Increased Plasma Norepinephrine Levels Research Articles

Effects of ibopamine on the increase in plasma norepinephrine levels during exercise in congestive heart failure

Congestive heart failure (CHF) is accompanied by increased levels of plasma norepinephrine (PNE) at rest. During exercise, PNE levels increase rapidly in patients with CHF, 1 causing skeletal vasoconstriction and muscle underperfusion. Because long-term sympathetic activation may be detrimental in patients with CHF, 2 inhibition of this sympathetic drive would appear to be beneficial. The oral dopamine agonist ibopamine causes vasodilation and reduces PNE levels at rest in patients with CHF. 3 However, the influence of ibopamine on peak oxygen consumption (VO 2) and PNE levels during exercise in patients with CHF is unknown, and was investigated in this study.

Modulation of noradrenaline release via activation of presynaptic beta-adrenoceptors in rabbits with adriamycin-induced cardiomyopathy.

We investigated the role of beta-adrenoceptors at postganglionic sympathetic nerve endings in noradrenaline release in rabbits with cardiomyopathic congestive heart failure produced by adriamycin (1 mg/kg, I.V., twice a week for 8 weeks). Plasma noradrenaline levels were measured before, 30 min after, and 60 min after the start of continuous intravenous administration of adrenaline (0.06 micrograms/kg/min) in adriamycin-treated and vehicle-treated rabbits in anesthetized condition and pithed condition with electrically stimulated sympathetic outflow (3 Hz, 1 ms square wave pulse, 90 V). In both the anesthetized and pithed conditions, adrenaline increased plasma noradrenaline levels in vehicle-treated rabbits. However, in the adriamycin-treated rabbits, adrenaline had no effect on the plasma noradrenaline level. Pretreatment with propranolol (0.2 mg/kg, bolus I.V. + 0.1 mg/kg/hr, continuous infusion) almost completely abolished the rise in plasma noradrenaline associated with adrenaline infusion in vehicle-treated rabbits. These results suggest that in rabbits with adriamycin-induced cardiomyopathy, the noradrenaline release from the sympathetic nerve endings via the activation of presynaptic beta-adrenoceptors is reduced. This might be due to down-regulation of presynaptic beta-adrenoceptors caused by the elevated plasma noradrenaline due to cardiac failure. However, other possibilities such as reduced affinity or impaired signal transduction cannot be excluded.

Effects of chronic tachycardia-induced cardiomyopathy on the β-adrenergic receptor system

Chronic supraventricular (or ventricular) tachycardia causes a dilated cardiomyopathy. Effective treatment requires ablation of the tachycardia using antiarrhythmic agents, cryoablation, electroablation, or surgical interruption/excision. However, the underlying pathophysiologic mechanisms responsible for the development of supraventricular tachycardia-induced cardiomyopathy have not been fully identified. We hypothesized that chronic supraventricular tachycardia is associated with significant changes in the beta-adrenergic system that may have implications for the pathophysiology and treatment of supraventricular tachycardia-induced cardiomyopathy. Accordingly, we examined the relationship between left ventricular function, plasma norepinephrine level, beta-receptor number and affinity, and response to a beta-agonist (isoproterenol) infusion in eight control pigs and eight pigs subjected to supraventricular pacing-induced tachycardia (240 beats/min for 3 weeks). Left ventricular function was measured using simultaneous echocardiography and catheterization. Left ventricular end-diastolic dimension and pressure increased in pigs with supraventricular tachycardia (5.1 +/- 0.4 cm and 27 +/- 2 mm Hg) versus control pigs (3.8 +/- 0.3 cm and 8 +/- 2 mm Hg), p < 0.05. Left ventricular fractional shortening decreased in supraventricular tachycardia (10 +/- 1%) versus control pigs (34 +/- 1%), p < 0.05. In addition, in the pigs with supraventricular tachycardia the fractional shortening versus left ventricular end-systolic stress relationship fell below the control relationship. Plasma norepinephrine level (measured by high-performance liquid chromatography) increased in pigs with supraventricular tachycardia (3592 +/- 1606 pg/ml plasma) versus control pigs (323 +/- 74 pg/ml plasma), p < 0.05. beta-Receptor number and affinity (measured by [3H]dihydroalprenolol binding) did not change in supraventricular tachycardia (98.6 +/- 11.5 fmol/mg protein and 7.2 +/- 1.1 nmol) versus control pigs (99.1 +/- 9.4 fmol/mg protein and 6.8 +/- 0.5 nmol). The response to isoproterenol infusion (10 micrograms/kg) in supraventricular tachycardia was blunted: the absolute increase in left ventricular peak (+)dP/dt was reduced in supraventricular tachycardia (833 +/- 233 mm Hg/sec) versus control pigs (2180 +/- 139 mm Hg/sec), p < 0.05. Chronic supraventricular tachycardia caused a decreased contractile state, increased plasma norepinephrine level, and caused no change in beta-receptor number or affinity; however, the response to beta-agonist infusion was blunted. These results suggest that chronic supraventricular tachycardia is associated with uncoupling of the beta-receptor from subsequent intracellular components of the beta-adrenergic system. Therefore medical management of chronic supraventricular tachycardia-induced cardiomyopathy before and immediately after definitive ablation may require use of pharmacologic agents whose actions do not depend on an intact beta-adrenergic pathway.

Effect of l-threo-3,4-dihydroxyphenylserine on muscle sympathetic nerve activity in humans

To clarify the effect of l-threo-3,4-dihydroxyphenylserine ( l-threo-DOPS), a precursor of norepinephrine (NE), the effect of this drug on microneurographically recorded muscle sympathetic nerve activity (MSA) from the tibial nerve was analyzed in ten healthy male volunteers. A single dose of 600 mg of l-threo-DOPS was orally administered and the effect of this norepinephrine precursor on MSA at resting and at upright standing positions, as well as the MSA responsiveness to head-up tilting was examined by comparing the data obtained after administration of the drug with those obtained under control conditions. The plasma NE levels were determined in two subjects. The results were as follows: (1) resting MSA increased significantly 80 min after administration of l-threo-DOPS and was accompanied by an increase in plasma NE levels; (2) standing MSA when treated with the drug was not significantly different from values obtained under control conditions; and (3) MSA responsiveness to orthostasis was reduced after l-threo-DOPS. We conclude from the activation of MSA by l-threo-DOPS that this drug raised blood pressure not only through an increase in metabolized plasma NE levels, but also through the enhancement of MSA by activation of descending noradrenergic or adrenergic pathways proximal to the recording site of the sympathetic discharge.

Release of neuropeptide Y and noradrenaline during afferent nerve stimulation

The present study was carried out to investigate the possibility that noradrenaline (NA) and neuropeptide Y (NPY) are co-released after afferent vagal or saphenous stimulation (1, 5, 10 and 20 Hz) in chloralose-anaesthetized dogs. Electrical stimulation of the vagus elicited an increase in plasma NA levels for the 5, 10 and 20 (but not 1) Hz frequencies. Blood pressure only increased after a 20-Hz stimulation. In contrast, no change in plasma NPY levels was observed whatever the frequency of stimulation. Electrical stimulation of the saphenous nerve failed to change plasma NA and NPY levels. The present data suggest that (1) the release of NA varies according to the frequency of stimulation of nociceptive fibres, (2) NPY release does not seem to be involved in the pressor effect elicited by the stimulation of nociceptive-sensitive fibres, and (3) NPY and NA release are not necessarily linked.

INFLUENCE OF BETA-BLOCKADE ON CIRCULATING PLASMA LEVELS OF 3-METHOXY-4-HYDROXY PHENYLETHYLENE GLYCOL (MHPG) DURING EXERCISE IN MODERATE HYPERTENSION

1. The effect of exercise testing and beta-blockade on plasma norepinephrine (PNE), and secretion of its metabolite 3-methoxy-4-hydroxyphenylethylene glycol (MHPG), was assessed in 28 mild-to-moderate hypertensives before and after the administration of dilevalol, a new beta-blocker with beta 2-agonism. 2. This double blind, placebo-controlled study consisted of two successive submaximal exercise tests before and after the administration of a single oral dose of dilevalol (200 mg, 400 mg or 600 mg). Plasma norepinephrine levels were determined at rest, at 100 watts step of exercise and at maximal effort (Emax). 3. During the control test, mean PNE levels increased from 1.73 +/- 0.52 nmol/L (resting value) to 8.01 +/- 4.01 nmol/L at Emax (P less than 0.01) as MHPG levels increased from 11.18 +/- 1.33 nmol/L (rest) to 17.50 +/- 1.15 nmol/L (Emax, P less than 0.01). After dilevalol, PNE increased significantly as compared to controls (P less than 0.05), from 2.32 +/- 0.99 to 12.42 +/- 5.97 nmol/L (P less than 0.01). PNE and MHPG levels were correlated, both at rest and during exercise. PNE levels after beta-blockade were linearly related to the dose of beta-blocker administered. MHPG levels were unaltered by the administration of dilevalol, both before and after exercise. 4. The increase in MHPG that occurs during bicycle exercise is largely generated from an increase in central nervous system noradrenergic activity. While dilevalol increases the peripheral sympathetic nervous system, both at rest and during exercise (which is reflected by increases in PNE levels) the drug does not alter resting central nervous system noradrenergic activity nor amplify the increase in central noradrenergic activity that occurs during exercise.

Left ventricular filling and stress response pattern in essential hypertension

purpose: To evaluate whether impaired left ventricular filling determines the hemodynamic responses to isometric and orthostatic stress in a population with mild essential hypertension. patients and methods: The study population consisted of 32 patients with essential hypertension who were subdivided into those with preserved left ventricular filling (15 patients) and those with impaired left ventricular filling (17 patients). Echocardiograms were obtained before hemodynamic assessment was performed. Isometric stress and head-up tilt tests were done with a recovery period of at least 10 minutes between each to allow for blood pressure and heart rate to return to baseline. Hemodynamic reassessment was performed during the last minute of each test and at the end of the recovery period. Plasma epinephrine, norepinephrine, and dopamine levels were determined by radioenzymatic method. results: Isometric stress increased mean arterial pressure by 30% (p <0.0001) by an increase in cardiac output (p <0.0001) and total peripheral resistance (p <0.0001) associated with an increase in plasma catecholamine levels (p <0.0001). Patients with preserved left ventricular filling had an increase in arterial pressure predominantly through an elevation in cardiac output (17%, p <0.0001) associated with a small increase in plasma norepinephrine levels (p <0.05) and in peripheral resistance (11%, p <0.05). In contrast, patients with impaired left ventricular filling had an increase in arterial pressure mainly through an increase in peripheral resistance (25%, p <0.0001) that was associated with a 45% elevation in plasma norepinephrine levels (p <0.0001). Orthostatic stress (passive head-up tilt) caused an exaggerated decrease in stroke volume (p <0.01) and cardiac output (p <0.01) in patients with impaired left ventricular filling when compared with those with preserved diastolic function. conclusion: Impaired left ventricular filling blunts the response of the heart to isometric and orthostatic stress. As a consequence, hypertensive patients with impaired ventricular filling respond to these stressors with enhanced sympathetic stimulation and exaggerated vasoconstriction.

Thermogenic and lipolytic effect of yohimbine in the dog

1. Lipid mobilization during a hypocaloric diet may be enhanced by a pharmacological approach using alpha 2-adrenoceptor antagonists since these drugs are known to increase sympathetic tone and stimulate lipolysis. Studies were undertaken in the dog in order to evaluate the effects of oral yohimbine administration (alpha 2-adrenoceptor antagonist) on heat production, metabolic, endocrinological and cardiovascular parameters. 2. Acute oral yohimbine (0.25 or 0.40 mg kg-1) provoked an increase in plasma non-esterified fatty acids. The drug increased sympathetic nervous system activity as indicated by the increased level of plasma noradrenaline. These effects persisted during the entire experimental period (4 h). The increase in plasma noradrenaline level was two fold higher with the higher dose of yohimbine (0.4 mg kg-1). The plasma adrenaline level was increased only with the higher dose. 3. Yohimbine transiently increased plasma insulin and the effect was dose-dependent. 4. Yohimbine (0.25 mg kg-1) enhanced heart rate and arterial blood pressure. 5. The effect of yohimbine on oxygen consumption, carbon dioxide and heat production was determined by indirect calorimetry. The drug (0.25 mg kg-1) increased O2 consumption and CO2 and heat production 30 min after its administration and the effect persisted over the experimental period. The respiratory quotient, rather low in the fasting animals, remained unchanged. 6. The present work indicates that thermogenesis and lipid mobilization are enhanced during fasting in the dog by alpha 2-adrenoceptor blockade. Yohimbine also induced a transient increase in plasma insulin level and increased heart rate and blood pressure. The lipid mobilization plus the action on thermogenesis observed after yohimbine draw attention to the putative interest of a2-antagonists in the pharmacological treatment of obesity during restricted calorie intake.

Insulin resistance and hyperinsulinemia in patients with chronic congestive heart failure

Congestive heart failure is a condition associated with increased plasma norepinephrine levels. Moreover, norepinephrine has been recently demonstrated to affect glucose homeostasis by decreasing insulin sensitivity. In the present study, eight patients suffering from chronic congestive heart failure and 10 healthy age- and body mass index-matched subjected were submitted to both an oral glucose tolerance test (OGTT; 75 g) and a euglycemic hyperinsulinemic glucose clamp. During the 360 minutes of the glucose clamp, insulin was infused at three different rates (25, 50, and 100 mU/kg/h), while d- 3H glucose infusion allowed determination of glucose turnover. In basal conditions, patients versus controls had similar plasma glucose (5.2 ± 0.1 v 4.9 ± 0.2 mmol/L, P = NS), but higher plasma insulin (125.7 ± 9.2 v 35.7 ± 3.3 pmol/L, P < .01), norepinephrine (5.39 ± 0.13 v 1.47 ± 0.22 nmol/L, P < .001), and free fatty acid (FFA) (927 ± 79 v 792 ± 88 μmol/L, P < .05) levels. In patients, basal plasma norepinephrine correlated with FFA levels ( r = .65, P < .025). After loading glucose, plasma glucose and insulin levels were still significantly higher in patients than controls. Euglycemic hyperinsulinemic glucose clamp produced a lower insulin-mediated inhibition of endogenous (hepatic) glucose production (HGP) and a greater increase in both glucose disappearance rate (Rd) and glucose metabolic clearance rate (gMCR) in patients than in controls during the first two insulin infusion rates (25 and 50 mU/kg/h). By contrast, these differences disappeared during the highest insulin infusion rate (100 mU/kg/h). Insulin-mediated decrease in plasma FFA levels was also lower in patients than controls. In conclusion, our study shows that in patients suffering from chronic congestive heart failure, an insulin-resistant state seems to occur as a consequence of a contemporary increase in plasma norepinephrine levels.

Oral Pharmacokinetics of Bisoprolol in Resting and Exercising Healthy Volunteers

The effects of exercise on bisoprolol oral pharmacokinetics were studied in eight healthy male volunteers in an open, randomized, three-period, crossover trial. Oral bisoprolol (20 mg) was given either at rest during 24 h or with iterative stress tests before and 2.5, 5, 10, and 24 h after dosing. Exercise tests were repeated on a third placebo period. Bisoprolol was assayed in plasma and urines, and plasma catecholamines were measured before and after stress tests, Cmax, Tmax, elimination t1/2, and renal clearance of bisoprolol were not significantly modified by exercise. AUC0-infinity significantly decreased by 7.5% (p less than 0.05) with stress test resulting in an increase in apparent oral clearance. The beta-blocking effect peaked at 2.5 h, lasted greater than 24 h, and was related to plasma levels. The exercise-induced increase in plasma norepinephrine levels was significantly augmented with bisoprolol. These results suggest that repeated exercise tests exerted only limited effects on the oral pharmacokinetics of bisoprolol.

Hemodynamic and neuroendocrine response to acute administration of the phosphodiesterase inhibitor BM 14.478 in patients with congestive heart failure

The benzimidazol analogue BM14.478 is a phosphodiesterase inhibitor with both vasodilator and positive inotropic properties. Hemodynamic parameters and plasma hormone levels of 8 patients (1 female, 7 male) with chronic congestive heart failure NYHA Classes II-IV (1 patient with coronary artery disease, 7 patients with primary dilated cardiomyopathy) were assessed before and until 6 h after the intravenous application of 1.0 mg BM14.478. There was a significant decrease of mean pulmonary artery pressure (28 +/- 11 vs. 23 +/- 11 mmHg; p less than 0.05), mean right atrial pressure (8.6 +/- 5.2 vs. 5.0 +/- 4.7 mmHg; p less than 0.02), and systemic vascular resistance (1651 +/- 484 vs. 1206 +/- 252 dynes.s.cm-5; p less than 0.05) as early as 10 min after injection of BM14.478. Pulmonary vascular resistance also was reduced (128 +/- 86 vs. 61 +/- 39 dynes.s.cm-5, 30 min after injection; p less than 0.02). Simultaneously there was a significant increase of cardiac index (2.3 +/- 0.7 vs. 3.1 +/- 0.8 l.min-1.m-2, 10 min after injection; p less than 0.02), and stroke volume index (28.8 +/- 11.7 vs. 33.9 +/- 8.5 ml.min-1.m-2; 30 min after injection; p less than 0.05). Although mean heart rate did not change significantly, some patients reacted with a transient increase. There was also a slight but insignificant increase of the double product. No serious side effects were observed. The hemodynamic improvement was followed by a delayed reduction of plasma levels of epinephrine (51 +/- 20 vs. 41 +/- 21 pg/ml; p less than 0.02; 30 min after injection) and atrial natriuretic peptide (229 +/- 283 vs. 121 +/- 168 pg/ml; p less than 0.05; 1 h after injection). Mean levels of plasma norepinephrine, however, did not change significantly and individual responses showed large variations, which could not be predicted by the behavior of the hemodynamic parameters. Three of eight patients (2 of these with elevated baseline filling pressures) even showed a marked increase of plasma norepinephrine levels after BM14.478. Response of plasma renin activity and plasma vasopressin levels to BM14.478 also was heterogeneous. According to the results of this study, acute administration of the phosphodiesterase inhibitor BM14.478 has an immediate beneficial hemodynamic effect in patients with severe congestive heart failure by reducing both preload and afterload, and by increasing cardiac index and stroke volume. However, this improvement of hemodynamic parameters is not necessarily accompanied by a favorable short-term response of plasma hormones, and therefore does not allow any conclusions on survival of these patients.

Chronic Effects of Metoprolol on Myocardial β-Adrenergic Receptors in Doxorubicin-Induced Cardiac Damage in Rats

This study was designed to clarify whether chronic administration of metoprolol had any influence on cardiac beta-adrenergic receptors (BAR) in doxorubicin (DOX)-induced cardiac damage. DOX was injected through the tail vein into rats (3 mg/kg/week, n = 22) for 5 weeks. One week after the final injection, the rats were randomly divided into two groups, M (with metoprolol, 10 mg/kg/day subcutaneously, s.c.; n = 11) and D (without metoprolol; n = 11). After 3-week infusion, plasma norepinephrine (NE) levels and BAR density [[125I]iodocyanopindolol (ICYP) binding on crude membranes] were measured. Left and right ventricular end-diastolic pressure (LVEDP, RVEDP) and myocardial NE levels were also measured, and the results were compared with those from an age-matched control group (C n = 11). Decreased BAR density and increased plasma NE levels were evident in group D, indicating downregulation. In group M, BAR density and plasma NE levels were similar to those in group C. The myocardial NE levels were decreased in group D, but were higher in group M than in group D. The LVEDP and RVEDP were increased in group D, but were almost normal in group M. These results suggest that metoprolol is a promising drug for treatment of DOX-induced cardiac damage.

Capsaicin‐sensitive sensory neurons are involved in the plasma catecholamine response of rats to selective stressors.

1. The effect of capsaicin pre-treatment on adrenal catecholamine (CA) secretion in response to stress is controversial. In earlier experiments performed under pentobarbitone anaesthesia, the release of CA in response to stress was complicated by the effects of the barbiturate anaesthesia. 2. In the present study we have used conscious freely moving rats with indwelling cannulae to study the effect of neonatal capsaicin pre-treatment on the plasma CA response to different types of stressors (swimming stress, hypovolaemic stress, immobilization stress and cold stress). 3. After swimming for 20 min, plasma noradrenaline (NA) levels increased by 8-fold and adrenaline by 2-fold in control rats. The increase in plasma NA levels in the capsaicin group was attenuated at 10 min of swimming compared with the vehicle group (P < 0.05). 4. With hypovolaemic stress, there were no differences in plasma CA levels, blood pressure and heart rate between the capsaicin group and the vehicle group. There were also no differences in plasma CA levels after immobilization stress between the two groups. 5. With cold stress, plasma NA levels increased 5-fold and adrenaline levels by 3-fold over basal at 45 min in the vehicle pre-treated rats. This increase was not observed in the capsaicin group. 6. Immunoreactive substance P was depleted by only 68% in the splanchnic nerve following capsaicin pre-treatment. If the remaining 32% was biologically active substance P then it could account for the maintenance of the response to hypovolaemic and immobilization stress. However, it might be possible that the responses to hypovolaemic and immobilization stresses could be attenuated if a more complete depletion were achieved. 7. These results in conscious rats indicate that capsaicin-sensitive sensory neurons are required for plasma CA response to selective stressors. They are required for CA output in response to cold stress and to the early phase of swimming stress, but not to hypovolaemic stress and immobilization stress.

FMRF-amide and L-Arg-L-Phe increase blood pressure and heart rate in the anaesthetised rat by central stimulation of the sympathetic nervous system

The neuropeptide FMRFamide (L-Phe-L-Met-L-Arg-L-Phe-NH2) increases mean arterial blood pressure (MABP) and heart rate (HR) in the anaesthetised rat at concentrations ranging from 10-1000 micrograms/kg. Here, we demonstrate that peptides containing L-arginyl-L-phenylalanine (L-Arg-L-Phe), the C-terminal sequence of FMRFamide, mimic its haemodynamic effects. L-Arg-L-Phe was approximately 4 fold more potent in increasing MABP and HR than FMRFamide. In 40 different peptides investigated, the following order of potency of the effective compounds was established: L-Arg-L-Phe-L-Ala = L-Arg-L-Phe greater than FMRFamide greater than L-Met-L-Arg-L-Phe = L-Arg-L-Trp greater than L-Arg-L-Tyr greater than D-Arg-L-Phe = L-Arg-L-Phe-OMe greater than L-Arg-L-Leu = L-Arg-L-Ile greater than L-Lys-L-Phe greater than L-Arg-L-Met. L-Arg-L-Phe or FMRFamide did not cause any pressor response in pithed rats, indicating a central mechanism of action. In anaesthetised rats, intravenous injections of FMRFamide or L-Arg-L-Phe (100 micrograms/kg) were associated with a 2-3 fold increase in plasma noradrenaline levels, whereas plasma adrenaline levels remained unchanged. Thus, L-Arg-L-Phe may represent the active principle of FMRFamide acting by a central mechanism involving the release of noradrenaline from sympathetic nerve terminals.

Effets de la lidocaïne sur la circulation artérielle et veineuse des membres chez l'homme

The effects of intravenous lidocaine on limb arteries and veins were investigated in a placebo-controlled study. Seven young healthy volunteers, 23 to 28 — years — old, were included. Electrocardiogram, arterial pressure and arm and leg blood flows were recorded continuously. Systolic and diastolic blood pressures were measured in the left arm by finger photoplethysmography. Limb blood flow and the limb venous system were studied by venous occlusive plethysmography. The venous parameters studied were venous tone, lowest closing pressure, venous volume at 30 mmHg, and venous distensibility. After an initial bolus of 1.5 mg · kg −1 lidocaine had been given, 30, and then 60, μg · kg −1 · min −1 were given for one hour each. Plasma noradrenaline and serum lidocaine titres were measured before giving the lidocaine, and at the end of each one hour period. Placebo consisted in a two hour infusion of 0.25 ml · min −1 normal saline. Lidocaine titres were 1.64 ± 0.40 μg · ml −1 after one hour, and 2.55 ± 0.69 μg · ml −1 after two hours. Lidocaine increased vascular resistances in both the forearm (+ 81 % to + 93 %) and the calf (+ 38 % to + 57 %). There was a concomitant increase in mean arterial blood pressure (+ 21 % to + 28 %) without any change in heart rate. There was a significant dose-dependent increase in plasma noradrenaline levels during the second period of the lidocaine infusion with respect to the preinfusion period and the same period during the placebo infusion. Venous capacitance measured before any infusion had been started was greater in the leg than in the arm. Lidocaine induced a progressive increase in forearm venous tone, which became significant during the period of higher infusion rate. There wasn't any change in calf venous tone. It would therefore seem that the arterial and venous effects of lidocaine which have been reported may be due to an increase in adrenergic tone. The vascular effects of therapeutic serum levels of lidocaine may contribute to the good cardiovascular tolerance of this drug, both as local anaesthetic agent, and as antiarrhythmic drug.

Adrenergic response to nicardipine in the management of postoperative hypertension

Nicardipine, a new dihydropyridine calcium channel blocking agent, has been shown to be effective in the management of hypertension. The adrenergic response to intravenous nicardipine as measured by changes in plasma catecholamine concentrations in seven patients undergoing treatment of postoperative hypertension is reported. Postoperative hypertension was defined as a systolic blood pressure (SBP) greater than 140 mm Hg. Nicardipine or placebo was administered in doses of 10 mg/h, 12.5 mg/h, and 15.0 mg/h for 5 minutes, 5 minutes, and 15 minutes, respectively, to achieve a therapeutic response defined as a reduction of SBP of 15% or more. Once a therapeutic response occurred, patients entered a maintenance period when the study drug infusion rate was reduced to the equivalent of 3.0 mg/h, and the dose was adjusted by 1.0 to 2.5 mg/h every 15 minutes as needed to maintain blood pressure control. Patients who did not respond to the study drug had their treatment code broken and, if on placebo, received open-label nicardipine. Blood samples were taken for the measurement of plasma norepinephrine (NE) concentrations at baseline prior to nicardipine infusion, at the time of therapeutic response, during maintenance, and after discontinuation of nicardipine. There were no significant differences between the baseline heart rate prior to nicardipine infusion and at the time of therapeutic response, during maintenance, or after discontinuation of the infusion. Mean NE concentrations at baseline prior to nicardipine infusion were 589.3 +/- 140.1 pg/mL (normal range, 75 to 480 pg/mL). Thus, hypertensive patients in the recovery room have a high degree of background sympathetic stimulation. Nicardipine did not further increase plasma NE levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Beta-adrenergic blockade decreases norepinephrine release in humans

Beta-Adrenergic blockade with propranolol (PRP) has been reported to cause an increase in plasma norepinephrine (NE) levels in humans, which suggests that a reflex increase in sympathetic nervous system (SNS) vasoconstrictor tone compensates for the hypotensive effect of beta-adrenergic blockade. However, plasma NE levels are an indirect measure of SNS activity. We have developed a two-compartment model of NE kinetics to estimate NE release into an extravascular compartment as a more comprehensive measure of systemic SNS activity. To determine whether beta-adrenergic blockade alters extravascular NE release, we studied nine healthy subjects during sequential infusions of saline and PRP. During PRP infusion, there was an increase in plasma NE levels [1.03 +/- 0.13 to 1.27 +/- 0.21 (SE) nM; P = 0.05], but the extravascular NE release rate decreased significantly (15.5 +/- 1.6 to 9.2 +/- 1.2 nmol.min-1.m-2, P = 0.0002). The plasma NE concentration increased despite the fall in extravascular NE release rate primarily because the clearance of NE from plasma declined (1.55 +/- 0.08 to 1.18 +/- 0.07 l.min-1.m-2, P = 0.0001); the NE spillover rate into plasma did not change (1.73 +/- 0.18 to 1.75 +/- 0.23 nmol.min-1.m-2, P = 0.89). We conclude that PRP decreases extravascular NE release in humans. Suppression of SNS activity may be an additional mechanism of action of nonselective beta-adrenergic antagonists in humans.

The effects of a single dose of dilevalol on [3H]‐noradrenaline plasma kinetics and plasma lipoprotein cholesterol concentrations.

1. A single oral dose of dilevalol (200 mg or 400 mg) or placebo was administered to 15 normal male volunteers in a double-blind, random order crossover study. 2. Dilevalol had no significant effect on supine blood pressures or heart rates, but caused a significant fall in systolic blood pressure 1 and 30 min following standing, and attenuated the rise in diastolic blood pressure and heart rate that accompanies standing. 3. Dilevalol caused a dose dependent increase in plasma noradrenaline levels from arterialized blood which was due to an increase in noradrenaline spillover with no change in clearance. 4. Dilevalol increased plasma levels of the noradrenaline metabolite 3,4-dihydroxyphenylethylene glycol (DHPG) (which is formed in sympathetic nerves following neuronal uptake of noradrenaline), indicating that the increase in noradrenaline spillover was not due to the blockade of neuronal uptake. 5. Acute dilevalol administration had no effect on total plasma cholesterol, HDL-cholesterol or LDL-cholesterol levels.

Decreased Cardiac Output in Infants of Mothers Who Abused Cocaine

Cocaine increases the level of circulating catecholamines by blocking the catecholamine reuptake receptors. The effect of intrauterine cocaine exposure on cardiac output was studied in 15 full-term newborn infants whose mothers used cocaine during pregnancy. A total of 22 healthy nonexposed full-term infants served as a control group. On the first day of life, cardiac output (183 +/- 12 vs 235 +/- 13 mL/kg per minute, mean +/- SD; P less than .05) and stroke volume (1.3 +/- 0.1 vs 1.9 +/- 0.1 mL/kg, mean +/- SD; P less than .005) were lower and arterial blood pressure (60 +/- 2 vs 41 +/- 2 mmHg, mean +/- SD; P less than .001) higher in the infants exposed to cocaine. On day 2, cardiac output, stroke volume, and mean arterial blood pressure were similar, probably because of the gradual excretion of cocaine and its metabolites by the infant. It was speculated that an increase in plasma norepinephrine levels is responsible for the cardiovascular effects of intrauterine cocaine exposure.

Plasma Norepinephrine Kinetics, Dopamine-β-Hydroxylase, and Chromogranin-A, in Hypothyroid Patients before and following Replacement Therapy*

Whether the increased plasma norepinephrine level reported in hypothyroidism is the result of impaired norepinephrine (NE) clearance or increased NE release by nerve terminals is unknown. We, therefore, measured plasma NE levels and clearance in 11 hypothyroid patients before [T4 index, 41.2 +/- 7.7 nmol/L (mean +/- SEM); TSH, 71.4 +/- 23.0 mU/L] and 4 +/- 0.5 months after thyroid replacement (T4 index, 136.4 +/- 24.4 nmol/L; TSH, 3.2 +/- 1.2 mU/L) and in 8 healthy volunteers. Plasma dopamine-beta-hydroxylase and chromogranin-A, which are coreleased with NE by sympathetic nerve endings, were also measured. Plasma NE was higher in the hypothyroid (2.37 +/- 0.24 nmol/L) than in the euthyroid state (1.86 +/- 0.24 nmol/L; P less than 0.02) or in the controls (1.87 +/- 0.27 nmol/L). Plasma clearance of NE, however, was not affected after thyroid replacement (hypothyroid, 2.08 +/- 0.31 L/min; euthyroid, 1.94 +/- 0.21 L/min; controls, 1.86 +/- 0.15 L/min). There was no significant change in plasma dopamine-beta-hydroxylase (hypothyroid, 720 +/- 139 nmol/mL.h; euthyroid, 553 +/- 97 nmol/mL.h) or plasma chromogranin-A (hypothyroid, 48.9 +/- 7.1 ng/mL; euthyroid, 42.9 +/- 5.3 ng/mL) after thyroid replacement. We conclude that the increased plasma NE in hypothyroid patients is not due to a change in plasma clearance, but is more likely secondary to increased NE release.