1
|
Molina CE, Johnson DM, Mehel H, Spätjens RLHMG, Mika D, Algalarrondo V, Slimane ZH, Lechêne P, Abi-Gerges N, van der Linde HJ, Leroy J, Volders PGA, Fischmeister R, Vandecasteele G. Interventricular differences in β-adrenergic responses in the canine heart: role of phosphodiesterases. J Am Heart Assoc 2014; 3:e000858. [PMID: 24904016 PMCID: PMC4309082 DOI: 10.1161/jaha.114.000858] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Background RV and LV have different embryologic, structural, metabolic, and electrophysiologic characteristics, but whether interventricular differences exist in β‐adrenergic (β‐AR) responsiveness is unknown. In this study, we examine whether β‐AR response and signaling differ in right (RV) versus left (LV) ventricles. Methods and Results Sarcomere shortening, Ca2+ transients, ICa,L and IKs currents were recorded in isolated dog LV and RV midmyocytes. Intracellular [cAMP] and PKA activity were measured by live cell imaging using FRET‐based sensors. Isoproterenol increased sarcomere shortening ≈10‐fold and Ca2+‐transient amplitude ≈2‐fold in LV midmyocytes (LVMs) versus ≈25‐fold and ≈3‐fold in RVMs. FRET imaging using targeted Epac2camps sensors revealed no change in subsarcolemmal [cAMP], but a 2‐fold higher β‐AR stimulation of cytoplasmic [cAMP] in RVMs versus LVMs. Accordingly, β‐AR regulation of ICa,L and IKs were similar between LVMs and RVMs, whereas cytoplasmic PKA activity was increased in RVMs. Both PDE3 and PDE4 contributed to the β‐AR regulation of cytoplasmic [cAMP], and the difference between LVMs and RVMs was abolished by PDE3 inhibition and attenuated by PDE4 inhibition. Finally LV and RV intracavitary pressures were recorded in anesthetized beagle dogs. A bolus injection of isoproterenol increased RV dP/dtmax≈5‐fold versus 3‐fold in LV. Conclusion Canine RV and LV differ in their β‐AR response due to intrinsic differences in myocyte β‐AR downstream signaling. Enhanced β‐AR responsiveness of the RV results from higher cAMP elevation in the cytoplasm, due to a decreased degradation by PDE3 and PDE4 in the RV compared to the LV.
Collapse
Affiliation(s)
- Cristina E Molina
- INSERM UMR-S 769, LabEx LERMIT, DHU TORINO, Châtenay-Malabry, France (C.E.M., H.M., D.M., V.A., Z.H.S., P.L., L., R.F., G.V.) Université Paris-Sud, Châtenay-Malabry, France (C.E.M., H.M., D.M., V.A., Z.H.S., P.L., L., R.F., G.V.)
| | - Daniel M Johnson
- Department of Cardiology, Cardiovascular Research Institute Maastricht, Maastricht University Medical Centre, 6202 AZ, Maastricht, The Netherlands (D.M.J., R.G.S., P.A.V.)
| | - Hind Mehel
- INSERM UMR-S 769, LabEx LERMIT, DHU TORINO, Châtenay-Malabry, France (C.E.M., H.M., D.M., V.A., Z.H.S., P.L., L., R.F., G.V.) Université Paris-Sud, Châtenay-Malabry, France (C.E.M., H.M., D.M., V.A., Z.H.S., P.L., L., R.F., G.V.)
| | - Roel L H M G Spätjens
- Department of Cardiology, Cardiovascular Research Institute Maastricht, Maastricht University Medical Centre, 6202 AZ, Maastricht, The Netherlands (D.M.J., R.G.S., P.A.V.)
| | - Delphine Mika
- INSERM UMR-S 769, LabEx LERMIT, DHU TORINO, Châtenay-Malabry, France (C.E.M., H.M., D.M., V.A., Z.H.S., P.L., L., R.F., G.V.) Université Paris-Sud, Châtenay-Malabry, France (C.E.M., H.M., D.M., V.A., Z.H.S., P.L., L., R.F., G.V.)
| | - Vincent Algalarrondo
- INSERM UMR-S 769, LabEx LERMIT, DHU TORINO, Châtenay-Malabry, France (C.E.M., H.M., D.M., V.A., Z.H.S., P.L., L., R.F., G.V.) Université Paris-Sud, Châtenay-Malabry, France (C.E.M., H.M., D.M., V.A., Z.H.S., P.L., L., R.F., G.V.)
| | - Zeineb Haj Slimane
- INSERM UMR-S 769, LabEx LERMIT, DHU TORINO, Châtenay-Malabry, France (C.E.M., H.M., D.M., V.A., Z.H.S., P.L., L., R.F., G.V.) Université Paris-Sud, Châtenay-Malabry, France (C.E.M., H.M., D.M., V.A., Z.H.S., P.L., L., R.F., G.V.)
| | - Patrick Lechêne
- INSERM UMR-S 769, LabEx LERMIT, DHU TORINO, Châtenay-Malabry, France (C.E.M., H.M., D.M., V.A., Z.H.S., P.L., L., R.F., G.V.) Université Paris-Sud, Châtenay-Malabry, France (C.E.M., H.M., D.M., V.A., Z.H.S., P.L., L., R.F., G.V.)
| | - Najah Abi-Gerges
- Department of Translational Safety, DrugSafety and Metabolism, AstraZeneca R&D Innovative Medicines and Early Development, Alderley Park, Macclesfield, SK10 4TG, Cheshire, UK (N.A.G.)
| | - Henk J van der Linde
- Global Safety Research, Preclinical Development & Safety, Discovery Sciences, Janssen Research & Development, Beerse, Belgium (H.J.L.)
| | - Jérôme Leroy
- INSERM UMR-S 769, LabEx LERMIT, DHU TORINO, Châtenay-Malabry, France (C.E.M., H.M., D.M., V.A., Z.H.S., P.L., L., R.F., G.V.) Université Paris-Sud, Châtenay-Malabry, France (C.E.M., H.M., D.M., V.A., Z.H.S., P.L., L., R.F., G.V.)
| | - Paul G A Volders
- Department of Cardiology, Cardiovascular Research Institute Maastricht, Maastricht University Medical Centre, 6202 AZ, Maastricht, The Netherlands (D.M.J., R.G.S., P.A.V.)
| | - Rodolphe Fischmeister
- INSERM UMR-S 769, LabEx LERMIT, DHU TORINO, Châtenay-Malabry, France (C.E.M., H.M., D.M., V.A., Z.H.S., P.L., L., R.F., G.V.) Université Paris-Sud, Châtenay-Malabry, France (C.E.M., H.M., D.M., V.A., Z.H.S., P.L., L., R.F., G.V.)
| | - Grégoire Vandecasteele
- INSERM UMR-S 769, LabEx LERMIT, DHU TORINO, Châtenay-Malabry, France (C.E.M., H.M., D.M., V.A., Z.H.S., P.L., L., R.F., G.V.) Université Paris-Sud, Châtenay-Malabry, France (C.E.M., H.M., D.M., V.A., Z.H.S., P.L., L., R.F., G.V.)
| |
Collapse
|
2
|
Li QS, Liu FQ. Effects of thoracic epidural analgesia on plasma cAMP and cGMP levels in patients with heart failure. J Cardiothorac Surg 2013; 8:217. [PMID: 24279592 PMCID: PMC4222055 DOI: 10.1186/1749-8090-8-217] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2012] [Accepted: 11/19/2013] [Indexed: 11/23/2022] Open
Abstract
Background and aim The progression of heart failure is affected by several factors, including chronic stimulation of the β-adrenoceptor. This clinical study was designed to measure the effects of thoracic epidural analgesia (TEA) on the plasma levels of norepinephrine (NE), cAMP, and cGMP in patients with heart failure and assess the clinical implication of TEA. Methods Forty patients with heart failure were randomly assigned to TEA (TEA plus standard care) and control groups (standard care). The plasma concentrations of cAMP, cGMP, brain natriuretic peptide (BNP), and NE were measured using ELISA before treatment, the second and fourth weeks of treatment. Results The plasma concentrations of cAMP, cGMP, BNP, and NE in the TEA group were significantly reduced by the fourth week compared to their initial concentrations (P < 0.01, for all parameters) and the control group (P < 0.05, P < 0.05, P < 0.01, and P < 0.05, respectively). The values for left ventricular end diastolic diameter (LVEDD), ejection fraction (EF), and fractional shortening (FS) in the TEA group improved significantly compared to their initial values and the control group. However, the changes in levels for these indices in the control group were no statistical significant compared to the initial levels. Conclusions TEA can effectively decrease the plasma concentrations of cAMP and cGMP and improve cardiac function in patients with heart failure. The decreased levels of NE and cAMP occurred before the improvement in cardiac function, indicating that the abnormal epidural signal transduction can be corrected in patients with heart failure.
Collapse
Affiliation(s)
- Qing-Shu Li
- Department of Cardiology, First Affiliated Hospital of Harbin Medical University, Harbin 150001, China.
| | | |
Collapse
|
3
|
Kiriazis H, Jennings NL, Davern P, Lambert G, Su Y, Pang T, Du X, La Greca L, Head GA, Hannan AJ, Du XJ. Neurocardiac dysregulation and neurogenic arrhythmias in a transgenic mouse model of Huntington's disease. J Physiol 2012; 590:5845-60. [PMID: 22890713 DOI: 10.1113/jphysiol.2012.238113] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Huntington's disease (HD) is a heritable neurodegenerative disorder, with heart disease implicated as one major cause of death. While the responsible mechanism remains unknown, autonomic nervous system (ANS) dysfunction may play a role. We studied the cardiac phenotype in R6/1 transgenic mice at early (3 months old) and advanced (7 months old) stages of HD. While exhibiting a modest reduction in cardiomyocyte diameter, R6/1 mice had preserved baseline cardiac function. Conscious ECG telemetry revealed the absence of 24-h variation of heart rate (HR), and higher HR levels than wild-type littermates in young but not older R6/1 mice. Older R6/1 mice had increased plasma level of noradrenaline (NA), which was associated with reduced cardiac NA content. R6/1 mice also had unstable R-R intervals that were reversed following atropine treatment, suggesting parasympathetic nervous activation, and developed brady- and tachyarrhythmias, including paroxysmal atrial fibrillation and sudden death. c-Fos immunohistochemistry revealed greater numbers of active neurons in ANS-regulatory regions of R6/1 brains. Collectively, R6/1 mice exhibit profound ANS-cardiac dysfunction involving both sympathetic and parasympathetic limbs, that may be related to altered central autonomic pathways and lead to cardiac arrhythmias and sudden death.
Collapse
Affiliation(s)
- Helen Kiriazis
- Baker IDI Heart and Diabetes Institute, 75 Commercial Road, Melbourne, Victoria 3004, Australia
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
4
|
Ishikawa K, Chemaly ER, Tilemann L, Fish K, Ladage D, Aguero J, Vahl T, Santos-Gallego C, Kawase Y, Hajjar RJ. Assessing left ventricular systolic dysfunction after myocardial infarction: are ejection fraction and dP/dt(max) complementary or redundant? Am J Physiol Heart Circ Physiol 2012; 302:H1423-8. [PMID: 22307667 DOI: 10.1152/ajpheart.01211.2011] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Among the various cardiac contractility parameters, left ventricular (LV) ejection fraction (EF) and maximum dP/dt (dP/dt(max)) are the simplest and most used. However, these parameters are often reported together, and it is not clear if they are complementary or redundant. We sought to compare the discriminative value of EF and dP/dt(max) in assessing systolic dysfunction after myocardial infarction (MI) in swine. A total of 220 measurements were obtained. All measurements included LV volumes and EF analysis by left ventriculography, invasive ventricular pressure tracings, and echocardiography. Baseline measurements were performed in 132 pigs, and 88 measurements were obtained at different time points after MI creation. Receiver operator characteristic (ROC) curves to distinguish the presence or absence of an MI revealed a good predictive value for EF [area under the curve (AUC): 0.998] but not by dP/dt(max) (AUC: 0.69, P < 0.001 vs. EF). Dividing dP/dt(max) by LV end-diastolic pressure and heart rate (HR) significantly increased the AUC to 0.87 (P < 0.001 vs. dP/dt(max) and P < 0.001 vs. EF). In naïve pigs, the coefficient of variation of dP/dt(max) was twice than that of EF (22.5% vs. 9.5%, respectively). Furthermore, in n = 19 pigs, dP/dt(max) increased after MI. However, echocardiographic strain analysis of 23 pigs with EF ranging only from 36% to 40% after MI revealed significant correlations between dP/dt(max) and strain parameters in the noninfarcted area (circumferential strain: r = 0.42, P = 0.05; radial strain: r = 0.71, P < 0.001). In conclusion, EF is a more accurate measure of systolic dysfunction than dP/dt(max) in a swine model of MI. Despite the variability of dP/dt(max) both in naïve pigs and after MI, it may sensitively reflect the small changes of myocardial contractility.
Collapse
Affiliation(s)
- Kiyotake Ishikawa
- Cardiovascular Research Center, Mount Sinai School of Medicine, New York, New York 10029-6574, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
5
|
Beyersdorf F. The use of controlled reperfusion strategies in cardiac surgery to minimize ischaemia/reperfusion damage. Cardiovasc Res 2009; 83:262-8. [PMID: 19351741 DOI: 10.1093/cvr/cvp110] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Ischaemia and reperfusion occur during almost every cardiac operation, and one of the key elements to achieve a successful operation is to counteract the detrimental effects of induced ischaemia and reperfusion during the operation. The cardiac surgeon is in a unique position to protect the heart before ischaemia is induced and to avoid further damage during the reperfusion period. The surgeon can alter the composition of the reperfusate and the conditions of reperfusion so that the ischaemia/reperfusion injury is minimal, even after very complex procedures that require long aortic cross-clamp periods. This in turn allows him to perform a near-perfect surgical repair of the underlying disease without the pressure of time. The vast knowledge gained in this field over the years has led to application in other organs, such as the limbs (acute limb ischaemia), lungs (lung transplantation), kidney and liver (kidney and liver transplantation), and more recently even for the brain [acute cerebral artery occlusion (stroke)] and the whole body (cardiopulmonary resuscitation). Further improvements in reperfusion strategies will allow salvage of tissue and even whole body after ischaemic periods thought previously to be irreversibly damaged.
Collapse
Affiliation(s)
- Friedhelm Beyersdorf
- Department of Cardiovascular Surgery, Albert-Ludwigs-University Freiburg, Hugstetterstr. 55, D-79106 Freiburg i. Br., Germany.
| |
Collapse
|
6
|
Chin BB, Metzler SD, Lemaire A, Curcio A, Vemulapalli S, Greer KL, Petry NA, Turkington TG, Coleman RE, Rockman H, Jaszczak RJ. Left ventricular functional assessment in mice: feasibility of high spatial and temporal resolution ECG-gated blood pool SPECT. Radiology 2007; 245:440-8. [PMID: 17940303 DOI: 10.1148/radiol.2452061973] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
PURPOSE To prospectively determine feasibility of evaluating murine left ventricular (LV) function with electrocardiographically (ECG)-gated blood pool single photon emission computed tomography (SPECT). MATERIALS AND METHODS All animal studies had institutional animal care and use committee approval. SPECT was performed with conventional time-binned acquisition (eight frames per ECG cycle) in normal mice (normal group A, n = 6) and mice with myocardial infarction (MI) (n = 8). To determine feasibility of high temporal resolution and rapid data acquisition, another group of normal mice (normal group B, n = 4) underwent imaging with conventional (eight-frame) time-binned and list-mode (LM) acquisitions. LM acquisitions were reconstructed with eight and 16 frames per ECG cycle and 10 minutes of data (short LM). SPECT images were assessed visually, and LV-to-lung background activity ratios were calculated. LV end-systolic and end-diastolic volumes were defined with a phase analysis and threshold method. LV ejection fraction (LVEF) was calculated from LV volumes and count-based methods (n = 18 mice). Fractional shortening (FS) at echocardiography defined MI dysfunction (mild MI: FS > or = 50%; severe MI: FS < 50%). Group means were compared for significant differences with analysis of variance. RESULTS ECG-gated blood pool SPECT demonstrated normal, concentric LV contraction in all normal mice (n = 10). LV-to-lung background ratio was more than 10:1 (range, 10.3-29.4; n = 18). Focal wall motion abnormalities were detected at SPECT both visually and with phase analysis in all mice with severe MI (n = 5). Mice with severe MI had significantly lower LVEF than normal group A mice (32% +/- 14 [standard deviation] vs 64% +/- 8%; P < .001). All mice with mild MI (n = 3) had normal contraction and LVEF. In paired acquisitions in normal group B mice, all reconstructions (n = 16) showed normal LV contraction. LVEF was not significantly different (P = .88) between time-binned (71% +/- 12), eight-frame LM (71% +/- 12), 16-frame LM (77% +/- 10), and short LM (73% +/- 14) reconstructions. CONCLUSION Murine LV functional assessment is feasible with high spatial and temporal resolution ECG-gated blood pool SPECT. LV dysfunction can be quantified and focal wall motion abnormalities detected in the MI model of heart failure.
Collapse
Affiliation(s)
- Bennett B Chin
- Department of Radiology, Duke University School of Medicine, Durham, NC 27710, USA.
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
7
|
Abstract
The concept that heart failure is simply the consequence of impaired pump function is now outmoded. Congestive heart failure is a neuroendocrine syndrome in with activation of the adrenergic nervous system and specific endocrine pathways is integral to its pathogenesis. It is now clear that chronic increases in adrenergic drive associated with heart failure have detrimental effects on myocardial function. The use of BAAs is now standard therapy for people who develop heart failure caused by systolic dysfunction. Beta-blockade may have a role in the management of dogs with heart failure.
Collapse
Affiliation(s)
- Jonathan A Abbott
- Department of Small Animal Clinical Sciences, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Technical Institute, Phase II Duckpond Drive, Blacksburg, VA 24061, USA.
| |
Collapse
|
8
|
Liang CS, Himura Y, Kashiki M, Stevens SY. Differential pre- and postsynaptic effects of desipramine on cardiac sympathetic nerve terminals in RHF. Am J Physiol Heart Circ Physiol 2002; 283:H1863-72. [PMID: 12384464 DOI: 10.1152/ajpheart.01131.2001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Right heart failure (RHF) is characterized by chamber-specific reductions of myocardial norepinephrine (NE) reuptake, beta-receptor density, and profiles of cardiac sympathetic nerve ending neurotransmitters. To study the functional linkage between NE uptake and the pre- and postsynaptic changes, we administered desipramine (225 mg/day), a NE uptake inhibitor, to dogs with RHF produced by tricuspid avulsion and progressive pulmonary constriction or sham-operated dogs for 6 wk. Animals receiving no desipramine were studied as controls. We measured myocardial NE uptake activity using [(3)H]NE, beta-receptor density by [(125)I]iodocyanopindolol, inotropic responses to dobutamine, and noradrenergic terminal neurotransmitter profiles by glyoxylic acid-induced histofluorescence for catecholamines, and immunocytochemical staining for tyrosine hydroxylase and neuropeptide Y. Desipramine decreased myocardial NE uptake activity and had no effect on the resting hemodynamics in both RHF and sham animals but decreased myocardial beta-adrenoceptor density and beta-adrenergic inotropic responses in both ventricles of the RHF animals. However, desipramine treatment prevented the reduction of sympathetic neurotransmitter profiles in the failing heart. Our results indicate that NE uptake inhibition facilitates the reduction of myocardial beta-adrenoceptor density and beta-adrenergic subsensitivity in RHF, probably by increasing interstitial NE concentrations, but protects the cardiac noradrenergic nerve endings from damage, probably via blockade of NE-derived neurotoxic metabolites into the nerve endings.
Collapse
Affiliation(s)
- Chang-Seng Liang
- Cardiology Unit, Department of Medicine, University of Rochester Medical Center, 601 Elmwood Avenue, Rochester, NY 14642, USA.
| | | | | | | |
Collapse
|
9
|
Wang X, Dhalla NS. Modification of beta-adrenoceptor signal transduction pathway by genetic manipulation and heart failure. Mol Cell Biochem 2000; 214:131-55. [PMID: 11195784 DOI: 10.1023/a:1007131925048] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The beta-adrenoceptor (beta-AR) mediated signal transduction pathway in cardiomyocytes is known to involve beta1- and beta2-ARs, stimulatory (Gs) and inhibitory (Gi) guanine nucleotide binding proteins, adenylyl cyclase (AC) and cAMP-dependent protein kinase (PKA). The activation of beta1- and beta2-ARs has been shown to increase heart function by increasing Ca2+ -movements across the sarcolemmal membrane and sarcoplasmic reticulum through the stimulation of Gs-proteins, activation of AC and PKA enzymes and phosphorylation of the target sites. The activation of PKA has also been reported to increase phosphorylation of some myofibrillar proteins (for promoting cardiac relaxation) and nuclear proteins (for cardiac hypertrophy). The activation of beta2-AR has also been shown to affect Gi-proteins, stimulate mitogen activated protein kinase and increase protein synthesis by enhancing gene expression. Beta1- and beta2-ARs as well as AC are considered to be regulated by PKA- and protein kinase C (PKC)-mediated phosphorylations directly; both PKA and PKC also regulate beta-AR indirectly through the involvement of beta-AR kinase (betaARK), beta-arrestins and Gbeta gamma-protein subunits. Genetic manipulation of different components and regulators of beta-AR signal transduction pathway by employing transgenic and knockout mouse models has provided insight into their functional and regulatory characteristics in cardiomyocytes. The genetic studies have also helped in understanding the pathophysiological role of PARK in heart dysfunction and therapeutic role of betaARK inhibitors in the treatment of heart failure. Varying degrees of defects in the beta-AR signal transduction system have been identified in different types of heart failure to explain the attenuated response of the failing heart to sympathetic stimulation or catecholamine infusion. A decrease in beta1-AR density, an increase in the level of G1-proteins and overexpression of betaARK are usually associated with heart failure; however, these attenuations have been shown to be dependent upon the type and stage of heart failure as well as region of the heart. Both local and circulating renin-angiotensin systems, sympathetic nervous system and endothelial cell function appears to regulate the status of beta-AR signal transduction pathway in the failing heart. Thus different components and regulators of the beta-AR signal transduction pathway appears to represent important targets for the development of therapeutic interventions for the treatment of heart failure.
Collapse
Affiliation(s)
- X Wang
- Institute of Cardiovascular Sciences, Department of Physiology, Faculty of Medicine University of Manitoba, Winnipeg, Canada
| | | |
Collapse
|
10
|
Du XJ, Gao XM, Jennings GL, Dart AM, Woodcock EA. Preserved ventricular contractility in infarcted mouse heart overexpressing beta(2)-adrenergic receptors. Am J Physiol Heart Circ Physiol 2000; 279:H2456-63. [PMID: 11045983 DOI: 10.1152/ajpheart.2000.279.5.h2456] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Effects of cardiac specific overexpression of beta(2)-adrenergic receptors (beta(2)-AR) on the development of heart failure (HF) were studied in wild-type (WT) and transgenic (TG) mice following myocardial infarction (MI) by coronary artery occlusion. Animals were studied by echocardiography at weeks 7 to 8 and by catheterization at week 9 after surgery. Post-infarct mortality, due to HF or cardiac rupture, was not different among WT mice, and there was no difference in infarct size (IS). Compared with the sham-operated group (all P < 0.01), WT mice with moderate (<36%) and large (>36%) IS developed lung congestion, cardiac hypertrophy, left ventricular (LV) dilatation, elevated LV end-diastolic pressure (LVEDP), and suppressed maximal rate of increase of LV pressure (LV dP/dt(max)) and fractional shortening (FS). Whereas changes in organ weights and echo parameters were similar to those in infarcted WT groups, TG mice had significantly higher levels of LV contractility in both moderate (dP/dt(max) 4,862 +/- 133 vs. 3,694 +/- 191 mmHg/s) and large IS groups (dP/dt(max) 4,556 +/- 252 vs. 3,145 +/- 312 mmHg/s, both P < 0.01). Incidence of pleural effusion (36% vs. 85%, P < 0.05) and LVEDP levels (6 +/- 0.3 vs. 9 +/- 0.8 mmHg, P < 0.05) were also lower in TG than in WT mice with large IS. Thus beta(2)-AR overexpression preserved LV contractility following MI without adverse consequence.
Collapse
Affiliation(s)
- X J Du
- Baker Medical Research Institute and Alfred Heart Centre, Alfred Hospital, Melbourne 8008, Victoria, Australia.
| | | | | | | | | |
Collapse
|
11
|
Shah AS, Atkins BZ, Hata JA, Tai O, Kypson AP, Lilly RE, Koch WJ, Glower DD. Early effects of right ventricular volume overload on ventricular performance and beta-adrenergic signaling. J Thorac Cardiovasc Surg 2000; 120:342-9. [PMID: 10917952 DOI: 10.1067/mtc.2000.107278] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
OBJECTIVE Right ventricular dysfunction is a poorly understood but persistent clinical problem. This study was undertaken to evaluate ventricular performance and beta-adrenergic receptor signaling in a tricuspid regurgitation model of right ventricular overload. METHODS Seventeen dogs were chronically instrumented with epicardial dimension transducers. By means of the shell-subtraction model, right ventricular pressure-volume relationships were evaluated in normal and right ventricular overload states. Right ventricular chamber performance was quantified by the stroke work at an end-diastolic volume relationship. RESULTS Right ventricular volume overload caused a 28% +/- 11% and 31% +/- 9% decline in chamber performance acutely and at 1 week, respectively, whereas end-diastolic volume increased from 45 +/- 21 to 60 +/- 30 mL (P =. 019). beta-Adrenergic receptor signaling in myocardial samples was assessed, examining adenylyl cyclase and G-protein-coupled receptor kinase activity. Stimulated adenylyl cyclase activity significantly decreased, and G-protein-coupled receptor kinase activity significantly increased in both left and right ventricular samples caused by increased levels of beta-adrenergic receptor kinase 1. No change in beta-adrenergic receptor density was seen at 1 week. CONCLUSIONS Early right ventricular overload is associated with impaired right ventricular chamber contractility, dilation, and, importantly, a biventricular alteration of beta-adrenergic receptor signaling.
Collapse
Affiliation(s)
- A S Shah
- Department of General and Thoracic Surgery, Duke University Medical Center, Durham, NC 27710, USA
| | | | | | | | | | | | | | | |
Collapse
|
12
|
Dong E, Yatani A, Mohan A, Liang CS. Myocardial beta-adrenoceptor down-regulation by norepinephrine is linked to reduced norepinephrine uptake activity. Eur J Pharmacol 1999; 384:17-24. [PMID: 10611414 DOI: 10.1016/s0014-2999(99)00652-4] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Chronic administration of norepinephrine for 8 weeks has been shown to reduce neuronal norepinephrine uptake activity and increase interstitial norepinephrine concentration in the heart. To determine whether the changes could lead to myocardial beta-adrenoceptor down-regulation or beta-adrenergic subsensitivity, we measured left ventricular contractile responses to dobutamine, myocardial beta-adrenoceptor density, beta subtype distribution, competitive inhibition agonist binding, and adenylyl cyclase activity activation by isoproterenol, 5'-guanylylimidodiphosphate, and forskolin in dogs after a norepinephrine or saline infusion for 8 weeks. We found that norepinephrine infusion reduced myocardial beta-adrenoceptor density, beta(1)-adrenoceptor subtype density, and high-affinity site for isoproterenol. Left ventricular contractile responses to dobutamine were reduced in the norepinephrine-infused animals. In addition, norepinephrine infusion decreased the basal adenylyl cyclase activity and the adenylyl cyclase responses to isoproterenol, 5'-guanylylimidodiphosphate, and forskolin. The findings indicate that a decrease in cardiac norepinephrine uptake predisposes the heart to norepinephrine-induced myocardial beta-adrenoceptor down-regulation, and that norepinephrine, when present in a sufficient amount over a long period as it is in chronic heart failure, can reduce myocardial beta-adrenergic responsiveness by both homologous and heterologous desensitization.
Collapse
Affiliation(s)
- E Dong
- Cardiology Unit, Box 679, Cardiology Research Laboratories, Department of Medicine, University of Rochester Medical Center, 601 Elmwood Avenue, Rochester NY, USA
| | | | | | | |
Collapse
|
13
|
Raju VS, Imai N, Liang CS. Chamber-specific regulation of heme oxygenase-1 (heat shock protein 32) in right-sided congestive heart failure. J Mol Cell Cardiol 1999; 31:1581-9. [PMID: 10423355 DOI: 10.1006/jmcc.1999.0995] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Heme oxygenase (HO)-1 is a stress protein (HSP 32) and, together with HO-2, catalyses oxidation of the heme molecule to generate carbon monoxide, a gas with vasodilatory properties, and bilirubin, an antioxidant. Right-sided heart failure (RHF) resulted in a two-fold increase in the HO-1 transcript (;1.8 kb) in the right ventricle (RV) of RHF dogs compared to that of controls. In contrast, the left ventricle showed no increase in HO-1 mRNA in RHF. The change in HO was unique to HO-1, because neither the HO-2 transcripts (;1.3 and 1.9 kb) nor the HSP 70 mRNA was altered in either ventricle. This increase in HO-1 mRNA in RV was accompanied by a two-fold increase in immunoreactive HO-1 protein, as judged by Western blot analysis, as well as by a significant increase in cGMP levels. There was, however, no significant increase in RV total nitric oxide synthase activity in RHF. Furthermore, since norepinephrine infusion also increased HO-1 transcript and protein levels, the HO-1 system probably was induced in RHF by the increased interstitial norepinephrine levels known to occur in failing myocardium. This differential regulation and induction of HO-1 gene in the failing ventricle might be one of the defense mechanisms by which the heart attempts to protect from stress caused by congestive heart failure.
Collapse
Affiliation(s)
- V S Raju
- Cardiology Unit, Department of Medicine, Rochester, New York, 14642, USA.
| | | | | |
Collapse
|
14
|
Sullebarger JT, D'Ambra PM, Clark LC, Thanikarry L, Fontanet HL. Effect of Digoxin on Ventricular Remodeling and Responsiveness of beta-Adrenoceptors in Chronic Volume Overload. J Cardiovasc Pharmacol Ther 1998; 3:281-290. [PMID: 10684510 DOI: 10.1177/107424849800300403] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
BACKGROUND: Digoxin improves baroreflex function and reduces neurohumoral activation in severe heart failure, but it is uncertain how digoxin affects ventricular remodeling and progression to left ventricular dysfunction. In addition, the effect of digoxin in in vitro beta-adrenoceptor density and function, and contractile reserve in vivo is not well understood. METHODS AND RESULTS: To study this, we compared digoxin with placebo treatment in rats with chronic volume overload induced by aortocaval fistula and in sham-operated control animals. Left ventricular end-diastolic cavity dimensions (LVDd) and wall thickness were measured weekly by in vivo transthoracic echocardiography, and left ventricular mass (LVM) and percent fractional shortening (%FS) were calculated. Six weeks after fistula creation, simultaneous echocardiographic and invasive hemodynamic evaluation at rest and in response to incremental dobutamine (1-10 µg/kg/min intravenously) were measured. Myocardial plasma membrane beta-adrenoceptor density and maximal adenylate cyclase responses (V(max)) to isoproterenol, 5'-guanylylimi dodiphosphate, and forskolin were measured in vitro. Volume overload induced progressive increases in LVDd and LVM over the 6-week study period. Percent fractional shortening at rest, and the change in %FS in response to dobutamine stress were dramatically reduced 6 weeks after fistula creation. Although 6-week fistula animals had unchanged beta-adrenoceptor density (B(max)) and binding affinity (K(d)) as compared with controls, maximal adenylate cyclase responses to stimulation in vitro (V(max)) were markedly reduced. Digoxin treatment prevented this loss of responsiveness of adenylate cyclase but did not affect beta-adrenoceptor density or affinity in vitro. Digoxin had no effect on LVDd, LVM, %FS, or the response to dobutamine infusion in vivo. CONCLUSIONS: Although digoxin prevented beta-adrenoceptor desensitization and improved in vitro myocardial adenylate cyclase response, the cardiac response to adrenergic stimulation in vivo was not significantly improved. These results suggest that the role of beta-adrenoceptor desensitization in the progression from volume overload hypertrophy to left ventricular dysfunction and heart failure may be less important than previously thought. Furthermore, although digoxin treatment did produce modest hemodynamic benefits, it did not prevent progressive remodeling in this model.
Collapse
Affiliation(s)
- JT Sullebarger
- Division of Cardiology, University of South Florida and Cardiology and Research Services, Tampa, Florida, USA
| | | | | | | | | |
Collapse
|
15
|
Chauhan A, Zubaid M, Buller ME, Moscovich MD, Ricci DR, Lepicq L, Fox R, Penn IM. Comparison of bailout versus elective stenting: time to reassess our benchmarks of outcome. CATHETERIZATION AND CARDIOVASCULAR DIAGNOSIS 1997; 41:40-7. [PMID: 9143765 DOI: 10.1002/(sici)1097-0304(199705)41:1<40::aid-ccd10>3.0.co;2-u] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The aim of this study was to compare the clinical outcome of elective and bailout stenting in an era of improved stent deployment techniques and antithrombotic therapy. We retrospectively analysed 136 consecutive patients undergoing stent implantation over a 15 mo period. There was no significant difference in the follow-up duration, length of hospital stay, or the total incidence of major complications between the two groups. Bailout stenting, as compared to elective stenting, was not associated with an increased incidence of in-hospital (no death vs. 1.4%, 4.6% non-Q myocardial infarction vs. 0%, 7.7% vascular complications vs. 7.0%) or late complications (no death vs. 1.4%, no non-Q myocardial infarction vs. 2.8%, 3.1% repeat angioplasty vs. 5.6%, 1.5% coronary artery bypass surgery vs. 1.4%). Stents can be implanted in cases of failed angioplasty with a success rate similar to that of elective stent implantation with a low incidence of complications and equivalent clinical outcome.
Collapse
Affiliation(s)
- A Chauhan
- Vancouver Hospital, University of British Columbia, Canada
| | | | | | | | | | | | | | | |
Collapse
|
16
|
Topaz O, Salter D, Janin Y, Vetrovec G. Emergency bypass surgery for failed coronary interventions. CATHETERIZATION AND CARDIOVASCULAR DIAGNOSIS 1997; 40:55-65. [PMID: 8993817 DOI: 10.1002/(sici)1097-0304(199701)40:1<55::aid-ccd11>3.0.co;2-t] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- O Topaz
- Division of Cardiology, McGuire V.A. Medical Center, Richmond 23249, USA
| | | | | | | |
Collapse
|
17
|
Spinale FG, Johnson WS, Wang Y, Wang Z, Mukherjee R, Hebbar L, Jones BU. Direct effects of chronic beta-adrenergic receptor blockade on left ventricular and myocyte function in a model of tachycardia-induced congestive heart failure. J Card Fail 1996; 2:311-8. [PMID: 8989646 DOI: 10.1016/s1071-9164(96)80018-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
BACKGROUND Chronic beta-receptor blockade (beta-blockade) has been reported to improve symptoms and increase survival in patients with congestive heart failure (CHF); however, whether the mechanisms for the effects of beta-blockade in CHF are due to modulating chronotropy, inotropy, or both remains unknown. To address this issue, left ventricular function and isolated myocyte function were examined with chronic beta-blockade in a rapid pacing model of CHF, thereby eliminating potential chronotropic effects of beta-blockade. METHODS AND RESULTS Pigs were randomly assigned to three groups of six pigs each: supraventricular tachycardia (SVT): 3 weeks of atrial pacing at 240 beats/min; SVT/beta-blockade: 3 weeks of rapid pacing and beta-blockade (25 mg atenolol twice daily on days 14-21 of pacing); control group, sham control animals. This dosage schedule for beta-blockade was chosen because catecholamines are persistently elevated by day 14 in this model of CHF. Left ventricular fractional shortening and end-diastolic dimension were measured by echocardiography in the conscious state with a resting ambient heart rate. Isolated left ventricular myocyte function was examined using high-speed videomicroscopy. Supraventricular tachycardia caused left ventricular dilation (5.4 +/- 0.1 vs 3.5 +/- 0.1 cm) and reduced fractional shortening (12 +/- 1% vs 35 +/- 1%) compared with control animals (P < .05). The SVT/beta-blockade group showed no significant effects on left ventricular size or function compared with the SVT group, but their ambient resting heart rate was reduced by 20% relative to the SVT group (P < .05). Myocyte shortening was reduced in the SVT group (2.2 +/- 0.1% vs 4.5 +/- 0.1%, P < .05) compared with the control group and increased from SVT-only values with beta-blockade (2.7 +/- 0.1%, P < .05). Similarly, myocyte shortening velocity was similarly reduced in the SVT and SVT/beta-blockade groups (31 +/- 1 and 32 +/- 1 microns/s) compared with the control group (51 +/- 1 microns/s, P < .05). With SVT/beta-blockade myocyte contraction duration was prolonged (525 +/- 5 ms) compared with SVT-only or control values (469 +/- 9 and 473 +/- 4 ms, P < .05). Thus, institution of beta-1-selective blockade during the development of SVT-induced CHF altered the temporal characteristics of the myocyte contraction process, which resulted in improved myocyte shortening. CONCLUSIONS In a model of CHF due to the maintenance of a chronically elevated heart rate, institution of beta-1-selective blockade during the progression of the CHF process minimally affected left ventricular size and function. At the level of the myocyte, chronic beta-1-receptor blockade prolonged the contraction interval and thereby increased myocyte shortening. These unique results suggest that a contributory mechanism for the effects of beta-blockade in the setting of CHF is chronotropic modulation.
Collapse
Affiliation(s)
- F G Spinale
- Department of Surgery and Anesthesiology, Medical University of South Carolina, Charleston 29425, USA
| | | | | | | | | | | | | |
Collapse
|
18
|
Lee YA, Liang CS, Lee MA, Lindpaintner K. Local stress, not systemic factors, regulate gene expression of the cardiac renin-angiotensin system in vivo: a comprehensive study of all its components in the dog. Proc Natl Acad Sci U S A 1996; 93:11035-40. [PMID: 8855304 PMCID: PMC38279 DOI: 10.1073/pnas.93.20.11035] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Cardiac hypertrophy is associated with altered expression of the components of the cardiac renin-angiotensin system (RAS). While in vitro data suggest that local mechanical stimuli serve as important regulatory modulators of cardiac RAS activity, no in vivo studies have so far corroborated these observations. The aims of this study were to (i) examine the respective influence of local, mechanical versus systemic, soluble factors on the modulation of cardiac RAS gene expression in vivo; (ii) measure gene expression of all known components of the RAS simultaneously; and (iii) establish sequence information and an assay system for the RAS of the dog, one of the most important model organisms in cardiovascular research. We therefore examined a canine model of right ventricular hypertrophy and failure (RVHF) in which the right ventricle (RV) is hemodynamically loaded, the left ventricle (LV) is hemodynamically unloaded, while both are exposed to the same circulating milieu of soluble factors. Using specific competitive PCR assays, we found that RVHF was associated with significant increases in RV mRNA levels of angiotensin converting enzyme and angiotensin II type 2 receptor, and with significant decreases of RV expression of chymase and the angiotensin II type 1 receptor, while RV angiotensinogen and renin remained unchanged. All components remained unchanged in the LV. We conclude that (i) dissociated regional regulation of RAS components in RV and LV indicates modulation by local, mechanical, not soluble, systemic stimuli; (ii) components of the cardiac RAS are independently and differentially regulated; and (iii) opposite changes in the expression of angiotensin converting enzyme and chymase, and of angiotensin II type I and angiotensin II type 2 receptors, may indicate different physiological roles of these RAS components in RVHF.
Collapse
Affiliation(s)
- Y A Lee
- Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115-6195, USA
| | | | | | | |
Collapse
|
19
|
Lai LP, Suematsu M, Elam H, Liang CS. Differential changes of myocardial beta-adrenoceptor subtypes and G-proteins in dogs with right-sided congestive heart failure. Eur J Pharmacol 1996; 309:201-8. [PMID: 8874140 DOI: 10.1016/0014-2999(96)00340-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
We have shown previously in dogs with right heart failure that the reduction of myocardial beta-adrenoceptor density occurs only in the failing right ventricle, while cardiac inotropic responses to beta-adrenergic stimulation are reduced in both the right and left ventricles. The purpose of the present study was to determine whether a post-receptor defect in the guanine nucleotide-binding regulatory proteins (G-proteins) existed which would explain, at least in part, the adrenergic subsensitivity in both ventricles of the heart failure dogs. Using both immunoblotting technique and the bacterial toxin-mediated ADP ribosylation assays, we found that the stimulatory G-protein (Gs) was reduced in both ventricles of the heart failure dogs. In contrast, there were no changes in the inhibitory G-protein (Gi). In addition, receptor subtype analysis showed that only beta(1)-adrenoceptors were reduced in the failing right ventricle of the heart failure animals. This study demonstrated that the reduction of beta-adrenoceptors in right heart failure was chamber-specific whereas the reduction of Gs was non-selective, occurring in both ventricles of right heart failure dogs. The findings further suggest that the reduction of Gs probably was caused by systemic neurohormonal activation, independent of local ventricular stress.
Collapse
Affiliation(s)
- L P Lai
- Department of Medicine, University of Rochester Medical Center, NY 14642, USA
| | | | | | | |
Collapse
|
20
|
Xiong L, Bouanani NE, Su JB, Crozatier B. Propranolol therapy in experimental heart failure in rabbits improves cardiac response to catecholamines without beta-adrenoceptor up-regulation. Fundam Clin Pharmacol 1995; 9:522-30. [PMID: 8808172 DOI: 10.1111/j.1472-8206.1995.tb00529.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Beta-blockade has been shown to improve cardiac response to catecholamines in heart failure but cellular mechanisms of the improvement are unknown. The effect on left ventricular function of a 14 day propranolol treatment was studied in seven treated and eight non-treated rabbits with experimental heart failure. All animals were subjected to a volume (aortic insufficiency) plus pressure (aortic constriction) overload and were instrumented with a left ventricular catheter and ultrasonic crystals measuring anteroposterior left ventricular diameter. Beta-adrenoceptors were measured using 125I-Cyanopindolol in crude membranes. With isoproterenol, the heart rate was slower in treated rabbits than in non-treated rabbits (p < 0.005) and isoproterenol increased more systolic diameter shortening in treated than in non-treated rabbits (p < 0.05). With norepinephrine, for matched pressures, % delta D increased in the treated group but it did not change in the non-treated group. This improvement of ventricular function was due, in a large part, to an increased diastolic response to norepinephrine: end-diastolic diameter increased in the treated group but not in the non-treated group. In contrast with the improved ventricular response to catecholamines, beta-adrenergic receptor density in the treated group was identical to that of the non-treated group (27.8 fmoles/mg/proteins) and was significantly lower than that of normal rabbits (58.2 fmoles/mg, p < 0.01). The improvement of ventricular response to catecholamines appears to be due to a myocardial protection by propranolol against the toxic effect of catecholamines in heart failure and not, at least in this model, to an up-regulation of beta-adrenoceptors.
Collapse
Affiliation(s)
- L Xiong
- Inserm U400, Faculté de Médecine, Créteil, France
| | | | | | | |
Collapse
|
21
|
Sullebarger JT, Fan TH, Torres F, Liang CS. Both cell surface and internalized beta-adrenoceptors are reduced in the failing myocardium. Eur J Pharmacol 1991; 205:165-9. [PMID: 1667386 DOI: 10.1016/0014-2999(91)90815-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
To study myocardial beta-adrenoceptor internalization in heart failure, we measured beta-adrenoceptor density in the particulate, light vesicle and supernatant fractions of ventricular tissue of dogs with experimental right ventricular failure and sham-operated dogs. Tissue was fractionated by centrifugation, and beta-adrenoceptors were measured by [125I]iodocyanopindolol binding. Compared to sham-operated controls, beta-adrenoceptors were reduced in all fractions of right ventricular tissue from heart failure animals. Thus, the decreased surface (particulate fraction) receptors observed cannot be explained by internalization alone, and must be associated with altered receptor synthesis or degradation.
Collapse
Affiliation(s)
- J T Sullebarger
- Department of Medicine, University of Rochester Medical Center, NY 14642
| | | | | | | |
Collapse
|