Plasma adrenaline and noradrenaline during orthostasis in man: the importance of arterial sampling

Plasma and Urinary Levels of Nerve Growth Factor Are Elevated in Primary Hypertension

Nerve growth factor (NGF) is the main neurotrophic factor that can control sympathetic nerve innervation and sympathetic neural activity in cardiovascular organs. Although NGF overproduction and its influences on the sympathetic nervous system have been shown in hypertensive animals, NGF status and its association with sympathetic nerve activity have not yet been explored in human hypertension. In the present study, therefore, plasma and urinary levels of NGF and those of catecholamines (i.e., indices for NGF status and sympathoadrenal activity, respectively) were compared between 83 untreated primary hypertensives without apparent cardiovascular damages and 81 healthy normotensive subjects. Plasma and urinary levels of NGF were significantly greater in the hypertensive group (311 ± 158 pg/mL and 72.7 ± 54.0 ng/g of Cr) than in the normotensive group (168 ± 188 pg/mL and 54.5 ± 38.8 ng/g of Cr) (p < 0.05 for each measurement), even if the baseline differences of age and gender between the groups were adjusted. Similarly, plasma and urinary levels of catecholamines were significantly higher in the hypertensive group than in the normotensive group except for plasma noradrenaline. In addition, despite no significant correlations between plasma levels of NGF and catecholamines in both groups, urinary NGF significantly correlated positively with both urinary noradrenaline and urinary adrenaline in the hypertensive group (r = 0.259, p=0.018 and r = 0.232, p=0.035), but not in the normotensive group (r = 0.115, p=0.307 and r = −0.018, p=0.871). On the contrary, plasma and urinary levels of NGF as well as those of catecholamines did not associate with any systemic hemodynamic indices such as blood pressure and pulse rate in either group. Thus, primary hypertension was characterized by the enhancements of both NGF status and sympathoadrenal activity and the positive relationship between them. Our data indicate that enhanced NGF status and subsequent NGF-induced sympathoadrenal overactivity could occur in primary hypertension.

A 14-year follow-up study of chest pain patients including stress hormones and mental stress at index event

BACKGROUND

Knowledge of long-term outcome in chest pain patients is limited. We reinvestigated patients who 14 years earlier had visited the emergency department due to chest pain, and were discharged without hospitalization. Extensive examinations were made at that time on 484 patients including full medical history, exercise test, a battery of stress questions and stress hormone sampling.

METHODS

From a previously conducted chest pain study patients still alive after 14 years were approached. Hospitalization or deaths with a diagnosis of ischemic heart disease or cerebrovascular disease were used as end point.

RESULTS

During the follow-up period 24 patients had died with a diagnosis of ischemic heart or cerebrovascular disease, and 50 patients had been given such a diagnosis at hospital discharge. Age (OR 1.12, CI 1.06-1.19), previous history of angina pectoris (OR 9.69, CI 2.06-71.61), pathological ECG at emergency department visit (OR 3.27, CI 1.23-8.67), hypertension (OR 5.03, CI 1.90-13.76), smoking (OR 3.04, CI 1.26-7.63) and lipid lowering medication (OR 14.9, CI 1.60-152.77) were all associated with future ischemic heart or cerebrovascular events. Noradrenalin levels were higher in the event group than in the non-event group, mean (SD) 2.44 (1.02) nmol/L versus 1.90 (0.75) nmol/L. When noradrenalin was included in the regression model high maximal exercise capacity was protective of an event (OR 0.986, CI 0.975-0.997).

CONCLUSION

In chest pain patients previous history of angina pectoris, hypertension, smoking, pathological ECG at primary examination, and age were the main risk factors associated with future cardiovascular or cerebrovascular events.

Circulatory galanin levels increase severalfold with intense orthostatic challenge in healthy humans

The purpose of this study was to test the hypothesis that plasma galanin concentration (pGal) is regularly increased in healthy humans with extensive orthostatic stress. Twenty-six test persons (14 men, 12 women) were brought to an orthostatic end point via a progressive cardiovascular stress (PCS) protocol consisting of 70° head-up tilt plus increasing levels of lower body negative pressure until either hemodynamically defined presyncope or other signs of orthostatic intolerance occurred (nausea, clammy skin, excessive sweating, pallor of the skin). We further tested for possible gender, gravitational, and muscular training influences on plasma pGal responses: PCS was applied before and after 3 wk of daily vertical acceleration exposure training on a Human Powered Centrifuge. Test persons were randomly assigned to active (with bicycle work) or passive (without work) groups (seven men, six women in each group). Resting pGal was 26 ± 3 pg/ml in men and 39 ± 15 pg/ml in women (not significant); women had higher galanin responses (4.9-fold increase) than men (3.5-fold, P = 0.017) to PCS exposure. Overall, PCS increased pGal to 186 ± 5 pg/ml ( P = 0.0003), without significant differences between presyncope vs. orthostatic intolerance, pre- vs. postcentrifuge, or active vs. passive gravitational training. Increases in pGal were poorly related to synchronous elevations in plasma vasopressin. We conclude that galanin is regularly increased in healthy humans under conditions of presyncopal orthostatic stress, the response being independent of gravity training but larger in women than in men.

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.

Flow dependence of forearm noradrenaline overflow, as assessed during mental stress and sodium nitroprusside infusion

OBJECTIVE

To evaluate the influence of blood flow on measurements of regional sympathetic nerve activity by radiotracer methodology ([3H]noradrenaline).

DESIGN

Ten healthy men were studied under two conditions of elevated forearm blood flow: mental stress (Stroop colour word conflict test) and an intra-arterial infusion of sodium nitroprusside.

METHODS

Arterial blood pressure was measured invasively and forearm blood flow with strain-gauge plethysmography. Arterial and venous plasma adrenaline and noradrenaline were measured with high-performance liquid chromatography, and regional and total noradrenaline spillover were calculated.

RESULTS

During mental stress, mean arterial pressure increased by 17%, heart rate by 16 beats/min, forearm blood flow by 117%, while forearm vascular resistance decreased by 44% (P < 0.001 for all). Sodium nitroprusside increased forearm blood flow dose-dependently, but elicited only minor effects on systemic haemodynamics. Mental stress increased arterial plasma noradrenaline by 52% (P < 0.001), and total body noradrenaline spillover by 75% (P < 0.001). During sodium nitroprusside infusion, arterial plasma noradrenaline increased only slightly and total body noradrenaline spillover was unaffected Forearm noradrenaline overflow increased from 5.4 +/- 0.9 to 16.9 +/- 2.6 pmol/min per I (P < 0.001) during mental stress and from 6.6 +/- 0.8 to 16.9 +/- 3.7 pmol/min per I (P < 0.001) during the second dose-step of sodium nitroprusside infusion. By intra-individual comparisons of forearm noradrenaline overflow increases during mental stress and during sodium nitroprusside infusion, with similar forearm blood flow increases, the flow dependence of forearm noradrenaline overflow was estimated. During mental stress, about 60% (median value, range 29-112%) of the increase in forearm noradrenaline overflow was attributed to the increase in forearm blood flow, whereas 40% was considered to reflect increased sympathetic nerve activity.

CONCLUSIONS

There seems to be a considerable flow dependence of the regional overflow of noradrenaline, that is, a component of simple wash-out of noradrenaline from the forearm tissues during vasodilation. However, the present results still indicate that sympathetic nerve activity in the forearm is increased during mental stress, justifying the radiotracer technique for semiquantitative measurements, also during vasodilation.

Effects of increased arterial epinephrine on insulin, glucose and phosphate

The relationship between sympathetic nervous system activity and glucose and insulin metabolism is not fully understood. In the present study we therefore investigated the effect of raising arterial plasma epinephrine within the lower pathophysiological concentration range on insulin, glucose and phosphate in blood. Arterial plasma epinephrine was raised over 60 min by a stepwise increasing intravenous infusion in healthy men aged 20-40 years (n = 40). Compared with infusion of saline, epinephrine caused a small but significant rise in serum insulin of 10 +/- 26 pmol/L (p = 0.016), more than 70% increase in serum glucose (p < 0.0001) and a decrease in serum phosphate (p < 0.0001). The changes in serum insulin during epinephrine infusion correlated negatively with the changes in arterial plasma epinephrine (r = -0.46, p = 0.003) and the changes in serum phosphate correlated negatively with the changes in serum glucose (r = -0.42, p = 0.007). Thus, arterial plasma epinephrine raised within the lower pathophysiological concentration range over a rather short period of time (60 min) has pronounced effects on insulin, glucose and phosphate in blood. These results suggest that epinephrine when infused acutely may suppress the insulin response to raised glucose, and that the acute hypophosphatemic effect of epinephrine is related to the glucose production. Thus, when epinephrine is released into the circulation during various forms of daily stress, e.g. mental stress, it may significantly affect insulin and glucose metabolism.

Effects of ovarian stimulation on blood pressure and plasma catecholamine levels

Effects of ovarian stimulation for in vitro fertilization on blood pressure and plasma catecholamine levels were studied in 10 women. The examinations were carried out before hormonal treatment with human menopausal gonadotropin (day three of the menstrual cycle, mean serum oestradiol concentration 0.2 nmol l-1, and on the day after ovulation induction with human chorionic gonadotropin (cycle days 10-12, mean serum oestradiol concentration 7.4 nmol l-1). Systolic and diastolic blood pressures (mean +/- SD) decreased 6.7 +/- 8.6 mm Hg, p = 0.049, and 5.3 +/- 4.7 mm Hg, p = 0.009, respectively), and venous plasma noradrenaline increased (42 +/- 44 pg ml-1, p = 0.02) during ovarian stimulation. No significant change was observed in either arterial noradrenaline, arterial adrenaline or venous adrenaline. After stimulation a positive correlation was observed between systolic blood pressure and arterial adrenaline (r = 0.73, p = 0.027), and between systolic blood pressure and the arterial-venous difference for adrenaline (r = 0.81, p = 0.007). The increased venous noradrenaline levels may be a reflex-mediated activation of the sympathetic nervous tone due to a decrease in blood pressure, or may indicate reduced neuronal re-uptake of released noradrenaline. The mechanisms behind the strong correlation between adrenaline and blood pressure are unclear, but may be induced by the supraphysiological oestradiol levels. Thus, adrenaline seems to be more important for blood pressure control in this particular setting.

Plasma catecholamines--analytical challenges and physiological limitations

Catecholamines in plasma may be measured to assess sympathoadrenal activity. Numerous assay methodologies have been published, illustrating the fact that there are many analytical problems. Different methodologies are discussed briefly. A plea for better validation, especially with regard to specificity (which should not be confused with sensitivity or reproducibility), is made. Plasma NA is a frequently used marker for sympathetic nerve activity in humans, but the data obtained are often misinterpreted due to lack of appreciation of the physiological determinants of the NA concentration measured. NA overflow from an organ gives a good reflection of nerve activity in that organ. However, sympathetic nerve activity is highly differentiated, particularly during stress, and conventional plasma NA levels (usually forearm venous samples) cannot be taken as an indication of 'sympathetic tone' in the whole individual. NA is rapidly removed from plasma, resulting in meaningless net veno-arterial concentration differences over organs unless its removal from arterial plasma is taken into account. In the forearm, for example, 40-50% of catecholamines are removed during one passage; about half of the NA in a venous sample is derived from the arm and half from the rest of the body. Therefore, conventional venous sampling overemphasizes local (mainly skeletal muscle) nerve activity. Whole-body sympathetic nerve activity may be monitored in arterial or mixed venous (i.e. pulmonary arterial) samples, which reflect NA overflow from all organs in the body. NA levels are determined both by overflow to plasma and clearance from plasma. NA turnover studies with 3H-NA infusions may be needed to assess clearance, but the simpler concentration measurements usually yield adequate information if the sampling site is relevant. NA overflow from an organ can be assessed (using 3H-NA or ADR as a marker for NA extraction in the organ) and provides valuable information on local sympathetic activity. Mental stress elicits marked circulatory responses, with mainly cardiorenal sympathetic activation and minor elevations of conventional venous plasma NA levels, thus illustrating the differentiated firing pattern of the sympathetic nerves. Circulating ADR is less important than neurogenic mechanisms in the responses to stress. Concentration-effect studies for infused catecholamines may be used for receptor sensitivity studies in vivo, but reflexogenic contributions to responses need to be determined. However, prejunctional mechanisms cannot be assessed without knowledge of the nerve activity present; for example, ADR infusion leads to increased nerve activity. When correctly sampled, measured and interpreted, plasma catecholamines can yield very valuable information on sympathoadrenal activity.

Regional differences of atrial natriuretic factors in humans

During sinus coronarius catheterization in humans undergoing diagnostic right-sided cardiac catheterization, levels of atrial natriuretic factor (ANF) measured in sinus coronarius (n = 12) were four times higher than in peripheral arterial blood. Atrial natriuretic factor underwent average extractions of 0.57, 0.40, and 0.28 in the kidneys (n = 14), liver (n = 15), and forearm (n = 15) respectively. However, a close relationship was observed between arterial and peripheral venous concentrations. The substantial clearance of ANF even over the forearm indicates that arterial sampling may be preferred in conditions with altered peripheral vascular resistance, since an uptake of ANF in the peripheral vascular bed is likely to have occurred.

Epinephrine and the genesis of hypertension

Several lines of evidence suggest a psychophysiological link between stress, adrenomedullary activation, and the genesis of hypertension. Experimental data support four important concepts: 1) epinephrine stimulates prejunctional beta 2-adrenergic receptors that facilitate norepinephrine release from sympathetic nerve endings; 2) epinephrine can be converted into a cotransmitter by neuronal uptake and on subsequent release augment the simultaneous discharge of norepinephrine; 3) exogenous epinephrine can induce sustained hypertension in rats; and 4) there is a period of critical sensitivity to endogenous epinephrine in a genetic model of rat hypertension. Plasma epinephrine concentrations are elevated in many young subjects with borderline or mild hypertension. The hypothesis that intermittent surges in epinephrine could initiate or promote the development of primary hypertension by amplifying peripheral neurotransmission, both directly (facilitative effect) and indirectly (cotransmitter action), is supported by reports that hemodynamic and noradrenergic responses to sympathetic activation can be augmented by increases in endogenous epinephrine or by its local or systemic (up to 30 ng/kg/min) infusion. Such responses have been documented in both normotensive and hypertensive subjects and can be blocked by propranolol. Although the weight of evidence (mostly indirect) indicates that epinephrine can augment norepinephrine release in humans, the epinephrine hypothesis, itself, remains unproven. Expression of hypertension by this mechanism may be restricted to a specific epinephrine-sensitive subset of individuals with a genetic predisposition to high blood pressure.

Cardiohemodynamic and serum catecholamine response to surgical removal of impacted mandibular third molars under local anesthesia: a randomized double-blind parallel group and crossover study

The aim of this study was to differentiate between the extent to which surgical stress and the epinephrine in local anesthetic solutions influence serum catecholamine, cAMP, and potassium levels, and contribute to changes in cardiohemodynamic parameters. One hundred sixty mg of articaine hydrochloride (4.0 mL of a 4% articaine hydrochloride solution) with two different epinephrine doses was injected into outpatients prior to removal of an impacted mandibular third molar in a randomized, double-blind parallel group and crossover design. The results showed that the amount of epinephrine absorbed from the intraoral injection site predominantly determined the serum epinephrine concentration. The anesthetic-induced increase in the serum epinephrine level did not correlate with changes in the cardiohemodynamic parameters under study at any time during the operative procedure. The serum cAMP changes correlated with those of epinephrine, whereas the serum potassium levels remained unchanged. The procedure of tooth extraction was a stressful event when the 1:200,000 epinephrine-containing anesthetic solution was used, showing that the risk of inducing a cardiovascular incident during oral surgery seems to be higher the greater the extent of operation and the lower the epinephrine dose in the anesthetic solution.

The epinephrine-blood platelet connection with special reference to essential hypertension

About three decades ago it was shown by an aggregometer that epinephrine activated blood platelets, and it was proposed that platelets could be the link between stress and cardiovascular disease. During the past 10 years this hypothesis has been tested in clinical studies. It has been found that subjects with hypertension consistently have raised plasma catecholamine levels and in particular elevated epinephrine levels. Arterial but not venous epinephrine concentrations correlated with plasma concentrations of the platelet-release reaction marker beta-thromboglobulin (BTG). Plasma BTG is elevated in hypertensive patients, and psychological stress (i.e., hypertension labeling) stimulates plasma epinephrine and BTG. When a physiologic dose of epinephrine is infused into essential hypertensive patients, platelet counts, platelet size, and plasma BTG concentrations increase more than in normotensive subjects. Data suggest that there is a connection between psychological stress, plasma epinephrine levels, and platelet function, especially in patients with essential hypertension.

Faster and more reliable absorption of adrenaline by aerosol inhalation than by subcutaneous injection

1. The aim of the present study was to compare absorption of adrenaline given by aerosol spray inhalation with absorption after subcutaneous injection. 2. Arterial plasma adrenaline was measured in nine healthy volunteers following adrenaline administration by both methods. 3. Following inhalation of 20 puffs of adrenaline aerosol, 0.15 mg/puff, a peak arterial adrenaline concentration after 1 min and a rapid fall to baseline from this peak occurred. 4. When given by subcutaneous injection absorption was slower with a peak arterial adrenaline concentration after 4 min. The fall in arterial adrenaline from this peak level was not statistically significant within 30 min after injection. 5. There was less intersubject variation of arterial adrenaline concentration following inhalation when compared with injection. 6. Heart rate, blood pressure and finger tremor followed the changes in arterial adrenaline concentrations. 7. These results indicate that absorption is more reliable when adrenaline is given by inhalation. The rapid fall in arterial adrenaline following inhalation, suggests that repeated inhalations are necessary when such adrenaline therapy is required.

Increased arterial adrenaline is related to pain in uncomplicated myocardial infarction

Plasma levels of catecholamines, beta-thromboglobulin (BTG) and arginine vasopressin (AVP), and degree of pain were examined in 22 patients with suspected uncomplicated myocardial infarction within 24 h following onset of chest pain. Sixteen patients developed infarction with peak creatine phosphokinase at 1280 Ul-1 (range 293-3770 Ul-1). Fifteen healthy men served as controls (C). Arterial adrenaline levels were significantly higher in patients with pain (1.15 +/- 0.23 nmol l-1, n = 8, mean value +/- SEM) than in those without pain (0.60 +/- 0.10 nmol l-1, n = 14, P less than 0.05). Plasma catecholamines were moderately but significantly elevated in myocardial infarction; the concentration of arterial adrenaline was 0.83 +/- 0.14 nmol l-1 and that of arterial noradrenaline was 2.70 +/- 0.28 nmol l-1 compared with 0.44 +/- 0.04 nmol l-1 (P less than 0.025) and 1.47 +/- 0.05 nmol l-1 (P less than 0.0005), respectively, in C. One week later, plasma catecholamines had returned to baseline levels. Plasma BTG showed borderline elevation (1.0 +/- 0.1 pmol l-1) compared with C (0.6 +/- 0.1 pmol l-1, P = 0.04), and remained unchanged 1 week later. Plasma AVP was at baseline level. Uncomplicated myocardial infarction, regardless of size, was associated with only moderately increased sympathetic tone. Plasma adrenaline was related more to the degree of pain than to the presence of acute myocardial infarction. Arterial adrenaline may be a sensitive marker of sympatho-adrenal activity related to pain.

A pressor effect of noncardioselective beta-blockers in mildly hypertensive patients during acute hospitalization

Pressor effects of noncardioselective beta-blockers have been demonstrated in situations of increased sympathetic activity; however, data are limited and the clinical significance of this finding is in doubt. The present study was performed to supply data about the effect of noncardioselective beta-blockers on the stress of acute hospitalization. Of 2,989 patients acutely admitted to a 50-bed unit of general internal medicine in a 647-bed teaching hospital, 234 had used beta-blockers without intrinsic sympathicomimetic activity (ISA) for at least six weeks because of mild hypertension; 199 were evaluable, 56 using nonselective, 143 using selective beta-blockers. The authors found a marked pressor effect of noncardioselective beta-blockers as compared with selective (mean arterial pressure 125 versus 102 mm Hg, p less than 0.001). In the patients who could continue their outpatient medication this effect could be attributed to an overall increase of total peripheral resistance and disappeared within five days of admission. In the patients admitted because of unstable angina pectoris (nonselective n = 15, selective n = 48) myocardial oxygen demand as estimated by the double product (systolic blood pressure heart rate) was significantly higher in the nonselective group (12.926 versus 9.581 mmHg.beats/min, p less than 0.01). The present study supports the need for more controlled data to determine the ultimate place of noncardioselective beta-blockers in situations of increased sympathetic activity.

Plasma catecholamines in some airline passengers

Assuming that the act of flying may provoke mental stress and increments in plasma catecholamines, in-flight plasma catecholamines were compared in two groups of passengers: a group of ordinary passengers (Group 1, n = 15) and a group of passengers who had just completed a cognitive, behavioural treatment programme against flight phobia (Group 2, n = 13). No difference in catecholamines was observed between the groups. However, 10 of the subjects in Group 1 and 12 of the subjects in Group 2 had in-flight plasma adrenaline higher than the highest mean +2 SD (above 0.40 nmol/l) of resting plasma adrenaline observed in healthy subjects in a long series of studies previously or simultaneously done in our laboratory. Subjects in Group 2 (n = 12) showed an average decrease of 50% from in-flight to post-flight plasma adrenaline. Plasma noradrenaline values were not elevated compared to normal resting levels, but an average reduction of 24% was observed between in-flight and post-flight in Group 2. We could not detect any difference between passengers treated for flight phobia and ordinary passengers. However, in-flight plasma catecholamines, particularly adrenaline, seem to be elevated in some airline passengers of various backgrounds. The most plausible explanation seems to be the discomfort and fear some people feel when flying; however, we cannot exclude that the physiological act of flying per se increased plasma catecholamines. Relatively larger variations in plasma adrenaline compared to noradrenaline may favour the first of these two possible explanations.

Plasma catecholamines: laboratory aspects

In this review the methods used for analysis of plasma catecholamines in clinical chemical laboratories are discussed. The physiology of catecholamines as well as their measuring indications are discussed, together with concise evaluation of the methods most commonly used, namely indirect radioenzymatic assays or direct determinations by high-performance liquid chromatography combined with either electrochemical or fluorometric detection. The main advantage of radioenzymatic assay is its sensitivity and thus the need for only a small sample. Liquid chromatographic methods in general are less tedious, relatively rapid, and cheap, and omit the use of radionuclides. Both of these methods, however, are subject to a number of analytical errors, which can only be avoided by proper development of methods and skilled use of these methods. Little routine work is done using either radioimmunoassay or gas-chromatography.

Haemodynamics as a determinant of the pharmacokinetics of and the plasma catecholamine responses to isoprenaline

The total body clearance and fractional extraction of isoprenaline (ISO) have been determined, and the relation between these parameters and cardiac output established. Whether desipramine, an inhibitor of neuronal uptake, altered the plasma catecholamine response to ISO was also investigated. Seven healthy subjects were given i.v., infusions of ISO in two, consecutive 25-min periods, at constant dose rates of 31-43 and 80-124 pmol.kg-1.min-1, respectively. The total-body (ER), pulmonary (ERp) and forearm (ERf) fractional extractions and the total body clearance (CL) of ISO were obtained from measurements of cardiac output and the steady-state ISO concentration in mixed central venous, arterial and forearm venous plasma. ISO-induced increases in cardiac output resulted in increases in CL, decreases in ER and no consistent change in ERf. ERp did not differ from zero. ISO also produced a dose-dependent increase in the mixed venous plasma concentrations of noradrenaline and 3,4-dihydroxyphenylglycol (DOPEG), and a decrease in that of adrenaline. Pretreatment with desipramine did not alter any of the pharmacokinetic parameters of ISO. Desipramine, however, reduced the mixed venous baseline plasma levels of noradrenaline (47%) and DOPEG (40%), and tended to reduce that of adrenaline (34%). It enhanced the plasma noradrenaline response 2.4-fold, abolished the plasma DOPEG response and did not alter the plasma adrenaline response to ISO. Hence, owing to its haemodynamic effects, ISO modifies its own pharmacokinetics which involve non-neuronal removal processes only. The increased DOPEG in plasma resulting from the ISO-induced increase in noradrenaline release was presynaptic in origin. Desipramine appears to reduce sympathetic activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Sodium depletion increases platelet and plasma catecholamines in hypertensive men

The catecholamine content in blood platelets is considerably higher than that in plasma, and platelet catecholamines must be taken up from plasma, since blood platelets lack enzymes for catecholamine synthesis. However, it is unknown whether platelets take up and store catecholamines during physiological in vivo increments in plasma catecholamines. Previously untreated 50-year-old men (n = 17) with mild to moderate essential hypertension were given a low sodium diet for 2 weeks. Urinary excretion of sodium decreased from 201 +/- 11 (SE) to 24 +/- 5 and 19 +/- 4 mmol/24 hr after 1 and 2 weeks, respectively. During the first week, the blood platelet concentration of norepinephrine increased from 27.2 +/- 2.9 to 39.6 +/- 4.7 pg/mg (p less than 0.005) and venous plasma norepinephrine increased from 3.7 +/- 0.4 to 5.6 +/- 0.5 pg/ml (p less than 0.005), and venous plasma dopamine increased from 26 +/- 4 to 41 +/- 5 pg/ml (p less than 0.05). During the second week, both plasma and platelet norepinephrine and dopamine remained elevated. Platelet epinephrine showed a small increase from baseline to the second week (p less than 0.05), but no concomitant increase in plasma epinephrine occurred. Thus, sodium depletion increases both platelet and plasma catecholamines and blood platelets may take up catecholamines in vivo. Platelet catecholamine content may be an integrated measure of plasma catecholamine concentrations during variations caused by sodium depletion.