Aging, cardiac proenkephalin mRNA and enkephalin peptides in the Fisher 344 rat

The Role of Endogenous Opioids in Cardioprotection

The opioid system involves opioid receptors (OPRs) and endogenous opioid peptides.This chapter will focus on the distribution of OPRs in the cardiovascular system, the expression pattern in the heart, the activation by opioid peptides, and the effects of OPRs activation with potential relevance in cardiovascular performance. In the heart, OPRs are co-expressed with beta adrenergic receptors (β-ARs) in the G-protein-coupled receptor (GPCR) superfamily, functionally cross-talk with β-Ars and modify catecholamine-induced effects. They are involved in cardiac contractility, energy metabolism, myocyte survival or death, vascular resistance. The effects of the opioid system in the regulation of systemic circulation at both the central and peripheral level are presented. The pathways are discussed under physiological (i.e., aging) and pathological conditions (atherosclerosis, heart failure, essential hypertension, ischemic stress). Stimulation of OPRs not only inhibits cardiac excitation-contraction coupling, but also protects the heart against hypoxic and ischemic injury. An enhanced sensitivity to opioids of endocrine organs and neuronal systems is operative in hypertensive patients. The opioid system can be pharmacologically engaged to selectively mimic these responses via cardiac and nervous signaling. The clinical opportunities for the use of cardioprotective effects of opioids require future investigations to provide more specific details of the impact on cardiac performance and electrophysiological properties.

Proteomic Analysis of Hypoxia-Induced Senescence of Human Bone Marrow Mesenchymal Stem Cells

Methods

Hypoxia in hBMSCs was induced for 0, 4, and 12 hours, and cellular senescence was evaluated by senescence-associated β-galactosidase (SA-β-gal) staining. Tandem mass tag (TMT) labeling was combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS) for differential proteomic analysis of hypoxia in hBMSCs. Parallel reaction monitoring (PRM) analysis was used to validate the candidate proteins. Verifications of signaling pathways were evaluated by western blotting. Cell apoptosis was evaluated using Annexin V/7-AAD staining by flow cytometry. The production of reactive oxygen species (ROS) was detected by the fluorescent probe 2,7-dichlorodihydrofluorescein diacetate (DCFH-DA).

Results

Cell senescence detected by SA-β-gal activity was higher in the 12-hour hypoxia-induced group. TMT analysis of 12-hour hypoxia-induced cells identified over 6000 proteins, including 686 differentially expressed proteins. Based on biological pathway analysis, we found that the senescence-associated proteins were predominantly enriched in the cancer pathways, PI3K-Akt pathway, and cellular senescence signaling pathways. CDK1, CDK2, and CCND1 were important nodes in PPI analyses. Moreover, the CCND1, UQCRH, and COX7C expressions were verified by PRM. Hypoxia induction for 12 hours in hBMSCs reduced CCND1 expression but promoted ROS production and cell apoptosis. Such effects were markedly reduced by the PI3K agonist, 740 Y-P, and attenuated by LY294002.

Conclusions

Hypoxia of hBMSCs inhibited CCND1 expression but promoted ROS production and cell apoptosis through activating the PI3K-dependent signaling pathway. These findings provided a detailed characterization of the proteomic profiles related to hypoxia-induced senescence of hBMSCs and facilitated our understanding of the molecular mechanisms leading to stem cell senescence.

Preprodynorphin gene mutation causes progressive cardiac conduction disease: A whole-exome analysis of a pedigree

AIMS

Progressive cardiac conduction disease (PCCD) is a rare heart disease that usually shows familial inheritance. Potential genetic risk factors for PCCD have been mostly limited to genes that encode ion channels, cardiac transcription factors, T-box transcription factors, gap junction proteins, energy metabolism regulators and structural proteins.

MAIN METHODS

Subjects in the present study came from a family who exhibited the autosomal dominant inheritance of PCCD. The primary proband had syncope and an electrocardiogram typical for PCCD, which started in the left bundle branch block, and passed to the atrioventricular block. The patient received a permanent pacemaker in 2013. Pathogenic mutations in the proband's family were identified using whole-exome sequencing and Sanger sequencing.

KEY FINDINGS

The results for the family members were verified using Sanger sequencing, while the results for healthy unrelated individuals were verified using SNaPShot. All patients in the family shared two adjacent missense mutations in the preprodynorphin (PDYN) gene (c.581A > T, c.580G > C; p.D194L).

SIGNIFICANCE

The PDYN double mutation c.581A > T and c.580G > C (p.D194L) may be linked to the onset of familial PCCD. The effects of these mutations on electrophysiology require further investigation.

Delta Opioid Receptors and Cardioprotection

The opioid receptor family, with associated endogenous ligands, has numerous roles throughout the body. Moreover, the delta opioid receptor (DORs) has various integrated roles within the physiological systems, including the cardiovascular system. While DORs are important modulators of cardiovascular autonomic balance, they are well-established contributors to cardioprotective mechanisms. Both endogenous and exogenous opioids acting upon DORs have roles in myocardial hibernation and protection against ischaemia-reperfusion (I-R) injury. Downstream signalling mechanisms governing protective responses alternate, depending on the timing and duration of DOR activation. The following review describes models and mechanisms of DOR-mediated cardioprotection, the impact of co-morbidities and challenges for clinical translation.

Opioid receptors and cardioprotection - 'opioidergic conditioning' of the heart

Ischaemic heart disease (IHD) remains a major cause of morbidity/mortality globally, firmly established in Westernized or 'developed' countries and rising in prevalence in developing nations. Thus, cardioprotective therapies to limit myocardial damage with associated ischaemia-reperfusion (I-R), during infarction or surgical ischaemia, is a very important, although still elusive, clinical goal. The opioid receptor system, encompassing the δ (vas deferens), κ (ketocyclazocine) and μ (morphine) opioid receptors and their endogenous opioid ligands (endorphins, dynorphins, enkephalins), appears as a logical candidate for such exploitation. This regulatory system may orchestrate organism and organ responses to stress, induces mammalian hibernation and associated metabolic protection, triggers powerful adaptive stress resistance in response to ischaemia/hypoxia (preconditioning), and mediates cardiac benefit stemming from physical activity. In addition to direct myocardial actions, central opioid receptor signalling may also enhance the ability of the heart to withstand I-R injury. The δ- and κ-opioid receptors are strongly implicated in cardioprotection across models and species (including anti-infarct and anti-arrhythmic actions), with mixed evidence for μ opioid receptor-dependent protection in animal and human tissues. A small number of clinical trials have provided evidence of cardiac benefit from morphine or remifentanil in cardiopulmonary bypass or coronary angioplasty patients, although further trials of subtype-specific opioid receptor agonists are needed. The precise roles and utility of this GPCR family in healthy and diseased human myocardium, and in mediating central and peripheral survival responses, warrant further investigation, as do the putative negative influences of ageing, IHD co-morbidities, and relevant drugs on opioid receptor signalling and protective responses.

Increased myocardial methionine-enkephalin with reduced arterial oxygenation in congenital heart disease

BACKGROUND

  Cardiac opioid peptides have been identified to exert important adaptive metabolic signalling for cardioprotection against ischaemia or hypoxia-related injury.

AIMS

  To determine myocardial methionine-enkephalin content in children with hypoxemic congenital heart defects and to correlate myocardial content of methionine-enkephalin with the extent of arterial oxygen desaturation.

METHODS

  Children (n= 20, median age of 16 months), undergoing cardiac surgical repair (tetralogy of Fallot, 17/20), were included in this study. Arterial oxygen saturation was measured on admission. Myocardial samples obtained during surgery were assayed via radioimmunochemistry for methionine-enkephalin content.

RESULTS

  Greater methionine-enkephalin content was measured in the right ventricles of the patients suffering from recent cyanotic spells compared with those with no recent spells (cyanotic spells: 2418 ± 844 pg/g wet weight tissue, n= 6; no spells: 1175 ± 189 pg/g wet weight tissue, n= 14, P= 0.04). An inverse correlation was evident between the arterial oxygen saturation and myocardial methionine-enkephalin content.

CONCLUSION

  Myocardial methionine-enkephalin levels increase with the severity of hypoxic stress in congenital cardiac disease and may play an important adaptive role in countering adrenergic over-activity and related excess demand on myocardial metabolic capacity.

The role of oxidative stress and inflammation in cardiovascular aging

Age is an independent risk factor of cardiovascular disease, even in the absence of other traditional factors. Emerging evidence in experimental animal and human models has emphasized a central role for two main mechanisms of age-related cardiovascular disease: oxidative stress and inflammation. Excess reactive oxygen species (ROS) and superoxide generated by oxidative stress and low-grade inflammation accompanying aging recapitulate age-related cardiovascular dysfunction, that is, left ventricular hypertrophy, fibrosis, and diastolic dysfunction in the heart as well as endothelial dysfunction, reduced vascular elasticity, and increased vascular stiffness. We describe the signaling involved in these two main mechanisms that include the factors NF-κB, JunD, p66^Shc, and Nrf2. Potential therapeutic strategies to improve the cardiovascular function with aging are discussed, with a focus on calorie restriction, SIRT1, and resveratrol.

Role of endogenous opioid peptides in the infarct size-limiting effect of adaptation to chronic continuous hypoxia

AIMS

The objective of this study was to examine the involvement of endogenous opioid peptides and opioid receptor (OR) subtypes in the cardioprotective effect of adaptation to chronic hypoxia in rats.

MAIN METHODS

Rats were exposed to continuous normobaric hypoxia (CNH; 12% oxygen) for 3 weeks. Myocardial ischemia was induced by 20-min coronary artery occlusion followed by 3-h reperfusion in anesthetized open-chest animals. Various OR antagonists were administered to rats prior to ischemia. The size of myocardial infarction and the incidence of ischemic ventricular arrhythmias were assessed. Myocardial and plasma concentrations of opioid peptides (met-enkephalin, β-endorphin, and endomorphins) were determined.

KEY FINDINGS

Adaptation to CNH significantly increased myocardial and plasma concentrations of opioids, potentiated their further elevation by ischemia/reperfusion, and reduced myocardial infarct size, but it did not affect the incidence of ischemic arrhythmias. The infarct size-limiting effect of CNH was abolished by OR antagonists naltrexone (non-selective), naloxone methiodide (non-selective peripherally acting), TIPP[ψ] (δ-OR), naltriben (δ2-OR), or CTAP (μ-OR), while BNTX (δ1-OR) and nor-binaltorphimine (κ-OR) had no effect.

SIGNIFICANCE

The results suggest that the infarct size-limiting effect afforded by adaptation to CNH is mediated by activation of peripheral δ2- and μ-ORs by elevated levels of endogenous opioid peptides.

Modulation of sarcoplasmic reticulum Ca(2+) cycling in systolic and diastolic heart failure associated with aging

Hypertension, atherosclerosis, and resultant chronic heart failure (HF) reach epidemic proportions among older persons, and the clinical manifestations and the prognoses of these worsen with increasing age. Thus, age per se is the major risk factor for cardiovascular disease. Changes in cardiac cell phenotype that occur with normal aging, as well as in HF associated with aging, include deficits in ss-adrenergic receptor (ss-AR) signaling, increased generation of reactive oxygen species (ROS), and altered excitation-contraction (EC) coupling that involves prolongation of the action potential (AP), intracellular Ca(2+) (Ca(i)(2+)) transient and contraction, and blunted force- and relaxation-frequency responses. Evidence suggests that altered sarcoplasmic reticulum (SR) Ca(2+) uptake, storage, and release play central role in these changes, which also involve sarcolemmal L-type Ca(2+) channel (LCC), Na(+)-Ca(2+) exchanger (NCX), and K(+) channels. We review the age-associated changes in the expression and function of Ca(2+) transporting proteins, and functional consequences of these changes at the cardiac myocyte and organ levels. We also review sexual dimorphism and self-renewal of the heart in the context of cardiac aging and HF.

Aging and arterial-cardiac interactions in the elderly

Cardiovascular system changes with aging, and these changes are modified by arteriosclerosis-risk factors, i.e., hypertension and diabetes, as well as arterial-cardiac interactions. Regarding age-related changes in the cardiovascular system, Lakatta et al. reported morphological and functional changes that are specific to the cardiovascular aging and are distinct from arteriosclerotic changes. After then, various studies on the mechanism of aging of the cardiovascular system have been performed from the viewpoint of cellular aging, endothelial or endocardial function, and fibroblast. Aging-related changes in the cardiovascular system include death and dysfunction of cell, and matrix fibrosis, but these can also be induced by various causes other than aging. To elucidate the relationship between aging and remodeling of the cardiovascular system, firstly, it is necessary to clarify the phenomena of cellular aging. Changes also differ between the heart and arteries, and there are time lags between aging and aging-associated morphological and functional changes in the cardiovascular system: some changes appear early (early type) or later (delayed type) and some changes occur at the same speed with aging (linear type). In this report, the latest findings concerning aging-associated functional and morphological changes in the arteries and the heart are reviewed and the studies are summarized. Arteries and the heart change with aging while interacting with each other. These arterial-cardiac interactions are also described.

Age-related physiologic changes and perioperative management of elderly patients

Aging itself only minimally increases operative risk, but with aging, there is an increase of the prevalence of chronic diseases and a progressive deterioration of organ function. Aging is associated with a progressive decrease in heart, lung and kidney performance. Under normal conditions, these physiologic changes do not produce any problems for the elderly, but when these patients are subjected to the stress of surgery or its complications, there may be inadequate functional reserve. It is very important to know age-related patho-physiological changes in order to be able to better evaluate elderly patients undergoing surgery, and to prevent and manage preoperative complications. In this review we try to identify and to describe the most frequent physiological changes in the elderly, how those impact pharmacodynamic and pharmacokinetic parameters, and how to assess and manage them.

Hypertensive state, independent of hypertrophy, exhibits an attenuated decrease in systolic function on cardiac kappa-opioid receptor stimulation

Opioids/opiates are commonly administered to alleviate pain, unload the heart, or decrease breathlessness in patients with advanced heart failure. As such, it is important to evaluate whether the myocardial opioidergic system is altered in cardiac disease. A hamster model of spontaneous hypertension was investigated before the development of hypertension (1 mo of age) and in the hypertensive state (10 mo of age) to evaluate the effect of prolonged hypertension on myocardial opioidergic activity. Plasma beta-endorphin was decreased before the development of hypertension and in the hypertensive state (P < 0.05). There was no change in cardiac beta-endorphin content at either time point. No differences were detected in cardiac or plasma dynorphin A, Met-enkephalin, or Leu-enkephalin, or in cardiac peptide expression of kappa- or delta-opioid receptors. mu-Opioid receptor was not detected in either model. To determine how hypertension affects myocardial opioid signaling, the ex vivo work-performing heart was used to assess the cardiac response to opioid administration in healthy hearts and those subjected to chronic hypertension. Agonists selective for the kappa- and delta-opioid receptors, but not mu-opioid receptors, induced a concentration-dependent decrease in cardiac function. The decrease in left ventricular systolic pressure on administration of the kappa-opioid receptor-selective agonist, U50488H, was attenuated in hearts from hamsters subjected to chronic, untreated hypertension (P < 0.05) compared with control. These results show that peripheral and myocardial opioid expression and signaling are altered in hypertension.

Endogenous cardiac opioids: enkephalins in adaptation and protection of the heart

Opiates have been used for thousands of years in the form of opium for relief of pain or fever and to induce sleep. However, it was only in the 1970s that the endogenous ligands for the opiate receptors were identified and termed opioid peptides. Opioid peptides activate G protein-coupled receptors in the central and autonomic nervous system, with marked effects on the regulation of pain perception, body temperature, respiration, heart rate and blood pressure. Cardiovascular regulatory effects of endogenous opioids were initially considered to originate from neural centres in the central nervous system, facilitating a regulatory role in neuro-transmission, as demonstrated by the presynaptic co-release from sympathetic neurones of norepinephrine with enkephalin or acetylcholine with enkephalin. However, opioid peptides of myocardial origin have also recently been shown to play a key role in local regulation of the heart. This brief review highlights the key features of the enkephalin opioids in the heart and the current understanding of their role in development, ageing, cardioprotection, hypertension, hypertrophy, and heart failure.

Augmented myocardial methionine-enkephalin in a murine model of cardiac angiotensin II-overexpression

INTRODUCTION

The endogenous opioid system has been reported to interact with both the cardiac sympathetic and renin-angiotensin systems in exerting a local regulatory action on the heart. The goal of this investigation was to examine how cardiac levels of enkephalin production are altered in the development of normotensive primary hypertrophy due to elevated intra-cardiac angiotensin II (Ang II) production.

METHODS

Atrial and ventricular methionine-enkephalin (ME) levels were measured by quantitative radioimmunoassay in 14 and 28-week-old male transgenic mice (TG1306/1R) and control mice. The TG1306/1R exhibit cardiac specific Ang II overexpression and cardiac hypertrophy, but not hypertension.

RESULTS

TG1306/1R mice had significantly higher heart/body weight ratios (15-20%) than control littermates at both 14 (p=0.02) and 28 weeks (p=0.04). Relative to controls, ME content was significantly elevated (approximately two-fold) in atria and ventricles in the older 28-week TG1306/1R mice only. A significant inverse correlation between heart size and ME level was observed for 28-week TG1306/1R only.

CONCLUSIONS

We have provided evidence that a marked elevation of myocardial enkephalin level is observed in the established (but not early) phase of cardiac hypertrophy associated with cardiac-specific Ang II-overexpression. This study identifies a potentially important relationship between two endogenous peptidergic signalling systems involved in the regulation of growth and function of the hypertrophic heart.

delta-Opioid receptor stimulation enhances the growth of neonatal rat ventricular myocytes via the extracellular signal-regulated kinase pathway

1. The aims of the present study were to determine whether delta-opioid receptor stimulation enhanced proliferation of and to investigate the role of the extracellular signal-regulated kinase (ERK) pathway in ventricular myocytes from neonatal rats. 2. At concentratins ranging from 10 nmol/L to 10 micromol/L, [D-Ala2,D-Leu5]enkephalin (DADLE) concentration-dependently promoted myocardial growth and DNA synthesis and altered the cytoskeleton. 3. At 1 micromol/L, DADLE also increased the expression and phosphorylation of ERK. 4. These effects of 1 micromol/L DADLE were abolished by 10 micromol/L naltrindole, a selective delta-opioid receptor antagonist, 10 nmol/L U0126, a selective ERK antagonist, 1 micromol/L staurosporine, an inhibitor of protein kinase (PK) C, and 100 micromol/L Rp-adenosine 3',5'-cyclic monophosphorothioate triethylammonium salt hydrate (Rp-cAMPS), an inhibitor of PKA. 5. In conclusion, delta-opioid receptor stimulation enhances the proliferation and development of the ventricular myocytes of neonatal rats. The ERK pathway and related signalling mechanisms, namely PKC and PKA, are involved.

Vagotonic effects of enkephalin are not mediated by sympatholytic mechanisms

This study examined the hypothesis that vagotonic and sympatholytic effects of cardiac enkephalins are independently mediated by different receptors. A dose-response was constructed by administering the delta-receptor opioid methionine-enkephalin-arginine-phenylalanine (MEAP) by microdialysis into the interstitium of the canine sinoatrial node during vagal and sympathetic stimulation. The right cardiac sympathetic nerves were stimulated as they exited the stellate ganglion at frequencies selected to increase heart rate approximately 35 bpm. The right cervical vagus was stimulated at frequencies selected to produce a two-step decline in heart rate of 25 and 50 bpm. A six-step dose-response was constructed by recording heart rates during nerve stimulation as the dose of MEAP was increased between 0.05 pmol/min and 1.5 nmol/min. Vagal transmission improved during MEAP at 0.5 pmol/min. However, sympathetically mediated tachycardia was unaltered with any dose of MEAP. In Study 2, a similar dose-response was constructed with the kappa-opioid receptor agonist trans(+/-)-3-4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzeneacetamide-HCl (U-50488H) to illustrate an independent sympatholytic effect and to verify its kappa-receptor character. U-50488H gradually suppressed the sympathetic tachycardia, with a significant effect obtained only at the highest dose (1.5 nmol/min). U-50488H had no effect on vagally mediated bradycardia. Surprisingly, the sympatholytic effect was not reversed by withdrawing U-50488H or by the subsequent addition of the kappa-antagonist 17,17'-(dichloropropylmethyl)-6,6',7,7'-6,6'-imino-7,7'-binorphinan-3,4',14,14'-tetroldi-hydrochloride (norBNI). Study 3 was conducted to determine whether the sympatholytic effect of U-50488H could be prevented by norBNI. NorBNI blocked the sympatholytic effect of the U50488H for 90 mins. When norBNI was discontinued afterward and U-50488H was continued alone, a sympatholytic effect emerged within 30 mins. Collectively these observations support the hypothesis that the vagotonic influence of MEAP is not dependent on a sympatholytic influence. Furthermore, the sympatholytic effect is mediated independently by kappa-receptors. The sympatholytic effect of sustained kappa-receptor stimulation appears to evolve gradually into a functional state not easily reversed.

Exploration of replicative senescence-associated genes in human dermal fibroblasts by cDNA microarray technology

The aging process is known to be regulated by specific genes in various organisms, including yeast, the nematode C. elegans, fruitflies and mice. To explore the novel genes involved in aging process, we applied cDNA microarray technology to a replicative senescence model of human dermal fibroblasts (HDF). Eighty-four genes, including inflammatory genes, cell cycle regulatory genes, cytoskeletal genes, and metabolic genes were found to show more than two fold expressional differences in young and old fibroblasts. Furthermore, 31 genes were confirmed to be up- or down-regulated during replicative senescence by semi-quantitative RT-PCR. The overexpressions of several genes including CD36, putative lymphocyte G0/G1 switch gene (G0S2), tumor protein D52-like 1 (TPD52L1), chemokine (C-X-C motif) ligand 6, myxovirus resistant gene 1 (MX1), and the down-regulation of the immunoglobulin superfamily containing leucine-rich repeat (ISLR), neurotrimin, insulin-like growth factor 2 associated protein (IGF2A), and apoptosis-related RNA binding protein (NAPOR3) were newly identified. These results suggest that fibroblasts show the deregulation of various cellular processes, such as inflammatory response, mitosis, cell adhesion, transport, signal transduction, and metabolism during replicative senescence.

Acute effects of beta-endorphin on cardiovascular function in patients with mild to moderate chronic heart failure

BACKGROUND

Cardiomyocytes produce opioid peptides and receptors. beta-Endorphin is increased in the plasma of patients with congestive heart failure (CHF). We evaluated whether an intravenous infusion of beta-endorphin exerted any effect on cardiovascular function and on the neurohormonal milieu in patients with mild to moderate CHF.

METHODS

According to a double-blind, placebo-controlled design, 10 patients (5 men, age 46.9 +/- 8.2 years [mean +/- SD]) with CHF and New York Heart Association functional class II to III received, in random order, 1-hour intravenous infusion of beta-endorphin (500 microg/h) and, on a separate occasion, received placebo and underwent echocardiographic and laboratory measurements at baseline and during infusions.

RESULTS

beta-Endorphin significantly increased left ventricular ejection fraction (LVEF) (P =.0001) and stroke volume (P =.0001), and reduced systemic vascular resistance (P =.031) in patients with CHF. These changes were paralleled by a significant increase in plasma levels of glucagon (P =.0001), GH (P =.0001), and IGF-1 (P =.0001), and a significant decrease in plasma levels of endothelin (P =.0001) and catecholamines (P =.01). No hemodynamic and neurohormonal changes were observed during the placebo study in any patient.

CONCLUSIONS

We conclude that a short-term, high dose infusion of beta-endorphin improves LVEF, reduces systemic vascular resistance, blunts the neurohormonal activation, and stimulates the GH/IGF-1 axis in patients with mild to moderate CHF.

Involvement of Rel/NF-kappa B transcription factors in senescence

Senescence is now established as a genetically controlled phenomenon that alters different cell functions, including proliferation, apoptosis, resistance to stress, and energetic metabolism. Underlying changes in gene expression are governed by some transcription factors, whose expression or activity must change with senescence as well. Transcription factors of the Rel/NF-kappa B family are good candidates to participate in the establishment of senescence. Arguments range from correlation between cell functions controlled by these factors and cell functions altered during senescence, to phenotypes resulting from in vitro manipulations of Rel/NF-kappa B activity.

Effect of Aging on Rat Tissue Peptidase Activities

The process of aging is known to involve alterations in the activity of peptidases and proteases. However, the precise changes in the activity of many peptidases in aged tissues have not yet been fully characterized, and both decreases and increases in both peptidase activity and peptide levels have been reported to occur during the aging process. In the present study, we measured the activity of several peptidases in selected tissues (brain cortex, brain stem, liver, kidney, heart, and lung) of the young adult (3 months old) and aged (18 months old and 22 months old) rat. The activities of prolyl endopeptidase, pyroglutamyl peptidase I, puromycin sensitive aminopeptidase, and aminopeptidase N were assayed using beta-naphthylamine aminoacidic derivatives as substrates. The activity of the soluble fractions of prolyl endopeptidase was found to be reduced in the lungs of aged animals, while reduced activity of soluble pyroglutamyl peptidase I and also aminopeptidase N was measured in the aged kidney and heart, respectively. In contrast, increased activity of particulate prolyl endopeptidase was measured in the brain stem of older animals. Since most of these changes can be correlated with known alterations in the levels of peptides controlled by each enzyme, the results of the present study indicate that the studied peptidases may play an important role in regulating tissue peptide levels during aging.

Bimodal delta-opioid receptors regulate vagal bradycardia in canine sinoatrial node

Methionine-enkephalin-arginine-phenylalanine (MEAP) introduced into the interstitium of the canine sinoatrial (SA) node by microdialysis interrupts vagal bradycardia. In contrast, raising endogenous MEAP by occluding the SA node artery improves vagal bradycardia. Both are blocked by the same delta-selective antagonist, naltrindole. We tested the hypothesis that vagal responses to intranodal enkephalin are bimodal and that the polarity of the response is both dose- and opioid receptor subtype dependent. Ultralow doses of MEAP were introduced into the canine SA node by microdialysis. Heart rate frequency responses were constructed by stimulating the right vagus nerve at 1, 2, and 3 Hz. Ultralow MEAP infusions produced a 50-100% increase in bradycardia during vagal stimulation. Maximal improvement was observed at a dose rate of 500 fmol/min with an ED50 near 50 fmol/min. Vagal improvement was returned to control when MEAP was combined with the delta-antagonist naltrindole. The dose of naltrindole (500 fmol/min) was previously determined as ineffective vs. the vagolytic effect of higher dose MEAP. When MEAP was later reintroduced in the same animals at nanomoles per minute, a clear vagolytic response was observed. The delta1-selective antagonist 7-benzylidenenaltrexone (BNTX) reversed the vagal improvement with an ED50 near 1 x 10-21 mol/min, whereas the delta2-antagonist naltriben had no effect through 10-9 mol/min. Finally, the improved vagal bradycardia previously associated with nodal artery occlusion and endogenous MEAP was blocked by the selective delta1-antagonist BNTX. These data support the hypothesis that opioid effects within the SA node are bimodal in character, that low doses are vagotonic, acting on delta1-receptors, and that higher doses are vagolytic, acting on delta2-receptors.

Perspectives on mammalian cardiovascular aging: humans to molecules

Age-related changes in cardiovascular function and structure in healthy adult volunteer community dwelling subjects (from 20 to 85 years) is remarkable for changes in pump function [impaired left ventricular (LV) ejection reserve capacity manifest by a reduced ejection fraction and accompanied by diminished cardioacceleration, LV dilation at end diastole and an altered diastolic filling pattern] and increased vascular afterloading. There is also evidence for a reduction in the number of cardiac myocytes with advancing age. Subcellular changes with aging (best understood in rodents) include certain regulatory factors of excitation-contraction-relaxation coupling (i.e. calcium handling), modulation by adrenergic receptor (AR) stimulation, and changes in the generation and sensitivity to the damaging effects of ROS. Coordinated changes in gene expression and/or protein function with aging result in a prolonged action potential (AP), Ca(i) transient, and contraction. L-type Ca(2+) current (I(Ca)) inactivates more slowly, and outwardly-directed K(+) currents are reduced, and likely contribute to AP-prolongation. The rate of Ca(2+) sequestration by the sarcoplasmic reticulum (SR) decreases in the senescent myocardium, in part underlying the prolonged Ca(i) transient. An age-associated reduction in transcription of the SERCA2 gene, coding for the SR Ca(2+) pump, accounts in part for a decrease in the SR pump site density. The contractile response to both beta(1)-AR and beta(2)-AR stimulation diminishes with aging due to decreased adrenergic augmentation of I(Ca), and thus the Ca(i) transient, in senescent vs. young hearts. The age-associated reduction in the postsynaptic response of myocardial cells to beta(1)-AR stimulation appears to be due to multiple changes in molecular and biochemical receptor coupling and post-receptor mechanisms. An increased basal production of ROS is paralleled by increased ROS-sensitivity, markers of chronic ROS damage and mitochondrial functional decline. Overall, these changes lead to a diminished (but not necessarily exhausted) capacity of the heart to adapt to physiological or pathological stress with advancing age.

Cardiovascular ageing in health sets the stage for cardiovascular disease

The incidence and prevalence of coronary disease, hypertension, heart failure and stroke increase exponentially with advancing age. While epidemiologic studies have discovered that aspects of lifestyle and genetics are risk factors for these diseases, age, per se, confers the major risk. Thus, it is reasonable to hypothesise that specific pathophysiological mechanisms that underlie these diseases become superimposed on cardiac and vascular substrates that have been modified by an 'ageing process', and that the latter modulates disease occurrence and severity. In order to unravel this age-disease interaction, the nature of the ageing process in the heart and vasculature requires elucidation. Some aspects of the current understanding of ageing of the heart and blood vessels in the absence of apparent disease are the focus of this review.

Age-associated cardiovascular changes in health: impact on cardiovascular disease in older persons

In the United States, cardiovascular disease, e.g., atherosclerosis and hypertension, that lead to heart failure and stroke, is the leading cause of mortality, accounting for over 40 percent of deaths in those aged 65 years and above. Over 80 percent of all cardio-vascular deaths occur in the same age group. Thus, age, per se, is the major risk factor for cardiovascular disease. Clinical manifestations and prognosis of these cardiovascular diseases likely become altered in older persons with advanced age because interactions occur between age-associated cardiovascular changes in health and specific pathophysiologic mechanisms that underlie a disease. A fundamental understanding of age-associated changes in cardiovascular structure and function ranging in scope from humans to molecules is required for effective and efficient prevention and treatment of cardiovascular disease in older persons. A sustained effort over the past two decades has been applied to characterize the multiple effects of aging in health on cardiovascular structure and function in a single study population, the Baltimore Longitudinal Study on Aging. In these studies, community dwelling, volunteer participants are rigorously screened to detect both clinical and occult cardiovascular disease and characterized with respect to lifestyle, e.g. exercise habits, in an attempt to deconvolute interactions among lifestyle, cardiovascular disease and the aging process in health. This review highlights some specific changes in resting cardiovascular structure and function and cardiovascular reserve capacity that occur with advancing age in healthy humans. Observations from relevant experiments in animal models have been integrated with those in humans to provide possible mechanistic insight.

Transient arterial occlusion raises enkephalin in the canine sinoatrial node and improves vagal bradycardia

The C-terminal proenkephalin sequence, Methionine-enkephalin-arginine-phenylalanine (MEAP), is abundant in the myocardium and when delivered into the sinoatrial (SA) node by microdialysis, the peptide had significant vagolytic activity. The study that follows was conducted to determine if an increase in endogenous nodal MEAP could be demonstrated during reduced nodal blood flow and was endogenous MEAP similarly vagolytic. Microdialysis probes were placed in the canine SA node and perfused at 5 microl per min. The SA node artery was occluded and released four times at 10-min intervals. The intermittent occlusions were followed by one or two prolonged occlusions (30 min). Vagally mediated bradycardia was compared before, during, and after occlusion of the artery. An increase in recovered MEAP (70-220 fmol) was recorded during each of the initial 10-min occlusions. MEAP returned to baseline during each subsequent 10-min reperfusion. There was a sustained increase in MEAP (110-150 fmol) during longer occlusions. Contrary to the hypothesis, the increased MEAP during arterial occlusion was coincident with improved vagal bradycardia. The improvement in vagally mediated bradycardia was highly reproducible and was observed again during a second 30-min occlusion. The improved vagal function was reversed or reduced, respectively, when naltrindole or glibenclamide was included in the microdialysis inflow during arterial occlusion. Although these observations suggested that opioid receptors and ATP-sensitive K+ channels might have been involved, only a single dose of each agent was practical. Therefore, the specificity of these two responses remains to be confirmed. In summary, the recovery of endogenous opioids from the sinoatrial node increased during reduced arterial perfusion of the node. Contrary to expectations, the increase in recovered endogenous opioids was accompanied byimproved rather than impaired vagal bradycardia.

Cardiac synthesis, processing, and coronary release of enkephalin-related peptides

Although preproenkephalin mRNA is abundant in the heart, the myocardial synthesis and processing of proenkephalin is largely undefined. Isolated working rat hearts were perfused to determine the rate of myocardial proenkephalin synthesis, its processing into enkephalin-containing peptides, their subsequent release into the coronary arteries, and the influence of prior sympathectomy. Enkephalin-containing peptides were separated by gel filtration and quantified with antisera for specific COOH-terminal sequences. Proenkephalin, peptide B, and [Met(5)]enkephalin-Arg(6)-Phe(7) (MEAP) comprised 95% of the extracted myocardial enkephalins (35 pmol/g). Newly synthesized enkephalins, estimated during a 1-h perfusion with [(14)C]phenylalanine (4 pmol x h(-1) x g wet wt(-1)), were rapidly cleared from the heart during a second isotope-free hour. Despite a steady release of enkephalins into the coronary effluent (4 pmol x h(-1) x g wet wt(-1)), enkephalin replacement apparently exceeded its release, and tissue enkephalins actually accumulated during hour 2. In contrast to the tissue, methionine-enkephalin accounted for more than half of the released enkephalin. Chemical sympathectomy produced an increase in total enkephalin content similar to that observed after 2-h control perfusion. This observation suggested that the normal turnover of myocardial enkephalin may depend in part on continued sympathetic influences.

Cardiac opioids

Opioid peptides have long been considered as neuropeptides or neurotransmitters. The more recent discovery of these same peptides in non-neuronal tissue suggests that the peptides may have autocrine, paracrine, or endocrine functions as well. The opioid peptides, enkephalins, dynorphins, and endorphins, have been found in isolated cardiac myocytes and heart tissue. This review will cover the recent literature on opioid peptides in respect to cardiac distribution, biochemistry, and function.

Enkephalin inhibits vagal control of heart rate, contractile force and coronary blood flow in the canine heart in vivo

The following studies were conducted to determine if the ability of the intrinsic cardiac opioid, met-enkephalin-arg-phe to interrupt vagal bradycardia can be generalized to include the disruption of vagal effects on atrial contraction and coronary blood flow. Anesthetized dogs were instrumented to measure heart rate and left atrial contractile force or heart rate and coronary blood flow. The response of each variable was recorded at rest and during vagal stimulation. During the evaluation of vagal effects on contractile activity and coronary blood flow, heart rate was maintained constant by electrically pacing the hearts above their resting heart rate. In the first protocol, vagal stimulation reduced both heart rate and atrial contractile force in a frequency dependent fashion. When met-enkephalin-arg-phe (MEAP) was infused systemically for three min at 3 nmol min(-1) kg(-1), there were no observed changes in resting heart rate or atrial contraction. However, when the vagal stimuli were reapplied during the peptide infusion, the previously observed vagal effects on rate and contractile force were reduced in magnitude by one-half to two-thirds. The ability of MEAP to interrupt the vagal control of heart rate and contractile activity involves opiate receptors since the effect was eliminated in both cases by prior opiate receptor blockade with the high affinity antagonist, diprenorphine. In the second protocol, vagal stimulation produced a transient increase in coronary blood flow and an accompanying increase in myocardial oxygen consumption. These effects were reduced by approximately 80% during the systemic infusion of MEAP. A similar increase in coronary blood flow mediated by the direct acting muscarinic agonist, methacholine, was unaltered by the infusion of peptide. In summary, these data suggest that the intrinsic cardiac enkephalin, MEAP, is capable of inhibiting the vagal control of heart rate, contractile force and coronary blood flow and probably does so through a common opiate receptor located prejunctionally on vagal nerve terminals or within nearby parasympathetic ganglia.

Preproenkephalin gene expression and [Met5]-enkephalin levels in the developing rat heart

[Met5]-enkephalin, encoded by the preproenkephalin (PPE) gene, serves as a growth factor (opioid growth factor, OGF) during cardiac development in addition to its role as a neuroregulator. This study examined the ontogeny and relationship of gene and peptide expression in the mammalian heart during late embryonic, preweaning, and postweaning periods. Values for PPE mRNA of hearts in rats from embryonic day 16 (E16) to postnatal day 1 were 33 to 50% of levels found in adults. Adult values for the mature heart were comparable to those in the caudate, an area of the rat brain rich in PPE mRNA. Message gradually decreased during the first postnatal week to 10% of adult values and remained so until weaning. PPE mRNA on days 35 and 50 were three- and sevenfold, respectively, higher than at 21 days, and in adults was more than 50% greater than at day 50. Message for PPE in neonatal heart was regulated rapidly and in a sustained fashion by excess opioid agonist (OGF) or blockade of opioid-receptor interaction. [Met5]-enkephalin levels increased sevenfold between E18 and E20, and another 1.6-fold until birth. Having reached a zenith in the neonate, values for enkephalin-like peptide decreased gradually through the 2nd postnatal week, and were extremely low in adulthood. Indeed, a 43-fold difference in peptide levels was detected between neonatal and adult rat heart. These data provide evidence for the expression of a tightly regulated and distinct growth factor (OGF) during the crucial periods of cell proliferation and differentiation in the mammalian heart, and reveal that the source of OGF is autocrine and/or paracrine.

Localization of preproenkephalin mRNA in rat heart: selective gene expression in left ventricular myocardium

The enkephalins are derived from a common precursor protein known as preproenkephalin (ppENK). Enkephalins appear to be one of the endogenous ligands for the opiate receptors. In the rat the ventricular myocardium contains more ppENK mRNA than any other tissue. To gain further insight into the role of cardiac enkephalins, the regional and developmental distribution of ppENK mRNA was studied by Northern blotting and in situ hybridization. In the early postnatal period, ppENK mRNA is low in atrial and ventricular myocardium. With maturation, ppENK expression increases threefold in left and right ventricular tissue, but not in the atria or cardiac conductive system. Interestingly, ppENK mRNA levels are four times higher in the left than in the right chamber. Thus, to our knowledge, ppENK is the only gene exhibiting marked differences in expression between the adult right and left ventricle. Given the left-side preference of ppENK expression, the possibility is raised that the left ventricle is an endocrine organ that supplies the body with enkephalins.

Opioid gene expression in the developing and adult rat heart

Opioid peptides are known to play a role in the function and growth of the mammalian heart. Although some information about gene expression of opioids in the heart is available, there is no data on the cellular location of opioid gene expression during development or in the adult. Using in situ hybridization and rat heart ranging from embryonic day 14 (E14) to adulthood, we have evaluated the distribution of gene expression for proenkephalin, proopiomelanocortin, and prodynorphin. With respect to preproenkephalin mRNA (PPE mRNA), message in the ventricle was abundant from E14 (the first time point examined) until shortly after birth, with a marked reduction noted on postnatal days 5, 10, and 21. Adults displayed considerable message, though less than in preparations of embryonic and neonatal heart. PPE mRNA was detected in epicardial, myocardial, and endocardial cells, as well as the walls of blood vessels, capillaries, and fibroblasts. Preproopiomelanocortin (POMC) mRNA was only found in adults, and was localized to the myocardium. Message for preprodynorphin could not be observed in the ventricles of developing or adult rats. These results are the first to define the temporal and spatial ontogeny of opioid gene expression with regard to the emergence of cardiac architecture. The data suggest that gene expression for proenkephalin is especially prevalent in embryonic and neonatal rats and may be related to the modulatory activity of the opioid growth factor, [Met5]-enkephalin, on cell proliferation and differentiation. The role of PPE and POMC mRNA in adult rat heart requires elucidation.

'Cross talk' between opioid peptide and adrenergic receptor signaling in isolated rat heart

BACKGROUND

Cardiac myocyte sarcolemma contains both catecholamine and opioid peptide receptors (OPRs). Opioid peptides are coreleased with catecholamines from nerve terminals in the heart. We investigated whether OPR stimulation influences the effects of beta-adrenergic receptor (beta-AR) stimulation in the isolated, isovolumic rat heart and whether the mechanism of such an interaction involves both beta-AR subtypes or an alteration in beta-AR-mediated increase in cAMP.

METHODS AND RESULTS

Norepinephrine (NE, 10(-7) mol/L) increased peak left ventricular systolic pressure (LVSP) and cAMP more than twofold compared with controls. The delta-OPR agonist leucine-enkephalin (LE, 10(-8) mol/L) markedly inhibited the beta1-AR-induced positive inotropic effect and increase in cAMP but alone had no effect on basal LVSP or basal cAMP levels. The OPR antagonist naloxone 10(-8) mol/L added to LE+NE perfusate reversed the LE-induced decrease in cAMP and LVSP even though naloxone alone had no effect on LVSP and cAMP levels. LE could not counteract the twofold increase in LVSP produced by the nondegradable cAMP analog CPT-cAMP 2.3x10(-5) mol/L or a high concentration of forskolin (10(-7) mol/L) but did reverse the 173+/-11.8% and 135+/-13.6% increases in LVSP stimulated by 10(-8) and 0.5x10(-8) mol/L forskolin, respectively. LE inhibited cAMP production at all concentrations of forskolin (10(-7), 10(-8), and 0.5x10(-8) mol/L). Pertussis toxin (PTX) pretreatment abolished LE effects on beta1-AR stimulation. Zinterol 10(-5) and 10(-6) mol/L, a specific beta2-AR agonist that elicits a cAMP-independent inotropic effect in rat heart, caused 225+/-14% and 182+/-5% increases in LVSP that could not be reversed by addition of LE.

CONCLUSIONS

Potent, inhibitory "cross talk" between delta-OPR and beta1-AR signaling pathways occurs via a PTX-sensitive G(i/o) protein involved in adenylyl cyclase inhibition in rat heart.

Techniques for high-speed cardiac magnetic resonance imaging in rats and rabbits

Progress in research on hypertension, heart failure, aging, post-infarct remodeling, and the molecular basis of cardiovascular diseases in general has been greatly facilitated in recent years by the development of specialized small-mammal models by selective breeding and/or genetic alteration. Routine noninvasive evaluation of cardiac function and perfusion in these animals models, however, is difficult using existing methods. In principle, MRI can be used for this purpose, but in practice this is difficult because of problems related to RF coils, cardiac gating, and imaging pulse sequences. In this article, solutions to these problems are described that have allowed us to use MRI to routinely image the hearts of rats and rabbits. Specifically described are four RF coils, cardiac gating schemes, and an imaging pulse sequence specially designed for cardiac imaging in these animals on a 4.7 T Omega chemical-shift imaging (CSI) spectrometer. These techniques can be used to obtain, within 2 min, eight double-oblique short-axis images of the rat at different cardiac phases with 200 x 400 microm in-plane resolution and a slice thickness of 2 mm. Moreover, myocardial tissue tagging can be performed with tag thicknesses and separations comparable to those used routinely in humans. The technical information is presented in sufficient detail to allow researchers at other sites to reproduce the results. This information should facilitate the use of MRI for the noninvasive examination of cardiac function and perfusion, which can be combined with other established techniques for the study of cardiovascular disease in specialized animal models.

Endogenous opiates: 1994

This article is the 17th installment of our annual review of research concerning the opiate system. It includes papers published during 1994 involving the behavioral, nonanalgesic, effects of the endogenous opiate peptides. The specific topics covered this year include stress; tolerance and dependence; eating; drinking; gastrointestinal, renal, and hepatic function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunological responses; and other behaviors.