[Regional distribution of the muscarinic cholinergic receptor in the human brain studied with 11C-benztropine and PET using an anatomical standardization technique]

We measured regional distribution of the muscarinic cholinergic receptor in the normal human brain with 11C-benztropine (BZT) and positron emission tomography (PET) using an anatomical standardization technique. Seven normal volunteers who gave informed consents were involved in this study. Immediately after intravenous injection of 11C-BZT into the subjects, we started dynamic PET scanning and serial frequent arterial blood sampling. Analyses of plasma metabolites were also performed at selected time points and plasma time activity curves (TAC) of unmetabolized ligand were generated. From these PET and TAC data, we obtained Patlak plot slope calculation images. Using the HBA (human brain atlas) system, the Patlak plot slope calculation image of each subject was transformed into the shape of the standard brain. Mean and standard deviation (SD) calculation images were generated from those anatomically standardized images. On these mean and SD images, we placed regions of interest which were previously outlined on a MR image of the standard brain. From those data, we found the highest receptor distribution in the striatum and occipital cortex, as well as high distribution in the frontal, parietal, and temporal cortices, which were consistent with previous reports. These results suggested that anatomical standardization of PET receptor images with 11C-BZT will be useful for delineating the physiological or pathological alterations of the muscarinic cholinergic receptor in the human brain.

Topographic representation in human intraparietal sulcus of reaching and saccade

Regional cerebral blood flow was measured by positron emission tomography in seven subjects during reaching with saccade, reaching without saccade, saccade and control tasks. The reaching with saccade task activated two spatially distinct areas in the contralateral intraparietal sulcus (IPS) compared with the control condition. The area located in the anterior part of the IPS was also activated during the reaching without saccade but not during the saccade task. The other area, located in the posterior part of the IPS was, in contrast, active during the saccade but not the reaching without saccade task. The results indicate that the human IPS is functionally heterogeneous, and that functional roles of its anterior and posterior parts include control of reaching movements and eye movements, respectively.

Assessment of a Continuing Education Evaluation Framework

This study analyzes a systems model for evaluation research of continuing education (CE) and reports on the result of a quasi-experimental study of a stoma care CE program. Holzemer's conceptual framework for evaluating CE consisting of the learner, setting, and program along with a systems model was used as an organizing framework. A quasi-experimental design (n = 24 experimental group and n = 27 control group) was used to evaluate the impact of the CE program. Pre- and post-tests of participants' knowledge and skills of stoma care were evaluated. Participants' satisfaction with the course was surveyed by questionnaire during the course, on completion and four months after the course. No significant differences were found between the two groups. The revised framework included the concept of needs assessment and the impact of the CE program on patient care.

Changes in regional cerebral blood flow during self-paced arm and finger movements. A PET study

The purpose of this study was to identify the functional fields activated in relation to the self-paced proximal and distal arm movements. The regional cerebral blood flow (rCBF) was measured with positron emission tomography (PET) and 15O-labelled H2O (H2(15)O) in eight healthy subjects. All subjects performed the following three tasks: (1) repetitive opposition of thumb and index finger of the right hand, (2) repetitive co-contraction of biceps and tricepts brachii muscles of the right arm, and (3) rest. The mean rCBF change images for each task minus control was calculated and fields of significant rCBF changes were identified. Each movement activated different fields in the primary motor area (MI), the dorsal aspect of the premotor area (PMA) and the superior part of the prefrontal area (PFA) of the contralateral hemisphere. In these areas, arm fields were located relatively dorsally to the finger fields. In addition, specific fields in the ventral part of the PMA, the supplementary motor area (SMA), the superior parietal lobule (SPL) of the contralateral hemisphere, and the ipsilateral PFA were consistently activated during both movements. Due to a limited a field of view of the PET scanner in the axial direction, the PET scan could not cover the cerebellum. The results indicate that there may be somatotopical organization not only in the MI but also in the dorsal part of the PMA and the PFA, and that the specific fields in the ventral part of the PMA, the SMA, the SPL, and the PFA may be involved in self-paced movement.

Internal thoracic artery holder for coronary artery bypass grafting

An arterial graft holder was designed to facilitate coronary artery bypass grafting using arterial conduits. It is possible to open the heel of the arterial conduit and stitch the most difficult angle of the anastomosis under optimal visualization. This internal thoracic artery holder is atraumatic and protects the arterial conduit wall from crush injuries caused by vascular forceps. Anastomosis without the endothelial injury may provide long-term patency of the coronary artery bypass graft.

Hypoperfusion in the limbic system and prefrontal cortex in depression: SPECT with anatomic standardization technique

Depression is a common psychiatric illness, and several reports have described cerebral blood flow (CBF) abnormalities on SPECT studies in affected patients. However, because region of interest analyses were used to determine significant CBF changes in these studies, there were methodological limitations. Therefore, we investigated CBF distribution abnormalities in depression on a pixel-by-pixel basis using SPECT and an anatomic standardization technique that has been commonly used for PET activation studies.

METHODS

Eleven patients with unipolar depression, six patients with bipolar depression and nine age-matched normal control subjects underwent HMPAO brain SPECT studies. The radioactivities of SPECT images for each subject were globally normalized to 100 counts/pixel. Then, each SPECT image was transformed for standard brain anatomy using a computerized Human Brain Atlas system. For each group, the mean and variance images were calculated from the standardized anatomic SPECT images, and group comparisons were performed on a pixel-by-pixel basis.

RESULTS

Significant decreases in CBF in the prefrontal cortices, limbic systems and paralimbic areas were observed in both depression groups compared with the normal control group.

CONCLUSION

Decreases in CBF in these regions may be related to impaired attention as well as cognitive and emotional responses, which have been recognized as usual symptoms in depression. The anatomic standardization technique promises to be useful for group comparison analysis of brain SPECT on a pixel-by-pixel basis for individual neurological and psychiatric diseases.

[Relation among lifestyle, social network, blood pressure and serum lipids in the elderly]

The relationships among seven lifestyle factors including stress, which is focused on as a risk factor for cardiovascular disease recently, social network, blood pressure and serum lipids in the elderly were examined in a cross sectional study of 85 males and 65 females aged 60 years or over in the city of Sayama, Saitama Prefecture. The seven lifestyle factors were as follows: (1) amount of alcohol consumption, (2) cigarette smoking, (3) Physical exercise, (4) sleeping time per night, (5) nutritional balance, (6) body weight, and (7) stress. As social network factors, marital status and coping factor for stress and/or anxiety were introduced. Stressful life events strongly associated with stress status were also discussed. In this study, it was clear that age, alcohol consumption, stress status and stressful life events caused higher blood pressure. On the other hand, the social network was associated with lifestyle status and a controlled blood pressure level. Obesity and physical exercise were significantly associated with serum lipids. There results suggest that it is very important for the maintenance and promotion of health and risk reduction of disease among the elderly to control socio-psychological factors such as stress and stressful life event, and that a social network helps maintain a healthy lifestyle.

[Normal CBF values by the ARG method using IMP SPECT: comparison with a conventional microsphere model method]

N-isopropyl-p[123I]iodoamphetamine (IMP) has been used as a flow tracer for SPECT, and measurement of cerebral blood flow (CBF) using IMP has been performed by conventional microsphere model method (MS method). Recently, the ARG method for measuring CBF by using IMP with one SPECT scan and one point blood sampling has been developed. This method was based on two-compartment model. In the present study, normal CBF values were measured in ten male healthy subjects (mean age +/- S.D.: 29.8 +/- 6.01, age range: 23-41) by the ARG and the MS methods. The mean CBF values (+/- S.D.) for the ARG method in which the Vd value was assumed to be 50 ml/ml were 41.7 +/- 9.4, 31.1 +/- 5.0, 40.7 +/- 9.7, 41.5 +/- 10.0, 38.2 +/- 9.2, 39.0 +/- 9.4, 41.9 +/- 10.6, 38.7 +/- 8.0 and 30.0 +/- 7.7 ml/100 ml/min in the cerebellum, pons, thalamus, basal ganglia, frontal, temporal, parietal, occipital lobe cortex and centrum semiovale, respectively. The mean CBF values for the MS method were 46.8 +/- 8.4, 37.5 +/- 5.6, 45.8 +/- 8.6, 46.5 +/- 8.9, 43.7 +/- 8.3, 44.4 +/- 8.7, 46.8 +/- 9.3, 44.3 +/- 7.3 and 36.3 +/- 8.1 ml/100 ml/min, respectively. The mean CBF values in the cerebral cortex region for the ARG method were lower than those previously reported by PET. This would be caused by low first-pass extraction fraction of IMP compared with oxygen-15 labeled water. The mean CBF values for the MS method were higher than those for the ARG method against previous studies. As reasons for this, errors in estimation of the SPECT brain counts at 8 min in the MS method were considered.

[A case of ACTH-producing thymic carcinoid tumor with Cushing syndrome]

ACTH-producing thymic carcinoid tumor with Cushing syndrome in a 41-year-old male was reported. Plasma ACTH and cortisol was high, and chest X-ray film and CT scan revealed a tumor mass in the anterior mediastinum. Extended thymectomy with pretracheal lymph node dissection was performed. The microscopic findings revealed that the mass was carcinoid tumor with metastasis of anterior mediastinal lymph node. ACTH and cortisol were restored to normal range 1 week after operation. Unfortunately, he admitted seven months later because of high level of ACTH and right supraclavicular lymph nodes swelling. He underwent right neck dissection. Pathological examination proved metastatic carcinoid tumors in the dissected nodes. It is important to perform supraclavicular lymph node dissection together with extended thymectomy for thymic carcinoid tumor.

Expression of oxytocin receptor in human pregnant myometrium

Around the onset of labor, uterine sensitivity to oxytocin (OT) increases tremendously. Although this is considered to reflect OT receptor (OTR) augmentation in myometrium, neither spatial expression of OTR nor the level of the receptor message during the course of pregnancy have been investigated at the molecular level. We examined the localization and expression of the OTR in human myometrium by means of in situ hybridization, immunohistochemistry, and Northern and Western blotting. In the term pregnant myometrium, OTR expressing smooth muscle cells are observed diffusely and heterogeneously. Some of the smooth muscle cells were expressed high levels of the receptor at the messenger RNA and protein level, and they were surrounded with cells weakly positive for the OTR or negative. The level of OTR transcripts increased according to the course of pregnancy. The receptor messenger RNA level reached over 300-fold at parturition compared with the nonpregnant myometrium. In the myometrium at 32 weeks of gestation and not in labor, a relatively large amount (about 100-fold) of the receptor message was expressed. In the nonpregnant myometrium, significant amount of the receptor protein was revealed by Western blotting. We also found that the receptor protein was augmented at term and after the onset of labor. These findings indicated that the expression of OTR changes dynamically at the transcription and protein level during pregnancy and that its expression is heterogeneous in the term myometrium.

Maintenance of imprinting of the insulin-like growth factor II gene (IGF2) and the small nuclear ribonucleoprotein polypeptide N gene (SNRPN) in the human uterus and leiomyoma

The insulin-like growth factor II gene (IGF2) is thought to be involved in the growth of uterine smooth muscle tumors. We studied the allele-specific expression of IGF2 in 20 patients with uterine leiomyomas by analyzing restriction fragment length polymorphisms (RFLP), because IGF2 is a maternally imprinted gene and only the paternal allele is exclusively expressed in human somatic tissue. We also studied the allelic expression of the small nuclear ribonucleoprotein polypeptide N gene (SNRPN), which is reportedly maternally imprinted in humans, and compared the imprinting status with that of IGF2. Nine patients (45%) were heterozygous at the ApaI site of IGF2, nine (45%) were heterozygous at the possible AccII polymorphic site of SNRPN, and three (15%) showed polymorphism in both genes. The genomic DNA of 15 patients showed heterozygosity in either or both of these genes, and the mRNA of these was expressed monoallelically in myometrial tissues and leiomyomas of these patients. These results demonstrated that IGF2 and SNRPN imprinting is completely maintained in human uteri and leiomyomas and that increased expression of IGF2 is not due to biallelic expression.

Reduced renal clearance of furancarboxylic acid, a major albumin-bound organic acid, in undialyzed uremic patients

3-Carboxy-4-methyl-5-propyl-2-furanpropionic acid (CMPF) is accumulated in uremic serum as a major albumin-bound organic acid. We determined both serum and urine levels of total CMPF to calculate renal clearance of CMPF in healthy subjects and undialyzed uremic patients. Urinary excretion of CMPF and renal clearance were significantly decreased in the uremic patients. The relative clearance ratios of CMPF to creatinine were as low as 0.43% in healthy subjects and 0.45% in uremic patients, indicating that only the protein-unbound, free form of serum CMPF (about 0.4%) is ultrafiltrated in the glomeruli and then excreted into urine. In conclusion, CMPF is accumulated in uremic serum as a consequence of its reduced renal clearance. Urinary excretion of CMPF may be explained only by glomerular filtration of free CMPF in the blood.

[Normal cerebral perfusion of 99mTc-ECD brain SPECT--evaluation by an anatomical standardization technique]

A single photon emitter labeled tracer, 99mTc-ethyl cysteinate dimer (99mTc-ECD), has now been used for rCBF studies with SPECT. However, normal distribution pattern of this agent in the brain still remains unclear. Therefore, the specific purpose of this study was to investigate the normal distribution pattern of 99mTc-ECD SPECT image. Regional cerebral distribution was measured with SPECT and 984 +/- 17 MBq of 99mTc-ECD in ten normal subjects. During the SPECT measurement, subjects were placed comfortably in a supine position with their eyes closed. Each SPECT image was anatomically standardized using a computerized brain atlas system of Roland et al. (HBA: Human Brain Atlas) and X-CT image. Anatomically standardized SPECT images were globally normalized to 100 count/voxel. Then, the mean and SD images of brain SPECT were calculated voxel-by-voxel basis. The highest radioactivity was found in the medial aspect of the occipital lobe. The results indicate that the normal distribution pattern of 99mTc-ECD in the human brain may be not simply reflect the regional cerebral blood flow.

Cerebral blood flow measurement with iodine-123-IMP SPECT, calibrated standard input function and venous blood sampling

We previously reported simple methods for measuring cerebral blood flow (CBF) with 123l-labeled N-isopropyl-p-iodoamphetamine (IMP) and SPECT: table look-up method and autoradiography. With these methods, the arterial input function is obtained by calibrating the standard input function using one-point arterial blood sampling 10 min after IMP infusion. In this study, we sought to determine if these approaches can be as successful when used with venous blood sampling.

METHODS

After IMP infusion, simultaneous arterial and venous blood samples were drawn from 30 subjects without heart or lung disease.

RESULTS

The activity ratios of venous whole blood from the cubital vein to arterial blood were 0.75 +/- 0.09, 0.77 +/- 0.10, 0.78 +/- 0.03 and 0.83 +/- 0.11, respectively, at 10, 20, 30 and 50 min after IMP infusion. Venous blood activities were always 20% lower than the artery values over 50 min. When blood was sampled from the dorsal hand vein, however, the respective ratios were 0.92 +/- 0.03, 0.93 +/- 0.05, 0.97 +/- 0.04 and 0.98 +/- 0.08 after 10, 20, 30 and 50 min. Furthermore, when the palm was exposed to heat during the sampling period, blood activity levels increased to 0.92 +/- 0.04, 0.96 +/- 0.04, 0.99 +/- 0.05 and 0.98 +/- 0.03. Thus, venous blood activities were consistent with arterial activity, presumably because of the numerous arteriovenous anastomoses in the palm. Optimal times for venous blood sampling, with and without palm heating, were determined by error analysis to be 15 and 20 min, respectively, after IMP infusion.

CONCLUSION

Venous blood sampling from the dorsal hand can be substituted for arterial blood sampling in IMP-CBF studies.

Overexpressed tau protein in cultured cells is phosphorylated without formation of PHF: implication of phosphoprotein phosphatase involvement

Pyramidal neurons in affected regions of Alzheimer's disease (AD) brain contain neurofibrillary tangles (NFT), aggregates of paired helical filaments (PHF) composed mainly of phosphorylated microtubule-associated protein tau. To explore the role of tau phosphorylation in the aggregation of tau into PHF, we constructed mammalian cell culture systems producing high levels of intracellular phosphorylated tau. COS-1 fibroblast-like cells were transiently transfected to simultaneously express tau, MAP kinase (MAPK), and MAP kinase kinase (MAPKK), or alternatively to express tau and glycogen synthase kinase 3 (GSK3). B103 neuron-like cells (which contain MAPK but little tau or GSK3) were stably transfected to express tau or tau and GSK3. In both systems, GSK3-transfected cells contained tau AT8/M (defined by AT8 staining and tau PHF-like mobility), but MAPK-transfected cells required phosphatase inhibitors, such as okadaic acid (OKA) or calyculin (CAL), to produce tau AT8/M. In vitro, the same concentrations of CAL and OKA inhibit phosphatases 1 and 2A (PP1 and PP2A), except that 100-1000 times as much OKA is needed to inhibit PP1. Inducing tau phosphorylation at the AT8 site in MAPK-transfected cells required 2-10 times more OKA than CAL, suggesting both PP1 and PP2A helped block the phosphorylation. Though levels of tau AT8/M reached 2-8% of total cellular proteins in COS-1 cells, the ratio of particulate to supernatant tau levels did not increase, and no tangles were observed; perhaps post-translational modifications or co-aggregating proteins are needed to induce PHF.

A Method for Purification of Clostridium perfringens Phospholipase C from Recombinant Bacillus subtilis Cells

We developed a method to purify Clostridium perfringens phospholipase C from a culture of recombinant Bacillus subtilis cells. This method consists of three purification steps, and it allowed us to obtain 6.2 mg of pure phospholipase C from 800 ml of culture.

Production of platelet-activating factor by porcine brain microvascular endothelial cells in culture

Endothelial cells produce platelet-activating factor (PAF), which is the key process in the interactions between the vascular wall and blood cells. To examine the production of PAF in brain microvasculature we have cultured brain endothelial cells and performed a comparative study with aortic endothelial cells. Fresh porcine brain was homogenized, and microvascular endothelial cells were separated by enzyme digestion. The cells were cultured in medium containing epidermal growth factor and bovine brain extract. Endothelial cells from the aorta of the same animal were cultured in a similar manner. Production of PAF was assessed by [3H]acetate incorporation into phospholipids or by radioimmunoassay. Prostacyclin was measured by radioimmunoassay of 6-ketoprostaglandin F 1 alpha. The cells produced 1760 +/- 403 and 2892 +/- 347 dpm/10(6) cells (n = 4) of PAF when stimulated with bradykinin and calcium ionophore A23187, each at 1 microM, respectively. Aortic endothelial cells produced 3911 +/- 2006 and 8052 +/- 2270 dpm/10(6) cells (n = 4), respectively, and these values were significantly higher than those in brain endothelial cells (p < 0.01, U-test). Prostacyclin production was also higher in aortic cells as compared to brain microvascular endothelial cells. In aortic endothelial cells both Ca ionophore A23187 and bradykinin significantly stimulated PMN adherence whereas in brain microvascular cells only Ca ionophore enhanced the adherence. Brain microvascular endothelial cells produce smaller amount of PAF and prostacyclin as compared to aortic endothelial cells, and this fact may imply that the functional integrity of the brain microvascular endothelium is maintained at a low level.

Regulation of classical HLA class I genes in human choriocarcinoma cells by nuclear proteins binding to MHC class I regulatory elements

PROBLEM

The regulation of classical HLA class I genes in choriocarcinoma have been reported.

METHODS

We determined whether four choriocarcinoma cell lines expressed classical HLA class I or HLA-G by a reverse transcription-polymerase chain reaction (RT-PCR) and studied the regulatory mechanism of classical class I using a gel mobility shift assay.

RESULTS

NUC1 and SCH expressed classical class I but not HLA-G. GCH1 and Jar did neither. Nuclear protein binding to the class I regulatory element (CRE) was detected in NUC1 and SCH. Interferon-gamma augmented both classical class I expression and the DNA-protein complex in NUC1. The DNA-protein complex was not observed in GCH1, and Jar showed a CRE-binding protein with different electrophoretic mobility and binding affinity from that of SCH and NUC1.

CONCLUSION

The CRE is one of the regulatory elements of classical HLA class I genes in choriocarcinoma cells.

Intussusception of the appendix: a report of three cases with different clinical and pathologic features

Three cases of intussusception of the appendix (IA) with distinctive pathologic changes were reported. All patients were women with different clinical presentations. Grossly, a complete intussusception was found in one case (case 1), while the others (cases 2 and 3) showed a partial intussusception. In case 1, almost the total segment of the appendix bearing the villous adenoma with focal malignant transformation became completely telescoped into the cecum. In case 2, no underlying appendiceal lesion was disclosed. In case 3, appendiceal endometriosis was found as the point of traction. Awareness of such a rare complication associated with various appendiceal lesions provides a clue for making an accurate diagnosis and selecting appropriate surgical management.

Effects on health of dietary supplementation with 100 mg d-alpha-tocopheryl acetate, daily for 6 years

To evaluate the clinical antioxidant effects of vitamin E, 161 healthy volunteers aged 39 to 56 years, were given 100 or 3 mg of d-alpha-tocopheryl acetate orally daily for 6 years using a randomized, double-blind design. Among the 147 volunteers who qualified for the analysis, seven of the 73 volunteers receiving 3 mg d-alpha-tocopheryl acetate daily and none of the 74 volunteers receiving 100 mg had coronary disorders including myocardial damage (P < 0.02). ST or T wave abnormalities on electrocardiograms were considered to indicate coronary disorders (four volunteers). The mean serum total tocopherol (TOC) concentration in the 100-mg group was significantly higher than that in the 3-mg group 6 months after the start of the study, and this raised value was maintained throughout the study; the level in the 3-mg group did not change significantly from the baseline value. The low-density lipoprotein cholesterol/total TOC ratio, a parameter of the inhibition of peroxidation of low-density lipoprotein cholesterol, was the only serum lipid parameter that was significantly different, at baseline, in the volunteers with coronary disorders compared with the others. These findings indicate that long-term supplementation with 100 mg tocopheryl acetate daily may prevent the early stages of coronary atherosclerosis by decreasing peroxidation of low-density lipoprotein cholesterol.

The novel variants of mb-1 and B29 transcripts generated by alternative mRNA splicing

The Ig-alpha/Ig-beta heterodimers encoded by mb-1 and B29 genes, respectively, are crucial for the constitution of the B-cell receptor (BCR). We report here novel variants of mb-1 and B29 transcripts produced by alternative mRNA splicing. The proteins encoded by these variants are predicted to conserve transmembrane and cytoplasmic portions of Ig-alpha and Ig-beta but lack a part of the extracellular portions containing cysteine residues which are required for intramolecular and intermolecular S-S bonds. Transfection studies revealed that the variant mb-1 and B29 did not contribute to the BCR expression on cell surfaces. Although peripheral B cells contain small amounts of the variant mb-1 and B29 transcripts, treatment with an anti-IgM antibody, LPS or IL-4 induces a significant increase in amounts of the variant transcripts. These observations suggest that B-cell activation induces alternative splicing of mb-1 and B29 transcripts which encode proteins unable to constitute the BCR.

[Normal cerebral perfusion of 99mTc-HMPAO brain SPECT--evaluation by ananatomical standardization technique]

Single photon labeled tracer 99mTc-hexamethylpropylene amine oxime (HMPAO) has been used for rCBF studies by SPECT. However, normal perfusion pattern of this agent still remains unclear. The purpose of this study was to investigate normal 99mTc-HMPAO SPECT image voxel by voxel. Eighteen male subjects without any prior or present history of medical illness participated in this study. All SPECT images were globally normalized to 100 count/voxel. Each subject had an X-ray CT scan at the same day of SPECT measurement. All subjects had normal X-ray CT scans. The standard anatomical structures of the computerized brain atlas of Roland et al. were fitted to X-ray CT images of a subject by linear and non-linear parameters. These parameters were subsequently used to transform SPECT images of the subject. After the anatomical standardization, mean and SD images of eight standardized images were calculated voxel-by-voxel basis. In the mean image, following structures showed relatively higher radioactivity; the putamen, the cerebellum, and the frontal lobe. In addition, the occipital lobe, parietal lobe, frontal lobe, and the putamen showed large degree of SD. Anatomical standardization of SPECT images may be useful as a reference to diagnose and evaluate various brain disorders.

Surgical treatment of mesenteric infarction, thoracoabdominal aortic aneurysm, and proper hepatic aneurysm in a middle-aged woman with Takayasu's arteritis

Although Takayasu's arteritis may present a wide variety of signs and symptoms depending on the vessel affected, it is rarely associated with acute abdomen requiring emergency laparotomy. We report a case of Takayasu's arteritis that required several surgical interventions for mesenteric infarction, thoracoabdominal aneurysm, and proper hepatic artery aneurysm, all of which were noted in succession within a 1-year period. This is also the first report, to our knowledge, of a hepatic artery aneurysm caused by Takayasu's arteritis.