A simple specific radioenzymatic assay for the simultaneous measurement of picogram quantities of norepinephrine, epinephrine, and dopamine in plasma and tissues
Abstract
A sensitive simple radiometric method for the simultaneous measurement of norepinephrine, epinephrine, and dopamine is described. Fifty microliters of plasma or tissue extract was incubated with catechol-O-methyl transferase and tritiated S-adenosylmethionine. The catecholamines were converted to their O-methylated tritiated derivatives. These derivatives were purified by solvent extraction and were isolated by one-dimensional silica gel thin-layer chromatography. The spots containing the O-methylated derivatives were scraped directly into vials and were counted by liquid scintillation. Approximately one picogram of each catecholamine could be measured with an interassay coefficient of variation of 4.3, 8.9, and 13.2% for norepinephrine, epinephrine, and dopamine, respectively. No cross-reactivity was noted for several compounds related to these catecholamines.
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Heart failure and 123I-MIBG scintigraphy: "comeback"
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Congestive heart failure is a often associated with an impairment of sympathetic nervous system, i.e., global hyperactivity and regional impairment of adrenergic system. Cardiac 123I-métaiodobenzylguanidine (MIBG) scintigraphy is a radionuclide technique which can explore the presynaptic adrenergic function. Cardiac fixation of MIBG is decreased in congestive heart failure, reflecting a reduction of norepinephrine uptake by the myocardial presynaptic ending nerves. The impairment of presynaptic function is early and actually involved in the pathogenesis of cardiac failure. Cardiac MIBG scintigraphy is a useful tool to explore the myocardial adrenergic stores in patients with congestive heart failure.
Impaired cardiovascular autonomic control in newly and long-term-treated patients with Parkinson's disease: Involvement of l-dopa therapy
2004, Autonomic Neuroscience: Basic and ClinicalIn idiopathic Parkinson's disease (PD), autonomic dysfunction is frequent, causing orthostatic hypotension. The respective roles of disease progression and dopaminergic treatment remain unclear. In this study, we investigated the autonomic control of cardiovascular functions and its relation to l-dopa therapy in both newly diagnosed (ND) and long-term-treated (LT) patients. Study subjects were: (1) nine ND patients never having undergone treatment with l-dopa; (2) 18 LT patients who had been receiving l-dopa treatment for a long period. ND patients were investigated before l-dopa treatment and after stabilization of their l-dopa dosage. LT patients were investigated once with their regular treatment and once after a 12-h interruption of l-dopa treatment; (3) nine healthy subjects served as controls. At each test session, blood pressure (BP), heart rate (HR), plasma catecholamines, heart rate variability (HRV), and spontaneous baroreflex sensitivity were assessed in the supine and upright positions. Before receiving l-dopa medication, ND patients had reduced E/I ratios (HR response/deep breathing) and lowered HRV when compared to controls; this was evidence of early effects of the disease on autonomic HR control. Introduction of l-dopa treatment reduced BP, HR, and plasma levels of adrenaline and noradrenaline. Similar changes were found in LT patients when contrasting the short-term treatment interruption and the usual l-dopa dosage. The treatment-linked increase in plasma dopamine also correlated with the decrease in noradrenaline. These results showed that mild impairment of autonomic cardiovascular control occurred early in the course of PD. They also provided evidence that the side effects of l-dopa aggravated the impairment of the autonomic control of BP and HR.
New approach to the simultaneous analysis of catecholamines and tyrosines in biological fluids
2003, Journal of Chromatography ANew high-performance liquid chromatographic (HPLC) methods with amperometric–CoulArray detection were developed for simultaneous analyses of norepinephrine, epinephrine, l-DOPA, dopamine, 3-nitrotyrosine, m-, o-, and p-tyrosines. Overall, detection limit was in the low pmol range with amperometry, and in the low fmol range for the CoulArray method. Linear (r2=0.99) detector performances were observed in the ranges of 2–200 pmol with amperometry, and 0.2–20 pmol for the CoulArray method. Analytical precision values were better than 80 and 95% for HPLC–amperometry and HPLC–CoulArray method, respectively. These methods offer sensitivity, specificity, minimal sample requirement, and especially the HPLC–CoulArray method allows simultaneous assessment of various similar biomolecules.
Graded vascular autonomic control versus discontinuous cardiac control during gradual upright tilt
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Increased responses of glucagon and glucose production to hypoglycemia with intraperitoneal versus subcutaneous insulin treatment
2000, Metabolism: Clinical and ExperimentalThe study aim was to investigate the effect of the route of insulin treatment on the glucagon and glucose production (GP) responses to hypoglycemia in the diabetic rat. Experiments were performed in 4 groups of rats: (1) streptozotocin (STZ)-induced diabetic, untreated (D, n = 7), (2) diabetic treated with subcutaneous insulin (DSC, n = 8), (3) diabetic treated with intraperitoneal insulin (DIP, n = 6), and (4) normal control (N, n = 10). Slow-release insulin implants were used in DSC and DIP rats for 10 to 14 days (3 U/d). A hyperinsulinemic (120 pmol · kg−1 · min−1 insulin)-hypoglycemic (glycemia = 2.5 ± 0.1 mmol/L) clamp following an isoglycemic basal period was performed in 5-hour fasted rats. Basal plasma glucose was normalized in both DSC and DIP rats; however, in DSC but not DIP rats, glucose normalization required peripheral hyperinsulinemia. Tracer-determined GP, which was elevated in D rats, was completely normalized in DIP but only partially corrected in DSC rats. Basal glucagon levels were similar in all groups. During hypoglycemia, GP was suppressed in D rats (Δ, −28.9 ± 5.0 μmol · kg−1 · min−1), moderately increased in DSC rats (Δ, 6.1 ± 5.6, P < .01 v D), but markedly increased in DIP and N rats (Δ, 34.5 ± 4.5 for DIP and 16.8 ± 2.8 for N; P < .01 v D, P < .05 for DIP v DSC or N). Plasma glucagon increased 6-fold in N (945 ± 129 pg/mL), only doubled in D (424 ± 54), and tripled in DSC (588 ± 83), but increased 5-fold in DIP rats (1,031 ± 75, P < .05 v D and DSC). We conclude that in STZ-diabetic rats, (1) intraperitoneal but not subcutaneous insulin treatment normalizes basal GP, and (2) intraperitoneal insulin treatment as compared with subcutaneous treatment alleviates peripheral hyperinsulinemia and results in increased glucagon and GP responses to hypoglycemia.
Effects of age and hypertension on cardiac responses to the α<inf>1</inf>- agonist phenylephrine in humans
1999, American Journal of HypertensionBoth aging and hypertension decrease the responsiveness of several receptor systems. The purpose of this study was to investigate the effect of aging versus hypertension on the blood pressure (BP), heart rate, and left ventricular (LV) responses to the α1-agonist phenylephrine in humans. Fourteen young (age, 21–40 years; range, 30 ± 1 years; mean ± SEM), and 18 older (age, 50–73 years; range, 60 ± 1 years) healthy volunteers, as well as 10 young (age, 30–39 years; range, 36 ± 1 years) and 15 older (age, 50– 64 years; range, 58 ± 1 years) hypertensive subjects were studied. Phenylephrine was administered at four incremental rates for 8 min each. Cardiac responses were assessed by echocardiography. Phenylephrine caused twofold larger increases in systolic BP in young and older hypertensives and older normotensives, compared with young normotensives, but similar decreases in heart rate in all four groups. Younger normotensive subjects exhibited the largest decreases in stroke volume index, ejection fraction, and cardiac index in response to phenylephrine, despite similar increases in end-systolic stress for all groups. There is an age- and hypertension-related decrease in reflex vagal restraint in response to α1-adrenoceptor stimulation in humans, which leads to significant attenuation of the decrease in heart rate as well as in LV function in response to a pressor stimulus, and presumably therefore to enhanced systolic BP responses relative to young normotensive subjects.