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The molecular mechanisms driving the conserved metazoan developmental shift referred to as the mid-blastula transition (MBT) remain mysterious. Typically, cleavage divisions give way to longer asynchronous cell cycles with the acquisition of a gap phase. In Drosophila, rapid synchronous nuclear divisions must pause at the MBT to allow the formation of a cellular blastoderm through a special form of cytokinesis termed cellularization. Drosophila Fragile X mental retardation protein (dFMRP; FMR1), a transcript-specific translational regulator, is required for cellularization. The role of FMRP has been most extensively studied in the nervous system because the loss of FMRP activity in neurons causes the misexpression of specific mRNAs required for synaptic plasticity, resulting in mental retardation and autism in humans. Here, we show that in the early embryo dFMRP associates specifically with Caprin, another transcript-specific translational regulator implicated in synaptic plasticity, and with eIF4G, a key regulator of translational initiation. dFMRP and Caprin collaborate to control the cell cycle at the MBT by directly mediating the normal repression of maternal Cyclin B mRNA and the activation of zygotic frühstart mRNA. These findings identify two new targets of dFMRP regulation and implicate conserved translational regulatory mechanisms in processes as diverse as learning, memory and early embryonic development.

Fragile X mental retardation protein (FMRP) is an RNA-binding protein that is required for the translational regulation of specific target mRNAs. Loss of FMRP causes Fragile X syndrome (FXS), the most common form of inherited mental retardation in humans. Understanding the basis for FXS has been limited because few in vivo targets of FMRP have been identified and mechanisms for how FMRP regulates physiological targets are unclear. We have previously demonstrated that Drosophila FMRP (dFMRP) is required in early embryos for cleavage furrow formation. In an effort to identify new targets of dFMRP-dependent regulation and new effectors of cleavage furrow formation, we used two-dimensional difference gel electrophoresis and mass spectrometry to identify proteins that are misexpressed in dfmr1 mutant embryos. Of the 28 proteins identified, we have identified three subunits of the Chaperonin containing TCP-1 (CCT) complex as new direct targets of dFMRP-dependent regulation. Furthermore, we found that the septin Peanut, a known effector of cleavage, is a likely conserved substrate of fly CCT and is mislocalized in both cct and in dfmr1 mutant embryos. Based on these results we propose that dFMRP-dependent regulation of CCT subunits is required for cleavage furrow formation and that at least one of its substrates is affected in dfmr1- embryos suggesting that dFMRP-dependent regulation of CCT contributes to the cleavage furrow formation phenotype., (Copyright (c) 2010 Elsevier Inc. All rights reserved.)

Unlabelled: Appearances of and increases in Graves' ophthalmopathy (GO) have been reported after treatment of patients with hyperthyroidism with radioiodine. We sought to determine the rates of appearance or increase in manifestations of GO in American patients treated with radioiodine for hyperthyroidism., Methods: The study population, which consisted of 76 patients (range, 10.6-72 y), included 61 women and individuals of diverse ethnicity. The patients were followed for 1 y after radioiodine treatment. The clinical activity score (CAS) included 10 items of ophthalmic change that were evaluated at 2 and 6 mo and at 1 y; appearance of a new item scored 1 point. We evaluated interactions of 6 covariates-prolonged hyperthyroidism, prolonged hypothyroidism, smoking, treatment with an antithyroid drug (ATD), and serum levels of thyroid-stimulating immunoglobulin (TSI) and of high free T3 (FT3)--with the numbers of patients with 2 or more CAS points and with exophthalmometer readings increased by at least 2 mm. In addition, patients completed a scored quality-of-life (QOL) questionnaire at baseline and at 1 y to assess eye symptoms., Results: The mean CAS points for all patients at 2 mo was 0.63 and was not significantly different at 1 y. In 9 of 10 CAS items, there were few patients affected at 1 y and for the most part there were fewer patients affected than at baseline. However, exophthalmometer readings increased in 39% of patients by a mean of 2.6 mm. Individual patients frequently exhibited increases and decreases in item manifestations. Exophthalmometer readings decreased by 2 mm or less in 13%. Of the covariates, only hyperthyroidism prolonged by at least 2.5 mo was significantly associated with 2 or more CAS points at 1 y; no covariate was significantly associated with the development of increased exophthalmometer readings. Eye symptoms recorded in the QOL were insignificantly improved over the year; symptoms did not correlate with CAS points or with exophthalmometer readings., Conclusion: After radioiodine treatment, no substantial change was seen in manifestations of CAS items except for a modest increase in exophthalmometer readings in 39% of patients. Manifestations of CAS items frequently appeared and disappeared. Prolonged hyperthyroidism is best avoided. Ocular symptoms were insignificantly fewer at 1 y after radioiodine therapy. The observed changes do not warrant prophylactic treatment of patients with steroids.

During the cleavage stage of animal embryogenesis, cell numbers increase dramatically without growth, and a shift from maternal to zygotic genetic control occurs called the midblastula transition. Although these processes are fundamental to animal development, the molecular mechanisms controlling them are poorly understood. Here, we demonstrate that Drosophila fragile X mental retardation protein (dFMRP) is required for cleavage furrow formation and functions within dynamic cytoplasmic ribonucleoprotein (RNP) bodies during the midblastula transition. dFMRP is observed to colocalize with the cytoplasmic RNP body components Maternal expression at 31B (ME31B) and Trailer Hitch (TRAL) in a punctate pattern throughout the cytoplasm of cleavage-stage embryos. Complementary biochemistry demonstrates that dFMRP does not associate with polyribosomes, consistent with their reported exclusion from many cytoplasmic RNP bodies. By using a conditional mutation in small bristles (sbr), which encodes an mRNA nuclear export factor, to disrupt the normal cytoplasmic accumulation of zygotic transcripts at the midblastula transition, we observe the formation of giant dFMRP/TRAL-associated structures, suggesting that dFMRP and TRAL dynamically regulate RNA metabolism at the midblastula transition. Furthermore, we show that dFMRP associates with endogenous tral mRNA and is required for normal TRAL protein expression and localization, revealing it as a previously undescribed target of dFMRP control. We also show genetically that tral itself is required for cleavage furrow formation. Together, these data suggest that in cleavage-stage Drosophila embryos, dFMRP affects protein expression by controlling the availability and/or competency of specific transcripts to be translated.

Unlabelled: When thyroid tissues exhibited concentrations of therapeutic (131)I that appeared to be less than that predicted by data from the preceding diagnostic (131)I, the phenomenon was called stunning. We hypothesized that stunning arose from the early effects of the therapeutic dose of (131)I and that the initial uptake of (131)I, observed within the first day, was not impaired by the diagnostic dose., Methods: The hypothesis was tested by 2 types of studies. In each type, the fractional concentrations of (131)I in residual neck thyroid tissues of patients with papillary thyroid carcinoma were quantified. In the first study, fractional concentrations of diagnostic and therapeutic (131)I were measured at 2 d, a time when stunning has been observed, and expressed as ratios of radioactivity: therapeutic/diagnostic (Rx/Dx). Three different doses of diagnostic (131)I were prescribed to assess a dose response. In the second study, patients were prospectively recruited and tested to record disappearances of radioactivity from thyroid tissues. Diagnostic doses were 1.0 mCi (37 MBq) in all; therapeutic doses were 150 and 30 mCi (5,550 and 1,110 MBq), each to half of the patients. The disappearance curves were extrapolated to the period between 0 and 1 d, an interval when maximum uptake of ingested (131)I would be expected. The fractional concentrations of (131)I at 2 d and at 0-1 d were compared in terms of Rx/Dx ratios to assess changes at each time point., Results: In the first study, after diagnostic doses of 2, 1, and 0.5 mCi (74, 37, and 18.5 MBq), mean 2-d Rx/Dx values in 24, 29, and 17 patients were 0.35, 0.50, and 0.46 (P = 0.087). Of all patients, 74% exhibited Rx/Dx <0.6. In the second study, 6 of 10 patients exhibited disappearance curves of (131)I in which Rx/Dx was <0.6 at 2 d; 5 of the 6 had Rx/Dx values >0.97 at the 0- to 1-d point. In 1 patient the Rx/Dx was 0.54 at 2 d and 0.66 at the earlier time point. The other 4 patients had disappearance curves in which Rx/Dx values were >1.0 throughout or were above 0.6 and did not greatly change., Conclusion: Two days after the administration of (131)I, the mean fractional concentration of radioactivity in thyroid tissues after a therapeutic dose is <60% of the diagnostic dose in most patients, but no correlation of Rx/Dx with the mCi in the diagnostic dose was seen. In 5 of 6 patients in whom the Rx/Dx at 2 d was <0.6, the maximum fractional concentrations of therapeutic and diagnostic (131)I (i.e., the tissue uptakes during the first day) were similar; this pattern was most apparent after therapies with 150 mCi. These results support the hypothesis that "stunning" of thyroid tissues, often observable by 2 d, is primarily the consequence of early destructive effects from therapeutic (131)I.

We describe the maternal-effect and zygotic phenotypes of null mutations in the Drosophila gene for the epsilon-subunit of mitochondrial ATP synthase, stunted (sun). Loss of zygotic sun expression leads to a dramatic delay in the growth rate of first instar larvae and ultimately death. Embryos lacking maternally supplied sun (sun embryos) have a sixfold reduction in ATP synthase activity. Cellular analysis of sun embryos shows defects only after the nuclei have migrated to the cortex. During the cortical divisions the actin-based metaphase and cellularization furrows do not form properly, and the nuclei show abnormal spacing and division failures. The most striking abnormality is that nuclei and spindles form lines and clusters, instead of adopting a regular spacing. This is reflected in a failure to properly position neighboring nonsister centrosomes during the telophase-to-interphase transition of the cortical divisions. Our study is consistent with a role for Sun in mitochondrial ATP synthesis and suggests that reduced ATP levels selectively affect molecular motors. As Sun has been identified as the ligand for the Methuselah receptor that regulates aging, Sun may function both within and outside mitochondria.

Fragile X syndrome, the most common form of inherited mental retardation, is caused by loss of function for the Fragile X Mental Retardation 1 gene (FMR1). FMR1 protein (FMRP) has specific mRNA targets and is thought to be involved in their transport to subsynaptic sites as well as translation regulation. We report a saturating genetic screen of the Drosophila autosomal genome to identify functional partners of dFmr1. We recovered 19 mutations in the tumor suppressor lethal (2) giant larvae (dlgl) gene and 90 mutations at other loci. dlgl encodes a cytoskeletal protein involved in cellular polarity and cytoplasmic transport and is regulated by the PAR complex through phosphorylation. We provide direct evidence for a Fmrp/Lgl/mRNA complex, which functions in neural development in flies and is developmentally regulated in mice. Our data suggest that Lgl may regulate Fmrp/mRNA sorting, transport, and anchoring via the PAR complex.

The early Drosophila embryo undergoes two distinct membrane invagination events believed to be mechanistically related to cytokinesis: metaphase furrow formation and cellularization. Both involve actin cytoskeleton rearrangements, and both have myosin II at or near the forming furrow. Actin and myosin are thought to provide the force driving membrane invagination; however, membrane addition is also important. We have examined the role of myosin during these events in living embryos, with a fully functional myosin regulatory light-chain-GFP chimera. We find that furrow invagination during metaphase and cellularization occurs even when myosin activity has been experimentally perturbed. In contrast, the basal closure of the cellularization furrows and the first cytokinesis after cellularization are highly dependent on myosin. Strikingly, when ingression of the cellularization furrow is experimentally inhibited by colchicine treatment, basal closure still occurs at the appropriate time, suggesting that it is regulated independently of earlier cellularization events. We have also identified a previously unrecognized reservoir of particulate myosin that is recruited basally into the invaginating furrow in a microfilament-independent and microtubule-dependent manner. We suggest that cellularization can be divided into two distinct processes: furrow ingression, driven by microtubule mediated vesicle delivery, and basal closure, which is mediated by actin/myosin based constriction.

Unlabelled: There is no consensus on the amount of (131)I for treatment of patients with well-differentiated thyroid carcinoma; usual amounts vary widely. Body retention of (131)I has been shown to be a valuable index of radiation toxicity. If a broad range of body retentions occurs among patients, then high and low retentions will be a basis for modifying the usual prescriptions for (131)I to ensure safety and increase efficacy., Methods: After withdrawal of thyroid hormone in 87 patients, the fractional retention of diagnostic (131)I in each body was measured at 2 d by a scintillation probe. In 43 patients, the retention was measured 2 d after therapeutic (131)I., Results: Diagnostic retention varied from 0.01 to 0.51, with a median of 0.15. These retentions did not correlate with any index of health, thyroid hormone, or carcinoma status. Seventeen patients, previously treated with (131)I, exhibited a significantly lower mean retention. In 43 patients, retention of diagnostic (131)I was highly correlated with retention of therapeutic (131)I: diagnostic predicted therapeutic retention with a mean error of 0.04. In 10 patients receiving thyroxine, the mean retention of diagnostic (131)I after recombinant human TSH (rhTSH) was strikingly lower, 0.06, with a range of 0.016-0.16., Conclusion: Body retentions of (131)I are easily measured and vary considerably among patients. Because increased therapeutic (131)I will impart greater irradiation of tumor, and body retention has been accepted as an index of toxicity from (131)I, the use of body retention could enable prescriptions of therapeutic (131)I that enable increased efficacy while ensuring safety. If tumor retention is not proportionally decreased with the body retention of (131)I after rhTSH, then rhTSH may enable increased therapeutic efficacy.

Unlabelled: In some patients with well-differentiated thyroid carcinoma, dosimetry is necessary to avoid toxicity from therapy and to guide prescription of the administered activity of radioiodine., Methods: The presentations and courses of 2 patients exemplify the points. In the second patient, the clues to the need for dosimetry were the large size of the tumor and high circulating levels of thyroxine in the absence of exogenous hormone. The other patient manifested hyperthyroidism from stimulation of the tumors by thyroid-stimulating immunoglobulin. Dosimetry was performed by published methods., Results: Dosimetry of radioactivity in the body and blood warned of increased irradiation per gigabecquerel of administered (131)I. In each patient, the tumors sequestered a substantial amount of administered (131)I and secreted (131)I-labeled hormones that circulated for days. In 1 patient, the blood time--activity curve was complex, making a broad range of predictions for irradiation to blood and bone marrow. Still, dosimetry gave information that helped to avoid severe toxicity. At, respectively, 1.85 and 2.2 GBq (131)I, initial treatments were relatively low. There was a modest escalation in subsequent administered activities. Leukopenia with neutropenia developed in each patient, and one had moderate thrombocytopenia and anemia, but toxicity appeared to be transient. Each patient had a marked increase in well-being and evidence of reduced tumor function and volume., Conclusion: Two patients with advanced, well-differentiated thyroid carcinoma illustrate the need for dosimetry to help prevent toxicity to normal tissues from therapeutic radioiodine. Conversion of radioiodide to circulating radiothyroxine by functioning carcinomas increases the absorbed radiation in normal tissues. Yet, dosimetric data acquired for 4 d or more may be insufficient for accurate calculations of absorbed radiation in blood. Guidelines suggested for avoiding toxicity are based on the circulating thyroxine concentrations, the presence of thyroid stimulators, the amount of radioactivity retained in the body at 48 h, and the general status of the patient.

Drosophila cellularization and animal cell cytokinesis rely on the coordinated functions of the microfilament and microtubule cytoskeletal systems. To identify new proteins involved in cellularization and cytokinesis, we have conducted a biochemical screen for microfilament/microtubule-associated proteins (MMAPs). 17 MMAPs were identified; seven have been previously implicated in cellularization and/or cytokinesis, including KLP3A, Anillin, Septins, and Dynamin. We now show that a novel MMAP, Lava Lamp (Lva), is also required for cellularization. Lva is a coiled-coil protein and, unlike other proteins previously implicated in cellularization or cytokinesis, it is Golgi associated. Our functional analysis shows that cellularization is dramatically inhibited upon injecting anti-Lva antibodies (IgG and Fab) into embryos. In addition, we show that brefeldin A, a potent inhibitor of membrane trafficking, also inhibits cellularization. Biochemical analysis demonstrates that Lva physically interacts with the MMAPs Spectrin and CLIP190. We suggest that Lva and Spectrin may form a Golgi-based scaffold that mediates the interaction of Golgi bodies with microtubules and facilitates Golgi-derived membrane secretion required for the formation of furrows during cellularization. Our results are consistent with the idea that animal cell cytokinesis depends on both actomyosin-based contraction and Golgi-derived membrane secretion.

Adrenal scintigraphy with 131I-labeled 6-beta-iodomethyl-19-norcholesterol (NP-59) is a technically demanding and complex procedure. However, it can provide crucial and unique information about the functional status of the adrenal glands and guide the appropriate therapeutic management of patients with biochemically proven disease. Since the introduction of this new investigational drug, scintigraphic imaging has been performed using conventional planar techniques. We present an interesting case of primary aldosteronism in which planar scintigraphy and SPECT were combined in an attempt to increase the sensitivity of the study. SPECT revealed scintigraphic evidence of bilateral adrenocortical hyperplasia. Interestingly, the CT scan of this patient showed only an equivocal abnormality in the left adrenal gland, suggestive of an adenoma.

Unlabelled: The high sensitivity of metaiodobenzylguanidine (MIBG) scintigraphy for sympathomedullary tumors such as neuroblastoma and pheochromocytoma is well documented. The specificity of MIBG scintigraphy for these tumors is also high but has been incompletely characterized for other neural crest tumors and non-neural crest tumors of childhood., Methods: The medical records and MIBG scans of all children who had undergone MIBG scintigraphy for known or suspected neuroblastoma or pheochromocytoma were retrospectively reviewed at five major referral centers. Those patients found to have pathologies other than neuroblastoma or pheochromocytoma form the basis of this study., Results: One hundred children with a total of 110 lesions met the inclusion criteria. All had negative MIBG scans except 1 of 2 children with infantile myofibromatosis, 1 of 2 with neuroendocrine carcinomas, 1 of 2 with pancreaticoblastomas and 1 of 10 with primitive neuroectodermal tumors., Conclusion: MIBG scintigraphy is highly specific for neuroblastoma and pheochromocytoma. Only 4% (4/100) of nonsympathomedullary tumors (non-pheochromocytoma and non-neuroblastoma) in childhood showed MIBG uptake, of which only 2% (2/100) were of non-neural crest origin.

The hedgehog gene of Drosophila melanogaster encodes a secreted protein (HH) that plays a vital role in cell fate and patterning. Here we describe a protein complex that mediates signal transduction from HH. The complex includes the products of at least three genes: fused (a protein-serine/threonine kinase), cubitus interruptus (a transcription factor), and costal2 (a kinesin-like protein). The complex binds with great affinity to microtubules in the absence of HH, but binding is reversed by HH. Mutations in the extracatalytic domain of FU abolish both the biological function of the protein and its association with COS2. We conclude that the complex may facilitate signaling from HH by governing access of the cubitus interruptus protein to the nucleus.

The Hedgehog (HH) signaling proteins control cell fates and patterning during animal development. In Drosophila, HH protein induces the transcription of target genes encoding secondary signals such as DPP and WG proteins by opposing a repressor system. The repressors include Costal2, protein kinase A, and the HH receptor Patched. Like HH, the kinase Fused and the transcription factor Cubitus interruptus (CI) act positively upon targets. Here we show that costal2 encodes a kinesin-related protein that accumulates preferentially in cells capable of responding to HH. COS2 is cytoplasmic and binds microtubules. We find that CI associates with COS2 in a large protein complex, suggesting that COS2 directly controls the activity of CI.

Unlabelled: Possible incremental diagnostic benefits of SPECT and delayed planar imaging with [123I]MIBG in neuroblastoma have not yet been fully established., Methods: Whole-body delayed planar [123I]MIBG imaging at 48 hr and SPECT imaging of the chest-abdomen or other suspected sites obtained at 24 hr were compared with routine planar imaging at 24 hr in 83 studies of 29 children with neuroblastoma. The sensitivity for each of the [123I]MIBG imaging methods was calculated on a study-by-study and on a lesion-by-lesion basis., Results: Fifty-one planar imaging studies were performed in 20 patients with evidence of disease which was detected in 48 studies by 24-hr imaging (94.1% sensitivity) and in 44 studies by 48-hr imaging (86.3% sensitivity). On a lesion-by-lesion basis, sensitivity was 88.8% for the 24-hr scan, 86.7% for the 48-hr scan and 92.2% for a combination of the two (p = ns). Forty-three SPECT studies were performed in 20 patients with evidence of disease in the field of view of the SPECT camera. Disease was detected in 40 SPECT studies (93% sensitivity), in 38 planar scans at 24 hr (84.4% sensitivity) and in 37 planar scans at 48 hr (86.0% sensitivity). On a lesion-by-lesion basis, sensitivity was 83.6% for the 24-hr planar scan, 86.1% for the 48-hr planar scan, 88.2% for a combination of the two planar scans and 97.9% for SPECT (p < 0.001 compared with planar). The anatomic locations of tumors were clearer on SPECT in 15 studies., Conclusion: Delayed 48-hr planar scanning may occasionally depict more lesions than 24-hr imaging, but it may also miss lesions with rapid washout. SPECT imaging significantly increases the number of lesions detected and better defines anatomic location of tumors.

Primary aldosteronism is a potentially curable cause of hypertension, especially when caused by an adrenal adenoma. Aldosteronomas because of their small size often elude techniques to locate them. This case illustrates the advantages, disadvantages and complications of noninvasive techniques used for their diagnosis. A patient with hypertension and hypokalemia underwent an adrenal venous effluent sampling for measurement of aldosterone concentrations. This procedure was complicated by an injury to the right adrenal gland. Subsequently, it was difficult to control the patient's hypertension and hypokalemia with medical therapy alone. A re-assessment years after his initial diagnosis included a CT scan, which now visualized a left adrenal tumor. The functional status of this tumor and lack of function of the previously injured right adrenal gland were demonstrated by NP-59 scintigraphy. This information modified the surgical intervention (adenectomy rather than total adrenalectomy) and the residual left sided adrenal tissue prevented adrenocortical insufficiency. A year later the patient remains euadrenal.

Unlabelled: The goals of this investigation were to characterize the uptake of 11C-hydroxyephedrine (HED) in neuroblastoma and to determine the feasibility and potential advantages of utilizing this compound as a tumor imaging agent., Methods: Seven patients with known or subsequently proven neuroblastoma were studied. Each patient underwent PET scanning with 11C-HED. Six of seven patients underwent scintigraphy with [123I]meta-iodobenzylguanidine (MIBG), and two patients were also studied with [18F]FDG PET. For six patients, CT or MR images were available for comparison., Results: Neuroblastomas were located by PET scanning with 11C-HED in all seven patients. The uptake of HED into neuroblastomas was rapid; tumors were evident on images within 5 min postintravenous injection. Those lesions in the field of view of the PET camera were also identified on [123I]MIBG scintigraphic images. In two patients, tumor deposits in the abdomen were better visualized with MIBG scintigraphy due to relatively less hepatic accumulation of MIBG than HED., Conclusion: PET scanning with HED for neuroblastoma results in high quality functional images of the tumors that can be obtained within minutes following injection.

Pheochromocytomas are potentially curable causes of hypertension. These tumors are currently located by functional imaging with meta-iodobenzylguanidine (MIBG), usually labeled with 131I, or anatomic imaging (computed tomography, magnetic resonance). Hydroxyephedrine (HED) is a newly developed radiotracer that concentrates in adrenergic nerve terminals. When HED is labeled with 11C, its distribution can be mapped in vivo using PET. The purposes of this investigation were to characterize the uptake of 11C-HED in pheochromocytoma and to determine the feasibility and advantages of utilizing this compound as a tumor imaging agent. Ten patients with known or suspected pheochromocytoma were studied. Each patient underwent PET scanning with 11C-HED and conventional scintigraphy with MIBG. Pheochromocytomas were localized by PET scanning in 9 of the 10 patients. Image quality was excellent and superior to that obtained from planar and tomographic MIBG studies. The uptake of 11C-HED into pheochromocytomas was rapid; tumors were evident within 5 min following intravenous injection. All lesions within the field of view that were identified by MIBG scintigraphy were readily apparent. PET scanning with 11C-HED localizes pheochromocytoma using a specifically designed radiotracer and advanced imaging technology. The method has promise for locating the more elusive tumors.

Myocardial beta adrenergic receptors play important roles in physiology and disease, but the receptors have not before been portrayed. The beta antagonist, iodocyanopindolol (ICYP), was used to develop a scintigraphic method for depicting the receptors in the living heart. Labeled with 125I, ICYP bound firmly to beta receptors in the rat heart; the data conformed to a mathematical model. In vivo saturation kinetics indicated binding sites with two affinities. Inhibition of ICYP binding by beta antagonists of different potency and different selectivity for beta-1 and beta-2 receptors produced the expected pharmacologic effects. Inhibition by lipophilic and hydrophilic antagonists gave no evidence that ICYP was appreciably bound to internalized receptors. Fractional binding by tracer quantities of (-) ICYP and (+/-) ICYP demonstrated stereospecificity. Labeled with 123I, ICYP bound to the hearts of intact dogs so that scintigraphic tomographs depicted ventricular myocardium. Small doses of beta antagonists selectively reduced the binding of ICYP to lung enabling better visualization of the heart. Thus, 123I-ICYP appears to portray the beta receptors in the living heart, and the characteristics of binding permit the development of mathematical models and lay the basis for quantifying this receptor binding.

The syndrome of multiple endocrine neoplasia type 2B (MEN 2B) resembles that of MEN 2A in that both include medullary carcinoma of the thyroid, pheochromocytoma, and autosomal dominant inheritance, but is distinct in that MEN 2B patients have neuromas of the mucous membranes. MEN2A has been linked to RBP3, D10S5, FNRB, D10S15, and D10Z1 near the centromere of chromosome 10. We examined linkage between MEN2B and RFLPs on chromosome 10 in all available members in two or three generations of 14 kindreds. The centromere marker D10Z1 was linked to MEN2B with a peak lod score of 5.42 at theta = 0.02. One possible recombinant was observed between D10Z1 and MEN2B. Multipoint analysis of RFLPs at FNRB, D10Z1, RBP3, and D10S15 gave a peak lod score of 7.12 at the midpoint between D10Z1 and RBP3 on the long arm (band q11). The most likely gene order FNRB-D10Z1-MEN2B was 27 times more likely than MEN2B-FNRB-D10Z1 and 31/2 times more likely than FNRB-MEN2B-D10Z1. Additional data will be required to establish the order of these loci with confidence.

Three children with Stage III neuroblastoma were treated with [125I]MIBG in a phase I toxicity study. Concepts of the treatment were: in small tumors, the absorbed dose of radiation from MIBG labeled with 131I is reduced but the absorbed dose from [125I]MIBG is less affected; and many recurrences of neuroblastoma arise from small tumors. Two patients exhibited only modest thrombocytopenia and leukopenia, the most sensitive indices of radiation toxicity, after receiving 261 and 407 mCi, and 83 and 104 rad of whole-body radiation. One patient died of progressive neuroblastoma; the other two patients have stable disease over 30 mo after treatment. Per millicurie given, [125I]MIBG imparts about one-fourth the radiation dose of [131I]MIBG to the whole body. Iodine-125-MIBG can be given in doses that impart over 100 rad of whole-body radiation and that exceed 400 mCi before toxicity becomes limiting, even in small children.

NP-59 concentrates in steroid hormone synthesizing tissues, enabling scintigraphic localization and characterization of endocrine dysfunction in the adrenal cortex and ovary. Studying 108 consecutive cases from 1982 to 1985 and using clinical, biochemical, radiographic, and pathologic data, we performed a rigorous assessment of the accuracy and pitfalls of NP-59 scintigraphy. The evaluation was divided into categories of abnormal hormone secretion: Cushing's syndrome, primary aldosteronism, and hyperandrogenism. Additional categories included euadrenal tumors (without detectable hormone dysfunction) and sites of residual adrenal cortical tissue. The accuracy of NP-59 scintigraphy ranged from 71% in primary aldosteronism and 75% in euadrenal tumors, to 100% for Cushing's syndrome and hyperandrogenism. However, more than in most nuclear medicine studies, NP-59 imaging requires well-defined indications to be met for it to be efficacious, including the fulfillment of clear clinical, biochemical, and radiographic criteria. The high reproducibility of NP-59 scintigraphic interpretation was demonstrated when 40 random cases underwent interinstitutional exchange and through interobserver evaluation at the University of Michigan. Responses of 85/126 medical centers to questionnaires revealed the high level of NP-59 safety.

Iodine-131 MIBG scintigraphy may be used to determine the presence or absence of metastases to the appendicular skeleton in malignant pheochromocytoma and neuroblastoma. Normal bones show no uptake of [131I]MIBG and the joints are seen as photon-deficient areas surrounded by background muscle activity. Discrete concentrations of radioactivity in bone are often seen in patients with malignant pheochromocytoma and neuroblastoma. Bone marrow involvement in neuroblastoma may be indicated by diffuse uptake of [131I]MIBG or focal accumulation at the metaphyses. Uncommonly, bone involvement may not be displayed by the [131I]MIBG images. Since conventional bone scanning agents may also fail to detect these tumors, skeletal scintigraphy with both [131I]MIBG and [99mTc]MDP is necessary to reliably stage malignant pheochromocytoma and neuroblastoma.

Apart from relieving effects of secreted catecholamines, treatments of malignant pheochromocytoma have achieved little success. When the radiopharmaceutical, meta-[131I] iodobenzylguanidine (I-131 MIBG ), was found to concentrate in some malignant pheochromocytomas, we calculated that this agent could impart therapeutic doses of radiation to these tumors. We therefore treated five patients with two to four doses of I-131 MIBG prepared in high specific activity, 8-11 Ci/mmol. Individual doses were given at 3- to 10-mo intervals and in 97- to 197-mCi amounts. Two patients exhibited subjective and objective benefits. Their tumors declined in size (to 28% and 30% of original volumes) and in hormone secretion (to 50% or less of baseline rates). The other three patients manifested few symptoms before treatment and showed few or no objective improvement afterward. The tumors of the patients who responded to I-131 MIBG (a) appeared to be more rapidly growing, (b) received more cumulative rads, and (c) were more predominantly in soft tissues (in contrast to bone) than those in the patients who obtained little benefit. No toxic effects were encountered during the treatments, and only minor and temporary untoward responses were seen later.

The radiopharmaceutical, metaiodobenzylguanidine (MIBG) acts as an analog of norepinephrine (NE). Experiments in rats were carried out to determine how closely the movements of [125I]MIBG in the heart mimicked those of [3H]NE, and if the changes [125I] MIBG concentrations would reflect injury to, and function of, adrenergic neurons in the heart. Injury to adrenergic neurons by 6-hydroxydopamine substantially reduced the uptake of [125I] MIBG into the left ventricle, but the effect was less than that on uptake of [3H]NE uptake and concentration of endogenous NE. Similarly, when desmethylimipramine was given to inhibit the uptake-1 pathway of neurons, the reduction in uptake of [125I]MIBG was statistically significant but less than that of [3H]NE; part of this difference may be attributable to partial uptake of [125I]MIBG into neurons by a diffusion pathway. Substantial fractions of [125I]MIBG and [3H]NE were displaced from the heart by the sympathomimetic drug, phenylpropanolamine. When adrenergic neurons of the heart were stimulated by feeding of rats, the disappearance rates of [3H]NE and [125I]MIBG from the heart were significantly increased. Although not a perfect analog of [3H]NE, [125I]MIBG appears to enter and leave the heart in patterns similar to those of [3H]NE. Thus, movements of [125I]MIBG give indices of adrenergic neuron injury and function in the heart.

Scintigraphy with 131I-MIBG has located most pheochromocytomas. The detected tumors have been intra-adrenal, extra-adrenal, malignant, and familial in type. The method is safe, but requires images taken over three days to attain optimal results. Because of its ability to screen all sites where primary pheochromocytomas may reside, scintigraphy should be employed as the initial procedure in the search for these tumors. It may be the only technique that will locate extra-adrenal pheochromocytomas. The rate of false-negative results is about 10 percent; therefore, other techniques such as computed tomography will be necessary to help find the few elusive pheochromocytomas.

Intense uptake of m-[131I] iodobenzylguanidine (I-131 MIBG ) has been observed in the salivary glands of patients undergoing scintigraphy for the location of suspected pheochromocytomas. This uptake of radioactivity was not due to free I-131 derived from the I-131 MIBG but rather to uptake of I-131 MIBG by sympathetic neuronal elements in the salivary glands. In keeping with this, administration of tricyclic antidepressants reversibly blocked salivary uptake of I-131 MIBG . Furthermore, I-131 MIBG uptake was markedly diminished by the ipsilateral salivary glands in a patient with Horner's syndrome, and was bilaterally diminished in a patient with severe idiopathic sympathetic autonomic neuropathy. The salivary gland uptake of I-131 MIBG may provide a means for the study of sympathetic innervation of these organs, and thus for the study of generalized disorders of autonomic innervation.

Radioiodinated m-iodobenzylguanidine (MIBG), a scintigraphic agent used in the detection of human pheochromocytomas, is thought to utilize the same uptake and retention mechanism(s) as norepinephrine (NE). Using primary cultures from 16 human pheochromocytomas, we compared the uptake of MIBG to that of NE. Two different uptake systems were identified. Both NE and MIBG were taken up by a sodium-dependent system that was characterized by: temperature dependency, high affinity, low capacity, saturability, ouabain sensitivity, and desmethylimipramine sensitivity. However, NE and MIBG were also taken up by a temperature-dependent, sodium-independent, apparently unsaturable system. The sodium-dependent uptake system fulfills many of the criteria for Uptake-one while the sodium-independent uptake system is most likely a passive diffusion process. Competitive inhibition studies demonstrated that NE and MIBG share a common uptake system; a concept consistent with the linear correlation between the rate of uptake of 1.0 microM NE and that of 1.0 microM MIBG (r = 0.942). At low concentrations, both NE and MIBG entered the tumor cells primarily by the sodium-dependent uptake system. Differential expression of the sodium-dependent and sodium-independent uptake systems, between different tumor cells, appears to be responsible for the variations of the kinetic parameters for both NE and MIBG. These studies provide the first direct characterization of a NE uptake mechanism in human pheochromocytoma cells.

The radiopharmaceutical m-[131I]iodobenzylguanidine (I-131 MIBG), which is readily taken up by adrenergic vesicles, produces scintigraphic images of pheochromocytomas in man but rarely visualizes normal adrenal glands. Iodine-123 has many potential advantages over I-131 as a radiolabel for MIBG, including shorter half-life, freedom from beta emissions, and increased gamma-camera efficiency. In this study, diagnostic doses of MIBG labeled with I-131 and I-123, with nearly equivalent radiation dosimetry, were compared as imaging agents in eight patients with known or suspected pheochromocytoma. Images of superior quality were obtained with I-123 MIBG, and lesions not visualized using I-131 MIBG were portrayed. In addition, the normal adrenal medullae were visualized on the I-123 MIBG scintigrams in six out of eight patients.

Iodine-123-4-amino-3-iodobenzylguanidine ([123I]AIBG), an analog of 123I metaiodobenzylguanidine ([123I]MIBG), has an advantage in having a more rapid and simple synthesis. This, combined with animal data that suggested a greater affinity of the new radiopharmaceutical for the autonomic innervation of the myocardium led us to study the biodistribution of [123I]AIBG in three men with metastatic pheochromocytoma. In all instances, [123I]AIBG revealed the same metastatic deposits shown by [123I]MIBG. Iodine-123 AIBG uptake, however, was greater than [123I]MIBG in lung, gut, and spleen. These higher backgrounds may pose diagnostic problems in some cases.

Heart intensity (HI) in the 24- and 48-hr images of meta-[131I]iodobenzylguanidine (I-131 MIBG), a pheochromocytoma-seeking guanethidine analog, were compared with concentrations of plasma and urinary catecholamines and their metabolites in nonpheochromocytoma and pheochromocytoma patients. HI was inversely related to plasma concentrations and urinary excretion rates of the hormones. Plasma norepinephrine had the highest inverse correlation with HI (r = -0.73 at 24 hr, -0.63 at 48 hr), and urinary metanephrine the lowest (r = -0.23 at 24 hr, -0.28 at 48 hr). A similar relationship was observed in the intensity of salivary-gland visualization, but with less marked variations. HI was much higher in nonpheochromocytoma patients than in pheochromocytoma patients. HI in an I-131 MIBG image provides useful information in the diagnosis of pheochromocytoma, and may provide a tool for the study of the influence of catecholamines on the heart.

Metaiodobenzylguanidine (MIBG) locates most pheochromocytomas and neuroblastomas. The tracer is concentrated in intracellular storage vesicles by an active process. Many other neuroendocrine tumors of the amine precursor uptake and decarboxylation (APUD) series have hormonal storage vesicles and, thus, the potential to take up [131I]MIBG. A variety of neuroendocrine tumors in 57 patients were studied 1, 2, and 3 days after 0.5 mCi [131I]MIBG. Views from skull to pelvis were obtained. Results of MIBG scans were compared with all available imaging modalities (including plain radiography, liver scan, ultrasound, computed tomography, and angiography) and surgical exploration. The neuroendocrine nature of the tumor was determined by histology, immunohistochemistry, electron microscopy, and the assay of appropriate biogenic amines and peptide hormones. Results were (positive/total cases): carcinoids (four of ten), nonsecreting paragangliomas (three of three), sporadic medullary carcinomas of the thyroid (MCT) (one of five), familial MCT (one of 26), chemodectomas (two of five), oat cell carcinomas (zero of four), choriocarcinoma (one of one), atypical schwannoma (with storage granules) (one of one), Merkel cell skin cancer (one of one), islet cell carcinoma (zero of one). We conclude that a wide range of neuroendocrine tumors show [131I]MIBG uptake; tumors other than pheochromocytomas and neuroblastomas are less often seen scintigraphically, but in certain cases (e.g., carcinoid and nonsecreting paragangliomas) scintigraphy may be useful in depicting the extent and location of disease and may indicate therapeutic potential. Iodine-131 MIBG shows promise in the diagnosis and staging of tumors of varied types.

Twenty -six adrenal pheochromocytomas and four normal adrenal medullae were studied immunohistochemically. These included four malignant tumors with proven metastases, six tumors in patients with neurofibromatosis, nine tumors in patients with multiple endocrine neoplasia type 2, and seven sporadic nonfamilial pheochromocytomas. Immunohistochemical localization of neuron-specific enolase (NSE) was seen in all tumors and in the four normal adrenals. Methionine enkephalin-like immunoreactivity was present in tumors from all four groups and in the normal adrenals. Corticotropinlike immunoreactivity was found focally in two normal adrenal medullae and in four benign pheochromocytomas. Our results indicated that NSE was present in all four major groups of pheochromocytomas, including benign and malignant tumors. This marker aided in distinguishing between adrenal cortical and medullary tumors in unusually difficult cases, since all normal adrenal cortex and adrenal cortical tumors had negative test results for NSE.

The human Class II major histocompatibility (MHC) antigens, or Ia antigens, which are thought to regulate immune cell interaction, can be detected in paraffin-embedded tissues by immunoperoxidase staining with a recently developed monoclonal antibody (LK8D3). HLA-DR antigens were observed in lymphoid tissues, Langerhans cells of the skin, some epithelial cells, and pulmonary alveolar macrophages. The expression of HLA-DR antigens was analyzed in formalin-paraffin sections by immunoperoxidase in 86 normal and abnormal thyroid epithelial tissues. All patients with Hashimoto's disease (8/8) and most patients with Graves' disease (6/8) expressed HLA/DR antigens in the thyroid epithelial cells and in adjacent inflammatory cells. Most papillary carcinomas (12/18), including 3 of 5 follicular variant of papillary thyroid carcinomas, had HLA-DR antigens detected in epithelial cells; whereas medullary thyroid carcinomas (0/5), follicular carcinomas (0/5), and multinodular goiters (0/4) did not have detectable HLA-DR immunoreactivity. A few other thyroid lesions had HLA-DR antigens detected in epithelial cells, including anaplastic carcinomas (2/5), Hurthle-cell tumors (1/16), and thyroid lymphomas (2/2). Monoclonal antibody LK8D3 and two other commercially available monoclonal antibodies against HLA-DR-stained tissues equally well in cryostat sections, but only antibody LK8D3 was effective in formalin-fixed paraffin-embedded tissue sections. These results indicate that epithelial cells from thyroids of patients with autoimmune diseases commonly express HLA-DR antigens. The presence of HLA-DR antigens in most papillary thyroid carcinomas may be helpful diagnostically in cases of follicular variants of papillary carcinomas. The role of HLA-DR expression in autoimmune thyroid disease and in papillary thyroid carcinoma remains to be determined.

The scintigraphic distribution of m-[131I]iodobenzylguanidine (I-131 MIBG), an adrenal medullary imaging agent, was studied to determine the patterns of uptake of this agent in man. The normal distribution of I-131 MIBG includes clear portrayal of the salivary glands, liver, spleen, and urinary bladder. The heart, middle and lower lung zones, and colon were less frequently or less clearly seen. The upper lung zones and kidneys were seldom visualized. The thyroid appeared only in cases of inadequate thyroidal blockade. The "normal" adrenal glands were seldom seen and faintly imaged in 2% at 24 hr after injection and in 16% at 48 hr, in patients shown not to have pheochromocytomas, whereas intra-adrenal, extraadrenal, and malignant pheochromocytomas usually appeared as intense focal areas of I-131 MIBG uptake at 24 through 72 hr.

A patient exhibited an unusual constellation of findings: His extraosseous lymphoma sequestered [99mTc]MDP, a bone-seeking agent, while at the same time it appeared to produce a factor that caused hypercalcemia. The dispersed lymphoma cells took up more [99mTc]MDP in vitro than did cultured lymphoblasts suggesting that the in vivo sequestration may have been, at least in part, an active intracellular process.

Ten patients with histologically proven neuroblastoma were studied by [131I]MIBG scintigraphy. Tumor uptake of the radiopharmaceutical showed a spectrum varying from no uptake in one case, to slight uptake in two, moderate uptake in two and intense uptake in five cases. Iodine-131 MIBG scintigraphy was more effective in demonstrating the extent of neuroblastoma spread than were conventional bone scan and CT in one patient, equal to these modalities in four cases, almost equal in two cases and significantly inferior in three cases. These preliminary results suggest that [131I]MIBG scintigraphy is useful in detecting the presence and delineating the distribution of neuroblastoma and may, in certain cases, have therapeutic potential.

Therapy with [131I]MIBG has produced partial remissions of malignant pheochromocytomas but not all patients respond. Responses correlate with the quantity of radiation delivered. We developed the conjugate-view method of imaging using 131I reference sources of known radioactivity placed on the surface of the patient and standard nuclear medicine equipment (gamma camera and computer), to estimate tumor uptake of [131I]MIBG. Such an estimate is a first step toward calculating radiation absorbed dose. Three different methods of background subtraction were evaluated with an anthropomorphic phantom and in five patients. In phantom results, measured tumor activity decreased exponentially with a half-life in agreement with that of 131I to within 3%. However, in the phantom studies, in which non-tumor activity is zero, no single method of background subtraction is superior. In patients, two background subtraction methods, which take their estimate from regions immediately surrounding or adjacent to the tumor and reference source, are less sensitive to reference source position and appear more accurate than a third method which uses a background region of interest displaced from the tumor. The agreement of the calculated activity concentration (nCi/g) with that measured by counting portions of the excised tumors gives validation to the method.

The mechanisms underlying the uptake of the radiopharmaceutical metaiodobenzylguanidine (MIBG) and the catecholamine norepinephrine (NE) were studied using cultured bovine adrenomedullary cells as an in vitro model system. Sodium-dependent and sodium-independent uptake systems have been identified and characterized for both MIBG and NE. The sodium-dependent uptake of NE and MIBG was inhibited by the selective Uptake-one inhibitors, desmethylimipramine (DMI) and cocaine, whereas the sodium-independent uptake for NE and MIBG was much less sensitive to inhibition by these agents. The sodium-dependent uptake system fulfills the criteria for the neuronal Uptake-one system, and the sodium-independent uptake system fulfills the criteria for a passive diffusion mechanism. Both NE and MIBG were transported into cultured bovine adrenomedullary cells by both uptake systems; the relative role of each uptake system was dependent upon the concentration of NE and MIBG in the media. Arterial concentrations proximal to the dog adrenal were very small suggesting that the sodium-dependent (Uptake-one) system is predominant in vivo. Consistent with the in vitro observations, the in vivo uptake of MIBG and NE into dog adrenal medullae was effectively blocked by pretreatment with DMI or cocaine. Therefore, iodine-131 MIBG scintigraphy of the adrenal appears to reflect uptake by way of the Uptake-one system.

For some patients with coronary artery disease (CAD), bypass operations prolong life. Angiograms, incurring some risk and considerable expense, are prerequisites to surgical therapy; they delineate the region and extent of disease. However, many people who complain of chest pain do not have disease that can be benefited by operation. Therefore, tests that will safely and economically select the appropriate individuals for angiography are most welcome. Yet, if the preliminary tests falsely declare affected people to be free of CAD, they will deny these patients angiography, and, consequently, surgical treatment that would prolong their lives. Decision analysis determines that a false-negative rate of less than 2% is necessary for tests preliminary to angiography if the average survival of patients is not to be shortened. No currently used procedure has attained this sensitivity. Radionuclide ventriculography approaches this precision, but its sensitivity must be sustained in more broadly based studies.

Thallium-201 scintigraphy has been used in the evaluation of thyroid neoplasms, but uptake in recurrent or persistent medullary thyroid cancer has not been reported. We present two cases where focal 201TI activity localized superior mediastinal recurrences which were subsequently resected. Postoperative 201TI scans in both cases showed elimination of the focal uptake seen before surgery, as well as return of previously elevated serum calcitonin levels to normal. Scanning with 201TI may be useful in the preoperative localization of recurrent medullary thyroid cancer.

Iodine-131 metaiodobenzylguanidine (MIBG) is an effective agent for the scintigraphic portrayal of pheochromocytomas of all types. Iodine-131 MIBG is a relatively stable radiopharmaceutical that is primarily excreted in the urine. Therefore, impaired renal function would be expected to alter [131I]MIBG pharmacokinetics which would thus affect blood levels, as well as scintigraphy. An 18-yr-old anephric male presented with hypertension and suspected pheochromocytoma. We have compared the [131I]MIBG scintigraphy and blood clearance kinetics in this anephric patient, two patients with renal insufficiency and four patients with normal renal function. The degree of renal insufficiency was directly correlated to the CPM/image (an index of whole-body retention) on all 3 days of imaging and the slower clearance of radioactivity from the blood. The relative distribution of radioactivity between the plasma and cell fractions was greatest in the patients with renal insufficiency. We therefore suggest that attention be paid to plasma creatinine levels prior to the administration of [131I] MIBG to permit accurate interpretation of scintigraphy. In addition, the effect of renal insufficiency on radiation dosimetry should be considered. It may thus be prudent to reduce the administered dose of [131I]MIBG given to anephric or renally insufficient patients to decrease radiation dose.

Metaiodobenzylguanidine (MIBG) localizes in adrenergic neurons; MIBG labeled with 123I then serves as an analog of norepinephrine, and concentrations of [123I]MIBG reflect sites of adrenergic neurons in organs. Movements of [123I]MIBG into and out of organs were measured by quantitative scintigraphy in man. We perturbed adrenergic neuron function in several ways, and [123I]MIBG concentrations in the heart were subsequently altered in patterns consistent with the concept that [123I]MIBG resides mostly in adrenergic neurons. Uptake of [123I]MIBG into the heart was inhibited by the tricyclic drug, imipramine, and this agent also accelerated the rate of loss of [123I]MIBG. Phenylpropanolamine, a sympathomimetic drug that acts by displacing norepinephrine from neurons, increased the rates of loss of [123I]MIBG from the heart. Exercise was followed by a movement of [123I]MIBG into blood and urine. Generalized autonomic neuropathies were associated with marked diminutions of [123I]MIBG uptake into the heart. We conclude that quantitative scintigraphy in patients will enable determinations of regional disturbances in integrity (by measuring uptake of [123I]MIBG) and function (by measuring rates of loss of [123I]MIBG) of the adrenergic nervous system in the heart.

The immunohistochemical localization of epinephrine (E), norepinephrine (NE), and chromogranin was analyzed in normal and neoplastic neuroendocrine cells. The immunohistochemical detection of tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), and phenylethanolamine N-methyltransferase (PNMT) was used to distinguish between uptake and biosynthesis of catecholamines. E, NE, chromogranin, TH, DBH, and PNMT were found in the normal human adrenal medulla and in pheochromocytomas. Although many neuroendocrine tissues outside of the adrenal gland contained immunoreactive NE, only a small percentage of these tissues contained DBH. E was found in a few neuroendocrine tissues outside of the adrenal, including cardiac paragangliomas, and the enzyme PNMT was localized in some of these neoplasms. There was very close agreement between the localization of chromogranin and of catecholamines in normal and neoplastic neuroendocrine tissues. These results indicate that the presence of catecholamines and chromogranin in neuroendocrine cells and tumors within the adrenal medulla and in many other sites may be closely related.

Iodine-131 metaiodobenzylguanidine ([131I]MIBG) is used to image and treat human pheochromocytoma. As part of a pharmacodynamic study of this agent, we have evaluated its excretion and metabolism in nine pheochromocytoma patients undergoing MIGB therapy. Following diagnostic doses of [131I]MIBG given prior to therapy, 40 to 55% of the administered radioactivity generally appeared in the urine within 24 hr and 70 to 90% was recovered within 4 days. Reverse-phase high performance liquid chromatography was used to identify radioactive metabolites following therapeutic doses of [131I]MIBG. Unaltered [131I]MIBG was the major radioactive urinary component found, representing 75 to 90% of the total in all but one of the nine patients examined. The urine samples from the patient, whose rate of urinary excretion was the lowest of the group, contained [131I]-m-iodohippuric acid ([131I]MIHA) in amounts equal to that of [131I]MIBG, as well as small amounts of [131I]iodide and [131I]-m-iodobenzoic acid ([131I]MIBA). Iodine-131 MIHA and [131I]iodide were also minor components in the urine samples from the other eight patients. Trace quantities of [131I]MIBA and 131I-4-hydroxy-3-iodobenzylguanidine ([131I]HIBG) were also detected in a few of the patient urine samples examined. The 4- to 5-day metabolism profiles varied from patient to patient but were similar for the same patient following therapy doses given 4 mo apart. There was no obvious correlation between the presence of metabolites and the location of the tumors or the plasma or urinary catecholamine levels. Extraction of radioactivity from two pheochromocytomas removed from patients was determined to be primarily MIBG. These studies suggest that [131I]MIBG is a rapidly excreted, relatively stable radiopharmaceutical agent.

Iodine-131 metaiodobenzylguanidine [131I]MIBG has proven to be an effective radiopharmaceutical for the scintigraphic localization of pheochromocytomas. Uptake of MIBG is inhibited by blockade of the neuronal uptake pathway for catecholamines ("uptake-1") and by depletion of catecholamine storage vesicle contents, but is not significantly affected by conventional alpha- and beta-adrenoreceptor blocking drugs. Labetalol is an antihypertensive agent with combined alpha- and beta-blocking properties that has been used to manage patients with suspected pheochromocytomas. We report eight patients in whom concurrent or recent therapy with labetalol significantly reduced the uptake of [131I]MIBG into salivary glands, liver, spleen, and general body background. Tumor uptake of MIBG was also reduced in two of the three patients who were proven to have pheochromocytomas. In one case, the effect of labetalol persisted for 36 hr after the drug had been discontinued. The inhibitory effect of labetalol on MIBG uptake in sympathomedullary tissues is likely to be a result of the drug's little-known, additional properties of uptake-1 blockade and depletion of storage vesicle contents, rather than its alpha- or beta-blocking effects. Additionally, labetalol would also appear to hasten clearance of MIBG from other tissues. Labetalol therapy should be discontinued for several days (possibly up to 1 wk) before undertaking [131I]MIBG scintigraphy. A comprehensive list of drugs that should be avoided in patients undergoing MIBG scintigraphy is appended.