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Ravinder J Singh

Publications and source records attributed to Ravinder J Singh.

At least 19 recordsLinked to original sources
PubMed2006

Association of adrenal steroids with hypertension and the metabolic syndrome in blacks.

Blacks have a high prevalence of hypertension and adrenal cortical adenomas/hyperplasia. We evaluated the hypothesis that adrenal steroids are associated with hypertension and the metabolic syndrome in blacks. Ambulatory blood pressures, anthropometric measurements, and measurements of plasma renin activity (PRA), aldosterone, fasting lipids, glucose, and insulin were obtained in 397 subjects (46% hypertensive and 50% female) after discontinuing antihypertensive and lipid-lowering medications. Hypertension was defined as average ambulatory blood pressure >130/85 mm Hg. Late-night and early morning salivary cortisol, 24-hour urine-free cortisol, and cortisone excretion were measured in a consecutive subsample of 97 subjects (40% hypertensive and 52% female). Compared with normotensive subjects, hypertensive subjects had greater waist circumference and unfavorable lipid profiles, were more insulin resistant, and had lower PRA and higher plasma aldosterone and both late-night and early morning salivary cortisol concentrations. Twenty-four-hour urine-free cortisol and cortisone did not differ. Overall, ambulatory blood pressure was positively correlated with plasma aldosterone (r=0.22; P<0.0001) and late-night salivary cortisol (r=0.23; P=0.03) and inversely correlated with PRA (r=-0.21; P<0.001). Plasma aldosterone correlated significantly with waist circumference, total cholesterol, triglycerides, insulin, and the insulin-resistance index. Based on Adult Treatment Panel III criteria, 17% of all of the subjects were classified as having the metabolic syndrome. Plasma aldosterone levels, but not PRA, were elevated in subjects with the metabolic syndrome (P=0.0002). The association of aldosterone with blood pressure, waist circumference, and insulin resistance suggests that aldosterone may contribute to obesity-related hypertension in blacks. In addition, we speculate that relatively high aldosterone and low PRA in these hypertensive individuals may reflect a mild variant of primary aldosteronism.

Adolescent↗
PubMed2006

C-3 epimers can account for a significant proportion of total circulating 25-hydroxyvitamin D in infants, complicating accurate measurement and interpretation of vitamin D status.

CONTEXT: We have recently introduced liquid chromatography-tandem mass spectrometry (LC-MS/MS) for 25-hydroxyvitamin D(2) (25OHD(2)) and 25OHD(3) testing. During subsequent clinical use, we identified significantly elevated results in some infants. We hypothesized this might represent assay interference caused by C-3 epimers of 25OHD(2) or 25OHD(3). OBJECTIVE: Our aims were to 1) determine the prevalence of C-3 epimers of 25OHD(2) or 25OHD(3) in human serum, and 2) identify the patient populations that might be affected. STUDY DESIGN: We modified our LC-MS/MS method to allow detection of C-3 epimers. We retested specimens from four patient groups with the new method and an extracted RIA: 1) children less than 1 yr old, 2) children 1-18 yr old, 3) adults aged 20-87 yr with liver disease, and 4) adults aged 19-91 yr without liver disease. RESULTS: In 172 children from group 1 with detectable 25OHD(2) or 25OHD(3), we identified C-3 epimers in 39 (22.7%). The epimers contributed 8.7-61.1% of the total 25-OHD. There was an inverse relationship between patient age and epimer percentage (r = 0.48; P < 0.002). The RIA gave accurate 25-OHD results that correlated with the modified LC-MS/MS method. No C-3 epimers were detected in any of the other groups. CONCLUSIONS: Significant concentrations of C-3 epimers of 25OHD(2) or 25OHD(3) are commonly found in infants. This can lead to overestimation of 25-OHD levels. Measurements in children less than 1 yr should therefore be performed with an assay that allows accurate detection of 25-OHD in the presence of its C-3 epimers.

25-Hydroxyvitamin D 2↗
PubMed2006

Simultaneous determination of 12 steroids by isotope dilution liquid chromatography-photospray ionization tandem mass spectrometry.

BACKGROUND: Serum steroid assays play an important role in the clinical evaluation of a number of common endocrine disorders. Among various assays, tandem mass spectrometry (MS/MS) has being increasingly applied in clinical laboratories for its high sensitivity, specificity, and simultaneous multi-analyte quantitation capability. Our first generation isotope dilution steroid profile assay by HPLC-tandem MS/MS with a C-18 column allowed for the measurement of 9 steroids in 18 min employing a sample volume of 760 ul serum. We describe our second generation steroid profile assay which allows for the quantitation of 12 steroids simultaneously employing HPLC-MS/MS and isotope dilution tandem MS in 11 min. This method requires a sample volume of 200 microl. METHODS: An API-5000 triple-quadrupole mass spectrometer (Sciex, Concord, Canada) coupled with the PhotoSpray source and Shimadzu HPLC system (Shimadzu Scientific Instruments, Columbia, MD) was used employing isotope dilution with deuterium labeled internal standard (IS) for each analyte. Two hundred microliters of serum were deproteinized by adding 300 microl of acetonitrile containing internal standards. After centrifugation, 450 microl of supernatant were diluted with 900 microl of water and 1000 microl aliquot were injected onto a C-8 column. After a 3 min wash the valve was activated to initiate the gradient elution program which eluted the steroids. Quantitation by MRM analysis was performed both in positive ion mode for 11 analytes and in negative ion mode for aldosterone. Within-day and between-day precision, reliability and accuracy of this method were assessed by correlation with other MS/MS and immunoassay methods and by recovery study. RESULTS: Within-day CVs were <11.5% for all analytes tested and between-day CVs ranged from 3.5% to 12.2%. The results of the comparison study yield r values ranging between 0.908 and 0.999. Recovery ranged from 90% to 110%. CONCLUSIONS: This method can simultaneously measure 12 steroids in serum within 11 min with minimal sample preparation. It can be routinely employed in a clinical environment and is attractive because of its simplicity in sample processing and high throughput.

Chromatography, High Pressure Liquid↗
PubMed2006

A two-center international evaluation of the Immulite 2000 automated serum gastrin assay.

OBJECTIVES: To assess the performance of the Immulite 2000 serum gastrin assay. DESIGN AND METHODS: Two-center validation and comparison with two manual gastrin assays. RESULTS: Serum, serum separator, EDTA and heparin tube results differed <20%. Samples showed <20% degradation for <6 h at room temperature, 3-day-refrigerated, and underwent 3 freeze-thaw cycles. Imprecision was <8% between 20 and 824 ng/L (10-393 pmol/L). Spike recovery was 88.5-106%, and recovery on dilution was 62-135%. There were no interferences from gastrin 1-14, pentagastrin, and cholecystokinin (CCK) 1-33 and CCK 26-33. The fasting reference range was <100 ng/L (<48 pmol/L). Regression slopes to the manual assays were 0.9 and 0.97, with comparable clinical performance. CONCLUSIONS: The Immulite 2000 assay is precise, accurate, and fast and compares well with established gastrin assays.

Automation↗
PubMed2006

Vitreous penetration of topical moxifloxacin and gatifloxacin in humans.

PURPOSE: To determine the vitreous penetration of the new fourth-generation topical fluoroquinolones moxifloxacin 0.5% and gatifloxacin 0.3%. METHODS: A prospective randomized clinical trial comprising 12 eyes of 12 patients scheduled for pars plana vitrectomy between August 2003 and September 2003 was performed in a clinical practice. The patients were randomly assigned to receive topical moxifloxacin 0.5% (n = 6) or gatifloxacin 0.3% (n = 6). One half the patients in each antibiotic group received 1 drop every 15 minutes for a total of 3 doses starting 1 hour before surgery, and the other one half self-administered the antibiotic drop 4 times daily for 3 days before surgery and at 7 am on the day of surgery. Undiluted vitreous samples were obtained and analyzed using high-performance liquid chromatography. RESULTS: Either moxifloxacin 0.5% or gatifloxacin 0.3% was detected in the vitreous in all 12 patients in the study. There was no significant difference between the mean vitreous concentration of moxifloxacin 0.5% given over 1 hour preoperatively (0.012 +/- 0.011 microg/mL) and that given in the 3-day regimen (0.011 +/- 0.008 microg/mL) (P = 0.93). There was also no significant difference between the mean vitreous concentration of gatifloxacin 0.3% given over 1 hour preoperatively (0.001 +/- 0.0003 microg/mL) and that given over 3 days (0.008 +/- 0.006 microg/mL) (P = 0.11). Vitreous concentrations of moxifloxacin 0.5% and gatifloxacin 0.3% in each eye were all lower than the 90% minimum inhibitory concentration for the commonest bacterial isolates causing endophthalmitis. With both dosing regimens, the mean vitreous concentration of moxifloxacin 0.5% was higher than that of gatifloxacin 0.3% administered at the same regimen, but this was not statistically significant. CONCLUSION: Both topical moxifloxacin 0.5% and gatifloxacin 0.3% penetrated the vitreous in the uninflamed eye, but the vitreous concentrations attained were all lower than the 90% minimum inhibitory concentration for the commonest bacterial pathogens causing acute postoperative endophthalmitis.

Administration, Topical↗
PubMed2006

Splanchnic cortisol production in dogs occurs primarily in the liver: evidence for substantial hepatic specific 11beta hydroxysteroid dehydrogenase type 1 activity.

Eight dogs underwent combined hepatic/portal vein catheterization and infusion of D4-cortisol in order to determine the relative contributions of the viscera and liver to splanchnic cortisol production. D4-cortisol concentrations progressively decreased from 2.6 +/- 0.1 to 2.4 +/- 0.1 to 1.7 +/- 0.1 microg/dl (P < 0.001 by ANOVA) from hepatic artery to portal vein to hepatic vein, respectively, indicating 8 +/- 3 and 28 +/- 3% extraction across the viscera and liver, respectively. On the other hand, hepatic artery, portal vein, and hepatic vein cortisol concentrations did not differ (0.31 +/- 0.12 vs. 0.28 +/- 0.11 vs. 0.27 +/- 0.10 microg/dl, respectively), indicating zero net cortisol balance. This meant that 1.0 +/- 0.1 microg/min of cortisol was produced within the splanchnic bed, all of which occurred within the liver (1.2 +/- 0.1 microg/min). On the other hand, visceral cortisol production did not differ from zero (-0.2 +/- 0.2 microg/min; P < 0.001 vs. liver). Flux through the 11beta hydroxysteroid dehydrogenase (HSD) type 1 pathway can be measured by determining the rate of conversion of D4-cortisol to D3-cortisol. D3-cortisol concentrations were lower in the portal vein than hepatic artery (0.45 +/- 0.03 vs. 0.48 +/- 0.02, respectively; P < 0.01) but did not differ in the portal vein and hepatic vein, indicating net uptake across the viscera but zero balance across the liver. D3-cortisol production with the viscera and liver averaged 0.2 +/- 0.1 microg/min (P = NS vs. zero production) and 0.6 +/- 0.1 microg/min (P < 0.001 vs. zero production; P < 0.001 vs. viscera production), respectively. We conclude that most, if not all, of splanchnic cortisol production occurs within the liver. Taken together, these data suggest that the high local cortisol concentrations generated via the 11beta HSD type 1 pathway within the liver likely contribute to the regulation of hepatic glucose, fat, and protein metabolism.

11-beta-Hydroxysteroid Dehydrogenase Type 1↗
PubMed2006

The effects of aerobic exercise on glucose and counterregulatory hormone concentrations in children with type 1 diabetes.

OBJECTIVE: To examine the acute glucose-lowering effects of aerobic exercise in children and adolescents with type 1 diabetes. RESEARCH DESIGN AND METHODS: Fifty children and adolescents with type 1 diabetes (ages 10 to <18 years) were studied during exercise. The 75-min exercise session consisted of four 15-min periods of walking on a treadmill to a target heart rate of 140 bpm and three 5-min rest periods. Blood glucose and plasma glucagon, cortisol, growth hormone, and norepinephrine concentrations were measured before, during, and after exercise. RESULTS: In most subjects (83%), plasma glucose concentration dropped at least 25% from baseline, and 15 (30%) subjects became hypoglycemic (< or = 60 mg/dl) or were treated for low glucose either during or immediately following the exercise session. The incidence of hypoglycemia and/or treatment for low glucose varied significantly by baseline glucose, occurring in 86 vs. 13 vs. 6% of subjects with baseline values <120, 120-180, and >180 mg/dl, respectively (P < 0.001). Exercise-induced increases in growth hormone and norepinephrine concentrations were marginally higher in subjects whose glucose dropped < or = 70 mg/dl. Treatment of hypoglycemia with 15 g of oral glucose resulted in only about a 20-mg/dl rise in glucose concentrations. CONCLUSIONS: In youth with type 1 diabetes, prolonged moderate aerobic exercise results in a consistent reduction in plasma glucose and the frequent occurrence of hypoglycemia when preexercise glucose concentrations are <120 mg/dl. Moreover, treatment with 15 g of oral glucose is often insufficient to reliably treat hypoglycemia during exercise in these youngsters.

Adolescent↗
PubMed2006

Cortisol metabolism in the Bolivian squirrel monkey (Saimiri boliviensis boliviensis).

New World squirrel monkeys (Saimiri spp.) have high circulating cortisol levels but normal electrolytes and blood pressures. The goal of the present study was to gain insight into adaptive mechanisms used by Bolivian squirrel monkeys to minimize the effects of high cortisol on mineralocorticoid receptor (MR) activity and electrolyte and water balance. Aldosterone levels in serum from 10 squirrel monkeys were 17.7 +/- 3.4 ng/dl (normal range in humans, 4 to 31 ng/dl), suggesting that squirrel monkeys do not exhibit a compensatory increase in aldosterone. The squirrel monkey MR was cloned and expressed in COS-7 cells and found to have similar responsiveness to cortisol and aldosterone as human MR, suggesting that squirrel monkey MR is not inherently less responsive to cortisol. To determine whether altered metabolism of cortisol might contribute to MR protection in squirrel monkeys, serum and urinary cortisol and cortisone were measured, and a comprehensive urinary corticosteroid metabolite profile was performed in samples from anesthetized and awake squirrel monkeys. The levels of cortisone exceeded those of cortisol in serum and urine, suggesting increased peripheral 11beta-hydroxysteroid dehydrogenase 2 activity in squirrel monkeys. In addition, a significant fraction (approximately 20%) of total corticosteroids excreted in the urine of squirrel monkeys appeared as 6beta-hydroxycortisol, compared with that in man (1%). Therefore, changes in cortisol metabolism likely contribute to adaptive mechanisms used by Bolivian squirrel monkeys to minimize effects of high cortisol.

Amino Acid Sequence↗
PubMed2005

17alpha-estradiol: a brain-active estrogen?

The estrogen 17beta-estradiol has profound effects on the brain throughout life, whereas 17alpha-estradiol, the natural optical isomer, is generally considered less active because it binds less avidly to estrogen receptors. On the contrary, recent studies in the brain document that 17alpha-estradiol elicits rapid and sustained activation of the MAPK/ERK and phosphatidylinositol 3-kinase-Akt signaling pathways; is neuroprotective, after an ischemic stroke and oxidative stress, and in transgenic mice with Alzheimer's disease; and influences spatial memory and hippocampal-dependent synaptic plasticity. The present study measured the endogenous content of 17alpha-estradiol in the brain and further clarified its actions and kinetics. Here we report that: 1) endogenous levels of 17alpha-estradiol and its precursor estrone are significantly elevated in the postnatal and adult mouse brain and adrenal gland of both sexes, as determined by liquid chromatography/tandem mass spectrometry; 2) 17alpha-estradiol and 17beta-estradiol bind estrogen receptors with similar binding affinities; 3) 17alpha-estradiol transactivates an estrogen-responsive reporter gene; and 4) unlike 17beta-estradiol, 17alpha-estradiol does not bind alpha-fetoprotein or SHBG, the estrogen-binding plasma proteins of the developing rodent and primate, respectively. 17alpha-Estradiol was also found in the brains of gonadectomized or gonadectomized/adrenalectomized mice, supporting the hypothesis that 17alpha-estradiol is locally synthesized in the brain. These findings challenge the view that 17alpha-estradiol is without biological significance and suggest that 17alpha-estradiol and its selective receptor, ER-X, are not part of a classical hormone/receptor endocrine system but of a system with important autocrine/paracrine functions in the developing and adult brain. 17alpha-Estradiol may have enormous implications for hormone replacement strategies at the menopause and in the treatment of such neurodegenerative disorders as Alzheimer's disease and ischemic stroke.

Adrenalectomy↗
PubMed2005

Obesity and type 2 diabetes do not alter splanchnic cortisol production in humans.

CONTEXT: Cortisol is a potent regulator of carbohydrate, fat, and protein metabolism. OBJECTIVE: The objective of the study was to determine whether obesity alone or in combination with type 2 diabetes increases splanchnic and/or leg cortisol production. DESIGN: Splanchnic and leg cortisol production were measured using the hepatic and leg catheterization technique combined with infusion of D4-cortisol. SETTING: The study was conducted in a General Clinical Research Center. PARTICIPANTS: Nine lean nondiabetic, 10 obese nondiabetic, and 11 obese diabetic subjects were studied. INTERVENTIONS: Diabetic volunteers were withdrawn from their glucose-lowering medications before study. MAIN OUTCOME MEASURES: Rates of total body, splanchnic and leg cortisol, and D3-cortisol production were measured. RESULTS: Rates of splanchnic cortisol production equaled or exceeded those occurring in extrasplanchnic tissues (e.g. the adrenals) in all three groups. However, because concurrent splanchnic cortisol uptake also occurred, net splanchnic cortisol release was minimal. Splanchnic cortisol production and splanchnic D3-cortisol production (an index of splanchnic 11beta-hydroxysteroid dehydrogenase type 1 activity) did not differ among the three groups. In addition, splanchnic cortisol production did not correlate with either visceral fat or endogenous glucose production. On the other hand, splanchnic cortisol uptake was greater in the obese diabetic than lean nondiabetic subjects (25 +/- 2.9 vs. 15.3 +/- 2.5 microg/min; P < 0.05). Splanchnic, but not leg, D3-cortisol production was correlated with total body D3-cortisol production (r = 0.70; P < 0.001). CONCLUSIONS: Although large amounts of cortisol are produced within the splanchnic bed, implying high intrahepatic glucocorticoid concentrations, rates do not differ in lean and obese nondiabetic humans and are not influenced by the presence of type 2 diabetes mellitus. On the other hand, obesity but not diabetes increases splanchnic cortisol uptake.

11-beta-Hydroxysteroid Dehydrogenase Type 1↗
PubMed2005

Elevated fibroblast growth factor 23 in women with malignant ovarian tumors.

OBJECTIVE: To determine whether fibroblast growth factor 23 (FGF23) concentrations are altered in women with ovarian cancers in which FGF physiology is known to be abnormal. PATIENTS AND METHODS: Between May 2002 and September 2003 at the Mayo Clinic in Rochester, Minn, plasma or serum FGF23 concentrations were measured in 39 healthy women and in 14 with benign ovarian tumors, 14 with early-stage ovarian cancer, and 13 with advanced-stage ovarian cancer. Immunohistochemistry using anti-human FGF23 antibodies was performed on tissue from benign masses and advanced-stage tumors. RESULTS: Serum or plasma FGF23 concentrations were significantly higher in women with advanced-stage ovarian cancer compared with concentrations in women with early-stage ovarian cancer or benign disease or in healthy women. A significant positive correlation was seen between serum iFGF23 and cFGF23 concentrations and stage of disease. Serum iFGF23 and cFGF23 concentrations were positively correlated with serum phosphorus among women with ovarian cancer. No patients with elevated iFGF23 or cFGF23 concentrations had hypophosphatemia. Immunohistochemistry detected FGF23 tissue staining in malignant ovarian cancer cells. CONCLUSION: Serum or plasma FGF23 concentrations are elevated in patients with advanced-stage epithellal ovarian cancer without reductions in serum phosphate concentrations. The presence of elevated FGF23 concentrations in patients with an ovarian mass should suggest advanced-stage disease.

Adult↗
PubMed2004

Quantitative, highly sensitive liquid chromatography-tandem mass spectrometry method for detection of synthetic corticosteroids.

BACKGROUND: Measurements of serum or urine concentrations of synthetic glucocorticoids are useful for assessing suspected iatrogenic hypothalamic-pituitary-adrenal axis suppression and Cushing syndrome. We have developed a liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for the simultaneous quantitative analysis of beclomethasone dipropionate, betamethasone, budesonide, dexamethasone, fludrocortisone, flunisolide, fluorometholone, fluticasone propionate, megestrol acetate, methylprednisolone, prednisolone, prednisone, triamcinolone, and triamcinolone acetonide. METHODS: Stable isotopes of cortisol-9,11,12,12-d(4) and triamcinolone-d(1) acetonide-d(6) were added as internal standards to calibrators, controls, and unknown samples. After acetonitrile precipitation, these samples were extracted with methylene chloride, and the extracts were washed and dried. Reconstituted extract (15 muL) was injected on a reversed-phase column and analyzed by LC-MS/MS in positive-ion mode. Assay precision, accuracy, linearity, and sample stability were determined by use of enriched samples. Clinical validation included analysis of 8 serum and 20 urine samples from patients with undetectable cortisol concentrations and analysis of different types of tablets. RESULTS: Functional assay sensitivity was as low as 0.6-1.6 nmol/L for all compounds except for triamcinolone (7.6 nmol/L). Interassay CVs were 3.0-20% for concentrations of 0.6-364 nmol/L for all analytes. Recoveries of all analytes (except triamcinolone in serum) were 82-138% at 19.2-693 nmol/L. All but one of the serum and urine samples from patients who were tested because of suppressed cortisol concentrations contained at least one synthetic steroid. Tablet analysis recovered 75% of the synthetic steroids in suspected drugs. CONCLUSIONS: LC-MS/MS allows simultaneous quantitative detection of various synthetic steroids in serum, plasma, urine, and tablets. This provides a valuable tool for evaluating the clinical effects of topical and systemic synthetic corticosteroids.

Adrenal Cortex Hormones↗
PubMed2004

Circulating free nitrotyrosine in obstructive sleep apnea.

Obstructive sleep apnea (OSA) has been increasingly linked to cardiovascular disease, endothelial dysfunction, and oxidative stress, generated by repetitive nocturnal hypoxemia and reperfusion. Circulating free nitrotyrosine has been reported as a novel biomarker of nitric oxide (NO)-induced oxidative/nitrosative stress. Nitrosative stress has been implicated as a possible mechanism for development of cardiovascular diseases. We tested the hypothesis that repetitive severe hypoxemia resulting from OSA would increase NO-mediated oxidative stress. We studied 10 men with newly diagnosed moderate to severe OSA who were free of other diseases, had never been treated for OSA, and were taking no medications. Nitrotyrosine measurements, performed by liquid chromatography-tandem mass spectrometry, were made before and after untreated apneic sleep. We compared free nitrotyrosine levels in these patients with those obtained at similar times in 10 healthy male control subjects without OSA, with similar age and body mass index. Evening baseline nitrotyrosine levels were similar before sleep in the control and OSA groups [0.16 +/- 0.01 and 0.15 +/- 0.01 ng/ml, respectively, P = not significant (NS)]. Neither normal nor disturbed apneic sleep led to significant changes of plasma nitrotyrosine (morning levels: control group 0.14 +/- 0.01 ng/ml; OSA group 0.15 +/- 0.01 ng/ml, P = NS). OSA was not accompanied by increased circulating free nitrotyrosine either at baseline or after sleep. This observation suggests that repetitive hypoxemia during OSA does not result in increased NO-mediated oxidative/nitrosative stress in otherwise healthy subjects with OSA.

Adult↗
PubMed2004

Measurement of plasma free metanephrine and normetanephrine by liquid chromatography-tandem mass spectrometry for diagnosis of pheochromocytoma.

BACKGROUND: Quantification of plasma free metanephrines is usually accomplished by HPLC with electrochemical detection, but sample preparation is labor-intensive and time-consuming, run times are long, and interfering substances sometimes obscure the relevant peaks. The aim of this study was to develop a sensitive and specific LC-MS/MS method for plasma free metanephrines. METHODS: After solid-phase extraction, chromatographic separation of normetanephrine (NMN) and metanephrine (MN) was accomplished by use of a cyano analytical column. NMN, MN, d(3)-NMN, and d(3)-MN positive ions were detected in the multiple-reaction monitoring mode using the specific transitions m/z 166-->134, 180-->148, 169-->137, and 183-->151, respectively, with an atmospheric pressure chemical ionization source. RESULTS: Multiple calibration curves exhibited consistent linearity and reproducibility. Interassay imprecision values (CV; n = 20) for NMN at 0.64, 1.9, and 2.7 nmol/L were 6.6%, 7.8%, and 13%, respectively. Interassay CV for MN at 0.60, 1.2, and 2.1 nmol/L (n = 20) were 9.2%, 6.8%, and 9.8%, respectively. The mean recoveries of NMN and MN relative to the internal standard were 100% and 96%, respectively. The assays were linear between 0.20 and 10.0 nmol/L. Deming regression of HPLC and LC-MS/MS results yielded slopes of 0.93 (95% confidence interval, 0.89-0.98) and 0.89 (0.85-0.93) and y-intercepts of -0.16 and 0.03 nmol/L for NMN (n = 132) and MN (n = 92), respectively. CONCLUSIONS: This novel LC-MS/MS approach provides a precise, rapid, and specific alternative method to HPLC for the quantification of the low nanomolar concentrations of free metanephrines in plasma.

Adrenal Gland Neoplasms↗
PubMed2004

Advances in metanephrine testing for the diagnosis of pheochromocytoma.

Pheochromocytoma is a lethal tumor of chromaffin cells of the adrenal medulla that produces episodes of hypertension with the symptoms of palpitations, severe headaches, and sweating. The diagnosis of pheochromocytoma is a challenging one; autopsy series suggest that many pheochromocytomas are not clinically suspected, and the undiagnosed tumor can be associated with morbid consequences. The testing of catecholamines, metanephrines, and Vanillylymandelic acid commonly is used for screening of pheochromocytoma. The diagnostic value of various biochemical tests,as reported in recent Mayo and National Institutes of Health studies, have been compared and discussed in detail. The recent developments in the methodologies of metanephrines testing also are presented.

Adrenal Gland Neoplasms↗