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Objective: Sympathoadrenal activity is decreased during overnight rest. This study assessed whether urinary-free normetanephrine, metanephrine and methoxytyramine in overnight/first-morning urine collections might offer an alternative to measurements in 24-h collections or plasma for diagnosis of pheochromocytoma and paraganglioma (PPGL)., Design and Methods: Prospective multicenter cross-sectional diagnostic study involving 706 patients tested for PPGL, in whom tumors were confirmed in 79 and excluded in 627 after follow-up. Another 335 age- and sex-matched volunteers were included for reference purposes. Catecholamines and their free O-methylated metabolites were measured in 24-h collections divided according to waking and sleeping hours and normalized to creatinine. Plasma metabolites from blood sampled after supine rest were measured for comparison., Results: Urinary outputs of norepinephrine, normetanephrine, epinephrine and metanephrine in the reference population were respectively 50 (48-52)%, 35 (32-37)%, 76 (74-78)% and 15 (12-17)% lower following overnight than daytime collections. Patients in whom PPGLs were excluded showed 28 (26-30)% and 6 (3-9)% day-to-night falls in normetanephrine and metanephrine, while patients with PPGLs showed no significant day-to-night falls in metabolites. Urinary methoxytyramine was consistently unchanged from day to night. According to receiver-operating characteristic curves, diagnostic accuracy of metabolite measurements in overnight/first-morning urine samples did not differ from measurements in 24-h urine collections, but was lower for both than for plasma. Using optimized reference intervals, diagnostic specificity was higher for overnight than daytime collections at similar sensitivities., Conclusions: Measurements of urinary-free catecholamine metabolites in first-morning/overnight urine collections offer an alternative for diagnosis of PPGL to 24-h collections but remain less accurate than plasma measurements.

Background: Neuroblastoma, the most common extracranial solid tumor of childhood, produces catecholamines that are metabolized within tumor cells. Homovanillic acid (HVA) and vanillylmandelic acid (VMA), the end products of catecholamine metabolism, have limited accuracy for testing of the tumors. This study assessed whether metabolites produced in earlier steps of catecholamine metabolism might offer improved diagnostic accuracy over urinary HVA and VMA., Procedure: Plasma concentrations of 3-methoxytyramine, normetanephrine, and metanephrine were measured in two pediatric cohorts: (i) 96 children with confirmed neuroblastoma and (ii) 41 children with signs and symptoms of a catecholamine-producing tumor or other neoplasms and in whom neuroblastoma was excluded. Additional measurements of plasma 3-O-methyldopa and relationships of metabolites to MYCN amplification were examined in patient subgroups., Results: Overall, 94 of the 96 patients with neuroblastoma had concentrations of 3-methoxytyramine or normetanephrine above age-specific upper limits of reference intervals, providing a diagnostic sensitivity of 97.9% that was higher (P < 0.0001) than that of 82.2% for HVA and VMA. One of the two patients with normal plasma results showed an elevation of plasma 3-O-methyldopa. Diagnostic specificities were, respectively, 95.1% and 84.8%. Areas under receiver-operating characteristic curves confirmed the superior diagnostic power of the plasma than the urinary test (0.994 vs 0.945; P = 0.0095). Ratios of plasma 3-methoxytyramine to normetanephrine were 7.2-fold higher (P < 0.0001) for patients who had neuroblastomas with MYCN amplification than without MYCN amplification., Conclusions: Measurements of plasma 3-methoxytyramine and normetanephrine provide a highly accurate diagnostic test for neuroblastoma and also offer potential for prognostic risk stratification., (© 2019 The Authors. Pediatric Blood & Cancer Published by Wiley Periodicals, Inc.)

Background: Availability of appropriately established reference intervals for biochemical tests can be troublesome in pediatrics. Here we establish age-specific continuous reference intervals for catecholamine O-methylated metabolites in children evaluated for catecholamine producing tumors, particularly younger children with suspected neuroblastoma., Methods: Plasma concentrations of 3-methoxytyramine, normetanephrine, metanephrine, and 3-O-methyldopa were analyzed by liquid chromatography tandem mass spectrometry in 533 children aged 2 days to 18 years., Results: Concentrations of plasma free normetanephrine, 3-methoxytyramine and 3-O-methyldopa were higher in neonates up until six months of age, but thereafter declined steeply to levels after one year that were <38% those of neonatal concentrations and to further lower concentrations in teenagers that were <23% those in neonates. In contrast, concentrations of plasma free metanephrine showed a reciprocal pattern with 50% lower concentrations in infants below one year compared to later in childhood., Conclusion: The dynamic reciprocal changes in plasma concentrations of normetanephrine, 3-methoxytyramine and 3-O-methyldopa compared to metanephrine during early childhood suggest underlying developmental changes in extra-adrenal and adrenal chromaffin tissue that must be considered for pediatric reference intervals, particularly in infants. With such reference intervals at hand, biochemical testing for catecholamine producing tumors in young children is substantially improved., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Background: Plasma or urinary metanephrines are recommended for screening of pheochromocytomas and paragangliomas (PPGLs). Measurements of urinary free rather than deconjugated metanephrines and additional measurements of methoxytyramine represent other developments. For all measurements there is need for reference intervals., Methods: Plasma free, urinary free and urinary deconjugated O-methylated catecholamine metabolites were measured by LC-MS/MS in specimens from 590 hypertensives and normotensives. Reference intervals were optimized using data from 2,056 patients tested for PPGLs., Results: Multivariate analyses, correcting for age and body surface area, indicated higher plasma and urinary metanephrine in males than females and sex differences in urinary normetanephrine and free methoxytyramine that largely reflected body size variation. There were positive associations of age with plasma metabolites, but negative relationships with urinary free metanephrine and methoxytyramine. Plasma and urinary normetanephrine were higher in hypertensives than normotensives, but differences were small. Optimization of reference intervals using the data from patients tested for PPGLs indicated that age was the most important consideration for plasma normetanephrine and sex most practical for urinary metabolites., Conclusion: This study clarifies impacts of demographic and anthropometric variables on catecholamine metabolites, verifies use of age-specific reference intervals for plasma normetanephrine and establishes sex-specific reference intervals for urinary metabolites., (Copyright © 2018 The Authors. Published by Elsevier B.V. All rights reserved.)

Background: Measurements of plasma or urinary metanephrines are recommended for diagnosis of pheochromocytoma and paraganglioma (PPGL). What test offers optimal diagnostic accuracy for patients at high and low risk of disease, whether urinary free metanephrines offer advantages over deconjugated metanephrines, and what advantages are offered by including methoxytyramine in panels all remain unclear., Methods: A population of 2056 patients with suspected PPGLs underwent prospective screening for disease using mass spectrometric-based measurements of plasma free, urinary deconjugated, and urinary free metanephrines and methoxytyramine. PPGLs were confirmed in 236 patients and were excluded in others on follow-up evaluation., Results: Measurements of plasma free metabolites offered higher ( P < 0.01) diagnostic sensitivity (97.9%) than urinary free (93.4%) and deconjugated (92.9%) metabolites at identical specificities for plasma and urinary free metabolites (94.2%) but at a lower ( P < 0.005) specificity for deconjugated metabolites (92.1%). The addition of methoxytyramine offered little value for urinary panels but provided higher ( P < 0.005) diagnostic performance for plasma measurements than either urinary panel according to areas under ROC curves (0.991 vs 0.972 and 0.964). Diagnostic performance of urinary and plasma tests was similar for patients at low risk of disease, whereas plasma measurements were superior to both urinary panels for high-risk patients., Conclusions: Diagnosis of PPGLs using plasma or urinary free metabolites provides advantages of fewer false-positive results compared with commonly measured deconjugated metabolites. The plasma panel offers better diagnostic performance than either urinary panel for patients at high risk of disease and, with appropriate preanalytics, provides the test of choice. Measurements of methoxytyramine in urine show limited diagnostic utility compared with plasma., (© 2018 American Association for Clinical Chemistry.)

Context: Measurements of plasma methoxytyramine, the O-methylated dopamine metabolite, are useful for detecting rare dopamine-producing pheochromocytomas and paragangliomas (PPGLs) and head and neck paragangliomas (HNPGLs), but utility for screening beyond that achieved using standard measurements of normetanephrine and metanephrine is unclear., Objective: Evaluation of the additional utility of methoxytyramine compared to plasma normetanephrine and metanephrine for diagnosis of PPGLs and HNPGLs., Design: Comparative prospective study., Methods: Comparison of mass spectrometric-based measurements of plasma methoxytyramine, normetanephrine and metanephrine in 1963 patients tested for PPGLs at six tertiary medical centers according to reference intervals verified in 423 normotensive and hypertensive volunteers., Results: Of the screened patients, 213 had PPGLs and 38 HNPGLs. Using an upper cut-off of 0.10 nmol/L for methoxytyramine, 0.45 nmol/L for metanephrine and age-specific upper cut-offs for normetanephrine, diagnostic sensitivity with the addition of methoxytyramine increased from 97.2% to 98.6% for patients with PPGLs and from 22.1% to 50.0% for patients with HNPGLs, with a small decrease in specificity from 95.9% to 95.1%. Addition of methoxytyramine did not significantly alter areas under receiver operating characteristic curves for patients with PPGLs (0.984 vs 0.991), but did increase ( P  < 0.05) areas for patients with HNPGLs (0.627 vs 0.801). Addition of methoxytyramine also increased the proportion of patients with PPGLs who showed highly positive predictive elevations of multiple metabolites (70.9% vs 49.3%)., Conclusions: While the benefit of additional measurements of plasma methoxytyramine for the detection of PPGLs is modest, the measurements do assist with positive confirmation of disease and are useful for the detection of HNPGLs., (© 2017 The authors.)

Objective: To document the influences of blood sampling under supine fasting versus seated nonfasting conditions on diagnosis of phaeochromocytomas and paragangliomas (PPGL) using plasma concentrations of normetanephrine, metanephrine and methoxytyramine., Design and Methods: Biochemical testing for PPGL was performed on 762 patients at six centres, two of which complied with requirements for supine sampling after an overnight fast and four of which did not. Phaeochromocytomas and paragangliomas were found in 129 patients (67 noncompliant, 62 compliant) and not in 633 patients (195 noncompliant, 438 compliant)., Results: Plasma concentrations of normetanephrine and methoxytyramine did not differ between compliant and noncompliant sampling conditions in patients with PPGL but were 49-51% higher in patients without PPGL sampled under noncompliant compared with compliant conditions. The 97·5 percentiles of distributions were also higher under noncompliant compared with compliant conditions for normetanephrine (1·29 vs 0·79 nmol/l), metanephrine (0·49 vs 0·41 nmol/l) and methoxytyramine (0·42 vs 0·18 nmol/l). Use of upper cut-offs established from seated nonfasting sampling conditions resulted in substantially decreased diagnostic sensitivity (98% vs 85%). In contrast, use of upper cut-offs established from supine fasting conditions resulted in decreased diagnostic specificity for testing under noncompliant compared with compliant conditions (71% vs 95%)., Conclusions: High diagnostic sensitivity of plasma normetanephrine, metanephrine and methoxytyramine for the detection of PPGL can only be guaranteed using upper cut-offs of reference intervals established with blood sampling under supine fasting conditions. With such cut-offs, sampling under seated nonfasting conditions can lead to a 5·7-fold increase in false-positive results necessitating repeat sampling under supine fasting conditions., (© 2013 John Wiley & Sons Ltd.)

Background: Measurements of plasma normetanephrine (NMN) and metanephrine (MN) provide a sensitive test for diagnosis of phaeochromocytomas and paragangliomas (PPGLs), but do not allow detection of dopamine-producing tumours. Here we introduce a novel mass spectrometric based method coupled to ultraperformance liquid chromatography (LC-MS/MS) for measuring NMN, MN and 3-methoxytyramine (MTY), the O-methylated metabolite of dopamine., Methods: Specific collision-induced fragment ions assessed by multireaction monitoring transitions were used for identification, with quantification according to signal intensities of analytes relative to stable isotope labelled internal standards. Results for solid-phase extracted samples from 196 subjects analysed by LC-MS/MS were compared with those analysed by liquid chromatography with electrochemical detection (LC-ECD). Concentration ranges in 125 volunteers were compared with those from 63 patients with PPGLs, including 14 with metastatic disease., Results: The LC-MS/MS method showed linearity over four orders of magnitude with analytical sensitivity sufficient to measure to 0.02 nmol/L. Intra- and inter-assay coefficients of variation ranged from 2.8% to 13.5%. NMN and MN were respectively measured 17% and 10% higher and MTY 26% lower by LC-MS/MS than by LC-ECD. Medians and ranges for 3-methoxytramine, NMN and MN were respectively 0.08 (0.03-0.13), 0.35 (0.13-0.95) and 0.15 (0.07-0.33) nmol/L in volunteers. Among patients with PPGLs, plasma methoxytyramine was six-fold higher in patients with than without metastastases (1.09 versus 0.19 nmol/L) and in three patients was the only metabolite increased., Conclusions: The LC-MS/MS method enables accurate, selective and sensitive measurements of catecholamine O-methylated metabolites that should be particularly useful for screening and management of dopamine-producing metastatic PPGLs.

Background: There are currently no reliable biomarkers for malignant pheochromocytomas and paragangliomas (PPGLs). This study examined whether measurements of catecholamines and their metabolites might offer utility for this purpose., Methods: Subjects included 365 patients with PPGLs, including 105 with metastases, and a reference population of 846 without the tumour. Eighteen catecholamine-related analytes were examined in relation to tumour location, size and mutations of succinate dehydrogenase subunit B (SDHB)., Results: Receiver-operating characteristic curves indicated that plasma methoxytyramine, the O-methylated metabolite of dopamine, provided the most accurate biomarker for discriminating patients with and without metastases. Plasma methoxytyramine was 4.7-fold higher in patients with than without metastases, a difference independent of tumour burden and the associated 1.6- to 1.8-fold higher concentrations of norepinephrine and normetanephrine. Increased plasma methoxytyramine was associated with SDHB mutations and extra-adrenal disease, but was also present in patients with metastases without SDHB mutations or those with metastases secondary to adrenal tumours. High risk of malignancy associated with SDHB mutations reflected large size and extra-adrenal locations of tumours, both independent predictors of metastatic disease. A plasma methoxytyramine above 0.2nmol/L or a tumour diameter above 5cm indicated increased likelihood of metastatic spread, particularly when associated with an extra-adrenal location., Conclusion: Plasma methoxytyramine is a novel biomarker for metastatic PPGLs that together with SDHB mutation status, tumour size and location provide useful information to assess the likelihood of malignancy and manage affected patients., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Purpose: To evaluate the usefulness of [(18)F]-6-fluorodopamine ([(18)F]-DA) and [(18)F]-L-6-fluoro-3,4-dihydroxyphenylalanine ([(18)F]-DOPA) positron emission tomography (PET) in the detection of subcutaneous (s.c.) and metastatic pheochromocytoma in mice; to assess the expression of the norepinephrine transporter (NET) and vesicular monoamine transporters 1 and 2 (VMAT1 and VMAT2), all important for [(18)F]-DA and [(18)F]-DOPA uptake. Furthermore, to compare tumor detection by micro-computed tomography (microCT) to magnetic resonance imaging (MRI) in individual mouse., Methods: SUV(max) values were calculated from [(18)F]-DA and [(18)F]-DOPA PET, tumor-to-liver ratios (TLR) were obtained and expression of NET, VMAT1 and VMAT2 was evaluated., Results: [(18)F]-DA detected less metastatic lesions compared to [(18)F]-DOPA. TLR values for liver metastases were 2.26-2.71 for [(18)F]-DOPA and 1.83-2.83 for [(18)F]-DA. A limited uptake of [(18)F]-DA was found in s.c. tumors (TLR = 0.22-0.27) compared to [(18)F]-DOPA (TLR = 1.56-2.24). Overall, NET and VMAT2 were expressed in all organ and s.c. tumors. However, s.c. tumors lacked expression of VMAT1. We confirmed [(18)F]-DA's high affinity for the NET for its uptake and VMAT1 and VMAT2 for its storage and retention in pheochromocytoma cell vesicles. In contrast, [(18)F]-DOPA was found to utilize only VMAT2., Conclusion: MRI was superior in the detection of all organ tumors compared to microCT and PET. [(18)F]-DOPA had overall better sensitivity than [(18)F]-DA for the detection of metastases. Subcutaneous tumors were localized only with [(18)F]-DOPA, a finding that may reflect differences in expression of VMAT1 and VMAT2, perhaps similar to some patients with pheochromocytoma where [(18)F]-DOPA provides better visualization of lesions than [(18)F]-DA., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Background: Pheochromocytomas are rare catecholamine-producing tumors derived in more than 30% of cases from mutations in 9 tumor-susceptibility genes identified to date, including von Hippel-Lindau tumor suppressor (VHL); succinate dehydrogenase complex, subunit B, iron sulfur (Ip) (SDHB); and succinate dehydrogenase complex, subunit D, integral membrane protein (SDHD). Testing of multiple genes is often undertaken at considerable expense before a mutation is detected. This study assessed whether measurements of plasma metanephrine, normetanephrine, and methoxytyramine, the O-methylated metabolites of catecholamines, might help to distinguish different hereditary forms of the tumor., Methods: Plasma concentrations of O-methylated metabolites were measured by liquid chromatography with electrochemical detection in 173 patients with pheochromocytoma, including 38 with multiple endocrine neoplasia type 2 (MEN 2), 10 with neurofibromatosis type 1 (NF1), 66 with von Hippel-Lindau (VHL) syndrome, and 59 with mutations of SDHB or SDHD., Results: In contrast to patients with VHL, SDHB, and SDHD mutations, all patients with MEN 2 and NF1 presented with tumors characterized by increased plasma concentrations of metanephrine (indicating epinephrine production). VHL patients usually showed solitary increases in normetanephrine (indicating norepinephrine production), whereas additional or solitary increases in methoxytyramine (indicating dopamine production) characterized 70% of patients with SDHB and SDHD mutations. Patients with NF1 and MEN 2 could be discriminated from those with VHL, SDHB, and SDHD gene mutations in 99% of cases by the combination of normetanephrine and metanephrine. Measurements of plasma methoxytyramine discriminated patients with SDHB and SDHD mutations from those with VHL mutations in an additional 78% of cases., Conclusions: The distinct patterns of plasma catecholamine O-methylated metabolites in patients with hereditary pheochromocytoma provide an easily used tool to guide cost-effective genotyping of underlying disease-causing mutations.

Context: Besides (123)I-metaiodobenzylguanidine (MIBG), positron emission tomography (PET) agents are available for the localization of paraganglioma (PGL), including (18)F-3,4-dihydroxyphenylalanine (DOPA), (18)F-fluoro-2-deoxy-D-glucose ((18)F-FDG), and (18)F-fluorodopamine ((18)F-FDA)., Objective: The objective of the study was to establish the optimal approach to the functional imaging of PGL and examine the link between genotype-specific tumor biology and imaging., Design: This was a prospective observational study., Intervention: There were no interventions., Patients: Fifty-two patients (28 males, 24 females, aged 46.8 +/- 14.2 yr): 20 with nonmetastatic PGL (11 adrenal), 28 with metastatic PGL (13 adrenal), and four in whom PGL was ruled out; 22 PGLs were of the succinate dehydrogenase subunit B (SDHB) genotype., Main Outcome Measures: Sensitivity of (18)F-DOPA, (18)F-FDG, and (18)F-FDA PET, (123)I-MIBG scintigraphy, computed tomography (CT), and magnetic resonance imaging (MRI) for the localization of PGL were measured., Results: Sensitivities for localizing nonmetastatic PGL were 100% for CT and/or MRI, 81% for (18)F-DOPA PET, 88% for (18)F-FDG PET/CT, 78% for (18)F-FDA PET/CT, and 78% for (123)I-MIBG scintigraphy. For metastatic PGL, sensitivity in reference to CT/MRI was 45% for (18)F-DOPA PET, 74% for (18)F-FDG PET/CT, 76% for (18)F-FDA PET/CT, and 57% for (123)I-MIBG scintigraphy. In patients with SDHB metastatic PGL, (18)F-FDA and (18)F-FDG have a higher sensitivity (82 and 83%) than (123)I-MIBG (57%) and (18)F-DOPA (20%)., Conclusions: (18)F-FDA PET/CT is the preferred technique for the localization of the primary PGL and to rule out metastases. Second best, equal alternatives are (18)F-DOPA PET and (123)I-MIBG scintigraphy. For patients with known metastatic PGL, we recommend (18)F-FDA PET in patients with an unknown genotype, (18)F-FDG or (18)F-FDA PET in SDHB mutation carriers, and (18)F-DOPA or (18)F-FDA PET in non-SDHB patients.

Objective: Imaging modalities available for the localization of phaeochromocytoma (PHEO) include computed tomography (CT), magnetic resonance imaging (MRI), [(123)I]- or [(131)I]-labelled metaiodobenzylguanidine ((123/131)I-MIBG) scintigraphy and 6-[(18)F]-fluorodopamine ((18)F-FDA) positron emission tomography (PET). Our aim was to investigate the yield of (18)F-FDA PET vs. biochemical testing and other imaging techniques to establish the diagnosis and location of PHEO., Patients and Measurements: The study included 99 consecutive patients (35 Males, 64 Females, mean +/- SD age 46.4 +/- 13.4 years), who underwent (18)F-FDA PET, biochemical testing (plasma catecholamines and free metanephrines) and CT and/or MRI. The majority (78%) also underwent (123/131)I-MIBG., Results: In total 26 patients had non-metastatic PHEO, 34 patients had metastatic PHEO, and PHEO was ruled out in 39 patients. Investigations to rule out or confirm PHEO yielded the following sensitivity/specificity: plasma metanephrines 97/95%, (18)F-FDA 92/90%, (123)I-MIBG 83/100%, (123/131)I-MIBG 70/100%, CT 100/41%, MRI 98/60%. Sensitivities for localizing non-metastatic PHEO on a per-lesion base were: CT 97%, MRI 92%, (18)F-FDA 78%, (123)I-MIBG 78% and (123/131)I-MIBG 76%. Sensitivities for detecting metastases on a per-patient base were: CT and MRI 100%, (18)F-FDA 97%, (123)I-MIBG 85% and (123/131)I-MIBG 65%., Conclusion: For tumour localization, (18)F-FDA PET and (123/131)I-MIBG scintigraphy perform equally well in patients with non-metastatic PHEO, but metastases are better detected by (18)F-FDA PET than by (123/131)I-MIBG.

Dysfunctional activity in the subthalamic nucleus (STN) is thought to underlie movement deficits of patients with Parkinson's disease. Alterations in STN firing patterns are also evident in the anesthetized rat model of Parkinson's disease, where studies show that loss of striatal dopamine and concomitant changes in the indirect pathway are associated with bursty and oscillatory firing patterns in STN output. However, the extent to which alterations in cortical activity contribute to changes in STN activity is unclear. As pyramidal neurons in the cingulate cortex project directly to the STN, cingulate output was assessed after dopamine lesion by simultaneously recording single-unit and local field potential (LFP) activities in STN and anterior cingulate cortex in control, dopamine-lesioned and non-lesioned hemispheres of urethane-anesthetized rats. Correlated oscillations were observed in cross-correlograms of spike trains from STN and cingulate layer V neurons with broad waveforms indicative of pyramidal neurons. One-2 weeks after dopamine cell lesion, firing rate, incidence of bursty and 0.3-2.5 Hz oscillatory activity of neurons and LFP power in the STN all increased significantly. In contrast, firing rate, incidence of bursty and 0.3-2.5 Hz oscillatory activity of cingulate layer V putative pyramidal neurons and power in cingulate LFPs did not differ significantly between dopamine-lesioned, non-lesioned or control hemispheres, despite significant loss of dopamine in the lesioned cingulate cortex. Data show that alterations in STN activity in the dopamine-lesioned hemisphere are not associated with alterations in neuronal activity in layer V of the anterior cingulate cortex in anesthetized rats.

Measurements of plasma-free normetanephrine and metanephrine provide a sensitive test for diagnosis of pheochromocytoma but may fail to detect tumors that produce predominantly dopamine. Such tumors are extremely rare, usually found as extraadrenal paragangliomas. This report describes measurements of plasma concentrations of free methoxytyramine, the O-methylated metabolite of dopamine, in 120 patients with catecholamine-producing tumors, including nine with extraadrenal paragangliomas secreting predominantly dopamine. In seven of these nine patients, tumors were found incidentally or secondary to the space-occupying complications of the lesions. Plasma concentrations of free methoxytyramine and dopamine were increased in all nine patients, including two with normal plasma and urinary normetanephrine and metanephrine and normal urinary outputs of dopamine. Relative increases above normal for plasma methoxytyramine (104-fold) and dopamine (56-fold) were much greater (P < 0.001) than those for urinary dopamine (3-fold). Insensitivity of the latter for identification of dopamine-secreting tumors was due to dependence of the urinary amine on renal extraction and decarboxylation of circulating 3,4-dihydroxyphenylalanine. Measurements of plasma-free methoxytyramine, in addition to normetanephrine and metanephrine, are unlikely to improve diagnosis of pheochromocytomas in hypertensive patients with symptoms of catecholamine excess but may be useful in selected patients for identification of tumors that produce predominantly dopamine.

This Hypertension Grand Rounds shows how applying new clinical laboratory techniques helped to diagnose pheochromocytoma in a difficult case. In the setting of long-standing, sustained hypertension, the patient had a hypertensive paroxysm during anesthesia induction for surgery, leading to suspicion of a pheochromocytoma. Conventional testing, including CT scanning and fractionated urinary metanephrine test, was not diagnostic. The patient had another hypertensive paroxysm during subsequent anesthesia induction, requiring intensive care. Consistently elevated plasma levels of free normetanephrine provided the first and only biochemical evidence for a pheochromocytoma in this case. 6-[18F]Fluorodopamine positron emission tomography and 123I-metaiodobenzylguanidine scintigraphy subsequently agreed on the existence of a small left adrenal mass, which when removed surgically proved to be a pheochromocytoma. Postoperatively, plasma levels of normetanephrine normalized, and there were no further hypertensive paroxysms, although the patient remained hypertensive. This case illustrates the superiority of plasma levels of free (unconjugated) metanephrines, compared with other biochemical tests, to detect pheochromocytoma. It also confirms that functional imaging by 6-[18F]fluorodopamine or 123I-metaiodobenzylguanidine scanning can localize pheochromocytoma in difficult cases in which other imaging tests are not diagnostic.

The purpose of the study was to assess the diagnostic utility of 6-[(18)F]-fluorodopamine ([(18)F]-DA) positron emission tomography scanning (PET) vs. [(131)I]-metaiodobenzylguanidine (MIBG) scintigraphy in patients with metastatic pheochromocytoma (PHEO). We studied 10 men and six women (mean age 38.2 +/- 11.5 yr) referred to our institution for metastatic PHEO; two patients were studied twice within a 2-yr interval. Imaging modalities included computed tomography (CT), magnetic resonance imaging (MRI), [(131)I]-MIBG scintigraphy, and [(18)F]-DA PET. Fifteen of 16 patients had positive findings on CT and/or MRI consistent with the presence of pheochromocytoma. [(18)F]-DA PET was positive in all patients, but seven patients had negative [(131)I]-MIBG scans. Thirty-eight foci of uptake were shown by both [(18)F]-DA PET and [(131)I]-MIBG scintigraphy, 90 only by [(18)F]-DA PET, and 10 only by [(131)I]-MIBG; most lesions were also visible on CT/MRI. In this initial series of patients with metastatic pheochromocytoma, [(18)F]-DA PET localized PHEO in all patients and showed a large number of foci that were not imaged with [(131)I]-MIBG scintigraphy. Thus, [(18)F]-DA PET was found to be a superior imaging method in patients with metastatic PHEO, in which correct detection of disease extension often determines the most appropriate therapeutic plan and future follow-up.

Objective: To describe a woman with metastatic carotid body tumor in whom hypotension occurred in the setting of exceedingly high plasma dopamine levels., Methods: We present a case report and review the literature on the topic of dopamine-secreting paraganglioma or pheochromocytoma., Results: A previously healthy 40-year-old Asian woman noted difficulty with swallowing and hoarseness. No neck mass was visible, and she had no symptoms of catecholamine excess and no family history of endocrine disorders or malignant disease. Indirect laryngoscopy revealed a paralyzed left vocal cord and a nonulcerating mass in the left parapharyngeal space. An initial needle biopsy was interpreted as undifferentiated carcinoma. After a second biopsy, this mass was diagnosed as a neuroendocrine tumor, consistent with paraganglioma. The patient underwent surgical resection and radiation therapy (total dose, 40 Gy), after which she remained asymptomatic for 11 years. Then loss of weight, fatigue, nausea, and hypotensive episodes (blood pressures as low as 70/35 mm Hg) prompted whole-body imaging with bone scans, computed tomography, and magnetic resonance imaging, which disclosed several lesions in the liver, lungs, and spine, suggestive of metastatic disease. The adrenal glands were unremarkable. A metaiodobenzylguanidine scan with use of (131)I was negative. Liver biopsy of a hypodense lesion revealed a neuroendocrine tumor by histologic and immunohistochemical studies. Because of the patient's history, malignant paraganglioma was diagnosed. The tumor secreted predominantly dopamine at extraordinary levels (plasma concentration 27,942 pg/mL; normal, <30). The patient died before further treatment could be initiated., Conclusion: Carotid body tumors usually do not secrete catecholamines but frequently metastasize. During progression, these neuroendocrine tumors may become able to produce and secrete selected catecholamines such as dopamine. Dopamine can lower the blood pressure rather than causing hypertension, even though hypertension is one of the main symptoms of a pheochromocytoma.

L-3,4-dihydroxyphenylalanine, the immediate precursor of dopamine, can be formed by two enzymes: tyrosine hydroxylase (TH) in catecholamine-producing neurons and chromaffin cells and tyrosinase in melanocytes. In this study we examined whether tyrosinase contributes to production of dopamine. Deficiency of TH caused marked reductions in norepinephrine in albino and pigmented 15-day-old mice. In contrast, peripheral levels of dopamine were reduced only in albino TH-deficient mice and were higher in pigmented than in albino mice, regardless of the presence or absence of TH. We next examined age-related changes in dopamine and cutaneous expression of tyrosinase and melanin in albino and pigmented TH wild-type mice. We found that the differences in peripheral dopamine between pigmented and albino mice disappeared with advancing age following changes in expression and function of tyrosinase. In young animals, tyrosinase was present in epidermis but did not produce detectable melanin. With advancing age, tyrosinase was localized only around hair follicles, melanin synthesis became more pronounced, and dopamine synthesis decreased. The data reveal a previously unrecognized TH-independent major pathway of peripheral dopamine synthesis in young, but not adult, mice. The transient nature of this source of dopamine reflects a developmental switch in tyrosinase-dependent production of dopamine to production of melanin.

Background: In postural tachycardia syndrome (POTS) and repeated neurocardiogenic presyncope (NCS), orthostatic intolerance occurs without persistent sympathetic neurocirculatory failure. Whether these conditions involve abnormal cardiac sympathetic innervation or function has been unclear., Methods and Results: Patients with POTS or NCS underwent measurements of neurochemical indices of cardiac release, reuptake, and synthesis of the sympathetic neurotransmitter norepinephrine based on entry of norepinephrine into the cardiac venous drainage (cardiac norepinephrine spillover), cardiac extraction of circulating (3)H-norepinephrine, and cardiac production of dihydroxyphenylalanine and measurement of left ventricular myocardial innervation density using 6-[(18)F]fluorodopamine positron emission tomographic scanning. Mean cardiac norepinephrine spillover in POTS (171+/-30 pmol/min, N=16) was higher and in NCS (62+/-9 pmol/min, N=20) was lower than in a large group of healthy volunteers (102+/-9 pmol/min, N=52) and in a subgroup of age-matched healthy women (106+/-18 pmol/min, N=11). Both patient groups had normal cardiac extraction of (3)H-norepinephrine, normal cardiac production of dihydroxyphenylalanine, and normal myocardial 6-[(18)F]fluorodopamine-derived radioactivity., Conclusions: POTS and NCS differ in tonic cardiac sympathetic function, with increased cardiac norepinephrine release in the former and decreased release in the latter. Both groups had normal values for indices of function of the cell membrane norepinephrine transporter, norepinephrine synthesis, and density of myocardial sympathetic innervation. Because POTS and NCS both include specific abnormalities of cardiac sympathetic function, both can be considered forms of dysautonomia.

Most, but not all, pheochromocytomas can be localized by computed tomography or magnetic resonance imaging. Here we introduce two novel approaches for localization of pheochromocytoma in a patient in whom conventional imaging modalities failed to show the tumor. First, we establish that measurements of plasma free metanephrines coupled with vena caval sampling are useful for localizing occult pheochromocytoma, particularly when elevations in plasma catecholamines are slight or intermittent. Second, we show that positron emission tomographic scanning using the imaging agent 6-[18F]fluorodopamine as a substrate for the norepinephrine transporter offers a highly effective method for tumor localization. These novel approaches may be of value in difficult cases, where biochemical and clinical evidence of pheochromocytoma is compelling, yet conventional imaging modalities fail to locate the tumor.

The diagnosis and treatment of pheochromocytoma depend critically on effective means to localize the tumor. Computed tomography and magnetic resonance imaging have good sensitivity but poor specificity for detecting pheochromocytoma, and nuclear imaging approaches such as (131)I-metaiodobenzylguanidine scintigraphy have limited sensitivity. Here we report initial results using 6-[(18)F]fluorodopamine positron emission tomography (PET) scanning in the diagnostic localization of pheochromocytoma. Twenty-eight patients with known or clinically suspected pheochromocytoma underwent PET scanning after intravenous injection of 6-[(18)F]fluorodopamine. Of the 28 patients, 9 had surgical confirmation of the tumor, 8 had previously diagnosed metastatic pheochromocytoma, and 11 had plasma levels of metanephrines that were within normal limits. All 9 patients with surgically proven pheochromocytoma had abnormal 6-[(18)F]fluorodopamine PET scans that identified the tumors. All 8 patients with metastatic pheochromocytoma had extra-adrenal sites of 6-[(18)F]fluorodopamine-derived activity. Of the 11 patients with normal plasma levels of metanephrines, 9 had negative 6-[(18)F]fluorodopamine PET scans, 1 had extra-adrenal foci of 6-[(18)F]fluorodopamine-derived activity, and 1 had symmetric uptake of 6-[(18)F]fluorodopamine in the region of the adrenal glands. In patients with known disease, 6-[(18)F]fluorodopamine PET scanning can detect and localize pheochromocytomas with high sensitivity. In patients in whom the diagnosis of pheochromocytoma is considered but excluded because of negative plasma metanephrine results, 6-[(18)F]fluorodopamine PET scans are consistently negative. These findings justify a clinical trial of 6-[(18)F]fluorodopamine PET scanning as a diagnostic tool.

Incubation of PC 12 cells with the sulfonylurea drug, glipizide (1-100 microM), increased intracellular levels of the acidic metabolites of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). The levels of these acids in the medium were decreased, indicating the presence of a sulfonylurea-sensitive organic anion transporter. In the present study, we demonstrate that the sulfonylurea-sensitive transport of acidic dopamine metabolites is unidirectional, ATP dependent, unaffected by ouabain or by tetrodotoxin and blocked by drugs that interact with the multidrug-resistance protein-1 (MRP1). However, over-expression of MRP1 did not affect transport of the acid metabolites. The pharmacological profile and ion dependence of the transporter also differs from that of known ATP-binding cassette (ABC) family members. Using microdialysis, we also demonstrated a sulfonylurea-sensitive transport process in the striatum of freely moving rats. These results show that acidic dopamine metabolites are actively secreted from dopaminergic cells into surrounding extracellular fluid by a previously undescribed transporter.

Sulfonylureas block ATP-dependent K(+) channels (K/ATP channels) in pancreatic beta cells and brain gamma-aminobutyric acid (GABA) containing neurons causing depolarization-evoked insulin or GABA release. In high concentrations, sulfonylureas also inhibit catecholamine release from bovine adrenal chromaffin cells and isolated guinea pig aorta. In this study, we examined the effect of glipizide, a sulfonylurea, on dopamine release from PC12 cells and found that neither basal nor K(+)-stimulated dopamine release was affected. Although PC12 cells expressed mRNA for the K/ATP channel, functional K/ATP channels could not be demonstrated electrophysiologically, consistent with the lack of effect of glipizide on dopamine release. Glipizide did, however, increase cytoplasmic retention of the acidic dopamine metabolites, 3, 4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), indicating blockade of their outward transport. The cellular accumulation of DOPAC was accompanied by reduced tyrosine hydroxylase activity and reduced formation of dopamine and its metabolites presumably by a negative feedback effect of the increased cytoplasmic concentrations of DOPAC.

Dopamine in the circulation occurs mainly as dopamine sulfate, the sources and physiological significance of which have been obscure. In this study, plasma concentrations of dopamine sulfate were measured after a meal, after fasting for 4 days, and during i.v. L-DOPA, nitroprusside, or trimethaphan infusion in volunteers; after dopamine infusion in patients with L-aromatic-amino-acid decarboxylase deficiency; in arterial and portal venous plasma of gastrointestinal surgery patients; and in patients with sympathetic neurocirculatory failure. Meal ingestion increased plasma dopamine sulfate by more than 50-fold; however, prolonged fasting decreased plasma dopamine sulfate only slightly. L-DOPA infusion produced much larger increments in dopamine sulfate than in dopamine; the other drugs were without effect. Patients with L-aromatic amino acid decarboxylase deficiency had decreased dopamine sulfate levels, and patients with sympathetic neurocirculatory failure had normal levels. Decarboxylase-deficient patients undergoing dopamine infusion had a dopamine sulfate/dopamine ratio about 25 times less than that at baseline in volunteers. Surgery patients had large arterial-portal venous increments in plasma concentrations of dopamine sulfate, so that mesenteric dopamine sulfate production accounted for most of urinary dopamine sulfate excretion, a finding consistent with the localization of the dopamine sulfoconjugating enzyme to gastrointestinal tissues. The results indicate that plasma dopamine sulfate derives mainly from sulfoconjugation of dopamine synthesized from L-DOPA in the gastrointestinal tract. Both dietary and endogenous determinants affect plasma dopamine sulfate. The findings suggest an enzymatic gut-blood barrier for detoxifying exogenous dopamine and delimiting autocrine/paracrine effects of endogenous dopamine generated in a "third catecholamine system."

1. The source and physiological significance of dopamine (DA) sulphate, which exists in plasma at much higher concentrations than free DA, have long been a puzzle. The present article reviews how the convergence of modern molecular and traditional clinical approaches is shedding new light on the origins and meaning of DA sulphate. 2. The sulphotransferase isoenzyme responsible for production of DA sulphate in humans (SULT1A3) has been cloned and shown to be expressed in large quantities in the gastro-intestinal tract, but not in liver. No orthologue of SULT1A3 has yet been identified in other species, consistent with the greater importance of sulphate conjugation of DA in humans than in most animals. 3. Diet has a major impact on plasma DA sulphate, with dramatic increases after ingestion of meals and foods rich in biogenic amines; however, substantial amounts of DA sulphate remaining after prolonged fasting indicate the presence of a mainly endogenous source. The lack of influence of acute or chronic changes in sympathetic outflow or of sympathoneural degeneration on plasma DA sulphate indicates that DA sulphate does not derive from sympathetic nerve. Relatively low rates of production from intravenously infused DA indicate that very little DA sulphate (< 2%) derives from metabolism of circulating DA, such as in red cells or platelets. 4. Consistent increments in DA sulphate from arterial to the outflowing venous plasma draining mesenteric organs, without increments across other organs or tissues (e.g., heart, lungs, liver), indicate that the gastrointestinal tract is a major source of more than 75% of DA sulphate produced in the body. The gastro-intestinal tract is also the site of a novel DA autocrine/paracrine system that produces nearly 50% of the DA in the body. Therefore, production of DA sulphate appears to reflect an enzymatic 'gut-blood' barrier for detoxifying dietary biogenic amines and delimiting autocrine/paracrine effects of endogenous DA generated in a novel 'third catecholamine system'.

1. Dopamine (DA) is a protective agent in the gastrointestinal (GI) tract in both rats and humans. Therefore, we have studied the site of DA production in rat and human GI tract using a variety of techniques, including immunocytochemistry (ICC), in situ hybridization histochemistry, reverse transcription-polymerase chain reaction, HPLC, western blotting and immunoelectron microscopy. 2. We found very high concentrations of DA that persisted after chemical sympathectomy (CS) in the gastric juice, the stomach mucosa and in the pancreas. Both the stomach mucosa and the pancreas also had tyrosine hydroxylase (TH) activity, most of which remained after CS. Double-labelling ICC showed that acid-producing parietal cells and the exocrine pancreas must also be capable of producing DA. 3. We isolated rat stomach parietal cells by cell fractionation and found that both DA and TH activity are present in isolated (denervated) parietal cells. These cells also have other features of aminergic cells: they are immuno- (and mRNA) positive for the DA plasma membrane transporter and vesicular monoamine transporter(s). In both gastric and duodenal mucosa, we demonstrated the presence of significant amounts of the D5 receptor that could serve as a target for locally produced DA. 4. Because DA, its biosynthetic enzymes and its transporters are also found in parietal cells in the human stomach, a mucosal protective system involving DA could be important clinically.

Tyrosine hydroxylase (TH) mRNA and activity and concentrations of 3,4-dihydroxyphenylalanine (DOPA) and catecholamines were examined as markers of sympathetic innervation and catecholamine synthesis in peripheral tissues of sympathectomized and intact rats. Chemical sympathectomy with 6-hydroxydopamine (6-OHDA) markedly decreased norepinephrine and to a generally lesser extent TH activities and dopamine in most peripheral tissues (stomach, lung, testis, duodenum, pancreas, salivary gland, spleen, heart, kidney, thymus). Superior cervical ganglia, adrenals and descending aorta were unaffected and vas deferens showed a large 92% decrease in norepinephrine, but only a small 38% decrease in TH activity after 6-OHDA. Presence of chromaffin cells or neuronal cell bodies in these latter tissues, indicated by consistent expression of TH mRNA, explained the relative resistance of these tissues to 6-OHDA. Stomach also showed consistent expression of TH mRNA before, but not after 6-OHDA, suggesting that catecholamine synthesizing cells in gastric tissue are sensitive to the toxic effects of 6-OHDA. Tissue concentrations of DOPA were mainly unaffected by 6-OHDA, indicating that much of the DOPA in peripheral tissues is synthesized independently of local TH or sympathetic innervation. The differential effects of chemical sympathectomy on tissue catecholamines, DOPA, TH mRNA and TH activity demonstrate that these variables are not simple markers of sympathetic innervation or catecholamine synthesis. Other factors, including presence of neuronal cell bodies, parenchymal chromaffin cells, non-neuronal sites of catecholamine synthesis and alternative sources of tissue DOPA, must also be considered when tissue catecholamines, DOPA and TH are examined as markers of sympathetic innervation and local catecholamine synthesis.

Dopamine (DA) has been suggested to be a protective factor in the gastrointestinal tract but neither a source of DA nor its exact targets of action have been identified. In this study, we demonstrate high levels of DA (and DOPA) which persist after chemical sympathectomy in the gastric juice of rats. Immunostaining and in situ hybridization histochemistry reveal the presence of tyrosine hydroxylase (TH), DA transporter and vesicular monamine transporters in the acid-producing parietal cells. Like DA, TH enzyme activity remains after chemical sympathectomy. We also demonstrate active reuptake and storage of DA that indicates a regulated release of this neurohormone from parietal cells. DA D1b receptor mRNA is the most abundant DA receptor subtype in gastric and duodenal epithelium. Therefore, we suggest that selective DA D1b receptor agonists may be useful adjuncts in the treatment of duodenal and gastric ulcers. Gastric epithelia possess the hallmarks of functional DA neuroendocrine cells, suggesting that DA has an important role in self-protective mechanisms of the gastrointestinal tract. These findings should allow elucidation of DA role in normal and disease states in the stomach and duodenum.

Considerable urinary excretion of dopamine metabolites indicates that large amounts of dopamine are produced in unknown locations of the body. This study assessed the contribution of mesenteric organs (gastrointestinal tract, spleen, and pancreas) to the total body production of dopamine in humans and examined the presence of the rate-limiting enzyme for dopamine synthesis, tyrosine hydroxylase, in gastrointestinal tissues. Blood sampled from an artery and portal and hepatic veins in eight subjects and from arterial and renal venous sites in other subjects was analyzed for plasma concentrations of dopamine and its metabolites. The activity and distribution of tyrosine hydroxylase was also examined in tissue samples from the stomach and duodenum. Higher concentrations of dopamine and its metabolites in portal venous than arterial plasma indicated substantial production of dopamine by mesenteric organs (12.0 nmol/min) amounting to 42-46% of the renal removal of circulating dopamine metabolites. Tissue samples showed immunoreactive tyrosine hydroxylase in nonneuronal cell bodies and detectable levels of tyrosine hydroxylase in nonneuronal cell bodies and detectable levels of tyrosine hydroxylase enzyme activity. The results show that mesenteric organs produce close to half of the dopamine formed in the body, most of which is unlikely to be derived from sympathetic nerves but may reflect production in a novel nonneuronal dopaminergic system.

Recently we have identified a dopamine-producing system in the gastric mucosa of rats. All the available morphological data suggest that parietal cells synthesize dopamine. In the present study we investigated the dopaminergic characteristics of isolated parietal cells by different methods. Mixed gastric mucosal cells were isolated and size-fractionated by elutriation. The proportion of neurons, parietal and endocrine cells in the fractions were determined by immunocytochemistry (ICC) using antibodies to neurofilament, proton pump and chromogranin A, respectively. No neurons were found in any of the cell preparations, while 56% parietal cell and 0.0% endocrine cell were achieved in the parietally enriched fraction. By Western blot, a tyrosine hydroxylase (TH, the rate-limiting enzyme of the catecholamine synthesis) immunoreactive protein species was demonstrated in isolated mucosal cells, comigrating with the TH immunoreactivity from PC12 cells. The TH immunoreactivity was colocalized to parietal cells by ICC. Dopamine transporter (DAT), a regulator of extracellular/intracellular dopamine balance in the nervous system, was also demonstrated in parietal cells. A significant amount of dopamine and DOPA were measured by HPLC (13.4 and 9.57 pg/10(6) cell, respectively) in parietally enriched cell fraction. Since this enriched cell fraction was virtually clear of both neurons and endocrine cells, demonstration of TH enzyme, DAT and dopamine in this fraction confirms that the parietal cell population might be a major source of dopamine in the rat stomach, supporting our previous results achieved using whole tissue samples.

Background: The classification of dysautonomias has been confusing, and the pathophysiology obscure. We examined sympathetic innervation of the heart in patients with acquired, idiopathic dysautonomias using thoracic positron-emission tomography and assessments of the entry rate of the sympathetic neurotransmitter norepinephrine into the cardiac venous drainage (cardiac norepinephrine spillover). We related the laboratory findings to signs of sympathetic neurocirculatory failure (orthostatic hypotension and abnormal blood-pressure responses associated with the Valsalva maneuver), central neural degeneration, and responsiveness to treatment with levodopa-carbidopa (Sinemet)., Methods: Cardiac scans were obtained after intravenous administration of 6-[18F]fluorodopamine in 26 patients with dysautonomia. Fourteen had sympathetic neurocirculatory failure--three with no signs of central neurodegeneration (pure autonomic failure), two with parkinsonism responsive to treatment with levodopa-carbidopa, and nine with central neurodegeneration unresponsive to treatment with levodopa-carbidopa (the Shy-Drager syndrome). The rates of cardiac norepinephrine spillover were estimated on the basis of concentrations of intravenously infused [3H]norepinephrine during catheterization of the right side of the heart., Results: Patients with pure autonomic failure or parkinsonism and sympathetic neurocirculatory failure had no myocardial 6-[18F]fluorodopamine-derived radioactivity or cardiac norepinephrine spillover, indicating loss of myocardial sympathetic-nerve terminals, whereas patients with the Shy-Drager syndrome had increased levels of 6-[18F]fluorodopamine-derived radioactivity, indicating intact sympathetic terminals and absent nerve traffic. Patients with dysautonomia who did not have sympathetic neurocirculatory failure had normal levels of 6-[18F]fluorodopamine-derived radioactivity in myocardium and normal rates of cardiac norepinephrine spillover., Conclusions: The results of 6-[18F]fluorodopamine positron-emission tomography and neurochemical analyses support a new clinical pathophysiologic classification of dysautonomias, based on the occurrence of sympathetic neurocirculatory failure, signs of central neurodegeneration, and responsiveness to levodopa-carbidopa.

Cells of the exocrine pancreas produce digestive enzymes potentially harmful to the intestinal mucosa. Dopamine has been reported to protect against mucosal injury. In looking for the source of dopamine in the small intestine, we found that the duodenal juice contains high levels of dopamine and that the pancreas itself has a high dopamine [and dihydroxyphenylalanine (dopa)] content that does not change significantly after chemical sympathectomy. Furthermore, we were able to demonstrate tyrosine hydroxylase (TH) activity in control pancreas as well as in pancreas from rats after chemical sympathectomy. Immunostaining and in situ hybridization histochemistry confirmed both the presence of TH, dopamine, and the dopamine transporter, and the mRNAs encoding TH and dopamine transporter, and the presence of both types of vesicular monoamine transporters in the exocrine cells of the pancreas. Since there are no catecholaminergic enteric ganglia in the pancreas, the above results indicate that pancreatic cells have all the characteristics of dopamine-producing cells. We suggest that the pancreas is an important source of nonneuronal dopamine in the body, and that this dopamine has a role in protecting the intestinal mucosa and suggests that dopamine D1b receptor agonists might be used to help mucosal healing in the gastrointestinal tract.

In mammals, the sympathetic neurotransmitter is norepinephrine (NE), and the main adrenomedullary hormone is epinephrine (EPI). The sources and physiological roles of the third endogenous catecholamine, dopamine (DA), outside the brain have been obscure. Several lines of evidence suggest that in the periphery, rather than DA serving only as the precursor for the active compounds, released from sympathetic nerves and the adrenal medulla, DA may also act as an autocrine/paracrine regulator of local organ function. Thus, in the kidneys, most of DA formation appears to be from proximal tubular uptake of plasma DOPA, and binding of locally formed DA to dopaminergic receptors decreases Na/K ATPase activity and thereby accentuates natriuresis. In the gastric mucosa, DA may modulate sodium absorption and acid secretion. Recent clinical and laboratory animal evidence has indicated that the lungs and mesenteric organs contribute substantially to total body production and metabolism of DA. Generation of DA in non-noradrenergic, non-adrenergic cells can explain why human urine contains higher concentrations of DA and its metabolites than of NE and its metabolites. The vast preponderance of plasma DA in humans is sulfoconjugated. Since patients with sympathoneural failure have normal plasma levels of DA sulfate, one may speculate that the sulfoconjugating mechanism is relatively independent of sympathetic nerves and acts to localize DA effects and inactivate DA entering the circulation. These considerations lead to the concept of a third peripheral catecholaminergic system, where DA derived from plasma DOPA acts as an autocrine/paracrine substance and is inactivated by conjugation.

Concentrations of catecholamines and their metabolites in plasma entering and exiting mesenteric organs, liver, and kidneys were examined to assess the regional production and metabolism of catecholamines in anesthetized swine. Higher portal venous than arterial plasma concentrations of norepinephrine and its metabolites, 3,4-dihydroxyphenylglycol (DHPG) and 3-methoxy-4-hydroxyphenylglycol (MHPG), and of dopamine and its metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), indicated substantial production of both catecholamines by mesenteric organs, representing 45-50% of total body production. Most dopamine was not metabolized to norepinephrine, suggesting a large nonnoradrenergic contribution to total body dopamine production. Concentrations of norepinephrine, DHPG, normetanephrine, and MHPG were lower in plasma exiting than entering the liver, whereas concentrations of the end-product of norepinephrine metabolism, vanillylmandelic acid (VMA), were higher in outflowing than inflowing plasma. Over 94% of the VMA removed by the kidneys was produced in the liver, consistent with the hepatic source of this metabolite. Removal of DOPAC and HVA by the liver exceeded removal by the kidneys or production by mesenteric organs, indicating greater hepatic than renal elimination of these metabolites from the body and underestimation of mesenteric organ dopamine production based on summed spillovers of dopamine metabolites from the liver into the systemic circulation.

Objectives: This study evaluated the safety, efficacy and validity of 6-[18F]fluorodopamine positron emission tomographic scanning of cardiac sympathetic innervation and function in humans., Methods: Positron emission tomography (PET) scans, arterial blood and urine were obtained after a 3-min intravenous infusion of 6-[18F]fluorodopamine (1 to 4 mCi, 188 to 809 mCi/mmol) in healthy volunteers, with or without pretreatment with oral desipramine to inhibit neuronal uptake of catecholamines., Results: 6-[18F]Fluorodopamine PET scanning visualized the left ventricular myocardium. Blood pressure increased slightly and transiently. The estimated absorbed radiation dose to the main target organ, the wall of the urinary bladder, was 0.8 to 1.0 rad/mCi of injected 6-[18F]fluorodopamine. By 24 h after the injection, the main 6F-compound in urine was 6F-vanillymandelic acid, a metabolite of 6F-norepinephrine. Desipramine attenuated accumulation of myocardial 6-[18F]fluorodopamine-derived radioactivity and plasma 6F-dihydroxyphenylacetic acid., Conclusions: 6-[18F]Fluorodopamine produces negligible hemodynamic effects and acceptable radiation exposure at doses that visualize the left ventricular myocardium. Sympathetic nerves take up 6-[18F]fluorodopamine, which is translocated from the axoplasm into storage vesicles, where is it beta-hydroxylated to the fluorinated analogue of the sympathetic neurotransmitter norepinephrine. Therefore, the basis for visualization of myocardium after 6-[18F]fluorodopamine injection in humans is radiolabeling by 6-[18F]fluorodopamine and 6-[18F]fluoronorepinephrine of vesicles in sympathetic terminals. 6-[18F]Fluorodopamine PET scanning provides a novel means for assessing sympathetic innervation and function noninvasively in the human heart.

Hypotheses concerning the pathophysiology of hypertension, cardiac failure and other cardiovascular disorders have imputed abnormal cardiac sympathoneural activity. Here we describe a technique to examine cardiac sympathetic innervation and function using positron emission tomographic (PET) scanning after systemic intravenous injection of 18F-6-fluorodopamine, and the effects of chemical sympathectomy by the neurotoxin, 6-hydroxydopamine (6-OHDA). Uptake of 18F-6-fluorodopamine by the heart of anesthetized dogs resulted in striking delineation of the left ventricular myocardium. Myocardial radioactivity declined bi-exponentially, with a half-life of approximately 2 h during the longer phase. In 6-OHDA-treated animals, the ventricular myocardium was barely distinguishable from the chamber; myocardial radioactivity declined rapidly and was virtually absent within 30 min after injection of 18F-6-fluorodopamine. The rates of decline in myocardial radioactivity in dogs treated with 6-OHDA were similar to those in dogs treated with reserpine, but the mechanisms of sympatholysis by these drugs were distinguished by arterial plasma levels of 6-fluorodihydroxyphenylacetic acid (6-FDOPAC). Plasma 6-FDOPAC levels were diminished in 6-OHDA-treated dogs and elevated in reserpinized dogs. The results confirm that, after injection of 18F-6-fluorodopamine, cardiac sympathetic nerve endings are radiolabeled, allowing visualization of sites of sympathetic innervation. Combined assessments of PET time-activity curves and plasma levels of metabolites of 18F-6-fluorodopamine constitute a new, potentially clinically applicable means by which to examine cardiac sympathetic function.

The plasma concentration of the dopamine (DA) metabolite, homovanillic acid (HVA), is used as an indicator of central nervous system dopaminergic activity. Using percutaneously inserted catheters we were able to obtain blood samples simultaneously from the right and left internal jugular veins. Veno-arterial HVA plasma concentration differences combined with adjusted organ plasma flows were used, according to the Fick Principle, to determine the HVA overflow from the brain. The HVA overflow from the liver was also measured. HVA overflow from the brain represented 12% of the total body HVA production. A similar amount was released from the liver, illustrating the limited validity of peripheral plasma HVA measurements as an indicator of central dopaminergic activity. HVA release from the human brain displayed a degree of asymmetry, the overflow into the left internal jugular vein being 36% greater than that into the right. Cerebral venous blood flow scans indicated that cortical cerebral regions drained preferentially into the right internal jugular; by inference the higher HVA overflow on the left originated from dopamine-rich subcortical brain areas. Since HVA in plasma may arise from the metabolism of DA existing either as a neurotransmitter or a norepinephrine (NE) precursor we measured the internal jugular vein plasma concentrations of NE, and its metabolite dihydroxyphenylglycol (DHPG), to determine whether they displayed a similar pattern of release to HVA. The overflow of both NE and DHPG into the right internal jugular vein was approximately double that on the left. Since the overflow of HVA did not parallel that of NE and DHPG it may be inferred that the origin of much of the subcortically produced HVA is from dopaminergic neurons and not from the metabolism of precursor DA in noradrenergic neurones or cerebrovascular sympathetic nerves.

Positron emission tomographic (PET) scanning after systemic i.v. injection of fluorine-18-6-fluorodopamine ([18F]-6F-DA) is a method for visualizing and measuring regional sympathetic nervous system innervation and function. Based on results of preclinical studies of rats and dogs and on previous literature about the fate of injected tracer-labeled catecholamines, dosimetric estimates for clinical studies are presented here. After injection of 1 mCi of [18F]-F-DA, the radiation dose would be highest to the wall of the urinary bladder (1.40 rem/mCi), due to accumulation of radioactive metabolites of [18F]-F-DA in urine. Radioactivity also would accumulate in bile. Organs receiving the next highest dose would be the kidneys (0.9 rem/mCi) and small intestine (0.2 rem/mCi). The parenchymal radiation dose would be lowest in the brain, since there is an effective blood-brain barrier for circulating catecholamines. Radiation doses to all organs after administration of 1 mCi of [18F]-F-DA to humans would be less than 3 rem and, therefore, within current FDA guidelines.

In evaluating positron-emitting analogs of dopamine (DA) as possible imaging agents for visualizing tissue sympathetic innervation and function, the metabolic fate of systemically injected [3H]-DA or [14C]-DA was compared with that of [3H]-2-fluoroDA in plasma and in sympathetically innervated tissues (left ventricle, spleen and salivary glands) of rats. By 60 min after the injection of [3H]-DA or [3H]-2-fluoroDA, concentrations of [3H]-DA. [3H]-2-fluoroDA, [3H]-norepinephrine ([3H]-NE) and [3H]-2-fluoroNE in tissue exceeded concentrations in plasma by up to several thousand-fold. Whereas most of the radioactivity in tissue was in catechols, radioactivity in plasma was due to O-methylated metabolites of DA, including homovanillic acid (HVA) and of NE, including normetanephrine (NMN) and methoxyhydroxphenylglycol (MHPG). Estimated ratios of tissue: blood radioactivity at 60 min after injection of [3H]-2-fluoroDA were 4.10 for the heart, 1.91 for the spleen and 2.10 for the salivary glands. The patterns of levels of catechol metabolites and analogs of HVA in plasma and effects of blockade of neuronal uptake with desipramine suggested that [3H]-2-fluoroDA was not as efficiently removed by neuronal uptake and not as efficiently beta-hydroxylated as the non-fluorinated compound. Concurrent administration of [3H]-DA and large amounts of non-radioactive 2-fluoroDA did not substantially alter the pattern of metabolites of [3H]-DA in plasma. After injection of [18F]-fluoroDA, visualization of sympathetic innervation of tissue should be feasible by position emission tomography.

Turnover rates of noradrenaline and of dopamine were examined in regions of the CNS (brainstem, frontal cortex, hippocampus, striatum) and in cardiac tissue of mice that had ingested ethanol for 2 or 7 days and during withdrawal of ethanol. Turnover of neurotransmitters was assessed from the accumulation of dihydroxyphenylalanine and from the depletion in levels of noradrenaline, dopamine and their deaminated metabolites in tissue, after irreversible inhibition of aromatic L-amino acid decarboxylase with DL-alpha-monofluoromethyldopa. There were no consistent changes in the turnover of noradrenaline or dopamine after 2 or 7 days of continuous ingestion of ethanol, but at the time that animals exhibited peak ethanol-withdrawal symptoms (8 hr after ethanol consumption was stopped), the turnover of dopamine in the striatum was markedly decreased to less than a third of that observed in control animals, whereas the turnover of noradrenaline in the brainstem was increased by a half. The changes in turnover of neurotransmitters in specific regions of the brain may reflect alterations in neuronal activity that result from withdrawal of ethanol, or may be determinants of particular ethanol-withdrawal symptoms.

The neuronal uptake and metabolism of 2-fluorodopamine (2F-dopamine), 6-fluorodopamine (6F-dopamine) and tritium-labeled dopamine were compared in heart, submaxillary gland and spleen of rats to assess the utility of 18F-labeled 2F- or 6F-dopamine for positron emission tomographic imaging of sympathetically innervated tissues. Tritiated dopamine with and without 2F- or 6F-dopamine, or tritiated 2F-dopamine alone, were injected i.v. into rats that were or were not pretreated with desipramine to block catecholamine neuronal uptake or with reserpine to block vesicular translocation of catecholamines. Tissue and plasma samples were obtained at intervals up to 1 hr after injections. At 1 hr after injection of tritiated dopamine, tritium-labeled norepinephrine, dopamine, dihydroxyphenylacetic acid and dihydroxyphenylglucol accounted for less than 2% of the tritium in plasma but up to 92% of that in tissues; tritiated norepinephrine accounted for 70% or more of the tritium in tissues. In contrast, at 1 hr after injection of tritiated 2F-dopamine, tritiated 2F-norepinephrine accounted for 30 to 46% of the tritium in tissues. Desipramine and reserpine pretreatment blocked the tissue accumulation of tritiated and fluorinated dopamine as well as their dihydroxy-metabolites, indicating that accumulation of exogenous norepinephrine and dopamine analogs was within sympathetic storage vesicles. Relative to the doses of dopamine precursors, less 2F- and 6F-norepinephrine accumulated in tissues than tritiated norepinephrine, due largely to inefficient beta-hydroxylation of fluorinated dopamine.(ABSTRACT TRUNCATED AT 250 WORDS)

1. Urinary excretion of dopamine (DA) increases during dietary salt loading. The majority of urinary DA is derived from circulating dihydroxyphenylalanine (dopa). Whether the increase in urinary DA excretion during salt loading results from increased efficiency of uptake of dopa by proximal tubular cells of the kidney, facilitation of intracellular conversion of dopa to DA, or increased delivery of dopa to tubular uptake sites, has been unknown. 2. In 10 inpatient normal volunteers on a constant diet, daily excretion of dopa and DA was assessed during normal sodium intake (109 mmol/day) for 1 week, low sodium intake (9 mmol/day) for 1 week and high sodium intake (249 mmol/day) for 1 week. 3. Urinary DA excretion exceeded urinary dopa excretion by about tenfold, and the excretion of both DA and dopa increased by about twofold between the low and high salt diets, with similar proportionate changes. Plasma dopa was unchanged by dietary salt manipulation. 4. The results indicate that increases in urinary DA excretion during dietary salt loading can be accounted for by increased delivery of dopa to sites of uptake by proximal tubular cells. Since dopa is released into the bloodstream by sympathetic nerve endings and by the brain, and since interference with decarboxylation of dopa attenuates natriuretic responses, dopa may function indirectly as a neurohormone involved in homoeostatic regulation of sodium balance.

Pheochromocytomas are catecholamine-producing tumors presenting with various clinical symptoms, but mostly with headache, sweating, palpitations and hypertension. If not properly diagnosed, secretion of catecholamines may lead to fatal cardiovascular consequences. Biochemical testing for pheochromocytoma should be performed not only in symptomatic subjects or in subjects with adrenal incidentaloma but also in subjects with a genetic predisposition for pheochromocytoma (multiple endocrine neoplasia type 2, Von Hippel-Lindau (VHL) syndrome, neurofibromatosis type 1 (NF 1)and mutations of succinate dehydrogenase (SDH) genes). Once a pheochromocytoma is proven, computed tomography (CT), magnetic resonance imaging (MRI) and functional imaging with [123I]-MIBG may be used for tumor localization. Adequate medical pre-treatment is essential for successful operation which is performed in most cases by laparoscopy. After tumor removal, further follow-up is necessary due to possible recurrence. Although prognosis after tumor resection is excellent, a significant proportion of pheochromocytomas recur, some as metastases. Thus, appropriate follow-up is mandatory. [ABSTRACT FROM AUTHOR]