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Biomedical subjects

R Schmidt

Publications and source records attributed to R Schmidt.

At least 325 records · Page 18Linked to original sources
PubMed1996

Distinct conformational preferences of three cyclic beta-casomorphin-5 analogs determined using NMR spectroscopy and theoretical analysis.

The conformational properties of three cyclic beta-casomorphin analogs based on the general formula H-Tyr-c[-D-Orn-2-Nal-D-Pro-Xaa-] (2-Nal = 2-naphthylalanine; Xaa = D-Ala, Sar or NMe-Ala) in DMSO solution were investigated using NMR spectroscopy in conjunction with molecular modeling techniques. The D-Ala5- and Sar5-analogs (compounds 1 and 2 respectively) are potent mixed mu-agonist/delta-antagonists with high mu- and delta-opioid receptor affinities, whereas the NMe-Ala5-analog (compound 3) is a potent mu-agonist and a weak partial delta-agonist. Distinct conformational differences emerged for the three compounds studied. Flexibility in the bare ring structures was found to increase in the order 3 < 2 < 1. The increased structural rigidity of 3 may be responsible for its low delta-receptor affinity as compared to the two other analogs. A low fractional population of conformers containing two cis peptide bonds was found for compound 2 but not for analog 1 or 3. Initial evidence for this observation was obtained from NMR differential line-broadening experiments and later confirmed by molecular mechanics simulations. Comparison of the temperature dependence of amide proton chemical shifts acquired for the three cyclic analogs indicate a large degree of intramolecular hydrogen bonding for 1 but not for the other two peptides.

Endorphins↗
PubMed1996

Estrogen replacement therapy in older women: a neuropsychological and brain MRI study.

OBJECTIVE: To determine if postmenopausal women receiving estrogen perform better on demanding cognitive tests than women without estrogen replacement and if this beneficial effect on cognition is caused by estrogen-related prevention of silent ischemic brain damage. DESIGN: Cross-sectional study comparing postmenopausal estrogen users and non-users. SETTING: Austrian Stroke Prevention Study. PARTICIPANTS: A total of 70 women currently using estrogen and 140 women who have never used estrogen from a subset of 222 postmenopausal women without neuropsychiatric or general disease undergoing extensive diagnostic work-up in a large-scale stroke prevention study among randomly selected community members. MEASUREMENTS: Neuropsychological test scores and focal brain abnormalities as well as size of ventricles and cortical sulci as assessed by 1.5 Tesla MRI. RESULTS: Estrogen users performed better than non-users on almost all neuropsychological tests administered. When ANCOVA was used to correct for slight differences between groups in age, length of education, mean arterial blood pressure and self-reported activation, values of P < .05 were noted on tasks assessing conceptualization, attention, and visuopractical skills. After adjustment for multiple comparisons, the differences in conceptualization and visuopractical skills remained significant. MRI showed a lower rate and extent of white matter hyperintensities and a significantly smaller total white matter hyperintensity area in women treated with estrogen (P = .043). The total white matter hyperintensity area was inversely related to the duration of estrogen replacement therapy(P = .040). However, there was no difference in neuropsychological performance between estrogen users with and without white matter abnormalities, and this was also supported by the lack of an association between cognitive test results and the extent of white matter disease. CONCLUSIONS: Our study demonstrated an association between estrogen replacement therapy and better cognitive functioning and a lower rate of clinically unsuspected ischemic brain damage in postmenopausal women.

Analysis of Variance↗
PubMed1996

Tumors after renal transplantation.

The purpose of this retrospective study was to analyze the development of malignancies after renal transplantation. 633 renal graft recipients with an organ function longer than 1 year were followed up over a mean period of 67.6 +/- 48.7 months. Only 12 recipients received grafts from living-related donors. 38 recipients (6.0%) exhibited cancer of either the skin, the genitourinary system, the bronchial system, the female breast, or the colon. All tumors were de novo malignancies. The number of patients developing a tumor was significantly higher in the cyclosporine-treated group than in patients with conventional immunosuppression. 15 patients died within a mean survival time of 7.7 +/- 12.1 months. The frequency of disorders makes it necessary for organ transplant recipients to have routine examinations both before and at regular intervals after transplantation. This includes examination of the patient's skin, native kidneys and cervical smears for females.

Adolescent↗
PubMed1996

Magnetic resonance imaging white matter hyperintensities in clinically normal elderly individuals. Correlations with plasma concentrations of naturally occurring antioxidants.

BACKGROUND AND PURPOSE: White matter hyperintensities are a common magnetic resonance imaging (MRI) observation in the elderly. They are believed to represent a subclinical form of ischemic brain damage, but the underlying pathophysiological mechanisms are still incompletely understood. We postulated that oxidative mechanisms may favor the development of these changes and therefore correlated their presence and extent with the plasma concentrations of 10 naturally occurring antioxidants. METHODS: We studied 355 clinically normal volunteers 45 to 75 years of age who were randomly selected from the official community register. A 1.5-T MRI of the brain and measurements of the plasma concentrations of antioxidants including zeaxanthin, cryptoxanthin, canthaxanthin, lycopene, alpha- and beta-carotene, retinol, gamma- and alpha-tocopherol, as well as ascorbate were performed in all study participants. White matter hyperintensities were graded as punctate, beginning confluent, and confluent abnormalities. RESULTS: Punctate, beginning confluent, and confluent white matter abnormalities occurred in 101 (28.5%), 44 (12.4%), and 14 (3.9%) individuals, respectively. Study participants with white matter damage were significantly older and had a higher frequency of arterial hypertension and cardiac disease but lower serum concentrations of total cholesterol. The plasma levels of lycopene and alpha-tocopherol were significantly lower in subjects with early confluent and confluent white matter hyperintensities, while individuals with punctate foci had an antioxidant status similar to those with normal MRI scans. Alpha-tocopherol was the only antioxidant that remained significantly and inversely related to the presence of beginning confluent and confluent white matter changes after adjustment for the between-group differences in age, arterial hypertension, cardiac disease, and cholesterol. The adjusted odds ratio for early confluent and confluent white matter abnormalities was 3.70 (95% CI, 1.69 to 8.10) in the lowest compared with the highest quartile of the alpha-tocopherol concentration. The odds ratio increased to 7.11 (95% CI, 1.63 to 22.84) when quintiles of the alpha-tocopherol level were compared. CONCLUSIONS: These data do not prove a causal relation, but they provide evidence of an association between low plasma concentrations of vitamin E and a higher risk of cerebral white matter disease in elderly normal subjects.

Aged↗
PubMed1996

Magnetic resonance imaging correlates of transient cerebral ischemic attacks.

BACKGROUND AND PURPOSE: MRI of patients with a transient ischemic attack (TIA) may provide more detailed morphological insights than CT. We therefore studied the frequency and type of TIA-related infarcts shown by MRI, examined the utility of intravenous contrast material, and searched for potential predictors of infarct occurrence. METHODS: We performed 1.5-T MRI of the brain of 52 patients (age range, 28 to 93 years; mean, 61 years) with a hemispheric TIA. Contrast material (Gd-DTPA) was given to 45 individuals. We recorded type, number, size, and location of ischemic brain lesions and related the presence of acute infarction to features of clinical presentation and probable causes for the TIA. RESULTS: MRI showed focal ischemic lesions in 50 patients (81%), but an acute TIA-associated infarct was seen in only 19 subjects (31%). In patients with an acute lesion, the infarcts were smaller than 1.5 cm in 13 (68%), purely cortical in 11 (58%), and multiple in 7 (37%) individuals. Contrast enhancement contributed to the delineation of an acute lesion in only 2 of 45 patients (4%). Acute infarction was unpredictable by clinical TIA features, but the frequency of identifiable vascular or cardiac causes was significantly higher in those patients with TIA-related morphological damage (odds ratio, 5.2 [95% confidence interval, 1.6 to 17.3]). CONCLUSIONS: More than two thirds of TIA patients showed no associated brain lesion even when MRI and contrast material were used, but the overall frequency of ischemic damage was high. TIA-related infarcts on MRI were mostly small and limited to the cortex and tended to consist of multiple lesions. A positive MRI underscores the need for comprehensive diagnostic workup since evidence of infarction appears to be associated with a higher frequency of significant vascular or cardiac disorders.

Adult↗
PubMed1996

Surfactant alterations in severe pneumonia, acute respiratory distress syndrome, and cardiogenic lung edema.

Bronchoalveolar lavage fluids (BALF) were analyzed for surfactant abnormalities in 153 patients with acute respiratory failure necessitating mechanical ventilation. Diagnoses were acute respiratory distress syndrome (ARDS) in the absence of lung infection (n = 16), severe pneumonia (PNEU; n = 88), ARDS and PNEU (n = 36), and cardiogenic lung edema (CLE; n = 13). The PNEU group was subdivided into groups with alveolar PNEU (n = 35), bronchial PNEU (n = 16), interstitial PNEU (n = 18) and nonclassified PNEU (n = 19). Comparison with healthy controls (n = 20) was undertaken. Total phospholipids (PL), proteins, PL classes (HPTLC) and surfactant apoproteins SP-A and SP-B (ELISA) were quantified in the original BALF. The 48,000 x g pellet from centrifugation of the BAL was used to assess the percentage of large surfactant aggregates (LSA) and the biophysical properties of the surfactant (pulsating bubble surfactometer). All groups with inflammatory lung injury (PNEU and/or ARDS) showed some decrease in the lavageable PL pool, a reduced LSA content in BALF, and a manifold increase in alveolar protein load. Marked changes in the PL profile were noted throughout the groups (a decrease in phosphatidylcholine (PC) and phosphatidylglycerol (PG) and an increase in phosphatidylinositol [PI] and sphingomyelin [SPH]). Concentrations of SP-A but not of SP-B in BALF were reduced. Minimum surface-tension values approached 0 mN/m in controls, and ranged from 10 to 25 mN/m in the absence of supernatant protein and from 20 to 35 mN/m in recombination with leaked protein in the groups with ARDS and/or PNEU. Abnormalities in alveolar PNEU surpassed those in bronchial PNEU, and interstitial PNEU presented a distinct pattern with extensive metabolic changes. All surfactant changes were absent in CLE except for a slight inhibition of surface activity by proteins. We conclude that pronounced surfactant abnormalities, comparable to those in ARDS in the absence of lung infection, occur in different entities of severe PNEU, but not in CLE.

Acute Disease↗
PubMed1996

[Dust emission from chicken and layer houses].

Dust concentration was measured by Laser-monitor in two at a time houses for layers with litter or with cages and in two at a time houses for growing chicken with litter or with cages in the middle of the keeping area, in the outlet opening and in 3, 10, 50 and 100 m distance over a period of 8 weeks in winter, summer and spring/autumn. Dust values have shown only less dynamics between 8 am and 5 pm. Significant positive correlation was found between dust concentration and age of poultry, keeping time resp. in litter housing system but not in cage housing system. Also, it was demonstrated a significant relation between dust concentration inside of poultry house, at the outlet openings and in 3 m distance in the outdoor air. There was no influence evident of indoor dust concentration on the dust value in the environment in more than 3 m distance to the poultry house. It was shown a low dust concentration of 0.1% up to 2.1%--compared to the indoor dust values--in 50 and 100 m distance to outlet ventilation system independent on housing, climatic and topographic factors.

Aging↗
PubMed1996

Rhesus thymic/liver xenografts in severe combined immunodeficient mice: immunologic reconstitution and intrathymic infection with simian immunodeficiency virus.

By serving as host recipients of xenografts from both humans and animals, severe combined immunodeficient (SCID) mice have become valuable to many laboratories interested in examining the pathophysiology of different diseases. To gain insight into the usefulness of the SCID mutation in retrovirus research, rhesus monkey fetal hematolymphoid tissues (liver and thymus) were used to construct a SCID-rhesus chimeric mouse (SCID-rh) and were engrafted in the renal capsule. The size and maturation of the thymic engrafts were monitored grossly, histologically, and immunologically. SCID mice were tolerant to rhesus tissues, and thymic engrafts contained thymocytes at different stages of maturation and differentiation that had morphologic features similar to age-matched rhesus thymus. Mature single positive CD2+, CD4+, and CD8+ T lymphocytes that were phenotypically similar to rhesus T lymphocytes were present at low levels (2% to 5%) in the peripheral blood and at moderately higher levels (7% to 15%) in the spleens of SCID-rh mice obtained between 12 and 15 weeks after thymus/liver engraftment. Within 3 weeks after engraftment, > 85% of the thymocytes in the thymic engrafts were immature double positive CD4+CD8+ T cells. The highest number of positive cells were seen in thymic engrafts obtained at 12 to 18 weeks. During these weeks, > 90% of the cells were double positive (CD2+CD4+, CD2+CD8+, and CD4+CD8+). After infection of the engrafted thymus tissue with simian immonodeficiency virus (SIVmac239), PCR analysis revealed successful viral infection of engrafts at 2 and 4 weeks after infection. No significant histopathologic and flow cytometric changes were observed in the thymic engrafts at 2 and 4 weeks after infection. An unrelated lesion of thymic lymphomas involving the SCID host thymus was seen in 12% of the mice. The data presented herein suggest that the SCID-rh is a valuable model for specific studies related to thymus-retrovirus interaction and that it could be used for further studies. The results are discussed in relation to current knowledge of thymus involvement during simian and human immunodeficiency virus infection.

Animals↗
PubMed1996

The aging glomerulus.

Glomerular filtration rate (GFR) decreases with advancing age, particularly in men, although the rate of decrease in GFR is highly variable. Renal vasoconstriction contributes to the decrease in GFR because of increased renal nerve activity, angiotensin II, endothelin, and decreases in vasodilatory prostacyclin levels. Intrarenal nitric oxide activity may be enhanced during aging, perhaps as part of a compensatory response. The atrial natriuretic peptide system is altered during aging, but there is probably no net change in intrarenal hemodynamic actions. Glomerular damage also contributes to age-dependent decreases in GFR. The primary mechanisms are unknown, but they involve a buildup of mesangial extracellular matrix materials. Increases in vasoconstrictor, growth promoting factors, and/or decreases in vasodilator, growth inhibiting factors may contribute. Androgens provide a risk factor. Glomerular hypertension and/or hypertrophy are not primary factors in the development of age-dependent glomerulopathy, but will worsen the process when present.

Aging↗
PubMed1996

MR of cerebral abnormalities concomitant with primary intracerebral hematomas.

PURPOSE: To determine whether arteriolar vessel wall degeneration in primary intracerebral hematomas might be associated with ischemic brain lesions and clinically silent (apparently intracerebral) previous hemorrhages. METHODS: The MR images of 120 consecutive patients (mean age, 60 years; age range, 22 to 84 years) with their first stroke caused by a primary intracerebral hematoma were reviewed retrospectively for coexisting ischemic damage and previous bleeds. RESULTS: Early confluent to confluent white matter hyperintensities, lacunes, or infarction were present in 83 (69%) of the patients, and 39 (33%) had had previous hemorrhages consisting of microbleeds or old hematomas. Extensive white matter hyperintensities and lacunes were most frequent in patients with thalamic primary intracerebral hematomas. There was no relationship between the frequency of old hemorrhages and the location of subsequent primary intracerebral hematomas. CONCLUSION: Clinically silent ischemic lesions and previous hemorrhages are a common finding on MR images of patients with primary intracerebral hematoma. They may therefore serve as evidence of diffuse microangiopathy with a possible increased risk for cerebral hemorrhage.

Adult↗
PubMed1996

[The "buried bumper" syndrome--a rare complication of percutaneous endoscopic gastrostomy].

Since initially being described in 1980, percutaneous endoscopic gastrostomy (PEG) has had a dramatic impact on enteral access and alimentation techniques. Knowledge of the problems makes it possible to lower the complication rate of this method. We report a case of partial penetration of the gastric wall by the internal bolster of the tube. We focus on the prevention, recognition, and management of this PEG-related problem.

Catheters, Indwelling↗
PubMed1996

[Drug dependence among physicians].

Physicians are at higher risk of addiction compared with the general population. Worldwide about 15% of physicians may be addicted to drugs or alcohol. In Germany, accurate epidemiological data are not available. The underlying issues of this occupational risk are the dangers of "role strain", features of a "typical" personality and a high rate of burnout among physicians. Most important is therefore prevention, the need to persuade physicians to "cherish themselves" and reduce work stress as far as possible. An US-program is described regarding identification and therapy of drug users among physicians.

Cross-Sectional Studies↗
PubMed1996

Long-term results of patients with clinical stage C prostate cancer treated by phototherapy and early orchiectomy. A retrospective analysis of 169 cases.

BACKGROUND: To evaluate the value of radiotherapy and immediate hormonal therapy in the treatment of stage C prostate cancer. PATIENTS AND METHOD: From 1977 to 1986, 169 patients with clinically stage C prostate cancer underwent irradiation with curative intent following early orchiectomy. Sixty-four patients had a transurethral resection, 22 patients a prostatectomy and 83 patients had only a biopsy. In 38 patients a grade Ia/b tumor was found, in 78 patients a grade IIa/b tumor and in 43 patients a grade IIIa/b tumor using the German grade of malignancy. Treatment fields included the prostate, the seminal vesicles and the locoregional lymphatics. Until 1979 the dose was 60 Gy for the tumor encompassing isodose and from then on 65 Gy with a single dose of 2 Gy. RESULTS: With a median follow-up of 98 months, the overall survival rate for 8 and 10 years was 51% and 37% and the cause specific survival rate was 84% and 77%, respectively. Thirty-two patients (19%) developed distant metastases. Patients with local tumor control (n = 148) had a significantly better overall survival rate of 45% for 10 years compared to patients with clinical local progression of disease (n = 21) of 22% (p < 0.05). Multivariate analysis showed the grade of malignancy and local control as independent factors for overall survival and cause-specific survival (p < 0.05). Twenty-three patients (14%) had at least one late side effect for the rectum or the bladder, in almost all cases grade I or II. Five patients (3%) showed severe late side effects RTOG grade III (n = 2) or IV (n = 3). One patient had a colostomy, in 2 patients a severe haemorrhagic cystitis was seen. CONCLUSIONS: Radiotherapy with photons and early orchiectomy for patients with stage C prostate cancer achieves high local control rates and a 30% to 40% 10-year survival rate with a low incidence of late side effects. The value of the radiotherapy of the locoregional lymphatics remains controversial.

Adult↗
PubMed1996

Effect of aromatic amino acid substitutions in the 3-position of cyclic beta-casomorphin analogues on mu-opioid agonist/delta-opioid antagonist properties.

The beta-casomorphin-5 analog H-Tyr-c[-D-Orn-2-Nal-D-Pro-Gly-] (2-Nal = 2-naphthylalanine) was the first reported cyclic opioid peptide with mixed mu agonist/delta antagonist properties [R. Schmidt et al. (1994) J. Med. Chem. 37, 1136-1144]. The 2-Nal3 residue in this peptide was replaced with benzothienylalanine (Bta) (3), His(Bzl) (4), Tyr(Bzl) (5), 4'-benzoylphenylalanine (Bpa) (6), 4'-benzylphenylalanine (Bzp) (7), thyronine (Thy) (8), thyroxine (Thx) (9), 4'-biphenylalanine (Bip) (10), 4'-biphenylglycine (Bpg) (12) and 3,3-diphenylalanine (Dip) (14), and the in vitro opioid activity profiles of the resulting compounds were determined in mu and delta receptor-representative binding assays and bioassays. Analogues 3, 12 and 14 were full agonists in the mu receptor-representative guinea-pig ileum (GPI) assay and also were agonists in the delta receptor-representative mouse vas deferens (MVD) assay. The agonist effects of the latter compounds in the MVD assay were antagonized by the highly selective delta antagonist H-Tyr-Tic-Phe-Phe-OH (TIPP), indicating that they were triggered by delta receptor activation. The Bzp3- and Bip3- containing peptides 7 and 10 turned out to be mu antagonists against the mu selective agonist H-Tyr-D-Ala-Phe-Phe-NH2 in the GPI assay. The other analogues were weak partial mu agonists which displayed remarkably decreased mu receptor affinity as compared to parent peptide 1. Compounds 4-10 were found to be delta antagonists in the MVD assay. Analogues 4 and 9 exhibited delta antagonist potency similar to that of parent peptide 1, while compounds 5-8 and 10 showed 3-12-fold higher delta antagonist potency against DPDPE and deltorphin I and, in most cases, increased delta receptor affinity. These results indicate that the delta receptor tolerates bulky aromatic side chains in the 3-position of cyclic beta-casomorphin analogs with either delta agonist or delta antagonist properties. However, these compounds displayed drastically reduced mu receptor affinity in nearly all cases.

Amino Acids↗
PubMed1996

[Magnetic resonance tomography of the brain in amyotrophic lateral sclerosis].

We compared the magnetic resonance imaging results of 15 patients suffering from amyotrophic lateral sclerosis (ALS) with those of 30 age-matched controls to search for disease specific cerebral abnormalities. Symmetric hyperintensity along the corticospinal tract on the proton density spin-echo sequence was exclusively found in 4 ALS patients. It was associated with younger age, rapid disease progression and evolution of symptoms starting in the lower extremities. Signal loss of the motor cortex on T2-weighted images was frequently seen in ALS (9 patients) but was also observed in controls. As MRI is capable of providing direct evidence for ALS besides excluding other diseases it should be included in the diagnostic work-up of these patients.

Adult↗
PubMed1995

Physical map and organization of Arabidopsis thaliana chromosome 4.

A physical map of Arabidopsis thaliana chromosome 4 was constructed in yeast artificial chromosome clones and used to analyze the organization of the chromosome. Mapping of the nucleolar organizing region and the centromere integrated the physical and cytogenetic maps. Detailed comparison of physical with genetic distances showed that the frequency of recombination varied substantially, with relative hot and cold spots occurring along the whole chromosome. Eight repeated DNA sequence families were found in a complex arrangement across the centromeric region and nowhere else on the chromosome.

Arabidopsis↗
PubMed1995

Oxygen sensors based on luminescence quenching: interactions of pyrene with the polymer supports.

Oxygen quenching of pyrene has been studied in a diverse series of polymers. Most measurements were made using homo- or copolymers containing a poly(dimethylsiloxane) region. Systematic variations in the polymer properties have been made in order to delineate the structural features important for satisfactory use as supports for oxygen sensors. In particular, quenching behavior was examined as a function of the type and amount of copolymer cross-linkers; these were added to produce domains of different polarity and rigidity that would segregate the sensor molecule. A domain model (Xu, W.; et al. Anal. Chem. 1994, 66, 4133-4141) was used to explain the variations in oxygen-quenching properties as a function of additives and cross-linkers. The relative affinity of the different domains for the pyrene and the efficacy of the domains for oxygen quenching controls the overall behavior of the sensing response.

Electrodes↗