Leptin in human plasma is derived in part from the brain, and cleared by the kidneys.
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Adult↗
Biomedical subjects
M Esler
Publications and source records attributed to M Esler.
Immune response to a single bout of exercise in young and elderly subjects.
The purpose of this investigation was to examine alterations in lymphocyte proliferation activity and T cell subsets following an acute bout of exercise in young and old subjects. Six young (26+/-3 years) and nine old (69+/-5 years) male subjects were tested at rest and immediately after 20 min of submaximal exercise at 50% peak work capacity. Arterial blood was sampled from an indwelling catheter for catecholamine and immunology assays. Peripheral blood lymphocytes were isolated for mitogen-induced phytohemagglutinin (PHA) proliferation capacity. Lymphocyte subsets were analyzed by dual-labeled flow cytometry. As has been shown in previous studies, baseline proliferative responsiveness was significantly lower in the old (down 22%) compared to the young subjects. In response to submaximal exercise, proliferative responsiveness to PHA increased significantly in the young subjects (up 55%), however, for the old subjects this response did not differ significantly from resting values (up 18%). The number of total lymphocytes, as well as CD4+ and CD8+ T cell subsets, at rest were lower for old subjects compared with young. Exercise-induced increases in T cell subset populations were similar across age groups. It was concluded that, while having lower initial T cell numbers and PHA responsiveness, immunoresponsiveness during a single bout of exercise is, in general, maintained in old when compared to young individuals.
Adult↗
Central and peripheral norepinephrine kinetics in heart failure, coronary artery disease, and hypertension.
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Central Nervous System↗
Effects of estrogen and estrous cycle on glucocorticoid and catecholamine responses to stress in sheep.
There have been relatively few studies of the effects of estrogen on hormonal responses to stress. We therefore studied changes in ACTH, cortisol, norepinephrine (NE), and epinephrine (Epi) after stress induced by a barking dog (audiovisual stressor) and insulin-induced hypoglycemia (metabolic stressor) in ovariectomized sheep treated with estradiol or placebo and in intact sheep in the follicular and luteal phases of the estrous cycle. Both stressors produced acute increases in ACTH, cortisol, Epi, and NE. A high physiological dose of estradiol significantly reduced the ACTH and cortisol responses to both stressors but did not affect Epi and NE responses. Plasma ACTH and cortisol responses to both stressors and Epi and NE responses to insulin were lower in the follicular than in the luteal phase, but catecholamine responses to the audiovisual stressor did not change during the estrous cycle. We conclude that in sheep, estrogen attenuates glucocorticoid responses to stress and that hormonal changes during the estrous cycle affect glucocorticoid responses to both metabolic and audiovisual stressors and catecholamine responses to a metabolic stressor.
Adrenocorticotropic Hormone↗
High blood pressure management: potential benefits of I1 agents.
SYMPATHETIC NERVOUS SYSTEM AND HYPERTENSION: Biochemical, electrophysiological, pharmacological and haemodynamic findings support the existence of sympathetic nervous system activation in primary human hypertension. Analysis of regional sympathetic nervous system function, using both neurophysiological methods for measuring sympathetic nerve firing rates, and neurochemical techniques for quantifying regional noradrenaline spillover to plasma has demonstrated activation of the sympathetic nervous outflows to the heart, the kidneys, and skeletal muscle vasculature, particularly in younger patients. The initiating cause of this sympathetic nervous stimulation is unknown, but estimation of central nervous system noradrenaline turnover in hypertensive patients, using measurements of the washout of noradrenaline and its lipophilic metabolites into the internal jugular veins, indicates that activation of forebrain pressor noradrenergic nuclei is the probable underlying mechanism. CONSEQUENCES OF INCREASED SYMPATHETIC ACTIVITY: The sympathetic activation present in human hypertension no doubt contributes to the blood pressure elevation, and is a legitimate target for therapeutic intervention with imidazoline receptor-binding agents such as rilmenidine. In addition, the sympathetic nervous activation seems to have adverse consequences in hypertensive patients beyond initiating the blood pressure elevation. There is evidence that neural vasoconstriction has metabolic effects, in skeletal muscle impairing glucose delivery to muscle, causing insulin resistance and hyperinsulinaemia, and in liver retarding postprandial clearing of lipids, contributing to hyperlipidaemia. Cardiac sympathetic activation is demonstrably a cause of sudden death in heart failure patients; a comparable arrhythmogenic effect is probable in hypertension. A trophic effect of sympathetic activation on cardiovascular growth is also likely, contributing to the development of left ventricular hypertrophy. Rilmenidine, through its central nervous system actions, has been demonstrated to powerfully reduce sympathetic nervous activity in essential hypertension patients. INHIBITING THE SYMPATHETIC SYSTEM: As the clinical consequences of sympathetic nervous activation in essential hypertension appear to go beyond that of hypertension pathogenesis, extending to a causal influence in atherosclerosis development, cardiovascular hypertrophy and cardiac arrhythmias, it is possible that, of all antihypertensive drugs, those inhibiting the sympathetic nervous system might best reduce cardiovascular risk. This remains to be tested.
Adrenergic Antagonists↗
Adrenergic nervous system in heart failure.
Recent demonstration that the level of sympathetic nervous drive to the failing heart in patients with severe heart failure is a major determinant of prognosis, and that mortality in heart failure is decreased by beta-adrenergic blockade with carvedilol, indicates the clinical relevance of cardiac neuroscience research. Important initial findings were observations that the plasma concentration of the sympathetic neurotransmitter, norepinephrine, is elevated in heart failure, and that overall clinical outcome is related to plasma norepinephrine concentration (although heart failure severity may be a confounder). Sympathetic nerve recording (clinical microneurography) and radiotracer methods measuring regional sympathetic activity in the heart (cardiac norepinephrine "spillover") have now largely supplanted antecubital venous norepinephrine measurements as research tools, with newer methods providing information on regional sympathetic function that was previously lacking. The cardiac sympathetic nerves are preferentially stimulated in severe heart failure, with norepinephrine release from the failing heart at rest in untreated patients increased up to 50-fold, which is similar to the level of release in healthy hearts during near maximal exercise. There is lesser stimulation of the sympathetic outflows to the kidneys and skeletal muscle. In early mild heart failure, it is only the cardiac sympathetic nerves that are activated. This preferential activation of cardiac sympathetic outflow contributes to arrhythmia development and probably to progression of heart failure and has been linked to mortality in mild and severe heart failure. The central nervous system mechanisms involved in the sympathetic nervous activation present in patients with heart failure remain uncertain. Increased intracardiac diastolic pressure seems to be one peripheral reflex stimulus with increased forebrain norepinephrine turnover being an important central mechanism.
Disease Progression↗
Regional sympathetic nervous activity and oxygen consumption in obese normotensive human subjects.
BACKGROUND: Disturbed sympathetic nervous function may be of importance in obesity; sympathetic underactivity could contribute to deficient thermogenesis, positive energy balance, and weight gain, while in contrast, sympathetic nervous overactivity would predispose to the development of obesity-related hypertension. Global indices of sympathetic nervous system (SNS) function such as plasma or urinary norepinephrine (NE) have been unable to define SNS status in obesity. Since regional SNS activity can be altered in the absence of global changes, we investigated SNS activity in the heart, kidneys, and hepatomesenteric bed in healthy human subjects across a wide body mass index (BMI) range of between 19.6 and 35.5. METHODS AND RESULTS: Whole-body and regional plasma NE kinetics using [3H]-labeled NE were assessed. Regional oxygen consumption was measured by combining arteriovenous differences in oxygen content and regional blood flow. Arterial plasma NE and whole-body plasma NE spillover were unrelated to BMI. With a BMI cutoff of 27, mean cardiac NE spillover was 46% lower in the obese subjects when compared with the lean subjects (P=.017). Renal NE spillover was significantly correlated with BMI (r=.668, P=.001), the mean value in the obese subjects being more than twice that in the lean subjects. Hepatomesenteric NE spillover was comparable in lean and obese subjects. Renal and hepatomesenteric oxygen consumption were both significantly higher in the obese subjects compared with lean subjects. CONCLUSIONS: Regional SNS activity is heterogeneous in the obese state. Important regional alterations, which may be clinically relevant, occur in the absence of changes in global indices of sympathetic nervous function. The enhanced renal NE spillover in obesity may have implications for the development of hypertension in this group, whereas the low cardiac sympathetic tone would be expected to be cardioprotective. Enhanced visceral oxygen consumption evident in the kidneys and hepatomesenteric circulation in proportion to body mass contributes to the greater resting oxygen consumption in obesity.
Adolescent↗
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.
Adult↗
Origin of homovanillic acid in plasma.
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Alcoholism↗
The relation of human cardiac sympathetic nervous activity to left ventricular mass: commentary.
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Humans↗
Postprandial sympatho-adrenal activity: its relation to metabolic and cardiovascular events and to changes in meal frequency.
1. Sympatho-adrenal activity was measured after the consumption of a 3.15 MJ mixed meal. Whole-body noradrenaline spillover rates, forearm plasma noradrenaline spillover and adrenaline secretion rates were derived using isotope dilution methodology. Heart rate and blood pressure spectral analysis measurements were also made. The relation of sympathoadrenal activity to thermogenic and cardiovascular events was studied. Sympathetic nervous and thermogenic responses were measured for 120 min after the single 3.15 MJ meal and compared with those after three 1.05 MJ meals, given 30 min apart. 2. Whole-body and forearm plasma noradrenaline spillover, and the 0.1 Hz component of systolic pressure power all increased significantly postprandially, while the 0.1 Hz component of heart rate variability, an indirect index of cardiac sympathetic nervous activity, remained unaltered. Adrenaline secretion was unaltered postprandially. Whole-body plasma noradrenaline spillover and thermogenesis during the 120 min postprandial period were 37% and 36% higher after the single meal as compared with the multiple meals, although this was not statistically significant. 3. The sympathetic neural responses were delayed in relation to peak plasma insulin levels and sustained in the face of declining insulin levels. Energy expenditure increased significantly postprandially, but there was no direct quantitative relationship to plasma noradrenaline spillover. Forearm oxygen consumption did not increase postprandially despite significant increases in regional noradrenaline spillover. Thus, no close relation was demonstrated between postprandial sympathetic nervous activation and either insulin secretion or thermogenesis.
Adult↗
Differential actions of desipramine on sympathoadrenal release of noradrenaline and adrenaline.
Spillovers noradrenaline (NA) and adrenaline (A) into plasma were examined before and after i.v. administration of 0.3-0.5 mg kg-1 desipramine (DMI) in 19 normal volunteers. DMI decreased the total body spillover of NA by 20 +/- 4%, but increased that of A by 45 +/- 10%. The results indicate differential sympathoadrenal actions of DMI, characterized by inhibition of NA release from sympathetic nerves and stimulation of A secretion from the adrenals. These effects of DMI provide an explanation for some of the cardiovascular complications of tricyclic antidepressant therapy and may also help to explain how sympathoadrenal function is differentially regulated.
Adult↗
Effects of aging on epinephrine secretion and regional release of epinephrine from the human heart.
In contrast to the sympathetic nervous system, which is activated by aging in at least some sympathetic nervous outflows, epinephrine release from the adrenal medulla appears to be either normal or low in the elderly. Using isotope dilution methodology, we studied the effect of aging on the secretion of epinephrine in 19 men, aged 20-30 yr, and 15 men, aged 60-75 yr. Measurements were made both at rest and during the application of laboratory stressors, as diminished adrenal medullary responsiveness possibly contributes to the impairment of some cardiovascular and metabolic responses to stress described previously in the elderly. Epinephrine secretion at rest was lower in the older men (mean +/- SEM, 0.86 +/- 0.10 nmol/min) than in the younger men (1.45 +/- 0.17 nmol/min; P < 0.05). Due to 20% lower plasma epinephrine clearance in the older men (P < 0.01), the reduction in the plasma concentration of epinephrine (0.37 +/- 0.03 vs. 0.52 +/- 0.06 nmol/L; P = 0.06) was proportionally less than that in epinephrine secretion. In the younger men, epinephrine secretion doubled or tripled during mental stress, isometric exercise, and dynamic exercise. Epinephrine responses to the stressors were reduced in older men, being equivalent to only 44% (P < 0.05), 44% (P = 0.1), and 33% (P = 0.01) of the corresponding responses in the younger men. After uptake from plasma, in some circumstances epinephrine is released from sympathetic nerves as a cotransmitter, where it can augment the release of the major sympathetic transmitter, norepinephrine. We also measured regional extraadrenal release of epinephrine from the heart to test whether the previously described increased release of norepinephrine from the cardiac sympathetic nerves with aging might result from facilitator effects of epinephrine released as a cotransmitter. At rest, epinephrine was released from the heart (9.4 +/- 2.6 pmol/min) in older men only (P < 0.01) despite the fact that adrenal medullary secretion of epinephrine was reduced. Failure of epinephrine and norepinephrine spillover from the heart to increase in parallel in the elderly during the sympathetic excitation accompanying exercise suggested that epinephrine lay outside the sympathetic nerves, perhaps arising from extraneuronal synthesis in the heart. We have not yet tested whether extraneuronal, in contrast to neuronal, epinephrine release in the heart could contribute to the observed higher rates of norepinephrine release in the elderly.
Adult↗
Sympathetic nervous system: contribution to human hypertension and related cardiovascular diseases.
Sympathetic nervous system activation has been documented in several cardiovascular disorders. In some, characterized by cardiac failure and portal hypertension accompanying hepatic cirrhosis, the sympathetic nervous stimulation is reflex and, to some extent, compensatory but has adverse consequences. For example, in cardiac failure, the sympathetic nerves of the heart are preferentially stimulated, providing adrenergic support to the failing myocardium but at the probable cost of arrhythmogenesis and progressive myocardial deterioration. The sympathetic activation present in patients with essential hypertension, which involves the sympathetic outflows to skeletal muscle, heart, and kidneys and is seen particularly in younger patients, differs from these examples in that the sympathetic nervous stimulation is apparently not reflex and the primary cause is unknown. There is, however, evidence that activation of forebrain pressor noradrenergic nuclei may be of importance as an underlying central nervous system mechanism. This sympathetic nervous stimulation in patients with essential hypertension, in addition to initiating the blood pressure elevation, may also contribute to the commonly associated metabolic abnormalities of insulin resistance and hyperlipidemia, with neural vasoconstriction having metabolic consequences, impairing glucose delivery and causing insulin resistance in muscle, and retarding postprandial clearing of lipids in liver. Trophic effects of sympathetic activation on cardiovascular growth are claimed but have yet to be demonstrated conclusively in humans.
Cardiovascular Diseases↗
Mineralocorticoid induced hypertension and noradrenaline spillover in man.
This study examined haemodynamics and noradrenaline spillover in five normal men before and on day 7 of oral fludrocortisone treatment, 0.3 mg/day. Resting systolic (105 to 115 mm Hg, standard error of the difference +/- 2.0, p < 0.01) and diastolic (65 to 73 mm Hg, +/- 3.0, p < 0.05) blood pressure increased, as did cardiac output, from 5.0 to 5.7 L/min (+/- 0.1, p < 0.01). Calculated total peripheral resistance fell from 21.2 to 20.0 mm Hg/L/min (+/- 0.4, p < 0.05). Fludrocortisone produced a fall in plasma potassium, renin and aldosterone concentrations and haematocrit and a rise in body weight. Cold pressor responses were increased by fludrocortisone, from 7.5 to 20 mm Hg (+/- 3.0, p < 0.01), and forearm vascular resistance rose 12 arbitrary resistance units (R) before and 36 R units after treatment (+/- 5.0, p < 0.01). Total body spillover of noradrenaline was decreased from 9.48 to 7.36 ng/kg/min (+/- 0.86, p < 0.05). There were no changes in forearm noradrenaline spillover at rest or during cold pressor stimulation. It appears unlikely that the sympathetic nervous system plays a major role in the pathogenesis of mineralocorticoid hypertension in man.
Adult↗
Impaired reactivity of the peripheral vasculature to pressor agents in alcoholic cirrhosis.
BACKGROUND: Studies of the in vivo vascular reactivity of the peripheral circulation to pressor agents in cirrhosis have produced conflicting results, possibly because of changes in mean arterial pressure that make it difficult to clearly separate peripheral and central effects. The aim of the present study was to assess the reactivity of the forearm circulation to pressor agents in vivo without activating central control systems. METHODS: Forearm blood flow was measured by venous occlusion strain gauge plethysmography in the basal state and during the infusion of subpressor doses of norepinephrine and angiotensin II into the brachial artery in 10 male patients with well-compensated alcoholic cirrhosis and 10 male age-matched controls. Plasma renin activity and aldosterone and angiotensin II concentrations were assayed. Forearm and systemic sympathetic nervous system activity was estimated using a norepinephrine spillover technique. RESULTS: Basal forearm blood flow, renin angiotensin aldosterone system activity, and forearm sympathetic nervous system activity were similar in both the control and cirrhotic groups. The cirrhotic patients showed an impaired response to both norepinephrine and angiotensin II. CONCLUSIONS: There is impaired reactivity of the peripheral vasculature to pressor agents in cirrhosis, indicating that the control of vascular tone is disturbed even in well-compensated cirrhosis.
Adult↗
Elevated total body noradrenaline spillover in normotensive members of hypertensive families.
1. In prehypertension, abnormalities in cardiovascular control mechanisms have been described. It has been postulated that this may involve hereditary disturbances in the sympathetic regulation of blood pressure. Since the neurochemical methods used to test sympathetic nervous system activity have been rather imprecise, in the present study we have applied noradrenaline plasma kinetic methodology to evaluate sympathetic activity in normotensive subjects with a familial predisposition to essential hypertension. 2. Total body noradrenaline spillover to plasma, an index of integrated sympathetic nerve firing rates, was calculated during infusion of l-[7-3H]noradrenaline in 11 normotensive offspring of essential hypertensive parents and 11 age-, height- and weight-matched normotensive offspring of normotensive parents. 3. The resting arterial plasma noradrenaline concentration was higher in healthy subjects with a family history of essential hypertension (1.41 +/- 0.15 nmol/l, mean +/- SEM, P < 0.002) than in normotensive subjects with no family history of essential hypertension (0.82 +/- 0.07 nmol/l). The overall rate of spillover of noradrenaline to plasma was also elevated in the normotensive offspring of hypertensive parents (4.34 +/- 0.54 nmol/min) compared with subjects with a negative family history of essential hypertension (2.02 +/- 0.20 nmol/min). Similarly, the arterial plasma concentration of the noradrenaline precursor 3,4-dihydroxyphenylalanine was higher in subjects with a positive family history of essential hypertension (7.55 +/- 0.24 nmol/l) than in normotensive control subjects (5.97 +/- 0.30 nmol/l, P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Clinical application of noradrenaline spillover methodology: delineation of regional human sympathetic nervous responses.
The proportionality which in general exists between rates of sympathetic nerve firing and the overflow of noradrenaline into the venous drainage of an organ provides the experimental justification for the use of measurements of noradrenaline in plasma as a biochemical measure of sympathetic nervous function. Static measurements of noradrenaline plasma concentration have several limitations. One is the confounding influence of noradrenaline plasma clearance on plasma concentration. Other drawbacks include the distortion arising from antecubital venous sampling (this represents but one venous drainage, that of the forearm), and the inability to detect regional differentiation of sympathetic responses. Clinical regional noradrenaline spillover measurements, performed with infusions of radiolabelled noradrenaline and sampling from centrally placed catheters, and derived from regional isotope dilution, overcome these deficiencies. The strength of the methodology is that sympathetic nervous function may be studied in the internal organs not accessible to nerve recording with microneurography. Examples of the regionalization of human sympathetic responses disclosed include the preferential activation of the cardiac sympathetic outflow with mental stress, cigarette smoking, aerobic exercise, cardiac failure, coronary insufficiency, essential hypertension and in ventricular arrhythmias, and the preferential stimulation or inhibition of the renal sympathetic nerves with low salt diets and mental stress, and with exercise training, respectively. By application of the same principles, regional release of the sympathetic cotransmitters neuropeptide Y and adrenaline can be studied in humans. Cotransmitter release, however, is detected only with some difficulty. In restricted circumstances we find evidence of regional cotransmitter release to plasma, such as the release of neuropeptide Y from the heart at the very high rates of sympathetic nerve firing occurring with aerobic exercise, and cardiac adrenaline release also with exercise and after loading of the neuronal adrenaline pool by intravenous infusion of adrenaline.
Animals↗