Biomedical subjects
Publications and source records attributed to G Xu.
We describe a polymorphic microsatellite in intron 38 of the neurofibromatosis type 1 (NF1) gene. The microsatellite consists of a CA/GT dinucleotide repeat detecting 8 alleles; it has a heterozygosity of 82%.
BACKGROUND: To explore the sexual difference in the feedback regulation of hepatic bile acid synthesis, glycodeoxycholic acid (GDCA) was administered to 15 male and 14 female rabbits. METHODS: After bile diversion, GDCA equivalent to the hepatic bile acid influx was infused intraduodenally. Biliary cholic acid output represented bile acid synthesis. Hepatic 3-hydroxy-3 methylglutaryl coenzyme A (HMG-CoA) reductase and cholesterol 7 alpha-hydroxylase activities and steady state messenger RNA (mRNA) levels were determined. RESULTS: GDCA inhibited bile acid synthesis less in female than in male rabbits. Hepatic HMG-CoA reductase activity decreased 39% in males, but increased 48% in females. Hepatic cholesterol 7 alpha-hydroxylase activity decreased similarly in males and females, and mRNA levels decreased 86% in males but were unchanged in females. CONCLUSIONS: (1) Total bile diversion stimulated both hepatic cholesterol and bile acid synthesis by activating the rate-controlling enzymes and increasing mRNA levels. (2) GDCA decreased mRNA levels of HMG-CoA reductase and cholesterol 7 alpha-hydroxylase in males, but mRNA levels did not decrease in females. (3) Bile acid synthesis was sustained in females because continued biosynthesis of cholesterol provided a substrate for cholesterol 7 alpha-hydroxylase and stimulus for enzyme formation.
A method for the determination of total N-nitroso compounds (NOC) and nitrite in fresh human gastric juice is described, which is based on earlier methods. A freshly obtained gastric juice sample is injected directly into refluxing ethyl acetate containing glacial acetic acid, HCl and HBr to determine the total concentration (A) of nitrite, total NOC and thermo- and acid-labile thermal energy analyser (TEA)-responsive compounds (TAC). Another fresh sample of the same juice (with or without the addition of sulfamic acid) is injected directly into refluxing ethyl acetate containing glacial acetic acid and HCl for determining the TAC level (B) and the total level (C) of nitrite and TAC. The NO released from nitrite, TAC and NOC is detected by TEA acting as a chemiluminescence detector. The differences between A and C and between C and B represent the concentrations of total NOC and nitrite, respectively. The method is rapid, reproducible (relative standard deviation 1-6%) and sensitive (detection limit 1.0 pmol). The behaviour of nitrite and NOC in the analytical system was studied and relevant techniques for the direct analysis of fresh gastric juice samples and for stabilization of fresh samples have been developed.
This study relates antioxidant status and blood pressure (BP) in 168 healthy residents of Augusta, GA, following usual diets. BP ranges were systolic (S) 84-152, mean 112 +/- 1 mm Hg, and diastolic (D) 52-96, mean 72 +/- 1 mm Hg. Plasma concentrations of ascorbic acid (AA) were significantly inversely related to SBP (r = -0.18, P < 0.05) and DBP (r = -0.20, P < 0.01); with regression equations SBP vs AA = -0.083C + 116 and DBP = -0.077C + 76. Highest and lowest quintiles of AA differed significantly in mean SBP (108 +/- 2, 113 +/- 2 mm Hg) and DBP (69 +/- 1, 74 +/- 2), P < 0.05. Plasma AA concentrations were significantly lower in the smokers. By deleting smokers, the inverse relations of SBP and DBP with plasma AA and the slopes of the equation were enhanced. Plasma selenium, alpha-tocopherol, alpha-tocopherol:cholesterol ratio, retinol and taurine were not related to BP; whereas male gender, body mass index, body fat distribution, plasma cholesterol, low density lipoprotein cholesterol, and triglycerides correlated.
Sialyl-linkage specificity of the sialidase of influenza B viruses isolated in different years from 1940 through 1990 (B/Lee/40,B/Setagaya/3/56,B/Tokyo/7/66,B/Kagoshima/1/68, B/Gifu/2/73, B/Kanagawa/3/76, B/Ibaraki/2/85, B/Yamagata/16/88, and B/Bangkok/163/90) was studied with N-acetylneuraminyl (alpha 2-3)- and (alpha 2-6)-lactoses, GM3 gangliosides containing the same sialyl-oligosaccharide sequences as sialyllactose, and also with type I and type II lacto-series gangliosides carrying Neu5Ac alpha 2-3Gal and NeuAc alpha 2-6Gal linkages as substrates. From an examination of up to nine strains, the sialidases of all viruses preferentially hydrolyze substrates with Neu5Ac alpha 2-3Gal linkage rather than the Neu5Ac alpha 2-6Gal linkage. It was found that the sialidase activity toward Neu5Ac alpha 2-6Gal linkage relative to Neu5Ac alpha 2-3Gal linkage is increased in later strains, whether sialyllactose or ganglioside is used as the substrate. These results suggested that the sialidase of influenza B virus isolates has shown a drift in linkage specificity which correlates with the year of isolation.
PURPOSE: To compare the academic performances of Asian-American medical students--before, during, and after medical school--with those of white students. METHOD: The 140 Asian-American graduates and 2,269 white graduates from the classes of 1981-1992 at Jefferson Medical College were studied prospectively: data on academic performance, indebtedness, and delayed graduation were analyzed and compared for all the graduates. F-tests, chi-square tests, and regression models were used. RESULTS: The Asian-Americans had statistically significantly higher scores on the SAT (Scholastic Aptitude Test) quantitative subtest and on the MCAT (Medical College Admission Test) chemistry, physics, and science problems subtests; the whites had significantly higher scores on the MCAT reading subtest; third-year grade-point averages for required clerkships; and scores on National Board of Medical Examiners Part I, II, and III examinations (NBME I, II, and III). No significant difference was found in the other performance measures, including ratings in the first year of residency. Regression analysis showed that the MCAT reading score was the major predictor of Asian-Americans' performances on the NBME I and II. CONCLUSION: Because the MCAT reading score is the major predictor of later performance for Asian-American students, schools should consider employing different criteria in predicting and monitoring these students' performances.
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Four isolates of spotted fever group rickettsiae isolated from ticks in China were compared with all known species and strains of spotted fever group rickettsiae by immunofluorescence assay, DNA polymerase chain reaction followed by restriction endonuclease fragment length polymorphism analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and Western immunoblot. The Chinese isolates belonged to three types, including a novel serotype which has not been described before. One isolate obtained from tick ova of Dermacentor nuttallii in Inner Mongolia was antigenically and genotypically identical to Rickettsia sibirica. Two isolates obtained from Dermacentor sinicus collected from Beijing were identical, different from other members of spotted fever group rickettsiae but apparently closely related to R. sibirica. HA-91, a strain isolated from Hyalomma asiaticum bv. kozlovi olenew, was antigenically and genotypically unique among spotted fever group rickettsiae, and we feel that data presented here should prompt consideration of it as a new species on the basis of current rickettsial taxonomy.
The regulation of the GTPase activity of the Ras proteins is thought to be a key element of signal transduction. Ras proteins have intrinsic GTPase activity and are active in signal transduction when bound to GTP but not following hydrolysis of GTP to GDP. Three cellular Ras GTPase-activating proteins (Ras-gaps) which increase the GTPase activity of wild-type (wt) Ras but not activated Ras in vitro have been identified: type I and type II GAP and type I NF1. Mutations of wt Ras resulting in lowered intrinsic GTPase activity or loss of response to cellular Ras-gap proteins are thought to be the primary reason for the transforming properties of the Ras proteins. In vitro assays show type I and type II GAP and the GAP-related domain of type I NF1 to have similar biochemical properties with respect to activation of the wt Ras GTPase, and it appears as though both type I GAP and NF1 can modulate the GTPase function of Ras in cells. Here we report the assembling of a full-length coding clone for type I NF1 and the biological effects of microinjection of Ras and Ras-gap proteins into fibroblasts. We have found that type I GAP, type II GAP, and type I NF1 show markedly different biological activities in vivo. Coinjection of type I GAP or type I NF1, but not type II GAP, with wt Ras abolished the ability of wt Ras to induce expression from an AP-1-controlled reporter gene. We also found that serum-stimulated DNA synthesis was reduced by prior injection of cells with type I GAP but not type II GAP or type I NF1. These results suggest that type I GAP, type II GAP, and type I NF1 may have different activities in vivo and support the hypothesis that while type I forms of GAP and NF1 may act as negative regulators of wt Ras, they may do so with differential efficiencies.
Information about physicians' practice problems was solicited through a structured questionnaire mailed to a group of family physicians, pediatricians, and orthopedic surgeons. Overall, a lack of personal time was the major concern across the three groups of physicians. Comparisons among the three types of physicians revealed two patterns: Family physicians reported more concerns in the "interpersonal" dimension, whereas orthopedic surgeons had more concerns in the "legal-economic" dimension. These patterns of differences persisted with two variables controlled: gender and time period in which they completed their residency program. These findings indicate that physicians' concerns in their practice vary among the specialties, and they imply that the changed economy and reimbursement system might have more impact on one than the other. Thus the effectiveness of residency training and continuing education might be improved by emphasizing the specialty-related problems in practice.
The study was conducted with a sample of third-year students (n = 584) at Jefferson Medical College to explore students' perception of patterns of differences between attending physicians and residents in their teaching behaviors during clinical clerkships. Attending physicians' teaching behaviors were perceived more in a mentorship mode whereas residents' teaching behaviors were equally divided between mentorship and preceptorship modes. Attending physicians and residents' teaching behaviors varied among clerkships. Results were discussed in terms of difference of teaching roles played by attending physicians and residents and relationship of the teaching behaviors to students' overall rating of clerkship.
This article reviews the main results in recent years of studies on the role of central Ach in pain modulation and analgesia, including: (1) cholinergically induced analgesia (CIA). Cholinomimetic drugs raised the pain threshold or inhibited the unit discharges of hypothalamus parafascicularis nuclens in rats, and these actions were revised by atropine not by nicotine. (2) Ach and acupuncture analgesia (AA). The effect of electroacupuncture was changed by administration of HC-3, atropine, etc. (3) Ach and stress analgesia (SA). Scopolamine reduced the hind foot shock induced analgesia, and this kind of SA was probably mediated by m-receptors existed at supraspinal, rather than spinal level. Swimming and immobilization analgesia were also related to Ach. These data suggested that the central cholinergic system is very important in pain modulation and analgesia and the central Ach is essential transmitter or modulator in this analgesic pathway. But the problem is whether the mechanism of CIA is involved in opiate analgesic system or not.
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Endoscopic sinus surgery has become popular during recent years. Here is a report of complications of endoscopic sinus surgery among 150 patients. Seven patients had complications, including one nasolacrimal duct injury, one temporary blindness, one orbital hematoma as a result of trauma to the lamina papyracea, two orbital infections, one CSF leakage and one death probably due to laceration of the internal carotid artery. The complication rate was 4.6%, and the mortality rate 0.6%. We conclude that the knowledge of anatomy, good training, and meticulous surgical technique are very important, and that endoscopic sinus surgery in patients with extensive lesions should be handled with care, especially in patients with bleeding or bone destruction involving the lateral wall of sphenoid sinus and skull base.
Serum levels of pancreatic polypeptide (SPP) responding to 75g glucose (oral) challenge were observed in 27 patients with end state renal failure (ESRF) and 27 normal subjects as a control. The results showed that the levels of SPP were significantly higher in ESRF patients than in normal subjects. Dialysis therapy seemed to have no effect on the levels of SPP. The elevated levels of SPP could return to normality after kidney transplantation. There was no positive correlation between the levels of SPP, the blood sugar, and the serum insulin. It is suggested that kidneys are the important sites for the metabolism of PP. The elevated SPP concentration in patients with ESRF may result from their renal failure, and may contribute to some gastrointestinal symptoms which are frequently associated with ESRF.