Age-dependence of noradrenaline kinetics in normal subjects

The Role of Exercise in Cardiac Aging: From Physiology to Molecular Mechanisms

Aging induces structural and functional changes in the heart that are associated with increased risk of cardiovascular disease and impaired functional capacity in the elderly. Exercise is a diagnostic and therapeutic tool, with the potential to provide insights into clinical diagnosis and prognosis, as well as the molecular mechanisms by which aging influences cardiac physiology and function. In this review, we first provide an overview of how aging impacts the cardiac response to exercise, and the implications this has for functional capacity in older adults. We then review the underlying molecular mechanisms by which cardiac aging contributes to exercise intolerance, and conversely how exercise training can potentially modulate aging phenotypes in the heart. Finally, we highlight the potential use of these exercise models to complement models of disease in efforts to uncover new therapeutic targets to prevent or treat heart disease in the aging population.

Neurogenic hyperadrenergic orthostatic hypotension: a newly recognized variant of orthostatic hypotension in older adults with elevated norepinephrine (noradrenaline)

Patients with neurogenic orthostatic hypotension (OH) typically have impaired sympathetic nervous system tone and therefore low levels of upright plasma norepinephrine (NE) (noradrenaline). We report a subset of patients who clinically have typical neurogenic OH but who paradoxically have elevated upright levels of plasma NE. We retrospectively studied 83 OH patients evaluated at the Vanderbilt Autonomic Dysfunction Center between August 2007 and May 2013. Based on standing NE, patients were dichotomized into a hyperadrenergic OH group [hyperOH: upright NE ≥ 3.55 nmol/l (600 pg/ml), n=19] or a non-hyperadrenergic OH group [nOH: upright NE < 3.55 nmol/l (600 pg/ml), n=64]. Medical history and data from autonomic testing, including the Valsalva manoeuvre (VM), were analysed. HyperOH patients had profound orthostatic falls in blood pressure (BP), but less severe than in nOH [change in SBP (systolic blood pressure): -53 ± 31 mmHg compared with -68 ± 33 mmHg, P=0.050; change in DBP (diastolic blood pressure): -18 ± 23 mmHg compared with -30 ± 17 mmHg, P=0.01]. The expected compensatory increase in standing heart rate (HR) was similarly blunted in both hyperOH and nOH groups [84 ± 15 beats per minute (bpm) compared with 82 ± 14 bpm; P=0.6]. HyperOH patients had less severe sympathetic failure as evidenced by smaller falls in DBP during phase 2 of VM and a shorter VM phase 4 BP recovery time (16.5 ± 8.9 s compared with 31.6 ± 16.6 s; P<0.001) than nOH patients. Neurogenic hyperOH patients have severe neurogenic OH, but have less severe adrenergic dysfunction than nOH patients. Further work is required to understand whether hyperOH patients will progress to nOH or whether this represents a different disorder.

Impact of age on myocardial uptake of ¹²³I-mIBG in older adult subjects without coronary heart disease

BACKGROUND

The purpose of this study was to examine the relationship between myocardial uptake of (123)I-mIBG and age in older normal adult subjects.

METHODS

94 subjects (age 29-82, mean 58.5) without coronary heart disease were studied. All subjects underwent early and delayed planar and 4-hour SPECT (123)I-mIBG imaging. (123)I-mIBG uptake was quantified as heart/mediastinum ratio on planar images (H/M p) and on SPECT images (H/M s) reconstructed by filtered backprojection, ordered subsets-expectation maximization (OSEM), and OSEM with compensation for collimator septal penetration (DSP). Relationships between age and (123)I-mIBG uptake were examined by correlation analysis, t-tests, and analysis of variance.

RESULTS

There was no significant correlation between age and H/M p, reflecting comparable increases in activity in the two regions of interest with age. Results on SPECT analyses were comparable, with no significant correlation between age and H/M s. Using DSP, (123)I-mIBG H/M s was significantly higher in subjects ≥70 of age compared with younger subjects.

CONCLUSIONS

Both cardiac and background uptake of (123)I-mIBG increase with age in older subjects without coronary heart disease, resulting in stability of H/M results (planar and SPECT). This study suggests that prognostic analyses of quantitative (123)I-mIBG uptake in patients with heart disease do not require adjustment for patient age.

Ganglion-specific impairment of the norepinephrine transporter in the hypertensive rat

Hypertension is associated with enhanced cardiac sympathetic transmission, although the exact mechanisms underlying this are still unknown. We hypothesized that defective function of the norepinephrine uptake transporter (NET) may contribute to the sympathetic phenotype of the spontaneously hypertensive rat, and that this may occur before the development of hypertension itself. The dynamic kinetics of NET were monitored temporally using a novel fluorescent assay of the transporter in cultured postganglionic sympathetic neurons from the cardiac stellate ganglion, the superior cervical ganglion, the celiac ganglia/superior mesenteric ganglia, and the renal sympathetic chain. All NET activity was blocked by desipramine. NET rate was significantly impaired in cardiac stellate sympathetic neurons from the prehypertensive spontaneously hypertensive rat compared with age-matched normotensive Wistar-Kyoto rats. A similar response was seen in hypertensive spontaneously hypertensive rats stellate sympathetic neurons. However, no reduction in transporter rate was observed at either age in the other major noncardiac sympathetic ganglia. Depolarization of cardiac stellate neurons by electrical field stimulation further potentiated the difference in transporter rate observed between the hypertensive and normotensive rats at both developmental ages. In conclusion, dysregulation of the norepinephrine transporter in the hypertensive rat is ganglion-specific, where NET impairment in the stellate neurons may contribute to the increased cardiac norepinephrine spillover seen in hypertension.

Behavioral and perceived stressor effects on urinary catecholamine excretion in adult Samoans

OBJECTIVES

The effects of perceptions and behaviors related to culturally patterned socioeconomic obligations on catecholamine excretion rates were studied in a cross-sectional sample of Samoan adults.

METHODS

A total of 378 participants, ages 29-62 years, from 9 villages throughout Samoa, provided timed overnight urine specimens, and self-reported perceptions and behaviors associated with contributions to one's family, aiga, and chief, matai, and communal gift exchanges, fa'alavelave. Urinary norepinephrine and epinephrine excretion rates were measured by high performance liquid chromatography with electrochemical detection. Age (≤40 vs. >40 years) and gender-specific regression models were estimated to detect associations with catecholamine excretion.

RESULTS

Young women who contribute more to their matai, who consider fa'alavelave to be a financial strain, and who view their contribution to their matai to be "just right," had significantly higher residence-adjusted norepinephrine excretion. Young women who contribute more to their matai, who consider fa'alavelave to be a financial strain, and who consider their contribution to their aiga not to be a burden, had higher epinephrine excretion. Older men who contribute more to their aiga and who perceive their contribution to their aiga to be "just right" had increased residence-adjusted epinephrine excretion.

CONCLUSIONS

Individual-level perceptions and behaviors related to traditional socioeconomic obligations are a significant correlate of increased overnight catecholamine excretion rates. Higher excretion rates may be attributed to psychosocial stress arousal associated with a discordance between personal desires for upward social mobility, and family and community-based socioeconomic obligations. Changes in patterns of individual-level psychosocial stress arousal may contribute to cardiovascular disease risk in modernizing Samoans.

Ecological and sociodemographic effects on urinary catecholamine excretion in adult Samoans

BACKGROUND

Ecological and sociodemographic correlates of stress may contribute to cardiovascular disease risk in modernizing Samoans.

AIM

The effects of peri-urban vs rural residence, education, occupation, caffeine intake and cigarette consumption on urinary catecholamine excretion were studied in Samoan adults.

SUBJECTS AND METHODS

Five hundred and seven participants, aged 29-69 years, were randomly selected from nine villages throughout Samoa. Sociodemographic and lifestyle factors were assessed by questionnaire. Epinephrine and norepinephrine excretion rates were measured by high performance liquid chromatography with electrochemical detection in overnight urine samples. Age ( ≤ 40 vs >40 years) and gender-specific regression models were estimated to detect associations with BMI-adjusted catecholamine excretion.

RESULTS

Norepinephrine was significantly higher in peri-urban young men and older women. Epinephrine was significantly higher in peri-urban older men. Adjustment for caffeine attenuated the relationship between residence and norepinephrine in young women.

CONCLUSION

General residential exposure to modernization in urban villages is a significant correlate of increased overnight catecholamine excretion rates and is consistent with past studies. Caffeine consumption in younger women plays a complex role in stress-related catecholamine excretion. Further studies of individual level attitudinal and behavioural factors in Samoans are needed to understand psychosocial stress, physiologic arousal and health.

The effect of rocuronium on heart rate variability in diabetic patients

BACKGROUND

Clinically rocuronium, a muscle relaxant, has no significant inhibitory effect on the autonomic nervous system in the healthy population. However, there has been no study done on rocuronium in diabetic patients. Therefore, we used heart rate variability (HRV) as a biomarker to investigate cardiac autonomic function after rocuronium administration to diabetic patients.

METHODS

In 21 diabetic adult patients, heart rate (HR), mean arterial blood pressure (BP), low frequency (LF, 0.04-0.15 Hz) power, high frequency (HF, 0.15-0.4 Hz) power, LF/HF ratio, SD1 and SD2 in the Poincare plot before induction of anesthesia, and immediately before and after rocuronium administration were calculated and compared.

RESULTS

HR, mean BP, LF, LF/HF ratio and SD2 after rocuronium administration did not differ significantly from the measurements taken before rocuronium administration. HF and SD1 decreased significantly after rocuronium administration (P = 0.022, P = 0.019 respectively). Covariates such as age, gender, weight, duration of diabetes mellitus and hypertension did not alter the effect of rocuronium on the autonomic nervous system.

CONCLUSIONS

Rocuronium produced a significant decrease in parasympathetic activity. Therefore, further study will be needed to determine whether vagal reduction caused by rocuronium could have potential to deteriorate hemodynamics in diabetic patients.

Age-dependent changes in Ca2+ homeostasis in peripheral neurones: implications for changes in function

Calcium ions represent universal second messengers within neuronal cells integrating multiple cellular functions, such as release of neurotransmitters, gene expression, proliferation, excitability, and regulation of cell death or apoptotic pathways. The magnitude, duration and shape of stimulation-evoked intracellular calcium ([Ca2+]i) transients are determined by a complex interplay of mechanisms that modulate stimulation-evoked rises in [Ca2+]i that occur with normal neuronal function. Disruption of any of these mechanisms may have implications for the function and health of peripheral neurones during the aging process. This review focuses on the impact of advancing age on the overall function of peripheral adrenergic neurones and how these changes in function may be linked to age-related changes in modulation of [Ca2+]i regulation. The data in this review suggest that normal aging in peripheral autonomic neurones is a subtle process and does not always result in dramatic deterioration in their function. We present studies that support the idea that in order to maintain cell viability peripheral neurones are able to compensate for an age-related decline in the function of at least one of the neuronal calcium-buffering systems, smooth endoplasmic reticulum calcium ATPases, by increased function of other calcium-buffering systems, namely, the mitochondria and plasmalemma calcium extrusion. Increased mitochondrial calcium uptake may represent a 'weak point' in cellular compensation as this over time may contribute to cell death. In addition, we present more recent studies on [Ca2+]i regulation in the form of the modulation of release of calcium from smooth endoplasmic reticulum calcium stores. These studies suggest that the contribution of the release of calcium from smooth endoplasmic reticulum calcium stores is altered with age through a combination of altered ryanodine receptor levels and modulation of these receptors by neuronal nitric oxide containing neurones.

Effects of life-long caloric restriction and voluntary exercise on age-related changes in levels of catecholamine biosynthetic enzymes and angiotensin II receptors in the rat adrenal medulla and hypothalamus

We examined if life-long mild caloric restriction (CR) alone or with voluntary exercise prevents the age-related changes in catecholamine biosynthetic enzyme levels in the adrenal medulla and hypothalamus. Ten-week-old Fisher-344 rats were assigned to: sedentary; sedentary+8% CR; or 8% CR+wheel running. Rats were euthanized at 6 or 24 months of age. Tyrosine hydroxylase (TH) mRNA expression was 4.4-fold higher in the adrenal medullae and 60% lower in the hypothalamus of old sedentary rats compared to young (p<0.01). Life-long CR reduced the age-related increase in adrenomedullary TH by 50% (p<0.05), and completely reversed the changes in hypothalamic TH. Voluntary exercise, however, had no additional effect over CR. Since angiotensin II is involved in the regulation of catecholamine biosynthesis, we examined the expressions of angiotensin II receptor subtypes in the adrenal medulla. AT(1) protein levels were 2.8-fold higher in the old animals compared to young (p<0.01), and while AT(1) levels were unaffected by CR alone, CR+wheel running decreased AT(1) levels by 50% (p<0.01). AT(2) levels did not change with age, however CR+wheel running increased its level by 42% (p<0.05). These data indicate that a small decrease in daily food intake can avert age-related changes in catecholamine biosynthetic enzyme levels in the adrenal medulla and hypothalamus, possibly through affecting angiotensin II signaling.

Aging alters regulation of visceral sympathetic nerve responses to acute hypothermia

Hypothermia produced by acute cooling prominently alters sympathetic nerve outflow. Skin sympathoexcitatory responses to skin cooling are attenuated in aged compared with young subjects, suggesting that advancing age influences sympathetic nerve responsiveness to hypothermia. However, regulation of skin sympathetic nerve discharge (SND) is only one component of the complex sympathetic nerve response profile to hypothermia. Whether aging alters the responsiveness of sympathetic nerves innervating other targets during acute cooling is not known. In the present study, using multifiber recordings of splenic, renal, and adrenal sympathetic nerve activity, we tested the hypothesis that hypothermia-induced changes in visceral SND would be attenuated in middle-aged and aged compared with young Fischer 344 (F344) rats. Colonic temperature (Tc) was progressively reduced from 38°C to 31°C in young (3 to 6 mo), middle-aged (12 mo), and aged (24 mo) baroreceptor-innervated and sinoaortic-denervated (SAD), urethane-chloralose anesthetized, F344 rats. The following observations were made. 1) Progressive hypothermia significantly ( P < 0.05) reduced splenic, renal, and adrenal SND in young baroreceptor-innervated F344 rats. 2) Reductions in splenic, renal, and adrenal SND to progressive hypothermia were less consistently observed and, when observed, were generally attenuated in baroreceptor-innervated middle-aged and aged compared with young F344 rats. 3) Differences in splenic, renal, and adrenal SND responses to reduced Tc were observed in SAD young, middle-aged, and aged F344 rats, suggesting that age-associated attenuations in SND responses to acute cooling are not the result of age-dependent modifications in arterial baroreflex regulation of SND. These findings demonstrate that advancing chronological age alters the regulation of visceral SND responses to progressive hypothermia, modifications that may contribute to the inability of aged individuals to adequately respond to acute bouts of hypothermia.

Age and ethnicity differences in short-term heart-rate variability

OBJECTIVE

Hypertension is more frequent and more severe in older individuals and in African Americans. Differences in autonomic nervous system activity might contribute to these differences. Autonomic effects on the heart can be studied noninvasively through analysis of heart rate variability (HRV). We examined the effects of age and ethnicity on HRV.

METHODS

We studied 135 subjects (57 African Americans and 78 Caucasian Americans), aged 23 to 54 years. Using their surface electrocardiogram (ECG) data, we calculated the HRV indices with spectral analyses. High frequency (HF) power was used to index parasympathetic activity, whereas the ratio of low to high frequency power (LF/HF) was used to index sympathovagal balance.

RESULTS

Three HRV indices (HF, LF power, and LF/HF) were significantly related to age in Caucasian Americans but not in African Americans. The effect of age, ethnicity, and the age-by-ethnicity interaction on HF and LF power was significant, even after controlling for gender, body mass index, and blood pressure.

CONCLUSIONS

Young African Americans manifested a pattern of HRV response similarly to older Caucasian Americans. These results suggest that young African American individuals might show signs of premature aging in their autonomic nervous system.

Sympathetic nerve function--assessment by radioisotope dilution analysis

Radioisotope dilution measurements of norepinephrine spillover (rate of entry of the transmitter into plasma) provide more accurate assessments of sympathoneural transmitter release than allowed by measurements of plasma catecholamine concentrations alone. Measurements of total body norepinephrine spillover, as an index of global sympathetic outflow, allow effects on plasma clearance to be distinguished from effects on release of catecholamines into plasma, while spillovers from specific tissues enable examination of regionalized sympathetic responses. However, spillovers of norepinephrine represent only a fraction of the transmitter that escapes neuronal and extraneuronal uptake after release by nerves. Numerous factors may influence this fraction and measures spillovers independently of transmitter release by nerves. Modified radioisotope dilution methods for assessment of rate processes operating within and between intracellular and extracellular compartments have further improved our understanding of the relationships of norepinephrine release, uptake, spillover, turnover, and metabolism. This article reviews the breadth of information about sympathetic nerve function attainable using catecholamine radioisotope dilution analyses against a backdrop of the relative advantages and methodological limitations associated with the methodology.

Unchanged G-protein-coupled receptor kinase activity in the aging human heart

OBJECTIVES

We sought to find out whether G-protein-coupled receptor kinase (GRK) activity is also increased in the aging human heart.

BACKGROUND

In the aging and failing human heart, cardiac beta-adrenoceptors (beta-AR) are desensitized. In heart failure (HF), an increase in cardiac GRK activity considerably contributes to this beta-AR desensitization.

METHODS

We assessed GRK activity (by in vitro rhodopsin phosphorylation) in the right atria (RA) from 16 children (mean age 9 +/- 2 years) and 17 elderly patients (mean age 67 +/- 2 years) without apparent HF and in the RA from four patients with end-stage HF.Cytosolic and membranous GRK activities in the RA from children were not significantly different from those in elderly patients; in contrast, cytosolic and membranous GRK activities in the RA from patients with end-stage HF were significantly increased.

CONCLUSIONS

In contrast to the failing human heart, in the aging human heart, GRK activity is not increased. Thus, GRK activity appears to not play an important role in beta-AR desensitization in the aging human heart.

The cardiovascular system

The ageing process is associated with important changes in the responses of the cardiovascular system to pharmacological stimuli. They are not limited to the arterial system, involved in the modulation of cardiac afterload and vascular resistance, but they also involve the low-resistance capacitance venous system and the heart. The main changes include loss of large artery compliance, dysfunction of some of the systems modulating resistance vessel tone, increased activity of the sympathetic nervous system, and reduced haemodynamic responses to inotropic agents. This review focuses on the effects of ageing on arterial and venous reactivity to drugs and hormones, the autonomic nervous system, and the cardiovascular responses to inotropic agents. Some of the age-related changes might be at least partially reversible. This may have important therapeutic implications.

Host and environmental determinants of heart rate and heart rate variability in four European populations

OBJECTIVE

In a population-based sample of nuclear families recruited in the framework of the European Project on Genes in Hypertension (EPOGH), we investigated the association between heart rate (HR) and its variability (HRV), and gender, age, posture, breathing frequency, body mass index, systolic blood pressure, family history of hypertension and various lifestyle factors, such as smoking, alcohol and coffee consumption and physical activity.

METHODS

RR interval and respiration were registered in the supine and standing positions (15 min each) in 1208 subjects in Bucharest (Romania, n= 267), Cracow (Poland, n= 323), Mirano (Italy, n= 323) and Novosibirsk (Russian Federation, n= 295). After exclusion of 199 participants on antihypertensive treatment and/or patients with diabetes mellitus (n= 40) or myocardial infarction (n= 4), 993 subjects were eligible for analysis. We evaluated 858 participants with high-quality recordings. Using fast Fourier transform, we decomposed HRV into low-frequency (LF: 0.04-0.15 Hz) and high-frequency (HF: 0.15-0.40 Hz) components, which were expressed in normalized units.

RESULTS

Mean values were 35.3 years for age, 24.3 kg/m for body mass index (BMI) and 121.0/77.2 mmHg for blood pressure. The group included 462 (53.8%) women. Across four centres, HR and HRV were similarly and independently associated with gender, age and postural position (P <0.001). In the supine position, HR was higher in women than men (67.2 versus 63.7 bpm). Men had higher normalized LF power than women (48.8 versus 41.5), but lower HF power (40.6 versus 47.4). The normalized HF power decreased with age (r = -0.43), whereas LF power increased (r = 0.32). On standing, HR increased (83.3 versus 65.6 bpm), normalized HF power declined (19.2 versus 44.3) and LF power increased (67.4 versus 44.9). The independent effects of respiration frequency, systolic blood pressure, family history of hypertension, body mass index and lifestyle factors on HRV differed between populations, and explained no more than 8% of the total variance.

CONCLUSIONS

Across four European populations, gender, age and posture were consistent and independent correlates of HR and HRV. Lifestyle seems to have small but varying influences on HR and/or HRV, probably depending on the environmental and cultural background of the population under study.

Age-dependent changes of cardiac neuronal noradrenaline reuptake transporter (uptake1) in the human heart

OBJECTIVES

The purpose of this study was to elucidate whether the neuronal noradrenaline reuptake transporter (uptake1) undergoes age-dependent regulation in the human heart.

BACKGROUND

Aging is associated with various alterations in cardiovascular function.

METHODS

We determined uptake1 density (by [3H]-nisoxetine binding to membranes) and activity (by accumulation of [3H]-noradrenaline into tissue slices) in the right atria (RA) of 42 patients (age range 3 months to 76 years) undergoing open-heart surgery without apparent heart failure. Moreover, the effects of 1 micromol/l desipramine on the noradrenaline-induced positive inotropic effect were assessed in the isolated, electrically driven RA trabeculae of these patients.

RESULTS

There was a significant negative correlation between RA uptake1 density and age; moreover, RA uptake1 activity was significantly reduced in elderly patients. Desipramine (1 micromol/l) significantly shifted noradrenaline concentration-response curves to the left; this shift was significantly more pronounced in younger patients than in older patients.

CONCLUSIONS

With increasing age, human myocardial uptake1 activity decreases, possibly because of age-dependent downregulation of uptake1 density.

Aging and calcium buffering in adrenergic neurons

The aging process at the cellular, organ and whole organism levels is in many respects a mystery. A common bias among those who study aging is that cellular homeostasis "generally falls apart". The assumption of a general deterioration in cellular homeostasis does not take into account that many individuals age quite well maintaining even robust physiological and mental functions. One facet of aging studies that has come to the forefront is the impact of age on the control of the ion messenger, calcium. Emerging evidence suggests that despite age-related declines in any one component or multiple components of the calcium buffering systems, compensatory mechanisms may be able to maintain overall calcium homeostasis. This brief review focuses specifically on the ability of peripheral neurons to maintain control of the ion messenger calcium with advancing age. In addition, the idea that the impact of age on calcium homeostasis may be more subtle due to complex and integrated mechanisms that control this ion is discussed.

Ketanserin versus urapidil: age-related cardiovascular effects in conscious rats

To examine whether serotonin (5-hydroxtryptamine, 5-HT)-mediated mechanisms for regulating blood pressure are influenced by advancing age, the cardiovascular effects of ketanserin and urapidil were compared in two groups of conscious rats at ages 4 (young) and 24 (old) months. Old rats had higher mean pressures but the same basal heart rates as young rats prior to drug treatment. Subsequent treatment with either ketanserin or urapidil produced similar cardiovascular effects. Both drugs in doses of 10 mg/kg i.v., lowered mean pressures more markedly in old than in young rats, and the larger hypotensive response in old rats was statistically significant even when expressed as percent reductions. Because drug treatment abolished the mild hypertension initially present in old rats, ensuing blood pressure levels no longer differed between age groups. On the other hand, neither drug had any appreciable effects on basal heart rate or angiotensin-induced reflex bradycardia at any age. Consequently, hypotensive enhancement in old rats cannot be due to age-related changes in reflex bradycardia. Inasmuch as ketanserin and urapidil, despite their differing modes of action on 5-HT receptors, were both equally adept at lowering blood pressure more in old rats, these results suggest that enhancement occurs selectively only with 5-HT-mediated hypotension. Thus, unlike other antihypertensive drugs (like prazosin or lisinopril) whose modes of action do not include 5-HT mediation and whose hypotensive effects do not increase with age, our results suggest that hypotensive responses to ketanserin and urapidil are selectively enhanced because of their actions on 5-HT receptors.

The process of aging changes the interplay of the immune, endocrine and nervous systems

The immune, endocrine and nervous systems interact with each other by means of cytokines, hormones and neurotransmitters. Interaction is dependent on specific receptors and respective signaling pathways in target cells. During aging, changes occur on many levels of these global systems which depend on oxidative damage, non-enzymatic glycosylation, mitochondrial mutations, defects in cell cycle control, mitotic dysregulation, genome instability, telomere shortening and other chromosomal pathologies. An alteration of the numerical value of a parameter of one system can lead to changes of the numerical value of a variable of another system. In a non-linear dynamic process these changes can contribute to the aging phenotype. Although it is extremely difficult to dissect linear interrelations of three global systems during aging, this review attempts to identify some simple linear pathways. Furthermore, it is demonstrated that chronic inflammatory diseases may accelerate the aging process. This review also reveals that new statistical and computational methods are necessary to unravel the complexity of the aging process.

The role of neuronal and extraneuronal plasma membrane transporters in the inactivation of peripheral catecholamines

Catecholamines are translocated across plasma membranes by transporters that belong to two large families with mainly neuronal or extraneuronal locations. In mammals, neuronal uptake of catecholamines involves the dopamine transporter (DAT) at dopaminergic neurons and the norepinephrine transporter (NET) at noradrenergic neurons. Extraneuronal uptake of catecholamines is mediated by organic cation transporters (OCTs), including the classic corticosterone-sensitive extraneuronal monoamine transporter. Catecholamine transporters function as part of uptake and metabolizing systems primarily responsible for inactivation of transmitter released by neurons. Additionally, the neuronal catecholamine transporters, recycle catecholamines for rerelease, thereby reducing requirements for transmitter synthesis. In a broader sense, catecholamine transporters function as part of integrated systems where catecholamine synthesis, release, uptake, and metabolism are regulated in a coordinated fashion in response to the demands placed on the system. Location is also important to function. Neuronal transporters are essential for rapid termination of the signal in neuronal-effector organ transmission, whereas non-neuronal transporters are more important for limiting the spread of the signal and for clearance of catecholamines from the bloodstream. Besides their presynaptic locations, NET and DAT are also present at several extraneuronal locations, including syncytiotrophoblasts of the placenta and endothelial cells of the lung (NET), stomach and pancreas (DAT). The extraneuronal monoamine transporter shows a broad tissue distribution, whereas the other two non-neuronal catecholamine transporters (OCT1 and OCT2) are mainly localized to the liver, kidney, and intestine. Altered function of peripheral catecholamine transporters may be involved in disturbances of the autonomic nervous system, such as occurs in congestive heart failure and hypernoradrenergic hypertension. Peripheral catecholamine transporters provide important targets for clinical imaging of sympathetic nerves and diagnostic localization and treatment of neuroendocrine tumors, such as neuroblastomas and pheochromocytomas.

Human ageing and the sympathoadrenal system

Over the past three decades the changes in sympathoadrenal function that occur with age in healthy adult humans have been systematically studied using a combination of neurochemical, neurophysiological and haemodynamic experimental approaches. The available experimental evidence indicates that tonic whole-body sympathetic nervous system (SNS) activity increases with age. The elevations in SNS activity appear to be region specific, targeting skeletal muscle and the gut, but not obviously the kidney. The SNS tone of the heart is increased, although this appears to be due in part to reduced neuronal reuptake of noradrenaline (norepinephrine). In contrast to SNS activity, tonic adrenaline (epinephrine) secretion from the adrenal medulla is markedly reduced with age. This is not reflected in plasma adrenaline concentrations because of reduced plasma clearance. Despite widely held beliefs to the contrary, sympathoadrenal responsiveness to acute stress is not exaggerated with age in healthy adults. Indeed, adrenaline release in response to acute stress is substantially attenuated in older men. The mechanisms underlying the age-associated increases in SNS activity have not been established, but our preliminary data are consistent with increased subcortical central nervous system (CNS) sympathetic drive. These changes in sympathoadrenal function with advancing age may have a number of important physiological and pathophysiological consequences for human health and disease.

Increased plasma norepinephrine response to yohimbine in elderly men

BACKGROUND

The effects of aging on sympathetic nervous system and adrenomedullary outflow were estimated by the measurement of plasma norepinephrine (NE) and epinephrine (EPI) responses to yohimbine and clonidine in healthy young and healthy older subjects.

METHODS

Yohimbine (0.65 mg/kg), clonidine (5 microg/kg), and placebo were administered on separate days in random order to 5 healthy older men (age 74 +/- 1 years) and 18 healthy young men (age 26 +/- 1 years). NE and EPI were measured by radioenzymatic assay in plasma samples obtained before and 30, 60, and 90 minutes after drug administration.

RESULTS

Plasma NE increases after yohimbine were greater in older men than in young men. but plasma NE decreases following clonidine did not differ between groups. Plasma NE and systolic blood pressure were higher in older men than in young men at baseline but no longer differed 90 minutes after clonidine. Plasma EPI increases after yohimbine and decreases after clonidine did not differ between groups.

CONCLUSIONS

These results suggest increased sympathetic nervous system outflow in human aging that is not a function of reduced responsiveness of alpha-2 adrenoreceptor-mediated feedback inhibition.

The sympathetic nervous system and baroreflexes in hypertension and hypotension

Blood pressure and blood volume are closely regulated by the interrelated actions of the sympathetic nervous system (SNS) and the renin-angiotensin-aldosterone system (RAAS). Reflex vasoconstriction caused by parallel SNS and RAAS activation is modulated by two interactive negative feedback systems called baroreflex. The aortic-carotid baroreflex systems respond to momentary changes in systolic blood pressure, adjusting the degree of SNS-dependent peripheral vasoconstriction and cardiac output to allow maintenance of a relatively constant perfusion pressure. Cardiopulmonary baroreflexes respond to momentary changes in cardiac filling, adjusting the degree of peripheral venoconstriction and venous return to maintain cardiac preload and stroke volume. Under normal conditions, each baroreflex system exhibits a degree of tonic negative feedback so that it can alter SNS output immediately, providing counterregulatory increases or decreases in pressure or volume to maintain homeostasis. The SNS is inappropriately active in obesity and hypertension and plays a causal or permissive role in all forms of chronic hypertension. If the negative feedback control exerted by the baroreflexes over the SNS and renin-angiotensin-aldosterone system (RAAS) were perfect, chronic hypertension would not occur. Activity of the baroreflexes, however, is chronically altered by maladaptive changes such as cardiac and vascular fibrosis and hypertrophy. Long-term increases in SNS and RAAS activity also exert ongoing deleterious effects on the heart and vasculature by directly facilitating further cardiac hypertrophy and arterial stiffening. These effects appear to contribute to a vicious cycle of chronic hypertension and target organ damage. Other syndromes of abnormal blood pressure (BP) control, including orthostatic hypotension and baroreflex failure are examples of abnormal baroreflex activity and SNS control.

Reduced epinephrine clearance and glycemic sensitivity to epinephrine in older individuals

To test the hypothesis that glycemic sensitivity to epinephrine is reduced in older individuals and to assess the impact of a sedentary lifestyle on responses to the hormone, we performed 30-min sequential intravenous infusions of epinephrine (0, 41, 82, 164, 246, and 328 pmol. kg-1. min-1) in young (n = 10) and older (n = 23) healthy subjects. We performed these again after 12 mo of physical training, which raised peak O2 consumption from 24.4 +/- 1.0 to 30.4 +/- 1.4 ml. kg-1. min-1 (P < 0.01) in most of the older subjects (n = 21). During epinephrine infusions, plasma epinephrine concentrations were higher (P = 0.0001) in older than in young subjects (e.g., final values of 7,280 +/- 500 vs. 4,560 +/- 380 pmol/l, respectively), indicating that the clearance of epinephrine from the circulation was reduced in the older individuals. Plasma epinephrine concentration-response curves disclosed reduced glycemic sensitivity to the hormone in the older subjects (P = 0.0001), a finding plausibly attributed to increased sympathetic neural activity, as evidenced here by higher plasma norepinephrine concentrations (P = 0.0001) in the older subjects and consequent desensitization of cellular responsiveness to catecholamines. Training did not correct reduced epinephrine clearance, reduced glycemic sensitivity to epinephrine, or raised norepinephrine levels. We conclude that aging is associated with reduced clearance of epinephrine from the circulation and reduced glycemic sensitivity to epinephrine, the latter plausibly attributed to an age-associated increase in sympathetic neural norepinephrine release. These age-associated changes are not the result of a sedentary lifestyle.

Norepinephrine kinetics in older women: relationship to physical activity and blood pressure

The sympathetic nervous system participates in the regulation of carbohydrate, lipid, and energy metabolism, and has been implicated in the pathogenesis of hypertension and obesity. Increased sympathetic nervous system activity with age may alter disease risk and contribute to the development of certain chronic diseases. Thus, we examined possible determinants of sympathetic nervous system activity in older normotensive women from infusions of tritiated norepinephrine (NE) to estimate rates of norepinephrine appearance and clearance. A secondary aim was to examine the association between norepinephrine kinetics and mean supine arterial blood pressure. Twenty-two older women (65.7 +/- 5.7 years) were characterized for resting NE kinetics, body composition, body fat distribution, peak aerobic capacity, leisure time physical activity energy expenditure (LTA), dietary carbohydrates, and daily energy intake. Analysis of univariate correlations revealed that only the LTA was significantly correlated with plasma NE appearance (r = 0.54, p < 0.01). Stepwise regression analysis identified LTA as the only significant predictor of plasma NE appearance rate with a total R2 = 0.29. The waist-to-hip ratio was selected as the only significant predictor of mean arterial blood pressure with an R2 = 0.30. When forced into the model, plasma NE appearance explained only 1% of the unique variance in mean arterial blood pressure. In summary, we found that: (1) higher levels of physical activity are related to higher plasma NE appearance in older women; (2) greater central body fatness is an independent predictor of mean arterial blood pressure; and (3) plasma NE appearance rate is a minor contributor to variation in mean arterial blood pressure in older, normotensive women.

Measurement and prediction of sympathetic nervous system activity in humans

The measurement of norepinephrine (NE) kinetics has broadened our understanding of sympathetic nervous system activity involvement in energy expenditure, blood pressure regulation and substrate utilization. This methodology, however, has several disadvantages that include administration of radioactivity to volunteers, its expense, and time consuming laboratory analyses. Thus, we developed an equation to predict plasma NE appearance rate (NEAP) derived from infusions of tritiated norepinephrine performed in 113 healthy men (18-78 yr.). The accuracy of the equation was tested using cross-validation procedures. Age, fat mass, plasma [NE], waist circumference, and body weight (BW) correlated significantly with plasma NE appearance rate. The resulting prediction equation in the validation group was: NEAP = 0.00003148 BW [NE], with R2 = 0.76 and was successfully cross-validated. Using pooled data from both groups the prediction equation was: NEAP (microg/min) = 0.00003108 x [NE (pg/ml)] x [Body weight (kg)] with an R2 = 0.70 and SEE = 0.096 microg/min. The magnitude of error associated with this equation allows for detection of age-associated, exercise-induced changes and blood pressure-related differences in plasma NE appearance rate published in the literature. We provide an equation that offers a relatively simple and accurate alternative to estimate plasma NE appearance from the measurement of arterialized plasma [NE] and body weight.

Impact of age on modulation of norepinephrine release from sympathetic nerves in the rat superior mesentery artery

There is an age-related increase in stimulation-evoked fractional norepinephrine release in tail arteries of Fischer 344 rats from 6-20 months of age. Previous studies have ruled out changes in the function of uptake and subsequent metabolism mechanisms, or feedback by prejunctional alpha2-adrenoceptors. The tail artery is important in thermoregulation, and there is the possibility that the previously observed increase in sympathetic nerve activity is due to age-related changes in thermoregulation as opposed to a fundamental age-related change in the regulation of sympathetic nerves. Thus, we measured stimulation-evoked norepinephrine release in another blood vessel model, the superior mesentery artery using HPLC with electrochemical detection. In this study fractional norepinephrine release was measured under three separate conditions, drug free Krebs'; in the presence of deoxycorticosterone and cocaine; in the presence of deoxycorticosterone and cocaine and the alpha2-adrenergic receptor antagonist, idazoxan. The most significant finding was that fractional norepinephrine release in mesentery arteries from 20-month-old animals was higher as compared to 6 months regardless of treatment condition. Furthermore, the elevation in norepinephrine release cannot be accounted for by changes in norepinephrine content, uptake and subsequent metabolism mechanisms or changes in basal norepinephrine release. These data from the mesentery artery model confirm and support our previous work in the rat tail artery model. In addition, the data from this study suggest the possibility that there are common mechanisms underlying the age-related increase in peripheral sympathetic nerve activity.

Psychological stress does not affect plasma catecholamines in subjects with cardiovascular disorder

Whereas the effects of cardiac transplantation on the catecholamine response to physical exercise have been studied previously, the impact on psychological stress is unknown. Here, the arterial catecholamine response to the Stroop test of patients with an orthotopic heart transplant (OHT) was compared with that in subjects who had received a coronary artery bypass graft (CABG) or who were in heart failure and destined for a heart transplant (HF). Subjects were tested whilst sitting and their usual drug therapy was maintained. The Stroop test increased subjects' subjective tension but did not affect arterial concentrations of adrenaline or noradrenaline in any group of subjects. Also, the concentration of both catecholamines was significantly higher in OHT and CABG subjects than in the HF group, but their relative concentration was unaffected by cardiovascular status or stress. It is concluded that the absolute concentrations of arterial catecholamines, but not their relative concentrations, depend on clinical status. Moreover, under these test conditions, subjects with a history of cardiovascular disorder do not show the normal catecholamine response to psychological stress.

Regulation of Peripheral Catecholamine Responses to Acute Stress in Young Adult and Aged F-344 Rats

Young adult (3-month-old) and aged (24-month-old) Fischer-344 male rats received i.v. infusions of 3H-labeled norepinephrine (NE) and epinephrine (EPI) to examine the effects of aging on the neuronal uptake of NE and sympathoadrenal release of NE and EPI. Spillovers of NE and EPI into plasma and their clearance from the circulation were estimated from plasma concentrations of endogenous and 3H-labeled NE and EPI. The efficiency of neuronal uptake was assessed from changes in plasma clearance of NE and concentrations of its intraneuronal metabolite, dihydroxyphenylglycol (DHPG), during immobilization stress or neuronal uptake blockade with desipramine. Stress-induced increases in plasma NE and higher plasma NE concentrations in aged compared to young adult rats were due to both decreases in NE clearance and increases in NE spillover. EPI spillover and clearance were reduced in aged compared to young adult rats, so that plasma EPI levels did not differ between groups. Young adult and aged rats had similar desipramine-induced decreases in NE clearance, whereas desipramine-sensitive decreases and stress-induced increases in plasma DHPG were larger in aged rats. This indicates that neuronal uptake is intact and that increased NE spillover at rest and during stress in aged rats reflects increased NE release from sympathetic nerves. The results show that aging is associated with divergent decreases in EPI release from the adrenal medulla and increases in NE release from sympathetic nerves. Increased plasma concentrations of NE in aged compared to young adult rats also result from decreased circulatory clearance of NE, but this does not reflect any age-related impairment of NE reuptake.

Alpha-2 adrenergic activity in perimenopausal women

Lipid alterations and increased blood pressure may occur during perimenopause. No data are available in perimenopausal women on the alpha-2 adrenergic activity which affects norepinephrine secretion. We studied cardiovascular and catecholamine responses to clonidine (300 mg per os) in a group of 15 perimenopausal women (PeriMW) and in a control group of 13 premenopausal women (PreMW). Nine of the perimenopausal women were also studied after 4-month percutaneous estrogen replacement therapy (PeriMWE). Systolic and diastolic blood pressure (SBP, DBP), heart rate (HR), plasma norepinephrine (NE) and epinephrine (E) were evaluated before and at 120 min, 130 min, 140 min after clonidine administration. Basal values of SBP, DBP and HR were not different (F = 0.7, p = NS; F = 0.2, p = NS and F = 0.1, p = NS respectively) between PeriMW both before and after therapy and PreMW. Resting levels of E were similar in PreMW and in PeriMW before and during estrogen therapy (F = 0.8, p = NS); PeriMW showed higher basal NE levels both before and during estrogen therapy than PreMW (F = 12; p < 0.001). Clonidine administration decreased SBP, DBP and NE levels in PreMW, in PeriMW and in PeriMWE without any difference between the groups (F = 1.2, p = NS; F = 0.5, p = NS and F = 1.3, P = NS respectively). HR decreased significantly after clonidine in PreMW (F = 5.4, p < 0.03) but not in PeriMW before (F = 1.0, p = NS) and during estrogen therapy (F = 0.5, p = NS). Clonidine did not affect plasma E in the three groups studied (F = 2.8, p = NS; F = 2.2, P = NS and F = 0.1, p = NS). The present study demonstrates that increased basal plasma NE levels are present in PeriMW. The cardiovascular and catecholamine response to clonidine in PeriMW both before and during estrogen therapy are similar to those observed in PreMW, suggesting a normal inhibitory alpha-2 receptor pathway.

Norepinephrine spillover at rest and during submaximal exercise in young and old subjects

Aging is associated with elevations in plasma norepinephrine concentrations. The purpose of this investigation was to examine total body and regional norepinephrine spillover as an indicator of sympathetic nerve activity. Eight young (26 +/- 3 yr) and seven old (69 +/- 5 yr) male subjects were studied at rest and during 20 min of submaximal cycling exercise at 50% of peak work capacity. Norepinephrine spillover was determined by continuous intravenous infusion of [3H]norepinephrine. Arterial norepinephrine concentrations were significantly greater at rest for old vs. young subjects (280 +/- 36 vs. 196 +/- 27 ng/ml, respectively). Whereas total norepinephrine spillover did not differ between groups at rest, hepatomesenteric norepinephrine spillover was 50% greater in old subjects compared with their young counterparts (51 +/- 7 vs. 34 +/- 5 ng/min, respectively). Additionally, norepinephrine clearance rates at rest were significantly lower for the old subjects (-23%). During exercise, plasma norepinephrine concentrations increased compared with rest, with old subjects again demonstrating greater values than the young group. Hepatomesenteric norepinephrine spillover was significantly greater (+36%) during exercise for old subjects compared with young; however, no difference was found for whole body spillover rates between age groups. Norepinephrine clearance rates remained depressed (-80%) in the old subjects during exercise. Clearance of epinephrine mirrored that for norepinephrine both at rest and during exercise across age groups. It was concluded that in old subjects, a reduction in norepinephrine clearance and an increase in regional norepinephrine spillover can account for the higher plasma norepinephrine concentrations observed at rest. This relationship is not exacerbated by the stress imposed during an acute bout of exercise.

Induction of tyrosine hydroxylase by forskolin: modulation with age

With aging, circulating catecholamines are elevated in both humans and animals. This may be related to the increased basal levels of tyrosine hydroxylase messenger RNA (mRNA) levels and tyrosine hydroxylase enzyme activity in the adrenal medulla of senescent compared with younger animals. In addition, tyrosine hydroxylase gene expression in the senescent rat is resistant to further stimulation by cold exposure as compared with younger animals. Collectively, these observations suggest either that tyrosine hydroxylase expression is already maximally stimulated in senescent rats or that tyrosine hydroxylase gene induction pathways are impaired with senescence. To help distinguish between these possibilities, we examined the induction of tyrosine hydroxylase mRNA, tyrosine hydroxylase immunoreactivity and tyrosine hydroxylase enzyme activity in the adrenal medulla following forskolin administration to young and old F-344 rats. Forskolin at doses of 1.8 and 3.5 mg/kg increased tyrosine hydroxylase mRNA levels 2.5-fold in adrenal medulla from young rats but did not increase either tyrosine hydroxylase immunoreactivity or tyrosine hydroxylase enzyme activity 5 h after administration. Prolonged treatment with forskolin (3 doses, 12 h apart) increased tyrosine hydroxylase mRNA levels and tyrosine hydroxylase immunoreactivity and tyrosine hydroxylase enzyme activity. In senescent rats, the baseline level of tyrosine hydroxylase mRNA was more than 2-fold higher compared with young rats. A single injection of the lower dose of forskolin increased tyrosine hydroxylase mRNA levels by the same increment in senescent as compared with young rats. These data indicate that the tyrosine hydroxylase gene in the adrenal medulla from senescent rats is still capable of further stimulation.

Oxygen consumption in the heart, hepatomesenteric bed, and brain in young and elderly human subjects, and accompanying sympathetic nervous activity

Although the reduction in whole-body energy expenditure with aging has been well documented, there is little information about the changes that individual organs undergo. We therefore measured oxygen consumption in the heart, hepatomesenteric bed, and brain in elderly subjects and young controls, using central venous catheter techniques and the application of Fick's principle. We also measured whole-body, cardiac, and hepatomesenteric sympathetic nervous activity using isotope dilution methodology. Cardiac, hepatomesenteric, and cerebral oxygen consumption was similar in both groups. Whole-body and hepatomesenteric sympathetic nervous activity was also similar in the study groups, whereas cardiac norepinephrine (NE) spillover was significantly higher in the elderly. In contrast to the young, cardiac sympathetic nervous activity as assessed from NE spillover was not related to either cardiac oxygen consumption or cardiac work in the elderly. The data suggest that although oxygen consumption in the heart, hepatomesenteric bed, and brain are not different between young and elderly individuals, the relationship between sympathetic nervous activity and oxygen consumption in individual organs may alter with aging.

Advancing age alters intracellular calcium buffering in rat adrenergic nerves

There is a marked increase with advancing age of stimulation-evoked neurotransmitter release from vascular adrenergic nerves in the rat, an effect correlated with increased levels of plasma norepinephrine. This increase in norepinephrine release could not be accounted for by an alteration in neuronal and extraneuronal uptake of norepinephrine or a decline in feedback inhibition of release by prejunctional alpha2-adrenergic receptors. Measurement of intracellular calcium in fura-2-labeled superior cervical ganglion cells revealed elevated K+-evoked calcium transients in old compared to young neurons. Blockade of mitochondrial calcium uptake with dinitrophenol resulted in increased calcium transients in old neurons only. Furthermore, following blockade of mitochondrial calcium uptake the rate of return of calcium to resting levels was reduced to a greater degree in old cells as compared to young cells. The effects of dinitrophenol in old cells were attenuated when extracellular calcium was reduced. These findings suggest that older cells are more dependent on mitochondrial calcium buffering, perhaps due to changes in ATP dependent calcium uptake. Increased calcium transients as a result of altered intracellular calcium buffering offer a reasonable explanation for our previous observation of increased stimulation evoked norepinephrine release.

Hypotensive and reflex bradycardic effects of ketanserin, but not of prazosin, enhanced selectively in aging conscious rats

To determine whether cardiovascular effects of ketanserin are altered differently with aging as compared with those of prazosin, we recorded blood pressure (BP) and heart rate (HR) changes produced by treatment with either drug in three age groups of conscious Sprague-Dawley rats. BP was decreased more by ketanserin in 24-month than in 4- or 14-month-old rats, but was decreased equally by prazosin in all age groups. Pressor responses to phenylephrine (PE) were consistently abolished by both drugs, indicating that the greater hypotensive effects of ketanserin in 24-month-old rats were not due simply to alpha 1-adrenergic blockade. By contrast, baroreflex sensitivity, determined from reflex HR responses to infused angiotensin or sodium nitroprusside (SNP), was altered differently in old rats by ketanserin but not by prazosin. Whereas enhancement of reflex bradycardia by prazosin occurred at all ages, it was demonstrable only with ketanserin in older rats. Moreover, reflex tachycardia was unaffected by prazosin but was reversed to bradycardia by ketanserin in older rats. Because these differences persisted even after the data had been normalized to compensate for differences in baseline pressures, effects on HR reflexes were considered age dependent for ketanserin but not for prazosin. Although the underlying mechanisms are not clear, the selective enhancement of reflex bradycardia and reversal of reflex tachycardia in old rats by ketanserin, but not by prazosin, could explain why hypotensive responses to ketanserin increase with age whereas those to prazosin do not.

Evidence for decline in intracellular calcium buffering in adrenergic nerves of aged rats

Age-related alterations in neuronal intracellular calcium regulation and neurotransmitter release have been widely reported. We have investigated the impact of age on neurotransmitter release and intracellular calcium buffering in adrenergic nerve endings of the isolated rat tail artery and on intracellular calcium in acutely dissociated cells from the superior cervical ganglion. Advancing age, from 6 to 27 months, resulted in significantly increased stimulation-evoked norepinephrine release from the isolated rat tail artery, an effect which persisted when neuronal and extraneuronal uptake were blocked with cocaine and deoxycorticosterone and presynaptic alpha adrenergic receptors were blocked with idazoxan. Alterations in extracellular calcium had significant effects on stimulation-evoked norepinephrine release, but these were much more marked in old, compared to young, arteries. Blockade of mitochondrial calcium accumulation with dinitrophenol had no significant effect on stimulation-evoked norepinephrine release from 6-month-old arteries, but in 20-month-old arteries, treatment with dinitrophenol resulted in a substantial increase in stimulation-evoked norepinephrine release. However, when extracellular calcium was increased to 5 mM in 6 month-old-arteries, then addition of dinitrophenol resulted in an increase in stimulation-evoked norepinephrine release. Measurement of intracellular calcium in acutely dissociated superior cervical ganglion cells using fura-2 revealed substantial age-related differences. Peak calcium transients in 20-month-old ganglion cells depolarized with 68 mM K+ were substantially higher than in 6-month-old cells. Together these findings support the hypothesis that in adrenergic nerves advancing age results in a disruption of intracellular calcium buffering leading to higher levels of intracellular calcium and increased transmitter release.

Sympathoadrenal activity and psychosocial stress. The significance of aging, long-term smoking, and stress models

Recent studies have indicated that the increase in plasma norepinephrine and sympathetic activity with aging in healthy subjects is largely due to long-term cigarette smoking. In patients who have or have had duodenal ulcer the increase in plasma norepinephrine with age was markedly increased. These patients as a group perceive their lives somewhat more stressful than the general population and they tend to die prematurely due to smoking-associated diseases. These patients may select dysfunctional coping strategies like smoking, which may result in organ pathologies and a compensatory increase in plasma norepinephrine. No close correlation has been established between plasma epinephrine and "ill health." High plasma epinephrine levels may have a deleterious effect on the cardiovascular system in elderly subjects during certain conditions. In a population study, we found, however, that low resting plasma epinephrine levels were associated with an unfavorable survival rate. We speculate that an inadequate response to psychosocial stress and the choice of dysfunctional coping strategies may be more harmful and cause more "ill health" than hypersecretion of stress hormones like epinephrine and cortisol, which has been the traditional view. We suggest that there are different stress states. Stress hormones like epinephrine and cortisol may play a major role during situations like combat, illness, and strenuous exercise. In response to psychosocial stress, dysfunctional coping strategies are, however, largely responsible for harmful effects of stress.

Effects of age and endurance training on beta-adrenergic receptor characteristics in Fischer 344 rats

The purpose of this investigation was to examine changes in beta-adrenergic receptor characteristics in various tissues with age and endurance training. Forty-eight young (6 months), middle-aged (15 months), and old (25 months) male Fischer 344 rats were assigned to either a trained or sedentary running group. Animals were endurance trained by 10 weeks of treadmill running at 75% maximal capacity, 1 h/day, 5 days/week. Animals were sacrificed at rest and the heart, liver, and soleus were removed for analysis. Percent of high and low affinity binding sites were determined by competitive binding experiments. Competition curves were generated using 12 concentrations of ICI-89406 (beta 1 antagonist) and ICI-118551 (beta 2 antagonist) to inhibit the total binding of (-) [125I] pindolol (IPIN). Maximal binding site number (Bmax) and affinity (KD) were determined by Scatchard analysis. Heart Bmax did not differ with age or training. An aging effect was observed in liver such that middle-aged and old animals had greater Bmax compared to young animals. In soleus, Bmax was not altered with training but decreased with age. While training had no affect on affinity in the liver and soleus, heart affinity increased with training in both the middle-aged (21%) and old (27%) animals. In soleus, affinity increased but remained unaltered in heart and liver with age. The ratio of beta 1:beta 2 receptors in the heart and liver did not differ with age or training. The influence of age and training on beta-adrenergic receptor characteristics appear to be tissue specific.