergic stimulation of intact pig hearts

Maintenance of adequate electrical activity of the heart depends critically on the ability of the Na-K pump to compensate for normal passive sodium and potassium fluxes. Using sudden injections of [3H]ouabain into the left coronary artery in anaesthetized open-chest pigs, we monitored transient changes in myocardial potassium balance by PVC-valinomycin mini-electrodes. When related to the number of pumps blocked and fractional inhibition, these data provided estimates of total Na-K pump capacity as well as actual pump rate and perturbations of the Na-K balance. Experiments were performed in hearts with and without intracoronary isoprenaline infusion (2.5 nmol min-1). After injection of 120 nmol [3H]ouabain into the left coronary artery, myocardial [3H]ouabain concentrations were 118 (74-178) and 103 (76-145) pmol g-1 and total concentrations of [3H]ouabain binding sites were 893 (752-1076) and 785 (691-877) pmol g-1 (median, 95% confidence interval) in isoprenaline-treated and control hearts respectively (differences not significant). The [3H]ouabain injection caused a net potassium release of 81 (56-132) and 43 (23-75) mumol 100 g-1 (median, 95% confidence interval) in isoprenaline-treated and control hearts respectively (n = 6-8; significance of difference, P = 0.03). Na-K pump rate estimated from mono-exponential release curves was 6363 (3942-10,858) K+ ions min-1 site-1 during beta-adrenoceptor stimulation and 2514 (1380-4322) in control (significance of difference, P = 0.03). This corresponds to 40 and 16%, respectively, of the maximum possible pump rate determined from ATP hydrolysis. Comparison of accumulated potassium release and relative Na-K pump rate indicates that catecholamines enhance the sensitivity of the Na-K pump for intracellular sodium.

Factors reducing left and right ventricular output during simultaneous atrioventricular activation in the pig heart

Forward stroke volume fell by 26% (23-30%) (median and 95% confidence interval) when simultaneous atrioventricular (AV) pacing was induced at constant heart rate in 10 anaesthetized open-chest pigs. To assess the relative importance of factors which could cause this reduction in right and left ventricular (RV and LV) output, we compared cardiac dynamics when either ventricular filling or forward stroke volume was equally reduced by caval constriction and simultaneous AV pacing. We estimated the degree of ventricular filling by recording segment lengths (SL) in the free walls of both ventricles. Our analysis revealed that abolished active LV filling by the left atrium reduced forward stroke volume by 11% (8-14%). The remaining fall in output could be attributed to mitral regurgitation. In the right side of the heart the response was different. The drop in RV filling during simultaneous AV pacing accounted for approximately one-half of the fall in forward RV stroke volume. Estimates based on SL recordings demonstrated that forward RV stroke volume fell by 7% (2-25%) because of tricuspidal regurgitation. Pulmonary artery pressure was 4.5 (3.4-5.7) mmHg higher during simultaneous AV pacing than during caval constriction, representing a relative rise in afterload that reduced the RV stroke volume by 6-8%. Thus, reduced ventricular filling during simultaneous AV pacing accounted for approximately one-half of the drop in forward output from both ventricles. Slightly more than one-half of the reduction in forward LV stroke volume could be attributed to mitral regurgitation. In the right side of the heart tricuspidal regurgitation and a relative rise in pulmonary artery pressure each accounted for about one-quarter of the fall in forward RV output.

Myocardial potassium balance during adrenergic stimulation

1) The primary receptor mechanism of catecholamine-induced myocardial potassium uptake is beta 1-adrenoceptor stimulation. Thus, K+ uptake seems to be a general effect of beta-adrenergic stimulation, dominated by beta 1-receptors in heart and by beta 2-receptors in skeletal muscle according to subtype preponderance in either tissue. In the myocardium there is also an effect of alpha 1-adrenoceptor stimulation which causes a significantly smaller uptake and requires higher catecholamine concentrations. 2) Both humoral and nervous adrenergic stimulation of the heart induce a significant potassium uptake which transiently reduces coronary sinus K+ concentration. It is likely that these changes affect cardiac functioning in vivo. During intense endogenous sympathetic activity and by high dose pharmacological interventions, the magnitude of change in coronary sinus concentration suggests that the reduction in extracellular K+ within the myocardium could be up to 1 mM. Under vulnerable conditions like hypokalemia and localized ischemia such changes might contribute to the risk for malignant arrhythmias. 3) Presumably net myocardial K+ accumulation is accompanied by a reciprocal reduction of intracellular Na+ concentration, which tends to reduce myocardial contractility and contribute to impaired cardiac function after a period of strong adrenergic stimulation. In vivo the negative inotropic effect could not be detected as long as catecholamines were supplied, but it occurred after stimulation was stopped. 4) In the intact beating heart beta-adrenergic stimulation increases Na,K-pumping 2.5 fold, from 15% of the maximum possible pump rate in control to 40% of maximum at high inotropy. These findings imply the presence of a substantial spare Na,K-pump capacity of the non-ischemic myocardium, even during intense sympathetic activity. Comparison of changes in pump rate and accumulated ionic shifts indicates that catecholamine-induced stimulation of Na,K-ATPase might be due to increased sensitivity for intracellular sodium.

Significance of right atrial function during right sided inotropic stimulation of pig hearts in situ

Cardiac adjustments to inotropic stimulation of the right side of the heart were examined in anaesthetised, open chest pigs by calcium chloride infusion (80 mumol.min-1) into the right coronary artery. At stable haemodynamic conditions and at constant heart rate, right ventricular (RV) pre-ejection segment length increased by 4.6 (2.7-7.2) % (median, 95 % confidence interval) (p less than 0.01), RV end diastolic pressure rose from 5.3 (3.4-7.7) to 6.0 (3.6-8.8) mm Hg (p less than 0.05), and stroke volume rose by 6.8 (4.2-10.8) % (p less than 0.001). When the effect of right atrial contraction on RV filling was excluded by simultaneous pacing of atria and ventricles, the RV pre-ejection segment length no longer increased, and stroke volume rose by only 3.5 (0.1-9.5) % (p less than 0.05) during right side inotropic stimulation. Right atrial inotropic stimulation improves right ventricular filling, and may cause redistribution of blood from the systemic to the pulmonary circulation. This redistribution would raise the pulmonary vascular pressures, and thereby also improve left ventricular filling. The improved right ventricular filling partly accounts for the rise in RV output.

Forward diastolic flow in pulmonary artery induced by right atrial contraction of pig hearts

To study whether right atrial contraction can forward blood into the pulmonary artery during diastole, blood volume was expanded in anesthetized open-chest pigs until mean right atrial pressure was 13-20 mmHg (range). In the control situation, blood flow in the pulmonary artery was only observed during ventricular systole. Forward diastolic pulmonary artery flow, coinciding with right atrial contraction, was observed when diastolic pulmonary artery pressure was reduced during selectively increased left-side contractility, during bradycardia after propranolol injection (0.5 mg/kg body wt iv), and during the prolonged diastolic interval after spontaneously occurring atrial extrasystoles. The prolongation of the diastolic interval in all three series caused the diastolic pulmonary artery pressure to decline and the filling of the right atrium to increase, thus further stimulating the right atrial Frank-Starling mechanism. The diastolic blood flow in the pulmonary artery constituted 11% of the stroke volume during increased left-side inotropic stimulation, 8% during bradycardia, and 6% in beats preceded by a prolonged diastolic interval. Thus, in the normal heart, blood can be ejected into the pulmonary artery during right atrial contraction.

Temporal relationship of contractility and myocardial potassium balance following beta-adrenergic stimulation of the in situ pig heart

Lower intracellular Na+ during beta-adrenergic stimulation provides an increased driving force for Na-Ca exchange, which might attenuate the inotropic response. Since (1) Na+ reduction is coupled to K+ uptake, and (2) K+ uptake lags behind the positive inotropic response to isoproterenol, we could examine the effect of Na-Ca exchange by comparing cardiac contractility and K+ balance following intracoronary isoproterenol infusion (0.6-0.8 microgram min-1). In 8 open-chest pigs, potassium concentrations were continuously measured by PVC-valinomycin mini-electrodes in arterial blood (a), and in myocardial venous blood in a shunt from the coronary sinus (cs) to the right atrium. Shunt flow, aortic flow, a left ventricular segment length and left ventricular pressure (LVP) were also continuously recorded. 64 (41-85)% (median and 95% confidence interval) of the LV dP/dt increase occurred within 1 min; thereafter contractility rose slowly. During the first minute of isoproterenol infusion, there was a small net myocardial K+ release, which then reversed to K+ accumulation. A maximum a-cs K+ concentration difference of 0.20 (0.09-0.39) mM occurred at 3.0 (2.0-4.25) min, falling to 0.05 (0.01-0.10) mM after 6.5 (3.75-8.75) min, at which point accumulated myocardial K+ uptake was 135 (27-219) mumol 100 g-1. Heart rate remained unchanged and intramural ECG indicated no sign of ischemia during the first 1.5 min of isoproterenol infusion. At 6.25 (5.0-8.0) min after stop of isoproterenol, LV dP/dt was 12 (9-24)% lower than before infusion (P less than 0.02) whereas myocardial K+ content remained higher than control. Thus, the monovalent cation shift succeeding the positive inotropic response was not associated with reduced contractility, but could explain the undershoot of LV dP/dt after stopping isoproterenol.

Myocardial potassium uptake and catecholamine release during cardiac sympathetic nerve stimulation

To determine whether sympathetic nerve stimulation induces a significant potassium uptake in the myocardium, the changes in myocardial potassium balance, catecholamine release, lactate uptake, and oxygen consumption were recorded in eight anaesthetised open chest pigs during electrical stimulation of the right intermediate cardiac nerve at 10 Hz. Potassium concentrations were continuously measured by polyvinylchloride valinomycin minielectrodes in arterial and coronary sinus blood. Potassium concentration in coronary sinus blood fell to a nadir 0.42(0.21-0.61) mmol.litre-1 below control values (median and 95% confidence interval) and resulted in a peak potassium uptake of 65(38-102) mumol.min-1 100 g-1 after 2.5(2.0-3.0) min, which correlated (r = 0.94, p less than 0.001) with cardiac noradrenaline release. Accumulated myocardial potassium uptake amounted to 139(82-241) mumol.100 g-1 when a stable potassium concentration difference between arterial and coronary sinus blood was reached after 5.5(4.25-6.50) min. Cardiac contractility (LV dP/dt), myocardial oxygen consumption, and lactate uptake rose from control to peak potassium uptake (p less than 0.001) by 140%, 158%, and 92% respectively. Coronary sinus blood noradrenaline and adrenaline concentrations rose significantly (p less than 0.01) from 58(44-87) pg.ml-1 at control to 2208(1159-5627) pg.ml-1 at peak uptake and from 15(11-19) pg.ml-1 to 85(64-230) pg.ml-1 respectively. Arterial noradrenaline increased from 29(19-41) pg.ml-1 to 374(176-640) pg.ml-1 and arterial adrenaline rose from 15(11-23) pg.ml-1 to 31(24-52) pg.ml-1 (p less than 0.001). It is concluded that sympathetic nerve stimulation induces a substantial myocardial potassium uptake in a dose dependent relation to cardiac noradrenaline release and alters the contractile and metabolic state of the heart substantially with only minor changes in arterial catecholamine concentration.

Spontaneous pneumothorax in chronic obstructive pulmonary disease: complications, treatment and recurrences

Data from 303 patients with 389 admissions for spontaneous pneumothorax from 1970 to 1980 at Ullevaal Hospital, Oslo, Norway, were reviewed. Spontaneous pneumothorax carried a significantly higher complication and mortality rate in patients suffering chronic obstructive pulmonary disease (COPD). Their higher median age compared to non-COPD patients contributed to this, but did not account for the increased mortality. The risk of developing wound infection and/or pneumonia was significantly higher after 7 days of chest tube treatment in both patient groups, independent of age. There was no association between recurrence rate and COPD/non-COPD, age or duration of chest tube treatment (1-7 days, 8 days or more). Complications were not more frequent after thoracotomies performed in COPD patients. Therefore operative treatment for both primary and COPD-related spontaneous pneumothorax should be considered if tube treatment is not successful after 1 week and there are no contraindications.

Myocardial potassium uptake during alpha- and beta-adrenoceptor stimulation

The changes in myocardial K+ balance during alpha- and beta-adrenoceptor stimulation were compared in 10 anesthetized open-chest pigs by intracoronary isoproterenol and phenylephrine infusions. K+ concentration was continuously recorded by polyvinyl chloride catheter-valinomycin minielectrodes in arterial and coronary sinus blood. The arterial-coronary sinus difference and accumulated myocardial K+ uptake were calculated after computerized data sampling. Isoproterenol (2.5 nmol/min ic) reduced coronary sinus K+ transiently to a nadir of 0.37 (0.23-0.53) mM (median and 95% confidence interval) below control. The accumulated K+ uptake amounted to 139 (63-215) mumol/100 g. After beta-blockade by propranolol, phenylephrine (100 nmol/min ic) induced a transient coronary sinus K+ lowering of 0.16 (0.13-0.21) mM and an accumulated K+ uptake of 30 (20-41) mumol/100 g, both values less than those of isoproterenol (P less than 0.001). Myocardial contractility increased only during isoproterenol infusion, arterial blood pressure rose slightly by phenylephrine, but changes in myocardial O2 extraction and lactate uptake did not indicate cardiac ischemia. We conclude that both alpha- and beta-adrenoceptor stimulation induce a myocardial K+ uptake presumably due to increased Na-K pump activity, the latter more efficiently.

Cardiac adjustments to left-side inotropic stimulation of in situ pig hearts

Cardiac adjustments to inotropic stimulation of the left side of the heart by continuous infusions of isoproterenol (0.6-0.8 microgram/min) and calcium chloride (240 mumol/min) into the left coronary artery were examined in open-chest pigs (17-36 kg) anesthetized with pentobarbital sodium. Both agents caused a reduction in the left ventricular (LV) preload and preejection segment length (PESL). Stroke volume (SV) rose by only 1.2 ml from 15.9 ml (P less than 0.01) during isoproterenol infusion, but when the reduction in LV PESL of 3.2% (P less than 0.01) was restored by saline infusion, SV increased by 27%. The LV PESL reduction was less at hypervolemia than at normovolemia. A computer-based model of the circulation predicted most of these changes and suggested redistribution of blood from the pulmonary to the systemic circulation. During isoproterenol infusion, the pulmonary arterial pressure fell, and the right ventricular end-ejection segment length declined. Reduced right ventricular afterload thus appears to be an important mechanism by which right ventricular output is increased during a selective increase in LV inotropy.

Catecholamine-induced myocardial potassium uptake mediated by beta 1-adrenoceptors and adenylate cyclase activation in the pig

The myocardial potassium uptake during intracoronary isoproterenol stimulation was characterized in 12 anesthetized pigs. The beta-receptor subtype specificity and the effect of adenylate cyclase activation were determined. Potassium concentrations were continuously recorded by PVC-valinomycin minielectrodes in the left atrial cavity and in coronary sinus blood diverted through a shunt to the right atrium. The difference in potassium concentration between the left atrial cavity and coronary sinus, and the accumulated myocardial potassium uptake were calculated after computerized data sampling. By intracoronary drug infusion, changes in heart rate and systemic effects were minimized. Isoproterenol (0.6-0.8 microgram/min), a nonspecific beta-agonist, reduced coronary sinus potassium concentration transiently to a nadir of 0.28 (0.15-0.43) mM (median and 95% confidence interval) below control values (n = 12). The potassium uptake, which amounted to 140 (79-202) mumol/100 g tissue, corresponding to an intracellular potassium increase of about 3 mM, was abolished after selective beta 1-blockade by pafenolol. The specific beta 1-agonist dobutamine (40 micrograms/min) caused a similar potassium uptake before and after selective beta 2-blockade by ICI 118, 551. Salbutamol (2 micrograms/min), a specific beta 2-agonist, induced a minor potassium uptake of 4 (1-20) mumol/100 g, blocked by pafenolol. After nonselective beta-blockade by propranolol the adenylate cyclase stimulator forskolin caused a myocardial potassium uptake of similar magnitude to that of isoproterenol before beta-blockade. We conclude that a myocardial potassium uptake ensues during beta 1-adrenoceptor stimulation and adenylate cyclase activation.