Search PubMed⌕ Search

Biomedical subjects

P Hammer

Publications and source records attributed to P Hammer.

At least 19 recordsLinked to original sources
PubMed2002

HLA-B*3531, a hybrid of B35 and B61, implications for diagnostic approaches to alleles with complex ancestral compositions.

The serological characterization of allelic variants that have been generated by large-scale interallelic recombination events indicates which residues may be involved in the formation of epitopes crucial for serological recognition. The allelic product of HLA-B*3531 is composed of B35 in its alpha1 domain and of B61(40) in its alpha2 domain. Both specificities are only weakly detectable with available sera. Allelic products with 'mixed' serology also represent a challenge to DNA-based HLA typing methods, as only the sequence motif of one ancestral allele may be recognized. In this case the hidden specificity would not be considered in the matching process and might not be recognized as an antigen 'unacceptable' to the recipient.

Alleles↗
PubMed2002

Immunolocalization of cholecystokinin-2 receptors in rat gastric mucosa.

BACKGROUND: Gastrin exerts trophic effects on the gastric mucosa by mechanisms not yet completely elucidated. Our aim was to localize the cholecystokinin-2 (CCK2) receptor in epithelial cells of foetal and adult rat stomachs in order to determine the cell types that are directly affected by gastrin. METHODS: Gastric tissue was subjected to indirect double immunofluorescence staining with antiserum against the C-terminal decapeptide of the CCK2 receptor and antibodies against 5' bromo-2-deoxyuridine, which had been injected into the rats I h before they were killed, the acid pump H,K-ATPase, the membrane-cytoskeletal linker ezrin, pepsin/pepsinogen or histidine decarboxylase. RESULTS: Undifferentiated foetal gastric epithelial cells expressed CCK2 receptors, whereas stem cells of adult gastric glands did not exhibit immunoreactivity. However, other epithelial cells in the progenitor zone of adult gastric glands did express CCK2 receptors. Some of these cells were faintly stained for H,K-ATPase; pepsin/pepsinogen was also detected in this region. Parietal cells in the isthmus/pit region of the glands contained ezrin, and some showed weak immunoreactivity for the CCK2 receptor. As expected, enterochromaffin-like cells also expressed CCK2 receptors. CONCLUSION: Our findings are consistent with the hypothesis that a CCK2 receptor mediates direct effects of gastrin on gastric epithelial cells during both stomach organogenesis and adult life.

Animals↗
PubMed1999

The class I metabotropic glutamate receptor antagonist, AIDA, improves short-term and impairs long-term memory in a spatial task for rats.

Effects of the class I selective metabotropic glutamate receptor antagonist, 1-aminoindan-1,5-dicarboxylic acid (AIDA), on spatial procedural learning and episodic short-term memory of rats were investigated in an appetitively reinforced 3-choice delayed match-to-position task. First, an acute intraperitoneal injection of AIDA (2 mg/kg) was given 20 min before a single training session of 20 trials using repeated reward position in one alcove out of three. AIDA caused facilitated short-term acquisition within such a session compared to saline treated controls. Secondly, injections were given before each of ten sessions (48 h intervals) also using constant reward position. The results showed AIDA induced inhibition of procedural between-session acquisition. Finally, the use of reward positions in a non-repetitive but trial-specific version of the 3-choice test revealed a facilitating effect of AIDA on episodic short-term memory.

Animals↗
PubMed1999

[Which zoonosis is it?].

Starting from the definition for zoonoses according to EU directive 92/117 EEC a brief and mainly tabulated summary is given on the occurrence of zoonoses worldwide and in Germany and related factors.

Animals↗
PubMed1997

Interpreting open- and closed-loop transfer relations between cardiorespiratory parameters: lessons learned from a computer model of beat-to-beat cardiovascular regulation.

A computer model of cardiovascular control has been developed based on the response characteristics of cardiovascular control components derived from experiments in animals and humans. Results from the model were compared to those obtained experimentally in humans, and the similarities and differences were used to identify both the strengths and inadequacies of the concepts used to form the model. Findings were confirmatory of some concepts but contrary to some which are firmly held in the literature, indicating that understanding the complexity of cardiovascular control probably requires a combination of experiments and computer models which integrate multiple systems and allow for determination of sufficiency and necessity.

Computer Simulation↗
PubMed1996

Bacillus sporothermodurans, a new species producing highly heat-resistant endospores.

Bacteria that differentiate into highly heat-resistant endospores (HHRS strains) may survive ultrahigh-temperature treatment of milk and germinate in the final product. They do not noticeably spoil the milk and are nonpathogenic. The complete (>96%) 16S rRNA genes from three HHRS strains were identical, and phylogenetic analysis placed them alongside Bacillus firmus in the B. megaterium group of the genus Bacillus. Moreover, the approximately 550 nucleotides between regions U2 and U5 were invariant for seven HHRS strains. However, three cloned 16S rRNA genes from one HHRS strain, M215, showed marked size and sequence variations within the V1 and V2 regions. DNA reassociation assays confirmed the distinction between a reference HHRS strain and closely related members of the B. megaterium group, notably, B. firmus (30%), B. benzoevorans (28%), and B. circulans (20%). Ribotyping and pyrolysis mass spectrometry both indicated that the HHRS strains belong to a homogeneous, species-ranked taxon, an exception being strain TP1248, which is slightly atypical. The HHRS strains are unusual in that they grow poorly, if at all, on nutrient agar; good growth is obtained on brain heart infusion agar. On subculture, most HHRS strains form long, filamentous rods which stain unevenly in the Gram reaction. They are strictly aerobic and do not produce acid from sugars. We propose the name Bacillus sporothermodurans for these bacteria, which are phenotypically and phylogenetically distinct from other Bacillus species. The type strain is M215 (= DSMZ 10599).

Animals↗
PubMed1991

'False-negative' and 'false-positive' prenatal cytogenetic results due to 'true' mosaicism.

A 37-year-old gravida was referred for CVS because of advanced maternal age. A trisomy 21 was present in all cells after short-term incubation (direct processing (DP)) and long-term culture. According to our policy, a retap was offered for confirmation of the result during the legally required 3-day waiting period between communication of the result and termination of pregnancy. Unexpectedly all cells after DP showed a normal male chromosome complement. Further investigations revealed mosaicism in trophoblast tissue and a normal karyotype in amniotic fluid cells and fetal blood (50 mitoses each). The parents elected to continue the pregnancy after extensive ultrasound examinations did not show suspicious findings. After the birth of a healthy child, cell cultures from ten different placental sites confirmed mosaicism. Four out of 100 mitoses from a lymphocyte culture showed an additional chromosome 21. The child had no dysmorphic features and the development was normal at the age of 10 weeks. This case demonstrates the restricted validity of prenatal cytogenetic analysis in the presence of true fetal mosaicism. It also stresses the benefit of our policy to offer a retap in cases with abnormal cytogenetic results prior to termination of pregnancy which is considered unnecessary by many cytogeneticists.

Adult↗
PubMed1991

Mosaicism and accuracy of prenatal cytogenetic diagnoses after chorionic villus sampling and placental biopsies.

Discrepant chromosome findings in placenta and fetus (false negative and false positive) after chorionic villus sampling (CVS) are mainly due to confined mosaicism. Non-mosaic normal or abnormal chromosome counts after direct preparation and culture nearly always correctly reflect the fetal chromosome constitution. False-negative results have almost exclusively been restricted to cytotrophoblast cells not representing a fetal chromosome abnormality. Diagnosis of placental mosaicism definitely requires an adequate follow-up by amniocentesis, fetal blood sampling, or sonography before a pregnancy is terminated. When direct preparations and cultured cells are used for cytogenetic diagnoses and placental mosaicism is not taken as proof for a chromosomal abnormality in the fetus, CVS is an accurate diagnostic tool.

Amniocentesis↗
PubMed1991

[Prenatal diagnosis with chorionic villi and placenta puncture biopsy in the 1st to 3d trimester of pregnancy: diagnostic value of chromosome studies].

Chorionic villus sampling and placental biopsies became established diagnostic alternatives to amniocentesis worldwide during the 80's. Safety and accuracy are the most important criteria for the evaluation of these newer techniques as compared to amniocentesis. We report on our experience with more than 3400 chromosome analyses between 1985 and 1990 from first to third trimester of pregnancy in a single centre. Most obvious is the higher frequency of mosaicism, which is often, but not always confined to the placenta. Mosaicism accounts for the overwhelming majority of all discrepant (so-called false negative or false positive) cytogenetic findings. The most important prerequisites for diagnostic accuracy of chromosome analyses are meticulous separation of villi immediately after the sampling procedure as well as simultaneous use of direct preparation and cell culture. If mosaicism is not taken as sound evidence for foetal aneuploidy, the accuracy of cytogenetic diagnoses after chorionic villus sampling and placental biopsies is in the same range as the one after amniocentesis.

Adult↗
PubMed1982

[Thrombocyte substitution in acute leukemia. Effect of histocompatibility on the clinical efficacy].

Thrombocyte substitution is an essential prerequisite for intensive cytoreductive therapy in acute leukemia. Evaluating 228 thrombocyte transfusions in 17 patients shows that the clinical effectiveness of thrombocyte concentrates can be increased by making the coordination of HLA antigens of donor and receiver as good as possible. When measured in the corrected increment (CI) 24 hours after transfusion, the effectiveness of A3/B1 match preparations (CI = 7.0 +/- 1.6) is significantly higher than that of random preparations (CI = 3.0 +/- 0.5). With the presence of HLA antibodies an effective substitution (CI24 greater than or equal to 4.5) can only be achieved by A3/B1 match thrombocytes. This can only be realized by applying the fourfold thrombapheresis of single donors.

Adolescent↗
PubMedDate not supplied

The effect of naturally occurring cellular constituents on phase separation and opacification in calf lens nuclear homogenates.

We have measured the change in the phase separation temperature, Tc, in calf nuclear homogenate produced by a variety of naturally occurring cellular constituents. For all of the compounds studied, increasing concentrations of test compound were found to lower Tc. Phosphorylated nucleotides had the greatest effect, lowering Tc by 165-305 degrees/mole of test compound. Reduced and oxidized glutathione reduced Tc by 69 and 100 degrees C/mole, respectively. Smaller effects were observed for amino and ascorbic acids and sugars. The pH of the homogenate was also found to affect Tc. In the normal lens, the concentration of each of these constituents is small. Therefore, for each individual component, the cataract associated decrease in concentration is insufficient to produce the large increase in Tc that has been observed during cataractogenesis in some model systems. However, the superposition of the effects of changes in many cellular constituents (including pH and hydration) could possible produce a change in Tc more consistent with the experimentally observed one. In support of this, we have found that combinations of test compound have an additive effect on the Tc of the nuclear homogenate.

Amino Acids↗