Effect of sample preparation and liquid chromatography column choice on selectivity and precision of plasma catecholamine determination

Continuous Ambulatory Peritoneal Dialysis is Responsible for an Increase in Plasma Norepinephrine

Objective

To investigate the reason for increasing norepinephrine (NE) levels reported in continuous ambulatory peritoneal dialysis (CAPD) patients.

Methods

Norepinephrine was measured in the plasma and peritoneal dialysate of CAPD patients ( n = 22) and in the plasma and the urine of healthy subjects ( n = 20). It was also measured in the plasma of patients with chronic renal failure (CRF) ( n = 15) and patients on hemodialysis (HD) ( n = 15).

Results

It was found that NE was increased in CAPD patients compared with healthy individuals (687 ± 221 pg/mL vs 199 ± 25 pg/mL, p < 0.01). The daily removal of NE from the peritoneum of CAPD patients was lower compared with the amount of NE excreted in the urine of healthy subjects. Plasma NE increased after infusion of peritoneal dialysate. In 15 new patients on CAPD, it was found that NE plasma levels increased from 329 ± 67 pg/mL before initiation of dialysis, to 584 ± 173 pg/mL after 12 months of treatment ( p < 0.01). Finally, plasma NE in CAPD patients (687 ± 221 pg/mL) was significantly higher compared with the already increased levels in patients on HD or with CRF (406 ± 143 pg/mL and 378 ± 142 pg/mL, respectively).

Conclusions

It is concluded that CAPD in patients with end-stage renal disease is responsible for a progressive increase of plasma norepinephrine.

Electro convulsive therapy: Modification of its effect on the autonomic nervous system using anti-cholinergic drugs

The antidepressant efficacy of electroconvulsive therapy (ECT) is correlated to the quality of the seizure as measured by EEG but has also been linked to the magnitude of changes in hemodynamic variables. Muscarinic receptor antagonists are frequently used in the treatment, and are known to affect the hemodynamic response. We hypothesized that atropine and glycopyrrolate alter the hemodynamic and autonomic hormonal response to ECT. In a randomized, cross-over study design 23 patients received either atropine, glycopyrrolate or placebo before ECT. Hemodynamic variable, EEG and EMG, and blood adrenaline, noradrenaline and pancreatic polypeptide was determined. No geriatric patients were included. Hemodynamic changes with ECT can be divided into three phases: Drop in blood pressure and pulse rate in 1st post-stimulus phase was less when using 1 mg atropine. In 2nd post-stimulus phase atropine gave a higher systolic blood pressure. No differences were seen in hormone levels after ECT in the three interventions. A significant longer tonic clonic seizure was seen in the glycopyrrolate group and a tendency of the same was seen with atropine. The study found that the changes in hemodynamic variables induced by ECT can be altered by concomitant administration of muscarinic receptor antagonist.

Favorable effects of carotid endarterectomy on baroreflex sensitivity and cardiovascular neural modulation: a 4-month follow-up

Carotid surgery variably modifies carotid afferent innervation, thus affecting arterial baroreceptor sensitivity. Low arterial baroreflex sensitivity is a well-known independent risk factor for cardiovascular diseases. The aim of this study was to assess the 4-mo effects of carotid endarterectomy (CEA) on arterial baroreceptor sensitivity and cardiovascular autonomic profile in patients with unilateral carotid stenosis. We enrolled 20 patients (72 ± 8 yr) with unilateral >70% carotid stenosis. ECG, beat-by-beat blood pressure, and respiration were continuously recorded before and 126 ± 9 days after CEA, at rest and during a 75° head-up tilt. Both pharmacological (modified Oxford technique, BRS) and spontaneous (index α, spectral analysis) arterial baroreflex sensitivity were assessed. Cardiovascular autonomic profile was evaluated by plasma catecholamines and spectral indexes of cardiac sympathovagal modulation [low-frequency R-R interval (LFRR), low frequency-to high frequency ratio (LF/HF), high-frequency R-R interval (HFRR)] and sympathetic vasomotor control [low-frequency systolic arterial pressure (LFSAP)] obtained from heart rate and SAP variability. After CEA, both the index α and BRS were higher (P < 0.02) at rest. SAP variance decreased both at rest and during tilt (P < 0.02). Before surgery, tilt did not modify the autonomic profile compared with baseline. After CEA, tilt increased LF/HF and LFSAP and reduced HFRR compared with rest (P < 0.02). Four months after CEA was performed, arterial baroreflex sensitivity was enhanced. Accordingly, the patients' autonomic profile had shifted toward reduced cardiac and vascular sympathetic activation and enhanced cardiac vagal activity. The capability to increase cardiovascular sympathetic activation in response to orthostasis was restored. Baroreceptor sensitivity improvement might play an additional role in the more favorable outcome observed in patients after carotid surgery.

Longitudinal changes in pituitary-adrenal hormones in South African women with burnout

The authors' goal was to document baseline pituitary-adrenal hormonal and related metabolic variables in 16 female patients with burnout. Then, following stress management intervention, to compare the changes with an equal number of untreated control subjects. At monthly intervals for 4 mo, 24-h urine samples were obtained for determination of free cortisol excretion. In addition, fasting blood samples were analyzed for levels of cortisol, dehydroepiandrosterone sulfate (DHEAS), ACTH, aldosterone, and catecholamines. Other biochemical measurements included growth hormone, prolactin, insulin, glucose, and lipid components. The Maslach Burnout Inventory, General Health Questionnaire- 28, and Zung depression rating scale were completed on each consecutive visit. The most striking finding was the reduction of urine free-cortisol excretion in the patients compared with controls. Initial urinary free cortisol was significantly lower in the patients (mean +/- SEM = 47.2 +/- 11.0 vs 79.0 +/- 6.8 nmol/L, p = 0.02) and remained significantly reduced at 4 mo (mean +/- SEM = 44.0 +/- 6.1 vs 91.1 +/- 8.8 nmol/L, p = 0.0001). There were no significant changes in the other hormonal and biochemical data. We conclude that there is functional hypocortisolism in burnout, which is not immediately restored on stress management intervention despite clinical and psychological improvement.

Leptin response to short-term fasting in sympathectomized men: role of the SNS

We studied plasma leptin levels in six people with high-lesion spinal cord injury [SCI; body mass index (BMI) 25.9 +/- 1.5 kg/m(2), age 37 +/- 3.0 yr] and six able-bodied (AB) controls (BMI 29.1 +/- 1.9 kg/m(2), age 35 +/- 3.5 yr) before and after 12, 24, and 36 h of fasting. The plasma leptin levels significantly decreased during 36 h fasting by 48.8 +/- 4.5% (pre: 11.3 +/- 2.3, post: 6.2 +/- 1.5 ng/ml) and 38.6 +/- 7.9% (pre: 7.6 +/- 5.0, post: 4.2 +/- 1.0 ng/ml) in SCI and AB, respectively. Plasma leptin started to decrease at 24 h of fasting in the SCI group, whereas plasma leptin started to decrease at 12 h of fasting in the AB group. The current study demonstrated that plasma leptin decreased with fasting in both SCI and AB groups, with the leptin decrease being delayed in the SCI group. The delayed leptin response to fasting in the SCI group may be because of increased fat mass (%body fat, SCI: 33.8 +/- 3.0, AB: 24.1 +/- 2.9) and sympathetic nervous system dysfunction.

Quantitative analysis of catecholamines in human dental pulp

Catecholamines are important elements of neuroendocrine regulation, and their concentrations in dental pulp are of interest. Two groups of teeth were used in this study: (i) healthy teeth and (ii) periodontally diseased teeth. After the processing of dental pulp obtained from the extracted teeth, the samples were analyzed in a computer-controlled Merck-Hitachi HPLC system at 280 nm wavelength. The external and internal standard methods of the HPLC Manager Program were used for validation. In healthy teeth the norepinephrine level of dental pulp was 4.86 +/- 0.96 micrograms/g, whereas the epinephrine level was 8.1 +/- 1.18 micrograms/g. In periodontally diseased teeth norepinephrine and epinephrine levels were significantly higher (p < 0.01) at 13.98 +/- 21.13 micrograms/g and 1.42 +/- 0.32 micrograms/g, respectively. Dopamine could not be demonstrated in 87% of the pulps. Summing up we succeeded in demonstrating norepinephrine and epinephrine in human pulp, but in most cases we could not demonstrate dopamine. Further investigations are needed on pulp tissue infected because of caries.

Neuroadrenergic activation and response to dobutamine in congestive heart failure secondary to idiopathic dilated cardiomyopathy

Detection of contractile reserve is important in heart failure patients. To determine if detection of contractile reserve is influenced by neuroadrenergic activation, we examined the relation between dobutamine stress echocardiography (DSE) findings and plasma norepinephrine levels (NE) at rest in 35 patients with nonischemic left ventricular (LV) dysfunction (New York Heart Association class >III in all; LV ejection fraction 0.27 +/- 0.5). Changes in global wall motion score (WMS), and separately in WMS of hypokinetic segments and akinetic segments, were analyzed. A patient was considered to be responsive to dobutamine if the change in global WMS was >/=4. Twenty-three patients were responsive and 12 were not responsive to dobutamine. Plasma NE and baseline heart rate were significantly higher in nonresponsive patients (p <0.001). Changes in global WMS and in hypokinetic segment WMS were inversely related to either plasma NE (r -0.68 and -0.67, respectively) or baseline heart rate (r -0.60 and -0.66, respectively). The change in akinetic segment WMS was related to plasma NE only (r -0.50). Changes in WMS were not related to age, diastolic and systolic LV volume, baseline global WMS, or number of akinetic segments at baseline. Plasma NE >602 pg/ml predicted a blunted or absent contractile reserve at DSE (sensitivity 92%; specificity 87%). Neuroadrenergic activation may influence contractile reserve found at DSE in patients with heart failure due to nonischemic LV dysfunction.

Study of salivary catecholamines using fully automated column-switching high-performance liquid chromatography

Cortisol and catecholamines are major physiological markers of human stress. In order to establish a fully automated assay system for both cortisol and catecholamines in saliva, which can be sampled without imposing stress, the previously developed system for salivary cortisol [Okumura et al., J. Chromatogr. B, 670 (1995) 11] was modified. The practical sensitivity was around 0.1 pmol ml(-1) for norepinephrine and epinephrine and 0.5 pmol ml(-1) for dopamine. The established assay procedure provided R.S.D. values of 2 approximately 3% and recoveries of 96 approximately 104% at 0.5 pmol ml(-1). Measurement of salivary catecholamines in more than 300 samples taken from about 50 healthy volunteers indicated that the normal values of norepinephrine and dopamine were very low, about 0.1 pmol ml(-1) each. In contrast to cortisol, salivary catecholamine levels did not parallel those in plasma. Nevertheless, since levels of salivary catecholamines may reflect the sympathetic nerve activity in the salivary gland, they were assayed in volunteers making a scientific presentation before a large audience. Four out of eleven volunteers reported strong feelings of fear or anxiety, and their salivary catecholamine levels were about ten times higher than normal.

Effects of octreotide on cardiovascular hormones and haemodynamics in conscious dogs

Octreotide inhibits the secretion of several hormones and exerts vasopressor effects. To clarify the mechanism of atrial natriuretic factor (ANF) secretion and to assess the cardiovascular effects of octreotide in relation to changes in vasoactive peptide secretion, four groups of conscious dogs were studied: group I (n = 11) received saline infusion after placebo, group II (n = 10), the same infusion after octreotide, group III (n = 10), placebo only and group IV (n = 10) octreotide injection only. Saline (10% body wt) was infused over 40 min after subcutaneous injection of placebo or octreotide (1 microgram/kg). Saline produced a rise (p < 0.001) of plasma ANF from 32.4 +/- 4.1 to 59.0 +/- 8.5 pM after placebo and from 35.6 +/- 5.5 to 77.0 +/- 12.6 pM after octreotide. This rise, not significantly different between groups I and II paralleled a 4-5-fold increase (p < 0.005) of right and left atrial pressures. With a higher dose of octreotide (4 micrograms/kg) injected in 4 dogs, plasma ANF increased by 27.5 +/- 5 pM. During hypervolemia, plasma endothelin-1 remained unchanged but plasma angiotensin II and epinephrine decreased (p < 0.05) approximately by 80% without being affected by octreotide. Octreotide did not influence the basal secretion of ANF, endothelin-1, angiotensin II and catecholamines. However, in basal conditions, octreotide injection resulted in a 9% increase (p < 0.005) of left ventricular systolic pressure, unobserved after placebo. Plasma glucose decreased (p < 0.005) in groups receiving octreotide. Thus, octreotide does not impair the stretch-mediated release of ANF which implies a release mechanism independent from somatostatin receptors and consequent changes in intracellular c-AMP. Octreotide has also a pressor effect, unrelated to changes in vasoactive peptide production.

Role of endogenous endothelin-1 in experimental renal hypertension in dogs

BACKGROUND

Endothelin-1, a vasoconstrictive peptide released by endothelium, may be involved in the pathophysiology of hypertension. The goal of the present study was to evaluate the role of endogenous endothelin-1 in renal hypertension in dogs. The model of hypertension consisted of silk tissue wrapping of the left kidney, which produced hypertension associated with perinephritis after 6 to 8 weeks.

METHODS AND RESULTS

Thirty-two anesthetized open chest dogs were studied randomly: 8 dogs with perinephritic hypertension received the nonpeptidic ETA-ETB receptor antagonist bosentan (group 1); 8 other hypertensive dogs received the vehicle solution (group 2); 8 healthy dogs received bosentan (group 3); and 8 healthy dogs received the vehicle solution (group 4). Bosentan was injected as an intravenous bolus (3 mg/kg) followed by a 1-hour infusion at a rate of 7 mg.kg-1.h-1. In hypertensive dogs, bosentan produced a similar decrease (P = .0001) of both left ventricular systolic and mean aortic pressures, which averaged 38 mm Hg (-22% and -24%, respectively). These parameters remained unchanged with the vehicle solution. Left ventricular end-diastolic and left atrial pressures also declined significantly with bosentan (P = .0005 and P < .05, respectively). Left ventricular lengths tended to decrease. The other cardiovascular parameters (heart rate, peak [+]dP/dt, time constant of relaxation, and coronary vascular resistance) did not change significantly. In healthy dogs, bosentan decreased mean aortic pressure by 19 mm Hg (P = .004). Vehicle solution had no effect. Plasma endothelin-1 levels, similar under basal conditions in healthy and hypertensive dogs, increased 30-fold with bosentan (P = .0001).

CONCLUSIONS

Specific endothelin-1 receptor antagonism markedly lowers blood pressure in experimental hypertension but is less effective on blood pressure of healthy animals. This suggests that endothelin-1 plays a role in the pathophysiology of hypertension but contributes to a lesser extent to the maintenance of normal blood pressure. This role of endothelin-1 is unrelated to its plasma levels. The increase of plasma endothelin-1 with bosentan, due either to a displacement of endothelin-1 from its receptor or to a feedback mechanism, does not prevent this blood pressure reduction.

Cardiovascular and endocrine effects of endothelin-1 at pathophysiological and pharmacological plasma concentrations in conscious dogs

BACKGROUND

Increased plasma concentrations of endothelin-1, a potent vasoconstrictor produced by the endothelium, have been reported in various pathological conditions. This study was conducted to evaluate effects of endothelin-1 at pathophysiological and pharmacological plasma concentrations.

METHODS AND RESULTS

Endothelin-1 was infused at increasing doses (2.5, 5, 10, and 20 ng/kg.min for 1 hour each) in nine conscious dogs. During endothelin-1 infusion, plasma endothelin-1 rose from a basal value of 1.8 +/- 0.4 pmol/l to 5.8 +/- 1.1 (pathophysiological), 20.8 +/- 3.9 (pathophysiological), 85.4 +/- 18.9 (pharmacological), and 311.4 +/- 55.7 (pharmacological) pmol/l at each dose, respectively. Heart rate increased at 2.5 ng/kg.min (from 129 +/- 7 to 146 +/- 12 beats/min) but decreased at 20 ng/kg.min (97 +/- 7 beats/min) (p less than 0.001). Such a biphasic response was also observed for peak (+)dP/dt and (dP/dt)/DP40 (p less than 0.005). Left ventricular systolic pressures, mean aortic pressure, and left atrial pressure increased over time (p less than 0.05, p less than 0.005, and p less than 0.001, respectively). The time constant of early isovolumic relaxation rose progressively (p less than 0.001). The percent systolic shortening decreased at 10 and 20 ng/kg.min (p less than 0.005). Pressure-segment length loops showed a reduction in systolic shortening associated with an increase in left ventricular systolic pressure at 20 ng/kg.min. Atrial natriuretic factor rose after 5 ng/kg.min from 28.5 +/- 6.5 to 92.0 +/- 18.2 pmol/l (p less than 0.005). Angiotensin II and catecholamines did not change significantly. Serum urea and creatinine rose progressively (p less than 0.05), whereas glucose decreased (p less than 0.05). The above results differed significantly from measurements obtained in a time-control group of six dogs.

CONCLUSIONS

A fourfold increase of plasma endothelin-1 obtained after doubling the infusion rate suggests a reduction in endothelin-1 clearance or endothelin-1 endogenous production. The biphasic response of heart rate is consistent with baroreflex-mediated effects resulting from vasodilation at the pathophysiological level and vasoconstriction at the pharmacological level. Hemodynamic data suggest an increase followed by a decrease in contractility at both levels, respectively. Finally, endothelin-1 is a stimulator of atrial natriuretic factor.

Analysis of drugs and other toxic substances in biological samples for pharmacokinetic studies

The importance of the role of analysis of drugs and other toxic substances in biological samples (bioanalysis) in medicine, toxicology, pharmacology, forensic science, environmental research and other biomedical disciplines is self-evident. Among these disciplines, bioanalysis plays a special pivotal role in pharmacokinetics. The pharmacokinetic parameters, such as half-life, volume of distribution, clearance and bioavailability, of drugs and other compounds are derived from the concentrations of these analytes assayed in the biological samples collected at specified time points. The capability of analysts to develop sensitive and specific analytical methods for the assay of low concentrations of drugs and other toxic compounds in small amounts of biological samples has contributed significantly to the theoretical advances in pharmacokinetics and its applications in clinical pharmacology and the management of drug therapy in patients. The increased demands for pharmacokinetic applications in turn have stimulated the innovation and improvement in bioanalytical technologies. The reliability of the pharmacokinetic conclusions depends on the accuracy and precision of the analytical methods employed to assay the biological samples. Factors that affect the integrity of the bioanalytical data should therefore be controlled in analysis of biological samples for pharmacokinetics studies. The biological samples for drug concentration determination should be collected as specified in the study protocol with respect to the time and site of sampling. These samples should be processed to avoid extraneous interactions between the analytes and sampling devices or additives resulting in the redistribution of the analytes between components of the biological samples, such as displacement of drug binding and changes in the distribution of the analytes between plasma and red blood cells. The stability of the drugs and other analytes in the samples should also be evaluated to establish the conditions suitable for the transportation and storage of the samples to avoid chemical, photochemical and enzymatic degradation of the analytes. Various technologies have been utilized to assay biological samples for pharmacokinetic studies. The most frequently used are chromatography (high-performance liquid chromatography, gas chromatography and thin-layer chromatography), immunoassays and mass spectrometry.(ABSTRACT TRUNCATED AT 400 WORDS)

Routine measurement of plasma catecholamines in clinical pharmacology by high-performance liquid chromatography with electrochemical detection

A method for the simultaneous determination of epinephrine, norepinephrine and dopamine in human plasma is described, which combines the advantages of liquid-liquid extraction sample preparation, high-performance liquid chromatography on weak cation-exchange stationary phases and dual-electrode coulometric detection. The limits of quantification are less than 5 pg/ml (at a signal-to-noise ratio greater than 5) for each analyte. The influence of various experimental parameters (e.g., composition of the mobile phase, pretreatment of the assay buffer, components of the re-extraction system) on the performance of the assay is reported in detail. A number of applications are presented, which demonstrate the quality of the data obtained in terms of sensitivity, reproducibility and significance.

Effects of low-dose atenolol on postural and postprandial changes in heart rate, blood pressure, venous plasma catecholamines, and plasma renin activity

The administration of a single dose of atenolol 50 mg 1 h before a standard 3100 kJ cold meal in fasting healthy subjects reduced the supine preprandial heart rate and systolic blood pressure, and blunted the postural and postprandial rises in mean heart rate and systolic blood pressure relative to placebo. It did not affect the preprandial supine diastolic blood pressure, nor the postural rise and postprandial drop in diastolic blood pressure. Preprandial administration of atenolol blunted the postural and postprandial rises in mean plasma renin activity, and it enhanced the rise in plasma noradrenaline during eating in the sitting position, and the postprandial concentrations of noradrenaline. The findings do not permit the conclusion that beta 1-adrenergic stimulation was the predominant cause of these atenolol-responsive changes.

Time course and nature of postprandial haemodynamic changes in normal man

The present study describes the nature and time course of the cardiovascular and neuro-endocrine changes that followed a standard 3100 kJ cold meal in 12 supine and fasting normal men who were studied in a balanced cross-over design. Heart rate, blood pressure, systolic time intervals and estimates of cardiac performance by impedance cardiography were measured every 10 min up to 4 h after eating. Eating caused a rapid and short-lasting increase in systolic blood pressure, estimated stroke volume and maximum velocity of impedance changes. Eating also caused a rapid and more protracted decrease in diastolic and mean blood pressure, PEP-i, QS2-i and estimated systemic vascular resistance with an increase in heart rate and estimated cardiac output. In the later phase of the profiling a drop in LVET-i was also observed. The differences vs. fasting were statistically significant and judged to be biologically relevant. Venous plasma noradrenaline rose during eating as a consequence of the postural change, but eating itself did not alter venous plasma noradrenaline, and plasma adrenaline even tended to decrease. This reflects both the roughness of venous catecholamines in estimating adrenergic changes and the complexity of the underlying mechanisms and related reflexes.

Improved solid-phase extraction and liquid chromatography with electrochemical detection of urinary catecholamines and 5-S-L-cysteinyl-L-dopa

We describe a rapid, precise, accurate liquid chromatographic procedure for determining urinary catecholamines and 5-S-L-cysteinyl-L-dopa. The catecholamines (norepinephrine, epinephrine, and dopamine) and 5-S-L-cysteinyl-L-dopa are extracted from 1.0 ml of urine together with internal standards, by using a Bond-Elut strong cation-exchange (SCX) and an affinity phenylboronic acid (PBA) extraction column in series. The eluate obtained from PBA column is then chromatographed on a reversed-phase C18 column with a mobile phase containing pentane- and heptanesulfonate as ion-pair reagents. The detection is achieved with an amperometric detector set at an oxidation potential of +0.55 V. The chromatography is complete is less than 8 min for catecholamines and less than 5 min for cysteinyldopa. The method can measure less than 2 micrograms/l for catecholamines and 5 micrograms/l for cysteinyldopa. Analytical recoveries of catecholamines and cysteinyldopa added to urine pool ranged from 90-107%. Between run coefficient of variation ranged from 4.7 to 8%. None of the drugs and catecholamines metabolites tested interfered with the assay.