Idiopathic pulmonary arterial hypertension (IPAH) is pathogenetically related to low levels of the vasodilator nitric oxide (NOcellular respiration ͉ nitric oxide ͉ oxygen consumption ͉ pulmonary hypertension ͉ mitochondrion I diopathic pulmonary arterial hypertension (IPAH) is a fatal disease of unknown etiology characterized by a progressive increase in pulmonary artery pressure and vascular growth (1, 2). Secondary forms of pulmonary arterial hypertension (PAH) are associated with known diseases, such as collagen vascular diseases or portal hypertension but in the absence of an identifiable etiology are classified as IPAH. Abnormalities in vasodilators, specifically nitric oxide (NO), have been implicated in the pathogenesis of pulmonary hypertension (1-5). NO is produced in the lung by NO synthases (NOS; EC 1.14.13.39) (6-8). There is conclusive evidence from animal models of pulmonary hypertension, mice genetically deficient in endothelial NOS (eNOS), and complementation studies with gene transfer of NOSs for the concept that NO is a critical determinant of pulmonary vascular tone (6, 7, 9). Furthermore, pulmonary and total body NO are lower in IPAH patients as compared with healthy controls (3,(10)(11)(12), and the decrease of NO has been linked to increased arginase II and decreased eNOS expression in IPAH pulmonary endothelial cells in vivo (10,13).In addition to effects on vascular tone, NO regulates cellular bioenergetics through effects on glycolysis, oxygen consumption by mitochondrion, and mitochondrial biogenesis (14-17). For example, eNOS-deficient mice, which have mild pulmonary hypertension under normoxia and an exaggerated pulmonary vasoconstrictive response to hypoxia (18), have reduced mitochondria content in a wide range of tissues in association with significantly lower oxygen consumption and ATP content (14-17). Mitochondria are essential to cellular energy production in all higher organisms adapted to an oxygen-containing environment, i.e., ATP produced through oxidative phosphorylation. The electrochemical gradient used by mitochondrial F 0 F 1 ATP synthase to synthesize ATP from ADP is generated by the proton pump action performed by Complexes I, III, and IV of the respiratory chain. The proton pumping is accompanied by electron shuttling, whereby Complexes I and II, along with the flavoprotein-ubiquinone oxidoreductase, transfer electrons from different sources to ubiquinone (coenzyme Q). The electrons are then transferred sequentially to Complex III, cytochrome c, Complex IV, and finally to molecular oxygen, the terminal electron acceptor. All multisubunit complexes of the respiratory chain (I-IV) are located in the mitochondrial inner membrane. Thus, mitochondria are the primary oxygen demand in the body, accounting for Ϸ90% of cellular oxygen consumption. Conversely, under limiting oxygen conditions, cells turn to glycolysis to generate energy. In endothelial cells, ATP is generated nearly equivalently by glycolysis and cellular respiration (19), accounting for a relative tolerance ...

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The trend toward focused surgical parathyroidectomy requires precise preoperative localization of parathyroid lesions in patients with hyperparathyroidism. The purpose of this study was to directly compare the diagnostic accuracy of 99m Tc-sestamibi/ 123 I subtraction SPECT with SPECT/CT for the localization of abnormal parathyroid glands in patients with primary hyperparathyroidism. Methods: A total of 61 consecutive surgical patients with primary hyperparathyroidism underwent both 123 I/ 99m Tc-sestamibi subtraction SPECT and SPECT/CT scans preoperatively, using a hybrid SPECT/CT instrument that combined a dual-detector SPECT camera with a 6-slice multidetector spiral CT scanner. Four hours after being given 123 I-sodium iodide orally, each patient received 99m Tc-sestamibi intravenously, followed immediately by a simultaneous, dual-isotope SPECT scan of the neck and upper chest. Then, without moving the patient, we performed a noncontrast-enhanced CT scan of the same body region. Normalization and subtraction of the 123 I SPECT images from the 99m Tc SPECT images were performed. The subtraction SPECT and the coregistered fused SPECT/CT studies were interpreted separately, with images scored on a 5-point scale. Surgical and histopathologic findings were used as the standard of comparison. Results: Surgery was successful in 57 patients (solitary parathyroid adenoma in 48 patients, double parathyroid adenomas in 6 patients, and 10 hyperplastic parathyroid glands in 3 patients). The sensitivities of SPECT (50/70 5 71%) and SPECT/CT (49/70 5 70%) were similar (P 5 0.779). The specificity of SPECT/CT (26/27 5 96%) was significantly greater than that of SPECT (13/27 5 48%; P 5 0.006). The receiver-operating-characteristic area under the curve of SPECT/CT (0.833) was significantly greater than that of SPECT (0.632; P , 0.001). Conclusion: SPECT/CT is significantly more specific than dual-isotope subtraction SPECT for the preoperative identification of parathyroid lesions in patients with primary hyperparathyroidism.

ClinicalTrials.gov NCT01586156FUNDING. This project was supported by NIH R01HL115008 and R01HL60917 and in part by the National Center for Advancing Translational Sciences, UL1TR000439.

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