Eta' photoproduction on the proton for photon energies from 1.527 to 2.227 GeV

Differential cross sections for the reaction gamma p --> eta' p have been measured with the CLAS spectrometer and a tagged photon beam with energies from 1.527 to 2.227 GeV. The results reported here possess much greater accuracy than previous measurements. Analyses of these data suggest for the first time the coupling of the eta'N channel to both the S11(1535) and P11(1710) resonances, known to couple strongly to the etaN channel in photoproduction on the proton, and the importance of J = 3/2 resonances in the process.

Search for Theta+ (1540) Pentaquark in High-Statistics Measurement of gammap-->K0K+n at CLAS

The exclusive reaction gammap-->K0K+n was studied in the photon energy range between 1.6 and 3.8 GeV searching for evidence of the exotic baryon Theta+ (1540)-->nK+. The decay to nK+requires the assignment of strangeness S=+1 to any observed resonance. Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility corresponding to an integrated luminosity of 70 pb-1. No evidence for the Theta+ pentaquark was found. Upper limits were set on the production cross section as function of center-of-mass angle and nK+ mass. The 95% C.L. upper limit on the total cross section for a narrow resonance at 1540 MeV was found to be 0.8 nb.

Beam-helicity asymmetries in double-charged-pion photoproduction on the proton

Beam-helicity asymmetries for the two-pion-photoproduction reaction gammap-->ppi(+)pi(-) have been studied for the first time in the resonance region for center-of-mass energies between 1.35 and 2.30 GeV. The experiment was performed at Jefferson Lab with the CEBAF Large Acceptance Spectrometer using circularly polarized tagged photons incident on an unpolarized hydrogen target. Beam-helicity-dependent angular distributions of the final-state particles were measured. The large cross-section asymmetries exhibit strong sensitivity to the kinematics and dynamics of the reaction. The data are compared with the results of various phenomenological model calculations, and show that these models currently do not provide an adequate description for the behavior of this new observable.

Onset of asymptotic scaling in deuteron photodisintegration

We investigate the transition from the nucleon-meson to the quark-gluon description of the strong interaction using the photon energy dependence of the d(gamma,p)n differential cross section for photon energies above 0.5 GeV and center-of-mass proton angles between 30 degrees and 150 degrees. A possible signature for this transition is the onset of cross-section s(-11) scaling with the total energy squared, s, at some proton transverse momentum P(T). The results show that the scaling has been reached for proton transverse momentum above about 1.1 GeV/c. This may indicate that the quark-gluon regime is reached above this momentum.

Proton source size measurements in the eA-->e'ppX reaction

Two-proton correlations at small relative momentum q were studied in the eA(3He,4He,C,Fe)-->e(')ppX reaction at E(0)=4.46 GeV using the CLAS detector at Jefferson Lab. The enhancement of the correlation function at small q was found to be in accordance with theoretical expectations. Sizes of the emission region were extracted, and proved to be dependent on A and on the proton momentum. The size of the two-proton emission region for He was measured in eA reactions for the first time.

Anastomotic leak prophylaxis using a vapor-heated fibrin sealant: report on 738 gastric bypass patients

BACKGROUND

Excluding pulmonary embolism, anastomotic leak is the leading cause of death and major morbidity in patients undergoing open or laparoscopic gastric bypass operations. We observed a number of these leaks (11 out of 1,120 Micropouch(SM) gastric bypass [MGB] patients; 0.9%). The majority (80%) required emergency laparotomy and drainage, massive fluid resuscitation, and aggressive nutritional support. Therefore, we designed a 2-year, prospective study to determine the therapeutic efficacy of vapor-heated fibrin sealant to prevent anastomotic leaks at the gastro-jejunostomy (GJS) site.

METHODS

Between April, 2000 and March, 2002, 738 patients underwent a primary (n=671) or revisionary (n=67) MGB procedure. The gastric reservoir was limited to the cardia of the stomach. Vapor-heated fibrin glue 1 cc was applied circumferentially to a 12-mm, non-banded GJS anastomosis. Once activated, fibrin sealant polymerized into a soft, closely adherent gel. No omental patch was used to cover the fibrin-sealed anastomosis.

RESULTS

Of 738 patients, 2 required emergency laparotomy for leaks and 2 for adhesive bands that contributed to a distal small bowel obstruction. There were no anastomotic leaks at the fibrin-sealed GJS sites. No gastro-gastric or gastro-enteric fistulas were recorded.

CONCLUSION

Fibrin sealant applied to the GJS site appears to have eliminated anastomotic leaks in our Micropouch(SM) gastric bypass patients. These results suggest that fibrin glue application may contribute to "leak prophylaxis" in patients undergoing open Rouxen-Y gastric bypass. Glue placements may also benefit patients undergoing a laparoscopic Roux-en-Y procedure, wherein anastomotic leaks have been reported early in the learning curve.

Fatal pulmonary embolism after bariatric operations for morbid obesity: a 24-year retrospective analysis

BACKGROUND

Pulmonary embolism (PE) is a leading cause of death following gastric bypass operations for morbid obesity. Although its incidence appears to be stable, the number of bariatric operations performed annually is increasing considerably; hence, the isolated fatal PE is no longer a rare occurrence. The records of patients undergoing bariatric surgical operations since 1979 were reviewed to determine specific factors that increased the risk of developing a fatal PE. Both recommended and optional indications for prophylactic inferior vena cava (IVC) filter placement in patients considered at high risk were also examined.

MATERIALS AND METHODS

Between September, 1979 and March, 2003, 5,554 operations were performed for clinically severe obesity. These operations included jejuno-ileal bypass, horizontal gastroplasty, Roux-en-Y gastric bypass with a 30-cc pouch, modified biliopancreatic diversion, the Sapala-Wood Micropouch gastric bypass (Micropouch(SM)), Lap-Band, and revisions. 12 fatal pulmonary emboli (0.21 %) were identified. All but 1 embolus occurred within 30 days following surgery.

RESULTS

In 11 of 12 patients, at least 1 co-morbidity known to increase the risk of postoperative venous thromboembolism (VTE) was identified. 4 co-morbidites were common to 4 patients (33%): venous stasis disease (VSD), BMI >/= 60, truncal obesity, and obesity hypoventilation syndrome/sleep apnea syndrome (OHS/SAS). 6 of 12 patients (50%) had a BMI >/= 60. Another 6 had chronic leg swelling with stasis dermatitis. 2 patients experienced a previous PE, and 1 patient reported a history of deep vein thrombosis (DVT).

CONCLUSION

4 patients (33%) demonstrated a combination of risk factors (VSD, BMI >/= 60, truncal obesity, OHS/SAS) recognized as significant for the development of postoperative VTE. In such patients, prophylactic IVC filter placement is highly recommended. Filter placement for other factors, such as age, body build, hypercoagulable state, etc., should be considered on an individual basis.

Two-nucleon momentum distributions measured in 3He(e,e'pp)n

We have measured the 3He(e,e'pp)n reaction at 2.2 GeV over a wide kinematic range. The kinetic energy distribution for "fast" nucleons (p>250 MeV/c) peaks where two nucleons each have 20% or less, and the third nucleon has most of the transferred energy. These fast pp and pn pairs are back to back with little momentum along the three-momentum transfer, indicating that they are spectators. Calculations by Sargsian and by Laget also indicate that we have measured distorted two-nucleon momentum distributions by striking one nucleon and detecting the spectator correlated pair.

Observation of an exotic baryon with S=+1 in photoproduction from the proton

The reaction gamma p-->pi(+)K(-)K(+)n was studied at Jefferson Laboratory using a tagged photon beam with an energy range of 3-5.47 GeV. A narrow baryon state with strangeness S=+1 and mass M=1555+/-10 MeV/c(2) was observed in the nK(+) invariant mass spectrum. The peak's width is consistent with the CLAS resolution (FWHM=26 MeV/c(2)), and its statistical significance is (7.8+/-1.0)sigma. A baryon with positive strangeness has exotic structure and cannot be described in the framework of the naive constituent quark model. The mass of the observed state is consistent with the mass predicted by the chiral soliton model for the Theta(+) baryon. In addition, the pK(+) invariant mass distribution was analyzed in the reaction gamma p-->K(-)K(+)p with high statistics in search of doubly charged exotic baryon states. No resonance structures were found in this spectrum.

Observation of an exotic S = +1 baryon in exclusive photoproduction from the deuteron

In an exclusive measurement of the reaction gammad-->K(+)K(-)pn, a narrow peak that can be attributed to an exotic baryon with strangeness S=+1 is seen in the K(+)n invariant mass spectrum. The peak is at 1.542+/-0.005 GeV/c(2) with a measured width of 0.021 GeV/c(2) FWHM, which is largely determined by experimental mass resolution. The statistical significance of the peak is (5.2+/-0.6)sigma. The mass and width of the observed peak are consistent with recent reports of a narrow S=+1 baryon by other experimental groups.

Measurement of the proton spin structure function g1(x,Q2) for Q2 from 0.15 to 1.6 GeV2 with CLAS

Double-polarization asymmetries for inclusive ep scattering were measured at Jefferson Lab using 2.6 and 4.3 GeV longitudinally polarized electrons incident on a longitudinally polarized NH3 target in the CLAS detector. The polarized structure function g(1)(x,Q2) was extracted throughout the nucleon resonance region and into the deep inelastic regime, for Q(2)=0.15-1.64 GeV2. The contributions to the first moment Gamma(1)(Q2)= integral g(1)(x,Q2) dx were determined up to Q(2)=1.2 GeV2. Using a parametrization for g(1) in the unmeasured low x regions, the complete first moment was estimated over this Q2 region. A rapid change in Gamma(1) is observed for Q2<1 GeV2, with a sign change near Q(2)=0.3 GeV2, indicating dominant contributions from the resonance region. At Q(2)=1.2 GeV2 our data are below the perturbative QCD evolved scaling value.

Measurement of ep-->e' ppi+ pi- and baryon resonance analysis

The cross section for the reaction ep-->e(')ppi(+)pi(-) was measured in the resonance region for 1.4<W<2.1 GeV and 0.5<Q2<1.5 GeV(2)/c(2) using the CLAS detector at Jefferson Laboratory. The data show resonant structures not visible in previous experiments. The comparison of our data to a phenomenological prediction using available information on N(*) and Delta states shows an evident discrepancy. A better description of the data is obtained either by a sizable change of the properties of the P13(1720) resonance or by introducing a new baryon state, not reported in published analyses.

First measurement of transferred polarization in the exclusive ep-->e'K+Lambda--> reaction

The first measurements of the transferred polarization for the exclusive e-->p-->e(')K+Lambda--> reaction have been performed at Jefferson Laboratory using the CLAS spectrometer. A 2.567 GeV beam was used to measure the hyperon polarization over Q2 from 0.3 to 1.5 (GeV/c)(2), W from 1.6 to 2.15 GeV, and over the full K+ center-of-mass angular range. Comparison with predictions of hadrodynamic models indicates strong sensitivity to the underlying resonance contributions. A nonrelativistic quark-model interpretation of our data suggests that the ssmacr; quark pair is produced with spins predominantly antialigned. Implications for the validity of the most widely used quark-pair creation operator are discussed.

Eta photoproduction on the proton for photon energies from 0.75 to 1.95 GeV

Differential cross sections for gammap-->etap have been measured with tagged real photons for incident photon energies from 0.75 to 1.95 GeV. Mesons were identified by missing mass reconstruction using kinematical information for protons scattered in the production process. The data provide the first extensive angular distribution measurements for the process above W=1.75 GeV. Comparison with preliminary results from a constituent quark model support the suggestion that a third S11 resonance with mass approximately 1.8 GeV couples to the etaN channel.

The Micropouch Gastric Bypass: Technical Considerations in Primary and Revisionary Operations

BACKGROUND

Roux-en-Y gastric bypass is an effective procedure for the long-term control of morbid obesity. An eventual revisionary operation, however, is necessary for some patients (0.8-29%). Redo procedures are required for pouch enlargement, staple-line dehiscence, or marginal ulceration. In 1994, the micropouch gastric bypass (MBG) was developed to eliminate the need for a repeat operation. Its design was based on two anatomical principles: 1) The fundus is elastic, aperistaltic, and may significantly dilate over time; 2) The proximal magenstrasse contains a high concentration of parietal cells, which potentiates the risk for marginal ulceration or gastroesophageal reflux after vertical pouch restriction. Construction of a micropouch limited to the gastric cardia avoids using the fundus and proximal lesser curvature, but requires a greater mobilization of the stomach and its peritoneal attachments.

METHODS

Between February 1994 and February 2000, 1,120 patients underwent the MGB as a primary or revisionary operation. The fundus was mobilized completely, including transection of the left phreno-esophageal and gastrophrenic ligaments. The transected pouch was limited to the gastric cardia with 1 cm of fundus incorporated into the gastrojejunostomy stoma (GJS).

RESULTS

There were 10 anastomotic leaks at the GJS (0.9%). All leaks sealed following surgical drainage or parenteral nutrition. One patient required re-operation (0.09%) for a dilated pouch and marginal ulceration. An additional patient (0.09%) developed a gastrogastric fistula secondary to a pharmacobezoar and stomal stenosis.

CONCLUSION

With an appreciation for the finer anatomy of the proximal stomach and intra-abdominal esophagus, the micropouch can be constructed safely in both primary and redo procedures. The MGB, now in its seventh year, is durable and has, with rare exception, eliminated pouch enlargement, staple-line separation, reflux esophagitis, and marginal ulceration.

Marginal ulcer after gastric bypass: a prospective 3-year study of 173 patients

BACKGROUND

Marginal ulceration (MU) after Roux-en-Y gastric bypass (RYGB) is a well-recognized complication. Its incidence varies between 1% and 16%. Factors associated with the development of MU include pouch size, pouch orientation, staple line integrity, and mucosal ischemia. Nonsteroidal anti-inflammatory drugs (NSAIDs) and Helicobacter pylori may also contribute to MU, but their mechanism of action in the RYGB patient has not been studied.

METHODS

In 1994 a prospective 3-year study was designed to document the incidence of MU after near-total gastric bypass (NTGB). In this procedure the transected pouch was limited to the cardia, and the gastrojejunostomy was made along the greater curvature. A total of 173 patients entered the study. All patients who experienced postoperative nausea, vomiting, or abdominal pain underwent endoscopic examination of the pouch, stoma, and proximal Roux-en-Y limb. Gastrograffin studies were used within the first 2 weeks of operation.

RESULTS

One year after operation, MU was not identified in any patient. At 3 years follow-up, MU was documented in one patient (0.6%) with a dilated gastric reservoir (60 cc).

CONCLUSION

This study reviews the etiology, diagnosis, and treatment of MU in the RYGB patient and offers specific recommendations to reduce its occurrence. It also confirms a preliminary impression that NTGB is an effective operation in preventing MU formation.

Influence of a forced air warming system on morbidly obese patients undergoing Roux-en-Y gastric bypass

BACKGROUND

Hypothermia during and after major abdominal surgery decreases host defenses, increases the incidence of coagulopathy and may alter blood pressure, cardiac contractility and myocardial stability.

METHODS

We designed a prospective randomized study to compare the benefits of a forced air warming system with warm blanket treatments in minimizing the effects of hypothermia on 64 morbidly obese patients undergoing Roux-en-Y gastric bypass.

RESULTS

Patients in the forced air warming group (n = 32) had significantly higher perioperative body core temperature, lower central venous pressure and blood pressure readings, lower incidence of shivering, less blood loss intraoperatively and achieved a higher post anesthesia Aldrete Score than those patients in the warmed blanket group (n = 32).

CONCLUSION

The forced air warming system is safe, cost effective and beneficial in minimizing the undesirable consequences of hypothermia in morbidly obese patients undergoing Roux-en-Y gastric bypass.

Removal of fascial staples from the midline incision in patients undergoing a second laparotomy procedure

A technique for removal of midline fascial staples is described. The staples are removed quickly and without significant anatomical distortion of the linea alba. In the majority of the patients a second row of fascial staples can be placed safely and in the same location as found in the original operation.

Stapler division of the omentum and small bowel mesentery in morbidly obese patients undergoing gastric bypass surgery

BACKGROUND

Roux-en-Y gastric bypass (RYGB) procedures can be technically demanding because of anatomical factors including fat distribution, organ fixation, and wound depth. We developed a technique using the Multifire Endo GIA 60 2.5 disposable surgical stapler which allows greater mobilization, less blood loss, and decreased operating time.

METHODS

A disposable stapler designed for laparoscopic surgery was used to transect the gastro-colic omentum and small bowel mesentery in 67 morbidly obese patients undergoing RYGB. Generally, five to six stapler cartridges were needed for the transections.

RESULTS

Stapler division of the gastro-colic omentum and small bowel mesentery decreased operating time by an average of 25 minutes.

CONCLUSIONS

Applying principles of laparoscopic surgery to RYGB resulted in more efficient mobilization of the stomach and the small bowel mesentery, as well as decreased blood loss and operating time.

Current considerations in patients with coexistent diabetes and hypertension

Primary health care providers frequently manage patients with diabetes and hypertension as co-morbid conditions. Because of the increased complexity and morbidity that occur when these conditions coexist, it is essential that practitioners remain aware of current treatment considerations and options, which are essential in helping patients manage this condition. This article reviews current considerations in the management and care of hypertension in diabetic patients. Possible differential diagnoses are considered, and current recommendations for essential nonpharmacological treatment approaches are reviewed. Particular emphasis is placed on the choice and initiation of pharmacological therapy for hypertension in the diabetic and the unique considerations necessary in this patient population. Standards of care for diabetic patients with the complication of hypertension are reviewed.

Verbal and visual problems in reading disability

Most individuals interested in reading disability favor the view that disordered language processing is the main cause of children's reading problems and that visual problems are seldom, if ever, responsible. Nevertheless, in a preliminary study (Eden, Stein, & Wood, 1993) we showed that visuospatial and oculomotor tests can be used to differentiate children with reading disabilities from nondisabled children. In the present study we investigated a larger sample of children to see if these findings held true. Using 93 children from the Bowman Gray Learning Disability Project (mean age = 11.3 years; 54 boys, 39 girls), we compared the phonological and visuospatial abilities of nondisabled children (children whose reading at fifth grade rated a Woodcock-Johnson reading standardized score between 85 and 115), and children with reading disability (whose reading standardized score was below 85 on the Woodcock-Johnson). In addition to performing poorly on verbal tests, the children with reading disability were significantly worse than nondisabled children at many visual and eye-movement tasks. A high proportion of the variance (68%) in reading ability of both the nondisabled children and those with reading disability could be predicted by combining visual and phonological scores in a multiple regression. These results provide further support for the hypothesis that reading disability may, to some extent, result from dysfunction of the visual and oculomotor systems.

Tuberculous lymphadenopathy: a collective review with a case report

A collective review of tuberculous lymphadenopathy is presented with respect to incidence, pathogenesis, clinical manifestations, diagnosis, differential diagnosis, and treatment. A typical case report is also presented. A thorough history and physical examination, a purified protein derivative (PPD) skin test and acid-fast bacillus (AFB) stains, and histopathology of the node may provide useful information. Positive culture results are the only means of confirming the diagnosis and for distinguishing between tuberculous and non-tuberculous mycobacteria. Treatment, at least initially, must be guided by the physician's clinical suspicions.Although there remains debate as to what is the best method of treating mycobacterial lymphadenopathy, chemotherapy is essential. Excisional biopsy is recommended when feasible. The possible exception is when the diagnosis of mycobacterium tuberculosis is suggested by constitutional symptoms, characteristic chest x-ray findings, a positive PPD skin test, and positive culture of mycobacterium tuberculosis from another source such as sputum or gastric washings. This needle aspiration for diagnosis is applicable as done in the case report patient. Surgery is, therefore, reserved for excisional biopsy to establish the diagnosis if systemic disease is not suspected, and also for removal of grossly enlarged nodes. Incisional biopsy should be avoided if possible, as it can result in the formation of fistulous tracts.

Two immunoreactive binding proteins for insulin-like growth factors in human amniotic fluid: relationship to fetal maturity

A binding protein for insulin-like growth factors (IGFs) has been purified from human amniotic fluid by IGF-I affinity chromatography and high performance reverse phase chromatography. This protein, with an apparent molecular mass of 28K nonreduced and 34K reduced, had an identical amino-terminus to a previously purified binding protein from amniotic fluid and to placental protein 12. The purified preparation (BP-28) bound both IGFs with high affinity [Ka, 6.55 +/- 2.24 (+/- SD) L/nmol for IGF-I and 3.23 +/- 1.05 L/nmol for IGF-II], with approximately 0.5 mol binding sites/mol BP-28 for either ligand. A 53K IGF-binding protein purified from human plasma (BP-53) did not cross-react in a RIA for BP-28, and BP-28 had less than 0.1% molar cross-reactivity in a RIA for BP-53. Human amniotic fluid reacted strongly in both assays. Fractionation of amniotic fluid samples by reverse phase chromatography showed that BP-28 and BP-53 immunoreactivities were present on separate proteins. In 40 third trimester amniotic fluid samples selected to cover a wide range of lecithin to sphingomyelin ratios, the mean concentrations of BP-28 and BP-53 were 37.6 +/- 17.6 (+/- SD) and 4.6 +/- 1.6 mg/L, respectively. Significant negative correlations were found between the levels of both BP-28 and BP-53 and the lecithin to sphingomyelin ratio, suggesting an association between the levels of both proteins and the degree of fetal maturity. A significant positive association was also found between the levels of BP-28 and BP-53. We conclude that the 28K IGF-binding protein from amniotic fluid, like the previously purified 53K binding protein, has high affinity for both IGF-I and IGF-II, that it coexists in amniotic fluid with BP-53 or a related protein, and that the levels of both proteins decline with increasing fetal maturity.

Our professional commitment as auxiliary staff members

A vast number of vulnerable new programs have been designed to provide appropriate education for all children. Perhaps most vulnerable are the programs for children with learning disabilities. Personal experience in a variety of job roles has revealed a number of skills and characteristics needed by auxiliary staff personnel to fulfill their professional commitment to children with learning disabilities, to establish their professional identity, and to find job satisfaction in programs that were implemented in haste to meet the new laws, regulations, and guidelines.

Brainstem electrical responses from selected tone pip stimuli

Brainstem-electrical responses were obtained from 10 normal hearing adult subjects using frequency specific tone pips as stimuli. The four frequency specific tone pips (500, 1000, 2000, and 4000 Hz) were diamond shaped with a 2.5-msec rise/fall time. Each tone pip was presented at four intensity levels (70, 50, 30, and 10 dB hearing threshold level), and graphic recordings were made for each frequency at the specific intensity levels. Frequency specific Wave V intensity-latency functions were plotted, and these results were compared to tone pip data obtained in previous studies. In addition, suggested test procedures for obtaining tone pip brainstem-evoked responses under diagnostic conditions are discussed.

Primary repair for closed lobar bronchus injury

Primary repair in a 19-year-old male who sustained a closed injury to the right bronchus in an auto accident was performed successfully. A 1.5-cm tear was found at operation extending from the right lower lobe bronchus into its distal portion. Nine months later, the patient showed a patent airway with minimal granulation around one suture.

The estimation of plasma valproate by gas-liquid chromatography

A gas chromatographic method for the plasma assay of the anticonvulsant, sodium valproate, is described. Derivatization is not necessary. 200 microliter plasma are required for a single estimation. The method involves a chloroform extraction of valproate and the internal standard, cyclopentane carboxylic acid, from acidified plasma. Gas-liquid chromatography using the stationary phase 10% SP-216-PS gives complete separation of valproate and the internal standard in eight minutes. The limit of detection is 20 mumol valproate/1 plasma (equivalent to 40 pmol on column). This is well below the lower therapeutic plasma level. The between-run precision of the method indicates a variation for each sample within+/-3% of its mean value.

Studies on the coordinate activity and liability of orotidylate phosphoribosyltransferase and decarboxylase in human erythrocytes, and the effects of allopurinol administration

A coordinate relationship between the activities of two sequential enzymes in the de novo pyrimidine biosynthetic pathway has been demonstrated in human red cells. The two enzymes, orotidylate phosphoribosyltransferase and decarboxylase are responsible for the conversion of orotic acid to uridine-5'-monophosphate. Fractionation of red cells, on the basis of increase of specific gravity with cell age, has revealed that these two enzymes have a marked but equal degree of lability in the ageing red cell. It is postulated that orotidylate phosphoribosyltransferase and decarboxylase form an enzyme-enzyme complex, and that the sequential deficiency of these two enzymes in hereditary orotic aciduria may reflect a structural abnormality in this complex. In patients receiving allopurinol, the activities of both enzymes are coordinately increased, and this increase appears to be due, at least in part, to stabilization of both orotidylate phosphoribosyltransferase and decarboxylase in the ageing red cell. Allopurinol ribonucleotide is an in vitro inhibitor of orotidine-5'-monophosphate decarboxylase and requires the enzyme hypoxanthineguanine phosphoribosyltransferase for its synthesis. However, the administration of allopurinol to patients lacking this enzyme results in orotidinuria and these patients have elevated orotidylate phosphoribosyltransferase and decarboxylase activities in their erythrocytes. Evidence is presented that the chief metabolite of allopurinol, oxipurinol, with a 2,4-diketo pyrimidine ring is capable of acting as an analogue of orotic acid. It is postulated that the in vivo formation of oxipurinol ribonucleotide, catalyzed by orotidylate phosphoribosyltransferase, after allopurinol administration, leads to inhibition of orotidine-5'-monophosphate decarboxylase. This inhibition results in the urinary excretion of excessive amounts of orotidine and orotic acid, and "pseudo-substrate" stabilization of orotidylate phosphoribosyltransferase and decarboxylase.