Myocardial norepinephrine, epinephrine and dopamine concentrations after cardiac autotransplantation in dogs

TNFα increases tyrosine hydroxylase expression in human monocytes

Most, if not all, peripheral immune cells in humans and animals express tyrosine hydroxylase (TH), the rate limiting enzyme in catecholamine synthesis. Since TH is typically studied in the context of brain catecholamine signaling, little is known about changes in TH production and function in peripheral immune cells. This knowledge gap is due, in part, to the lack of an adequately sensitive assay to measure TH in immune cells expressing lower TH levels compared to other TH expressing cells. Here, we report the development of a highly sensitive and reproducible Bio-ELISA to quantify picogram levels of TH in multiple model systems. We have applied this assay to monocytes isolated from blood of persons with Parkinson's disease (PD) and to age-matched, healthy controls. Our study unexpectedly revealed that PD patients' monocytes express significantly higher levels of TH protein in peripheral monocytes relative to healthy controls. Tumor necrosis factor (TNFα), a pro-inflammatory cytokine, has also been shown to be increased in the brains and peripheral circulation in human PD, as well as in animal models of PD. Therefore, we investigated a possible connection between higher levels of TH protein and the known increase in circulating TNFα in PD. Monocytes isolated from healthy donors were treated with TNFα or with TNFα in the presence of an inhibitor. Tissue plasminogen activator (TPA) was used as a positive control. We observed that TNFα stimulation increased both the number of TH+ monocytes and the quantity of TH per monocyte, without increasing the total numbers of monocytes. These results revealed that TNFα could potentially modify monocytic TH production and serve a regulatory role in peripheral immune function. The development and application of a highly sensitive assay to quantify TH in both human and animal cells will provide a novel tool for further investigating possible PD immune regulatory pathways between brain and periphery.

Where Is Dopamine and how do Immune Cells See it?: Dopamine-Mediated Immune Cell Function in Health and Disease

Dopamine is well recognized as a neurotransmitter in the brain, and regulates critical functions in a variety of peripheral systems. Growing research has also shown that dopamine acts as an important regulator of immune function. Many immune cells express dopamine receptors and other dopamine related proteins, enabling them to actively respond to dopamine and suggesting that dopaminergic immunoregulation is an important part of proper immune function. A detailed understanding of the physiological concentrations of dopamine in specific regions of the human body, particularly in peripheral systems, is critical to the development of hypotheses and experiments examining the effects of physiologically relevant dopamine concentrations on immune cells. Unfortunately, the dopamine concentrations to which these immune cells would be exposed in different anatomical regions are not clear. To address this issue, this comprehensive review details the current information regarding concentrations of dopamine found in both the central nervous system and in many regions of the periphery. In addition, we discuss the immune cells present in each region, and how these could interact with dopamine in each compartment described. Finally, the review briefly addresses how changes in these dopamine concentrations could influence immune cell dysfunction in several disease states including Parkinson's disease, multiple sclerosis, rheumatoid arthritis, inflammatory bowel disease, as well as the collection of pathologies, cognitive and motor symptoms associated with HIV infection in the central nervous system, known as NeuroHIV. These data will improve our understanding of the interactions between the dopaminergic and immune systems during both homeostatic function and in disease, clarify the effects of existing dopaminergic drugs and promote the creation of new therapeutic strategies based on manipulating immune function through dopaminergic signaling. Graphical Abstract.

Postoperative care of the transplanted patient

The successful delivery of optimal peri-operative care to pediatric heart transplant recipients is a vital determinant of their overall outcomes. The practitioner caring for these patients must be familiar with and treat multiple simultaneous issues in a patient who may have been critically ill preoperatively. In addition to the complexities involved in treating any child following cardiac surgery, caretakers of newly transplanted patients encounter multiple transplant-specific issues. This chapter details peri-operative management strategies, frequently encountered early morbidities, initiation of immunosuppression including induction, and short-term outcomes.

Determination of endogenous norepinephrine levels in different chambers of the rat heart by capillary electrophoresis coupled with amperometric detection

Capillary electrophoresis with end-column amperometric detection (CE-EC) was used to determine the regional distribution of norepinephrine (NE) in the hearts of sympathetically innervated (control) and chemically sympathectomized rats. Key features of the method are (i) the sample preparation and clean-up step that involved the application of off-line solid phase extraction (SPE) with a 95% NE recovery and (ii) the use of a diamond microelectrode for detection. NE was quantified in the left and right ventricle, the ventricular septum, and the left and right atrium. The NE concentration in the atria was three to five times higher than in the ventricles and ventricular septum of control rats. Basal NE levels in the left and right ventricle and the ventricular septum were reduced to below the detection limit (0.034 microg/g tissue) in tissues treated with the neurotoxin, 6-hydroxydopamine (6-OHDA), while only a moderate reduction was observed in the left and right atrium. Importantly, the diamond microelectrode provided low and stable background current and low peak-to-peak noise <or=0.65 pA at a detection potential of +0.86 V versus Ag/AgCl. A reproducible electrode response was observed for multiple injections of tissue homogenates with minimal response attenuation due to electrode fouling.

Exercise responses following heart transplantation: 5 year follow-up

Heart transplantation is an established treatment for end stage heart failure. In addition to increased life expectancy, heart transplant recipients report a remarkable improvement in symptoms and functional capacity. Exercise performance following heart transplantation, however, remains impaired even in the absence of exertional symptoms. We have assessed the response to exercise in 47 patients with cardiac failure prior to and then at yearly intervals to five years post transplantation. All patients performed incremental symptom limited exercise tests during which minute ventilation (V'E), oxygen consumption (V'O2) and carbon dioxide production (V'CO2) and heart rate (HR) were measured. Ventilatory response (V'E/V'CO2), anaerobic threshold (V'O2 AT %predicted) and heart rate response (HR/VO2) were calculated. The dead space to tidal volume ratio (VD/VT) and alveolar-arterial oxygen gradient (A-aO2) were computed from transcutaneous monitoring. Despite substantial improvement in subjective functional capacity, heart transplant recipients continue to have limited exercise performance [Maximal V'O2% predicted pre-transplant 41.3 (2.2); 1 year 48.6 (1.7), p <0.001: V'O2 AT% 31.5 (1.1); 1 year 35.6 (1.0); respectively p<0.05]. The maximal oxygen uptake continued to improve at two years post-transplant but, thereafter, there was no further significant change at up to 5 years post transplant [50.9 (1.5)]. At one year post-transplantation peak HR [65.2 (0.9) vs 79.1(1.4)] and the HR/VO2 response [24.0(1.8) vs 79.6(4.2)] were significantly reduced compared to pre-transplant values. The heart rate response remained lower compared to predicted at 5 years post-transplant although there was a significant increase compared to one year post-transplant (32.9 vs 24.0mls/bt). There was a weak but significant relationship between maximal VO2 and peak HR (0.39, p<0.05) and HR/VO2 (r= 0.37, p<0.05) at one year post-transplant. Prior to transplantation the ventilatory response to exercise was elevated [V'E/V'CO2 45.6 (2.5)] and decreased significantly following transplantation [1 yr 34.1 (1.3), respectively p<0.001]. In addition, despite significant improvement in VD/VT after transplantation, it remained higher than normal [Pre VD/VT at maximum exercise 0.35 (0.02); 1 yr 0.31 (0.02); p<0.05]. There was a further fall in the VE/VCO2 and VD/VT at two years post-transplantation with no further change at up to 5 years post transplantation [VE/VCO2 32.0 (1.0); VD/VT 0.29 (0.01)]. Although cardiac output is markedly improved after transplantation, due to chronotropic incompetence associated with denervation, its response remains subnormal and this may explain the residual abnormalities of ventilatory and gas exchange responses to exercise following transplantation.

Stroke rehabilitation and the cardiac transplantation patient

A paucity of information exists concerning the mechanism and occurrence rate of stroke associated with cardiac transplantation. Furthermore, the rehabilitation of such patients has not been elaborated on. This report explores these issues and reviews the medical history and rehabilitation progress of four individuals who suffered a stroke before, or associated with, the transplantation process. Physiologic factors relevant to the rehabilitation of the post-heart transplantation stroke patient will also be discussed.

Evaluation of sympathetic nerve terminals with [(11)C]epinephrine and [(11)C]hydroxyephedrine and positron emission tomography

BACKGROUND

The goal of the present study was to directly compare the new radiopharmaceutical agent [(11)C]epinephrine (EPI) with [(11)C]hydroxyephedrine (HED) through the use of PET.

METHODS AND RESULTS

Seven healthy volunteers and 10 patients were investigated after heart transplantation. PET images of both tracers were of excellent quality in the volunteers. Values for radiolabeled metabolites (measured in percent of blood activity) at 5, 20, and 60 minutes after injection were approximately 35%, approximately 82%, and approximately 86% for EPI and approximately 13%, approximately 47%, and approximately 78% for HED, respectively. At 35 minutes, metabolite-corrected mean myocardial retention fraction of EPI (0. 235+/-0.022 min(-1)) was significantly greater (P<0.01) than that of HED (0.142+/-0.012 min(-1)). Corrected tracer retention fractions of both EPI and HED were significantly reduced in transplant recipients (0.055+/-0.004 min(-1), P<0.0001; and 0.050+/-0.006 min(-1), P<0. 0001, respectively) compared with volunteers. Normalization of retention fractions of patients with transplantation within 1 year to volunteers resulted in a value (ratio expressed in percent) of 20. 6+/-1.8% for EPI, significantly (P<0.03) smaller than 27.8+/-0.8% for HED. In patients with transplantation later than 1 year, the values were 26.0+/-2.9% for EPI compared with 44.2+/-5.6% for HED (P<0.014).

CONCLUSIONS

Both tracers showed high selectivity for neuronal uptake in the heart, with a significant reduction in tracer retention in transplant recipients compared with volunteers. Compared with HED, EPI showed greater retention in volunteers and a lower retention ratio in transplant recipients, suggesting that EPI may be the superior tracer with higher sensitivity to neuronal abnormalities. Because EPI reflects neuronal uptake, metabolism, and storage, it may be more suitable for the study of neuronal integrity than HED, which primarily traces uptake-1 capacity.

Safety profile and hemodynamic responses to beta-adrenergic stimulation by dobutamine in heart transplant patients

STUDY OBJECTIVE

Dobutamine stress echocardiography (DSE) has been used as a screening tool for coronary artery disease after heart transplantation and in the identification of patients at risk for development of cardiac events. However, the safety profile of high-dose dobutamine in heart transplant patients has not been systematically examined. Accordingly, we studied the safety profile and hemodynamic responses to escalating doses of dobutamine to determine the influence of denervation.

DESIGN

We assessed the hemodynamic responses, heart rate (HR), and arterial BP indexes (mean arterial pressure, systolic BP [SBP], diastolic BP [DBP], and pulse pressure) to dobutamine in 87 heart transplant patients ([mean +/- SD] age, 51 +/- 1 years) and compared the results with 97 nontransplant patients (age, 63.0 +/- 1 years) who served as innervated control subjects.

MEASUREMENTS AND RESULTS

The baseline HR (84 +/- 2 vs 69 +/- 1 beats/minute, respectively; p < 0.001) and peak HR response (144 +/- 2 vs 117 +/- 2 beats/minute, respectively; p < 0.001) were significantly higher in heart transplant patients than in the nontransplant patients. SBP was lower in heart transplant patients than in nontransplant patients at baseline (131 +/- 2 vs 138 +/- 2 mm Hg, respectively; p < 0.02) and at peak (150 +/- 3 vs 158 +/- 3 mm Hg, respectively; p < 0.03). However, baseline DBP was higher in transplant patients than in nontransplant patients (86 +/- 1 vs 77 +/- 1 mm Hg, respectively; p < 0.001). The decrease in DBP was similar in both groups (15 mm Hg). The dose-response curve for HR was shifted leftward in heart transplant patients. Heart transplant patients attained a higher absolute HR at each infusion stage and higher rates of increase, but the decrease in DBP was not significantly different in the two groups.

CONCLUSIONS

These results show that there is augmented chronotropic response and expected decline in DBP in response to dobutamine infusion in heart transplant patients. This increase in myocardial oxygen demand and a decrease in coronary perfusion pressure may be important mechanisms in the development of ischemic abnormalities that are detectable as regional dysynergy on echocardiography.

Evidence of time-dependent autonomic reinnervation after heart transplantation

BACKGROUND

Confirming the clinical significance of reinnervation is important in understanding and anticipating how heart rate (HR) responses of transplant recipients to physiologic stress differs early and late after transplant from that of normal individuals.

OBJECTIVES

To evaluate the functional significance of cardiac reinnervation early and late after heart transplantation.

METHODS

Handgrip and deep breathing tests, passive 80 degrees head-up tilt, and heart rate (HR) responsiveness of 33 transplant recipients (n = 16 at < 5 months and n = 17 at > 1 year after transplant) were compared with those of 16 age- and sex-matched control participants.

RESULTS

HR responses to handgrip and passive tilt were absent early after transplant. HR acceleration normalized but was blunted late after transplant. These findings are consistent with late (>1 year) sympathetic reinnervation in transplant recipients.

CONCLUSIONS

When caring for transplant recipients, nurses should consider the time elapsed since transplant in evaluating HR responsiveness to common procedures and interventions.

Optimal cardiac pacing after heart transplantation

The transplanted heart is characterized physiologically by autonomic denervation, chronotropic incompetence, intermittent episodes of allograft rejection, and frequently by diastolic dysfunction. Sinus node dysfunction resulting in bradycardia is common in the early postoperative period following standard orthotopic cardiac transplantation. Bradycardia tends to remit spontaneously but there are no factors that accurately identify patients who will need long-term pacing. Patients in whom bradycardia persists beyond the second postoperative week despite treatment with theophylline require permanent pacemaker implantation. It has been observed that chronotropic incompetence and diastolic dysfunction are important determinants of exercise capacity following heart transplantation. Pacing that restores chronotropic competence improves exercise capacity, confirming the importance of impaired heart rate response. As in other settings, pacing that preserves atrioventricular (AV) synchrony results in increased cardiac output. For these reasons when pacing is necessary we recommend the DDDR mode (AAIR if intact AV nodal conduction is present) so that the 30%-50% of patients who remain pacemaker-dependent long-term obtain maximal benefit from their transplant.

Functional deficits in medial gastrocnemius grafts in rats: relation to muscle metabolism and beta-AR regulation

This study tested the hypothesis that alterations in the metabolic integrity of grafted muscle contribute to its diminished ability to sustain power. Compared with control muscles, muscles studied 120 days after the grafting procedure had lower specific force and sustained power. The sustained power protocol resulted in a depletion of muscle glycogen in control (83%) and grafted (85%) animals. Grafts had lower pre- and poststimulation glycogen, diminished citrate synthase activity, and greater hexokinase activity. No differences were observed in phosphofructokinase activity, glucose transporter GLUT-4 content, fiber type, beta-adrenergic-receptor (beta-AR) density, or binding affinity. Isoproterenol-stimulated adenylyl cyclase activity was lower in grafted vs. control muscle, suggesting an uncoupling of the beta-AR-effector complex. Thus the diminished ability of the grafted muscle to sustain power may be explained, in part, by a decrease in energy available from glycogen stores and/or a decrease in oxidative capacity.

Long-term sequential changes in exercise capacity and chronotropic responsiveness after cardiac transplantation

BACKGROUND

Peak exercise capacity improves early after orthotopic cardiac transplantation. However, the physiological response to exercise remains abnormal, with a reduced rate of heart rate (HR) rise and reductions in peak exercise HR and the increment in HR from rest to peak exercise. This chronotropic incompetence is due in large part to cardiac denervation. If reinnervation occurs after transplantation, it might result in an improvement in both chronotropic responsiveness and maximal exercise capacity. We therefore hypothesized that the chronotropic response to exercise and maximal exercise capacity would improve with time after transplantation.

METHODS AND RESULTS

Peak symptom-limited cardiopulmonary exercise tests performed in 57 clinically stable cardiac transplant recipients (mean age, 45 +/- 2 years) serially for up to 5 years after transplantation and in 33 control subjects without heart disease were analyzed retrospectively. Pretransplantation exercise tests were also performed in 41 patients an average of 4.7 +/- 0.6 months before transplantation. At 1 year after transplantation, peak oxygen consumption was 16.6 +/- 0.9 mL.kg-1.min-1, reflecting a 43% increase versus pretransplantation. Nevertheless, compared with control subjects, maximal exercise capacity and the HR response to exercise were subnormal in transplant recipients. There were no further increases in peak exercise capacity, peak exercise HR, or the peak increment in HR with exercise up to 5 years after transplantation.

CONCLUSIONS

One year after cardiac transplantation, peak exercise capacity and chronotropic responsiveness are subnormal. There is no further improvement in peak exercise capacity or chronotropic responsiveness as late as 5 years after transplantation. These data indicate that with regard to chronotropic responsiveness, functionally significant cardiac reinnervation does not occur between the first and fifth years after transplantation.

Hemodynamic adaptation to orthostatic stress after orthotopic heart transplantation

OBJECTIVES

The purpose of this study was to compare the effects of orthostatic stress on cardiovascular stability in heart transplant recipients early and late after transplantation and in healthy controls.

BACKGROUND

After transplantation, cardiac reinnervation is heterogeneous, with reports of sympathetic reinnervation after 5 months and parasympathetic reinnervation after 2 to 3 years.

METHODS

Sixteen heart transplant recipients early (less than 5 months) after transplantation, 17 recipients late (1 year or more) after transplantation, and 16 matched healthy controls were subjected to 45 minutes of passive upright tilt, with the following variables measured before, during, and after the procedure: cardiac output, heart rate, stroke volume, mean arterial pressure, systemic vascular resistance, and plasma norepinephrine.

RESULTS

At rest, heart rate (p < 0.0005) and mean arterial pressure (p = 0.003) were higher, and stroke volume was lower (p < 0.0005), in transplant recipients than they were in controls. With orthostasis, heart rate increased by 30% in controls and by 23% in the late posttransplantation group compared with 13% in the early posttransplantation group (p = 0.028); drop in stroke volume was three times more among controls than among those in either transplantation group (p < 0.001); late transplant recipients had higher norepinephrine increases than did the other two groups (p = 0.012).

CONCLUSION

With the exception of heart rate, patterns of hemodynamic response to orthostatic stress after transplantation remain consistent over time and differ from controls. Among transplant recipients, higher mean arterial pressure mitigates the force of gravity and prevents drops in stroke volume. Clinicians may anticipate that transplant recipients will tolerate postural maneuvers well. Later after transplantation, however, orthostatic tolerance is associated with increased norepinephrine release, consistent with enhanced sympathoactivation.

Scintigraphic evaluation of cardiac autonomic innervation

Alterations in cardiac autonomic neuronal function have become the focus of intense research in various cardiovascular diseases. Both single-photon emission tomography (SPECT) and the positron emission tomography (PET) imaging techniques in combination with radio-labeled neurotransmitters and receptor ligands have become available for the scintigraphic visualization of presynaptic and postsynaptic neuronal function. Several clinical studies have shown changes in tracer distribution in different clinical conditions, such as ischemic heart disease, congestive heart failure, malignant arrhythmias, heart transplantation, and in patients with diabetes. In patients with congestive heart failure, previous in vitro investigations have concentrated on the postsynaptic level of the sympathetic innervation. However, alterations in presynaptic nerve function have been demonstrated with scintigraphic investigations by decreased presynaptic tracer retention. Moreover, correlation between scintigraphic findings and clinical outcome was shown in patients with heart failure, providing important prognostic information superior to conventional risk assessment. In conclusion, scintigraphic evaluation by SPECT and PET allows functional characterization of cardiac presynaptic and postsynaptic neurons. Regional tracer uptake can be used as an index for the integrity of innervation in various diseases. Newer tracer approaches may allow the noninvasive quantification of neuronal function by PET.

Reinnervation of the transplanted human heart as evidenced from heart rate variability studies

This study evaluated heart rate variability (HRV) after cardiac transplantation in humans in an attempt to test the hypothesis that cardiac reinnervation occurs in the post-transplant period. HRV was measured using 24-hour Holter recordings performed on 37 ambulant patients 1 to 122 months after cardiac transplantation. All patients were free of histologic rejection and were taking no medication likely to influence HRV. Time and frequency domain were analyzed and circadian rhythm of hourly average heart rate was calculated. HRV increased with time after the transplant. Compared with patients in the early post-transplant period, patients > 36 months after transplant had lower 24-hour heart rates (86 vs 93 beats/min), an increased average of all 5-minute SDs of NN intervals (17.6 vs 11.3), and higher low-and high-frequency power. Ten of the 27 patients > 3 years after transplantation had evidence of functional cardiac reinnervation. Compared with patients who had no reinnervation, these patients had increased circadian variability with lower nocturnal heart rates (76 vs 91 beats/min) and greater sympathetic activity during daytime (natural logarithm sympathetic power -0.36 vs -1.45) and nighttime (natural logarithm sympathetic power -0.43 vs -1.98). Despite lower nocturnal heart rates, there was no HRV evidence for an increase in parasympathetic activity. Thus, patients late after cardiac transplantation have HRV evidence for an increase in sympathetic control of the heart.

Dobutamine stress-induced angina in patients with denervated cardiac transplants. Clinical and angiographic correlates

BACKGROUND

The clinical consequences of cardiac denervation include the inability of the heart transplant recipient to sense cardiac pain. This is due mainly to interruption of ventricular sympathetic afferents normally responsible for transmission of cardiac pain. Although angina has been reported in transplant recipients, to our knowledge, its temporal relationship to myocardial ischemia has not been previously demonstrated.

OBJECTIVE AND METHODS

Eighty-two patients with heart transplants were serially evaluated by dobutamine stress echocardiography (DSE). In patients who developed angina during DSE, we sought to determine if the onset of angina was related to myocardial ischemia as demonstrated by stress-induced wall motion abnormalities. Coronary angiography was performed within 48 h of DSE in 45 of 82 patients.

RESULTS

Mean patient age and time since transplant were 53.1 +/- 1.1 years and 57.7 +/- 30.4 months, respectively (mean +/- SEM). Eleven patients developed typical angina during DSE. Three of the 11 (27%) had diagnostic ECG changes. All 11 had stress-induced regional wall motion abnormalities (WMA). Nine of the 11 patients (82%) had coronary angiographic data available that demonstrated significant coronary artery disease (CAD) in 8 (89%). All coronary lesions matched the observed segmental WMA. There was no difference between the angina (n = 11) and no angina (n = 71) groups with respect to peak heart rate (HR) (141 +/- 7 vs 145 +/- 3 beats/min; p = NS), peak systolic blood pressure (SBP) (155 +/- 8 vs 149 +/- 3 mm Hg; p = NS), or rate pressure product (21,699 +/- 1,490 vs 21,646 +/- 621 mm Hg x beats/min; p = NS). However, the mean time since transplant was significantly higher in patients with DSE-induced angina (80.3 +/- 6.2 vs 57.3 +/- 3.5 months; p < 0.05).

CONCLUSIONS

These data suggest that (1) the occurrence of angina in long-term transplant recipients with CAD is directly related to myocardial ischemia despite anatomic ventricular denervation, and (2) sympathetic reinnervation in the long-term may account for the occurrence of angina in cardiac transplant recipients.

Iodine-123 metaiodobenzylguanidine scintigraphic assessment of the transplanted human heart: evidence for late reinnervation

OBJECTIVES

This study attempted to determine whether cardiac sympathetic reinnervation occurs late after orthotopic heart transplantation.

BACKGROUND

Metaiodobenzylguanidine (MIBG) is taken up by myocardial sympathetic nerves. Iodine-123 (I-123) MIBG cardiac uptake reflects intact myocardial sympathetic innervation of the heart. Cardiac transplant recipients do not demonstrate I-123 MIBG cardiac uptake when studied < 6 months from transplantation. However, physiologic and biochemical studies suggest that sympathetic reinnervation of the heart can occur > 1 year after transplantation.

METHODS

We performed serial cardiac I-123 MIBG imaging in 23 cardiac transplant recipients early (< or = 1 year) and late (> 1 year) after operation. In 16 subjects transmyocardial norepinephrine release was measured late after transplantation.

RESULTS

No subject had visible I-123 MIBG uptake on imaging < 1 year after transplantation. However, 11 (48%) of 23 subjects developed visible cardiac I-123 MIBG uptake 1 to 2 years after transplantation. Only 3 (25%) of 12 subjects with a pretransplantation diagnosis of idiopathic cardiomyopathy demonstrated I-123 MIBG uptake compared with 8 (73%) of 11 with a pretransplantation diagnosis of ischemic or rheumatic heart disease (p = 0.04). All 10 subjects with a net myocardial release of norepinephrine had cardiac I-123 MIBG uptake; all 6 subjects without a net release of norepinephrine had no cardiac I-123 MIBG uptake.

CONCLUSIONS

Sympathetic reinnervation of the transplanted human heart can occur > 1 year after operation, as assessed by I-123 MIBG imaging and the transmyocardial release of norepinephrine. Reinnervation is less likely to occur in patients with a pretransplantation diagnosis of idiopathic cardiomyopathy than in those with other etiologies of congestive heart failure.

Functional and neurochemical evidence for partial cardiac sympathetic reinnervation after cardiac transplantation in humans

BACKGROUND

The presence of cardiac reinnervation in humans after cardiac transplantation has been widely debated, based on the application of differing methods for the assessment of neuronal function. Some of these techniques have been rather indirect; consequently, the time course and extent of cardiac reinnervation remains uncertain.

METHODS AND RESULTS

To test for the presence of cardiac reinnervation after transplantation, we examined neurochemical (radiolabeled norepinephrine [NE] kinetics) and functional markers (power spectral analysis, heart rate response to exercise) of cardiac sympathetic nerve integrity in 15 cardiac transplantation recipients and 25 healthy control subjects of similar age. Cardiac transplantation subjects were studied 9 weeks to 8 years after cardiac transplantation (10 "early" patients < 18 months and 5 "late" patients > 2 years after cardiac transplantation). At rest, cardiac NE spillover was markedly attenuated early after transplantation (11.2 +/- 18.3 pmol/min) compared with subjects late after transplantation (105 +/- 11 pmol/min, P < .01) or in healthy control subjects (103 +/- 15 pmol/min, P < .01). Heart rate variability (measured by total spectral power) was significantly reduced in cardiac transplantation recipients compared with control subjects (59.4 +/- 30 vs 1673 +/- 516 milliseconds squared; P < .05), with evidence of a trend toward increasing spectral power late after transplantation. During exercise, the cardiac NE spillover was significantly lower in early cardiac transplantation recipients when compared with control subjects (163 +/- 50 vs 1876 +/- 418 pmol/min, P < .01). Late cardiac transplantation subjects showed a response intermediate (1080 +/- 254 pmol/min) between that of the early cardiac transplantation and control groups. However, measurements of the neuronal reuptake process for NE (assessed by the fractional extraction of plasma labeled NE across the heart and tritiated dihydroxyphenylglycol release) were significantly depressed in both early and late cardiac transplantation subjects.

CONCLUSIONS

The present study demonstrates a partial restoration of cardiac sympathetic nerve function in humans up to 8 years after heart transplantation.

Sympathetic dysfunction in heart failure

CHF is a common, complex and life-threatening clinical syndrome. It is widely accepted that enhanced peripheral vascular tone plays a major role in the pathophysiology of CHF. Increased activity of the sympathetic nervous system is one of the most important factors responsible for the increased afterload in CHF. This increase in sympathetic activity occurs early in the course of development of CHF. Efferent sympathetic activity is distributed in a non-uniform way in CHF, with significant increases to the heart and kidney but normal activity to some other organs such as the lung. Increased renal sympathetic activity contributes significantly to altered neural haemodynamics, sodium and water retention, and modulation of the actions of other vasoactive hormones. The regional alteration in sympathetic activity may be largely responsible for the changes in resting regional blood flow to different organs in CHF and the maldistribution of blood flow that occurs during the stress of exercise. Disordered function of cardiovascular reflexes is observed in CHF and may contribute to disordered sympathetic function. In CHF there are significant interactions between the sympathetic nervous system and other humoral systems such as the renin-angiotensin system, AVP, ANP, endothelin and renal DA. The various drugs used in the treatment of CHF have different effects on sympathetic activity: digitalis and ACE inhibitors tend to suppress activity while diuretics may have the opposite effect. Following cardiac transplantation, there is a prompt return of sympathetic function towards normal, although the heart may remain significantly denervated for a long time, with gradual reinnervation. Cyclosporin therapy tends to increase sympathetic activity and this may contribute to post-transplant hypertension.

Evidence for regional catecholamine uptake and storage sites in the transplanted human heart by positron emission tomography

Positron emission tomography in combination with the newly introduced catecholamine analogue [11C]hydroxyephedrine ([11C]HED) enables the noninvasive delineation of sympathetic nerve terminals of the heart. To address the ongoing controversy over possible reinnervation of the human transplant, 5 healthy control subjects and 11 patients were studied after cardiac transplant by this imaging approach. Regional [11C]HED retention was compared to regional blood flow as assessed by rubidium-82. Transplant patients were divided into two groups. Group I had recent (less than 1 yr, 4.4 +/- 2.3 mo) surgery, while group II patients underwent cardiac transplantation more than 2 yr before imaging (3.5 +/- 1.3 yr). [11C]HED retention paralleled blood flow in normals, but was homogeneously reduced in group I. In contrast, group II patients revealed heterogeneous [11C]HED retention, with increased uptake in the proximal anterior and septal wall. Quantitative evaluation of [11C]HED retention revealed a 70% reduction in group I and 59% reduction in group II patients (P less than 0.001). In group II patients, [11C]HED retention reached 60% of normal in the proximal anterior wall. These data suggest the presence of neuronal tissue in the transplanted human heart, which may reflect regional sympathetic reinnervation.

Myocardial catecholamine content after heart transplantation

Myocardial catecholamine levels have not yet been determined in the transplanted human heart. We measured norepinephrine, epinephrine, and dopamine in endomyocardial biopsies from 19 short-term (organ age, 6.6 +/- 6 months) and five long-term (organ age, 62 +/- 2 months) heart transplant patients. Results were compared with those from 10 normal control subjects. In 17 of 19 short-term heart transplant patients, myocardial catecholamines were undetectable, indicating values below 0.1 pg/micrograms noncollagen protein, which was the detection threshold of our assay. In the remaining two patients, myocardial catecholamines (pg/microgram noncollagen protein) were norepinephrine (1.4 and 3.2), epinephrine (0.8 and 1.9), and dopamine (0.9 and 2.3), respectively. In the five long-term heart transplant patients, myocardial catecholamines were not detected. Catecholamine concentrations in 10 healthy control subjects were norepinephrine (10.3 +/- 2.9), epinephrine (0.36 +/- 0.51), and dopamine (0.52 +/- 0.40). Low myocardial norepinephrine levels (less than 20% of control values) with unexplained high levels of epinephrine and dopamine were found in single transplant patients. In most heart transplant patients, however, myocardial catecholamines were undetectable up to five years after transplantation, indicating that the adrenergic response of these hearts probably depends on variations in plasma catecholamines or cardiac beta-receptor density.

Immunohistochemical demonstration of human cardiac innervation before and after transplantation

Knowledge about the distribution and origins of peptide-containing nerves in the innervated and transplanted heart is lacking. Immunohistochemical and histochemical techniques were used to visualize human cardiac innervation before and after transplantation. In the recipient heart cardiac nerve fibers and fascicles displayed immunoreactivity for general neural (protein gene product 9.5 and synaptophysin) and Schwann cell markers (S-100). A major proportion of cardiac nerves displayed neuropeptide tyrosine and tyrosine hydroxylase immunofluorescence staining. Subpopulations of nerves contained somatostatin, vasoactive intestinal polypeptide, calcitonin gene-related peptide, substance P- or neurokinin-like immunoreactivity, and acetylcholinesterase activity. Tissues from cardiac allografts (5 weeks to 63 months after transplantation) contained nerves and ganglion cells that were acetylcholinesterase positive and immunoreactive for the general neural markers. These nerves were less numerous than in recipient hearts and rarely displayed neuropeptide immunostaining. Atrial natriuretic peptide immunoreactivity was localized to myocardial cells in transplanted hearts as well as explanted recipient and postmortem hearts. While most human cardiac allografts remain functionally extrinsically denervated, they appear to contain viable intrinsic nerves, and myocardial cells retain the capacity to produce atrial natriuretic peptide.

New insights into pacemaker syndrome gained from hemodynamic, humoral and vascular responses during ventriculo-atrial pacing

Ventricular pacing is performed during programmed electrical stimulation and during normal functioning of single chamber (VVI or VVIR) pacemakers. In many patients, retrograde ventriculoatrial (V-A) conduction may occur and evoke hemodynamic and reflex neurohumoral responses, which are unique to this pacing mode. Accordingly, forearm blood flow, forearm vascular resistance, mean and phasic arterial pressure, cardiac output and plasma norepinephrine, epinephrine and dopamine were measured during atrial, ventricular and V-A pacing at a cycle length of 600 ms (100 beats/min) before and after regional alpha blockade with intraarterial phentolamine in 16 patients with a left ventricular ejection fraction greater than 35% and little or no symptoms of congestive heart failure. During V-A pacing, cardiac output decreased by 10%, whereas forearm vascular resistance increased from 52 +/- 7 to 70 +/- 9 U (p less than 0.001) and plasma norepinephrine increased from 183 +/- 27 to 232 +/- 27 pg/ml (p less than 0.01). Phentolamine nearly abolished the increase in forearm vascular resistance in response to V-A pacing (18 +/- 4.1 U before vs 5.8 +/- 1.5 U after, p less than 0.05). The change in forearm vascular resistance with V-A pacing correlated with systolic arterial pressure, but not with changes in mean arterial pressure, pulse pressure, cardiac output, mean or peak right atrial pressure, pulmonary artery or pulmonary capillary wedge pressure. These results suggest that forearm vascular resistance responses to V-A pacing are mediated mainly by alpha-adrenergic receptors, through the arterial baroreflexes.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac and peripheral vascular responses to adrenoceptor stimulation and blockade after cardiac transplantation

A denervated heart coupled to a periphery previously exposed to high catecholamine levels provides a unique model to study adrenoceptor physiology. Six orthotopic transplant patients (1.3 +/- 0.8 years postoperative) were age matched with six atropine-treated normal subjects. Simultaneous two-dimensionally targeted left ventricular echo-cardiograms and calibrated carotid pulse tracings were recorded. Left ventricular contractility was assessed with use of heart rate- and load-independent end-systolic indexes. Studies were performed at baseline and during dobutamine infusion with and without beta-adrenergic blockade with use of propranolol; effects were assessed during afterload changes generated by the alpha 1 agonist methoxamine. There were no differences in baseline contractility or reserve between transplant patients and normal subjects. The heart rate response to dobutamine was greater for transplant patients (p less than 0.001). In both groups, the positive inotropic and chronotropic effects of dobutamine were ablated by propranolol. Dobutamine plus propranolol (unopposed alpha 1 effect) did not change mean systemic pressure in transplant patients while markedly raising mean systemic pressures in normal subjects (36 +/- 18 mm Hg; p less than 0.001). In addition, during initial challenge with methoxamine, the transplant patients required 60% more alpha 1 agonist than did the normal subjects (p less than 0.001) to obtain a pressor effect. In summary, transplant patients who were previously in severe heart failure have normal left ventricular inotropic response to beta 1 activation and blockade, exaggerated chronotropic response to dobutamine and reduced sensitivity to stimulation with alpha 1-adrenoceptor agonists. These findings are consistent with a differential response of adrenoceptors to long-term stimulation after cardiac transplantation.

Cellular abnormalities in chronically denervated myocardium. Implications for the transplanted heart

Heart transplantation involves chronic effects due to denervation, rejection, and treatment of rejection. The chronically denervated dog heart provides a model for the effects of denervation alone. These hearts have been shown to contain intrinsic neurons with VIP and NPY as possible neurotransmitters. Myocardial tissue noradrenaline concentration falls to very low levels after degeneration of postganglionic sympathetic neurons, but dopamine remains in near-normal concentration and is probably synthesized extraneuronally. ANP is present and released normally; however, the natriuretic response to atrial distension is blunted, suggesting that this response is mainly due to a reflex mechanism. Chronically denervated myocardial tissue exhibits increased oxygen consumption in vitro and increased Na-K, ATPase activity but has normal tissue levels of ATP and creatine phosphate. Glucose oxidation is inhibited in vivo, associated with increased levels of fructose-6-phosphate but normal glucose-6-phosphate, suggesting inhibition of phosphofructokinase activity. However, the enzyme protein concentration of phosphofructokinase, as judged by maximal in vitro activity, is normal. Maximal in vitro activities of succinate dehydrogenase, cytochrome oxidase, monoamine oxidase, calcium-dependent ATPase, and glyceraldehyde-3-dehydrogenase are also normal. From these findings, we would predict that patients with transplanted hearts are likely to show myocardial metabolic inefficiency.

Arterial baroreflex abnormalities in heart failure. Reversal after orthotopic cardiac transplantation

Arterial baroreflex control of the heart and peripheral circulation is markedly impaired in humans and animals with congestive heart failure. After reversal of heart failure in animal models, arterial baroreflex control of heart rate remains impaired for up to 8 months. Cardiac transplantation restores normal ventricular function and completely reverses heart failure, but does it normalize arterial baroreflex control of heart rate in humans? We studied baroreflex sensitivity in 11 patients with severe heart failure, six normal control patients, and 23 patients at 2 weeks to 4 years after orthotopic cardiac transplantation. Baroreflex sensitivity was assessed with intravenous bolus injections of phenylephrine and is expressed as change in RR or PP interval (msec) per millimeters of mercury rise in systolic arterial pressure. Atrial rate of both donor (denervated) and recipient (innervated) atria were measured in the transplant group. Baroreflex sensitivity in patients with severe heart failure was 2.0 +/- 0.3 msec/mm Hg, but in patients after cardiac transplantation, it was 13.0 +/- 0.9 msec/mm Hg (p less than 0.001). The responses in the transplant group were similar to those observed in normal controls (10 +/- 1.2 msec/mm Hg, p = NS). Our data indicate that patients with severe congestive heart failure have marked abnormalities of baroreflex control, which are reversed as early as 2 weeks after cardiac transplantation. In view of this rapid reversal, we consider it unlikely that abnormal baroreflex sensitivity seen in heart failure is due to structural alterations in the baroreceptors. We speculate that neurohumoral rather than structural abnormalities account for depressed baroreflex sensitivity in heart failure.

Impairment of cardiopulmonary baroreflex after cardiac transplantation in humans

There is ample evidence for efferent cardiac denervation in patients after cardiac transplantation. However, little is known regarding the effects of the cardiac deafferentation that also results. We examined responses to graded lower-body negative pressure and thus cardiopulmonary baroreceptor unloading in 23 patients 3 to 12 months after cardiac transplantation and compared their responses with those of nine normal subjects. Responses of mean arterial pressure, forearm vascular resistance, and plasma norepinephrine were assessed during lower-body negative pressure and the cold pressor test. Reflex increases in forearm vascular resistance (1.5 +/- 1, 5.0 +/- 1.4, and 6.4 +/- 2.1 vs 14.5 +/- 4.5, 20.3 +/- 6.5, and 34 +/- 11 units) and plasma norepinephrine (42 +/- 12, 58 +/- 15, and 62 +/- 13 vs 49 +/- 14, 94 +/- 25, and 173 +/- 36 pg/ml) during lower-body negative pressure (at -10, -20, and -40 mm Hg) were strikingly smaller in cardiac transplant patients than in normal subjects. The impaired responses of the cardiac transplant patients were not the result of a nonspecific depression of cardiovascular reflexes, since increases in mean arterial pressure (12 +/- 3 vs 10 +/- 2 mm Hg), forearm vascular resistance (19.5 +/- 3.4 vs 18 +/- 5.8 units), and plasma norepinephrine (56 +/- 8 vs 42 +/- 11 pg/ml) during cold pressor test were not significantly different in the two groups. Furthermore, the impaired responses were not caused by the immunosuppressive agents used to treat the cardiac transplant patients, since patients with renal transplants on similar regimens had augmented forearm vasoconstrictor responses.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent reinnervation of the autotransplanted heart in dogs

Patients have been observed with a chest pain syndrome after cardiac transplantation. For this pain to be cardiac in origin the afferent nerves carrying sensory information from the heart would have to reinnervate the heart. A previous study in dogs indicated that afferent reinnervation is uncommon during the first 2 years after transplantation. The purpose of this study was to determine whether afferent reinnervation of the heart occurs in the long term. The decreases in arterial pressure and renal nerve activity resulting from chemical stimulation of left ventricular sensory receptors with vagal afferents with cryptenamine (veratrum alkaloid) were assessed in three dogs 8 to 12 years and in four dogs 6 to 8 weeks after cardiac autotransplantation and in six sham-operated dogs (thoracotomy-pericardiotomy 6 to 8 weeks before study). Responses of renal nerve activity to physiologic stimulation of cardiac receptors by volume expansion were also determined. Left ventricular cryptenamine inhibited renal nerve activity by 72 +/- 8% in dogs with long-term and by 10 +/- 6% in dogs with short-term autotransplantation and by 92 +/- 5% in sham-operated dogs. Decreases in mean arterial pressure in these groups were 34 +/- 4, 11 +/- 3 and 67 +/- 16 mm Hg, respectively. Volume expansion inhibited renal nerve activity in long-term autotransplant (43%) and sham-operated (48%) groups but less in the short-term transplant group (33%) for comparable increases in cardiac filling pressure. It is concluded that in dogs there is extensive afferent reinnervation of the long-term autotransplanted heart that results in relatively normal cardiopulmonary baroreflex responses to volume expansion.(ABSTRACT TRUNCATED AT 250 WORDS)