Biomedical subjects

R Kuhn

Publications and source records attributed to R Kuhn.

At least 109 records · Page 6Linked to original sources

PubMed1997

Sterilization of women with Eisenmenger syndrome: report of 4 cases.

Maternal mortality exceeding 50% and perinatal loss of more than 45% contraindicate pregnancy in females with Eisenmenger syndrome. Sterilization is the contraceptive method of choice. Any operation carries a very significant risk in persons with Eisenmenger syndrome; the anaesthetic mortality has been reported to be 19%. This paper details the successful sterilization of 4 women with Eisenmenger syndrome at our institution.

Adolescent↗

PubMed1997

Saline infusion sonohysterosalpingography, an underutilized technique.

Saline infusion sonohysterography (SIS) is an important gynaecological diagnostic tool which is little used in Australia. We herein report the findings in 60 women referred for SIS, the procedure being uneventfully performed in 55. Forty-nine of the 60 referrals were for investigation of abnormal uterine bleeding. The technique described allows examination of the uterine cavity and the Fallopian tubes. In 26 of the patients information was obtained which improved or altered the diagnosis made on B mode and colour Doppler ultrasound. Unlike hysteroscopy, SIS is always performed as an outpatient procedure, appropriate disinfection procedures are relatively simple to implement (1), and vasovagal reactions are rare. Hysteroscopy was avoided in 11 patients, there were other benefits in 4 patients, and in only 1 of 16 patients did the hysteroscopy findings differ with SIS. If diagnostic pitfalls are avoided by careful attention to detail, SIS offers a powerful new gynaecological investigative tool in the investigation of bleeding disorders (including menorrhagia, intermenstrual and postmenopausal bleeding), uncertain endometrial findings on vaginal ultrasound, infertility, and in the investigation of congenital and acquired uterine abnormalities.

Adult↗

PubMed1997

Taenia solium cysticercosis: host-parasite interactions and the immune response.

Taenia parasites have developed elaborate mechanisms of interacting with their intermediate hosts. The oncospheres which invade the intermediate host are susceptible to antibody and complement. However, by the time the host has generated an antibody response, the parasites have begun to transform to the more resistant metacestode. The metacestodes have elaborate means of evading complement-mediated destruction, including paramyosin which inhibits C1q, taeniaestatin which inhibits both classical and alternate pathways, and sulfated polysaccharides which activate complement away from the parasite. Similarly, antibody does not seem to be able to kill the mature metacestode. In fact, the parasites may even stimulate the host to produce antibody, which could be bound via Fc receptors and used as a source of protein. Finally, taeniaestatin and other poorly defined factors may interfere with lymphocyte proliferation and macrophage function, thus paralyzing the cellular immune response. Since the symptoms of NCC are typically associated with a brisk inflammatory response, we hypothesize that disease is primarily caused by injured or dying parasites. This hypothesis raises important questions in assessing the role of chemotherapy in the management of NCC, as well as in the evaluation of clinical trials, most of which were uncontrolled.

Adult↗

PubMed1996

[Ruptured pseudoaneurysm of the splenic artery. A complication of chronic pancreatitis].

HISTORY AND FINDINGS: A pale looking 33-year-old man with a history of perforated gastric ulcer and pancreatitis with surgically drained pseudocyst was admitted because of painless anal bleeding. Heart rate was 100/min, blood pressure 90/60 mm Hg. INVESTIGATIONS: Haemoglobin concentration (6.3 g/dl) and RBC count (2.4 mill./microliters) indicated anaemia due to bleeding. Sonography and computed tomography demonstrated chronic calcifying pancreatitis and thrombosis of splenic and mesenteric veins. There were grade 1 oesophageal varices on endoscopy. The source of bleeding was found by coloscopy to be a submucous pulsating tumour in the region of the left flexure, which on angiography was an aneurysm of the splenic artery. TREATMENT AND COURSE: The pseudoaneurysm of the splenic artery, which had perforated into the colon, was resected together with a partial pancreas excision and splenectomy. There were no complications and the patient was discharged symptom-free after 15 days, and there had been no further bleeding 6 months later. CONCLUSION: Pseudoaneurysm of a visceral artery is a rare, but life-threatening, complication of pancreatitis. Treatment options are operation and/or interventional catheter embolisation.

Adult↗

PubMed1996

Cellular localisation of metabotropic glutamate receptors in the mammalian optic nerve: a mechanism for axon-glia communication.

It has been proposed that neurotransmitter signalling can occur between axons and glia in the mammalian optic nerve in the absence of synaptic specialisations, and that this may be glutamate mediated. Here, the cellular distribution of five metabotropic glutamate receptors (mGluR's 1a, 1b, 1c, 2/3 and 5) have been assessed in the rat optic pathway using specific antibodies. Positive immunoreactivity is found for mGluR2/3 and 5. Both are found in axons, although only mGluR5 is present in the majority of these. Strong immunoreactivity for mGluR2/3 is found in cells in the optic pathway and thalamus. The cellular morphology and distribution is consistent with their being astrocytes. Examination of brain sections stained for mGluR2/3 is consistent with this notion, with many cells having end-feet processes terminating on blood vessels or the pial surface. The axonal immunoreactivity could represent the presence of these receptors on axons, but it is more probable that the receptor protein synthesised in the ganglion cell soma is being transported to the cell terminal in sufficient concentration to be revealed by immunohistochemistry. The reason for the axon-astrocyte signalling is unclear, and may be associated with metabolic coupling. In development, communication between axons and glia mediates a range of functions including pathway selection and myelination. It is probable that in the adult this form of signalling underpins a range of functions that have yet to be described.

Animals↗

PubMed1996

Immunohistochemical distribution of metabotropic glutamate receptor subtypes mGluR1b, mGluR2/3, mGluR4a and mGluR5 in human hippocampus.

The metabotropic glutamate receptors (mGluRs) can be classified into three families based on amino acid sequence homology, signal transduction mechanisms and pharmacological properties. Generally, class I mGluRs mediate an excitation of neurons while activation of class II and III mGluRs results in a depression of synaptic transmission. In this study we have analyzed the expression pattern of mGluRs in human hippocampus using a panel of polyclonal antibodies specific for mGluR1b, mGluR2/3, mGluR4a, and mGluR5. Immunoreactivity for mGluR1b and mGluR5, i.e., the subtypes representing class I mGluRs, was found in all hippocampal neurons. The mGluR1b antiserum stained perikarya and proximal dendrites, whereas immunoreactivity for mGluR5 was also detectable in the distal dendritic compartments. Immunoreactivity for mGluR2/3, members of class II mGluRs, was present in all principle neurons in the dentate gyrus as well as in the CA4, CA3 and CA2 regions. Pyramidal cells of the CA1 region exhibited only weak labeling for mGluR2/3. Glial cells were also mGluR2/3-immunoreactive. The reaction obtained with an antiserum directed against mGluR4a, a member of class III mGluRs, was confined to the mossy fiber projection field in CA3 stratum lucidum. These data demonstrate differential expression of mGluR variants in the human hippocampus and may provide an important basis for future studies of mGluRs under various neuropathological conditions such as temporal lobe epilepsy, ischemia and neurodegenerative disorders.

Aged↗

PubMed1996

Activation of group III metabotropic glutamate receptors is neuroprotective in cortical cultures.

(RS)-alpha-Methyl-4-phosphonophenylglycine (MPPG) and (S)-alpha-methyl-3-carboxyphenylalanine (M3CPA), two novel preferential antagonists of group III metabotropic glutamate (mGlu) receptors, antagonized the neuroprotective activity of L-2-amino-4-phosphono-butanoate (L-AP4) or L-serine-O-phosphate in mice cultured cortical cells exposed to a toxic pulse of N-methyl-D-aspartate. In contrast, MPPG did not influence the neuroprotective activity of the selective group II mGlu receptor agonist, (2S,1'R,2'R,3'R)-2-(2,3-dicarboxy-cyclopropyl) glycine (DCG-IV). These results indicate that activation of group III mGu receptors exerts neuroprotective activity against excitotoxic neuronal death. At least one of the two major group III mGlu receptor subtypes, i.e. mGlu4 receptor, is expressed by cultured cortical neurons, as shown by immunocytochemical analysis with specific polyclonal antibodies.

Alanine↗

PubMed1996

Compartmental localization of a metabotropic glutamate receptor (mGluR7): two different active sites at a retinal synapse.

The distribution of the metabotropic glutamate receptor 7 (mGluR7) was studied in the rat retina using a specific antiserum. Punctate immunofluorescence that corresponded to synaptic localization was present exclusively in the inner plexiform layer. Double-labeling experiments suggested that mGluR7 is expressed at the synaptic terminals of certain cone bipolar cells. Electron microscopy showed that mGluR7 was present both presynaptically, as an autoreceptor in cone bipolar cell ribbon synapses, and postsynaptically in amacrine cells. There are usually two postsynaptic processes at a bipolar cell ribbon synapse; however, the presynaptic aggregation of mGluR7 was restricted to one half of the active zone and therefore was opposed to only one of the postsynaptic processes. This selective localization of mGluR7 could differentially regulate the glutamate release from the ribbon synapse, thus leading to a differential activation of the postsynaptic neurons.

Amino Acid Sequence↗

PubMed1996

Racemization of amino acids in solid-phase peptide synthesis investigated by capillary electrophoresis.

The rate of racemization during solid-phase peptide synthesis was studied using capillary electrophoresis and 18-crown-6 tetracarboxylic acid as chiral selector. For this purpose, the tripeptide D-Tyr-L-Lys-L-Trp as a model compound was synthesized by solid-phase peptide synthesis. A separation method based on capillary electrophoresis was developed which allowed all eight optical isomers of the tripeptide to be separated in a single run. The separation method was validated and was found to be well suited for purity analysis, with a limit of detection of 0.05% of the major compound. The method was revealed to be highly sensitive even to small variations in the buffer pH. Capillary electrophoresis was also employed to prove the enantiomeric purity of the Fmoc-protected amino acids used for peptide synthesis. A separation method based on micellar electrokinetic chromatography and gamma-cyclodextrin was developed for this purpose. The formation of optical isomers during peptide synthesis was investigated in the final product without hydrolyzing the tripeptide. This strategy allowed the rate of racemization to be determined by activation of amino acids in coupling cycles and cleavage of the peptides from the resin and from side-chain protecting groups. The formation of stereoisomers could be verified and was 0.4% or less per synthesis cycle. The experimental data agreed well with theoretical considerations, showing that racemization takes place mainly at the carboxy-activated amino acid during coupling.

Amino Acid Sequence↗

PubMed1996

Leishmania promastigotes selectively inhibit interleukin 12 induction in bone marrow-derived macrophages from susceptible and resistant mice.

Leishmania major promastigotes were found to avoid activation of mouse bone marrow-derived macrophages (BMM0) in vitro for production of cytokines that are typically induced during infection with other intracellular pathogens. Coexposure of BMM0 to the parasite and other microbial stimuli resulted in complete inhibition of interleukin (IL) 12 (p40) mRNA induction and IL-12 release. In contrast, mRNA and protein levels for IL-1(alpha), IL-1(beta), tumor necrosis factor (TNF) alpha, and inducible NO synthase (iNOS) were only partially reduced, and signals for IL-10 and monocyte chemoattractant protein (MCP-1/JE) were enhanced. The parasite could provide a detectable trigger for TNF-alpha and iNOS in BMM0 primed with interferon (IFN) gamma, but still failed to induce IL-12. Thus IL-12 induction is selectively impaired after infection, whereas activation pathways for other monokine responses remain relatively intact. Selective and complete inhibition of IL-12(p40) induction was observed using BMM0 from either genetically susceptible or resistant mouse strains, as well as IL-10 knockout mice, and was obtained using promastigotes from cutaneous, visceral, and lipophosphoglycan-deficient strains of Leishmania. The impaired production of the major physiological inducer of IFN-gamma is suggested to underlie the relatively prolonged interval of parasite intracellular survival and replication that is typically associate with leishmanial infections, including those producing self-limiting disease.

Animals↗

PubMed1996

The second intracellular loop of metabotropic glutamate receptor 1 cooperates with the other intracellular domains to control coupling to G-proteins.

Metabotropic glutamate receptors (mGluR) share no sequence homology with any other G-protein-coupled receptors (GPCRs). The characterization of their G-protein coupling domains will therefore help define the general rules for receptor-G-protein interaction. To this end, the intracellular domains of mGluR3 and mGluR1, receptors coupled negatively to adenylyl cyclase and positively to phospholipase C, respectively, were systematically exchanged. The ability of these chimeric receptors to induce Ca2+ signals were examined in Xenopus oocytes and HER 293 cells. The chimeric receptors that still possessed the second intracellular loop (i2) of these proteins were targeted correctly to the plasma membrane. Consistent Ca2+ signals could be recorded only with chimeric mGluR3 receptors that contains i2 and at least one other intracellular domains of mGluR3 have to be replaced by their mGluR1 equivalent to produce optimal coupling to G protein. These observations indicate that i2 of mGluR1 is a critical element in determining the transduction mechanism of this receptor. These results suggest that i2 of mGluRs may play a role similar to i3 of most other GPCRs in the specificity of coupling to the G-proteins. Moreover, as in many other GPCRs, our data revealed cooperation between the different mGluR intracellular domains to control efficient coupling to G-proteins.

Amino Acid Sequence↗

PubMed1996

Localization of two metabotropic glutamate receptor genes, GRM3 and GRM8, to human chromosome 7q.

Metabotropic glutamate receptors (GRMs) are neurotransmitter receptors that respond to glutamate stimulations by activating GTP-binding proteins and modulating second-messenger cascades. Eight related GRMs have been identified to date. In this study, we have mapped GRM3 and GRM8 to human chromosome 7q21.1-q21.2 and 7q31.3-q32.1, respectively, using somatic cell hybrid and fluorescence in situ hybridization analysis. A yeast artificial chromosome contig was constructed surrounding the genes, allowing their location to be integrated into the genetic and physical map of chromosome 7.

Animals↗

PubMed1996

Profiling of oligosaccharide-mediated microheterogeneity of a monoclonal antibody by capillary electrophoresis.

Based on complex formation of borate with carbohydrates in alkaline solutions, the oligosaccharide microheterogeneity of a monoclonal antibody was studied using capillary zone electrophoresis. In borate buffers characteristic separation patterns were found that could be attributed to the same antibody by their UV spectra, while in a phosphate buffer, under otherwise the same conditions, only a single peak was observed. N- and O-glycans were chemically hydrolyzed by trifluoromethane sulfonic acid, resulting in a completely deglycosylated protein; alternatively, N-glycans were enzymatically cleaved by incubation with peptide N-glycosidase F (PNGase F). In both approaches a changed antibody pattern was detected, indicating that the separation is due to carbohydrate microheterogeneity of the protein. Deglycosylation of the antibody by treatment with PNGase F was investigated by matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS). A shift to lower molecular masses of approximately 1500 Da for the enzymatically treated protein, compared with the intact glycoprotein, was found. The separation method was validated for linearity and reproducibility of migration time and peak area and optimized in terms of buffer pH, capillary temperature and borate concentration. This technique is sensitive to analyze batch-to-batch consistency in production and to test the stability of galenical formulations. After antibody storage in glass vials for 3 months at 37 degrees C, the separation profile changed distinctly due to degradation at the carbohydrate or sialic acid moiety of the antibody, as indicated by MALDI-TOF-MS.

Antibodies, Monoclonal↗

PubMed1996

The C-terminal domain of the mGluR1 metabotropic glutamate receptor affects sensitivity to agonists.

The metabotropic glutamate receptor (mGluR) subtype 1 exists as at least three variants (-1a, -1b, and -1c) generated by alternative splicing at the C-terminal domain. Fluorometric Ca2+ measurements were used to compare the concentration dependency of agonist-induced rises in intracellular free Ca2+ concentration ([Ca2+]i) in human embryonic HEK 293 cells transiently expressing rat mGluR1a, mGluR1b, or mGluR1c. The rank order of agonist potencies was quisqualate >> (2S,1'S)-2-(carboxycyclopropyl)glycine (L-CCG-I) > (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid [(1S,3R)-ACPD] and did not differ among the splice variants. However, agonists were consistently more potent at mGluR1a than at mGluR1c and mGluR1b. In the same system, we characterized the agonist pharmacology of two chimeric rat mGluR3/1 receptors where the first and/or the second intracellular loop(s) and the C-terminal domain were exchanged with the corresponding mGluR1a or mGluR1c sequences and that were previously shown to mediate elevations in [Ca2+]i in response to agonists. The potency of agonists was higher at the chimera having the C-terminus of mGluR1a as compared with those having the mGluR1c C-terminus. Both chimeric mGluR3/1 receptors had the same rank order of agonist potencies: L-CCG-I >> (1S,3R)-ACPD approximately quisqualate. These data support the hypothesis that the C-terminal domain of mGluRs plays a role in determining the potency of agonists for inducing mGluR-mediated functional responses.

Amino Acids, Dicarboxylic↗

PubMed1996

Group II and group III metabotropic glutamate receptors in the rat retina: distributions and developmental expression patterns.

We have studied the distributions of group II metabotropic glutamate receptors, mGluR2 and mGluR3, and a group III metabotropic glutamate receptor, mGluR4, in the adult rat retina and during postnatal development using receptor specific anti-peptide antisera. Of the three receptors examined, mGluR3 was not expressed in the retina. MGluR2 showed a distinct stratification pattern in the inner plexiform layer (IPL). Double-labelling immunocytochemistry revealed that mGluR2 was localized in the processes of cholinergic amacrine cells. MGluR4 was found throughout the entire IPL. At the subcellular level, both mGluR2 and mGluR4 were found to be localized exclusively in processes postsynaptic to bipolar cell synapses in the IPL. During postnatal development, labelling for mGluR2 was detected at around postnatal day five. MGluR4 was already present at postnatal day one, prior to the establishment of synaptic connections in the IPL. The differential expression patterns of individual metabotropic glutamate receptors in the adult and developing rat retina suggest distinct roles for these receptors in retinal synaptic circuitry.

Amino Acid Sequence↗

PubMed1996

Immortalized hypothalamic neurons express metabotropic glutamate receptors positively coupled to cyclic AMP formation.

We have characterized the expression pattern and pharmacological profile of activation of metabotropic glutamate receptors (mGluRs) in immortalized, gonadotropin releasing hormone (GnRH)-secreting GT1-7 cells, which represent a homogeneous cellular population of hypothalamic origin. These cells are known to respond to the mGluR agonist (1S,3R)-cyclopentanedicarboxylic acid (1S,3R-ACPD) with increased GnRH release. To establish which specific mGluR subtypes are expressed by GT1-7 cells, we used polyclonal antibodies raised against non-conserved regions of the carboxy-terminal domains of individual subtypes. The selectivity of these antibodies was tested in HEK 293 cells transiently transfected with each mGluR subtype. GT1-7 cells stained positively for the subtypes mGluR1a, -1b and -5 (belonging to group I mGluR2/3 (group II) and mGluR7 (group III). Agonists of group I mGluRs, including 1S,3R-ACPD, activated phosphoinositide hydrolysis in GT1-7 cells. This effect, however, was manifested only when cell density was low, and it disappeared when cells reached confluence. Stimulation of phosphoinositide hydrolysis could not therefore have been related to hormone secretion because 1S,3R-ACPD effectively released GnRH in confluent cultures. We then focused on group II and III mGluRs, which in transfected cells are negatively linked to adenylate cyclase activity. Unexpectedly, however, agonist which preferentially activate group II and III mGluRs increased both basal and forskolin-stimulated cAMP accumulation in GT1-7 cells. Stimulation of cAMP accumulation by mGluR agonists was not prevented by enzymatic depletion of endogenous adenosine, but was obliterated when cells were incubated with agonists of receptors positively coupled to adenylate cyclase, such as beta-adrenergic and prostaglandin E2 receptors. These results suggest that GT1-7 cells express a novel mGluR subtype positively coupled to adenylate cyclase, which shares the same transduction pathway of other classical receptors coupled with a Gs-type of GTP-binding protein.

Animals↗

PubMed1996

Comparison of an enzyme-linked immunosorbent assay vs radioimmunoassay for measuring serum progesterone at low levels.

Reports have suggested a correlation between low serum progesterone (P) levels prior to human chorionic gonadotropin (hCG) administration and increased pregnancy rates in patients undergoing in vitro fertilization (IVF) patients. We have published two opposite conclusions, dependent upon the methodology used. Pregnancy rates were higher when P by radioimmunoassay (RIA) was < 1 ng/mL, but no increase in pregnancy rates were found when P was measured by the same company's non-isotopic assay. To test if the lack of correlation was attributable to the P method, sera from IVF patients were assayed by two methods, RIA and enzyme linked immunosorbent assay (ELISA). There was 81.8% agreement between methods. Further studies are needed to determine the importance of low P; however, if non-isotopic methods are used, the IVF center should carefully determine the accuracy of their assay in the low range.

Chorionic Gonadotropin↗

PubMed1996

Relationship of early follicular phase sera follicle stimulating hormone and luteinizing hormone levels as measured by a radioimmunoassay and an enzyme-linked immunosorbent assay to number of oocytes retrieved.

A study was performed to see if the level of serum follicle stimulating hormone (FSH) or luteinizing hormone (LH) obtained in the early follicular phase could predict the number of oocytes retrieved following in vitro fertilization (IVF). For each patient the sera FSH and LH were measured by both an enzyme-linked immunosorbent assay (ELISA) and a radioimmunoassay (RIA) method. With the ELISA method when early follicular phase serum FSH was < or = to the group median (9.0 mIU/mL) 16.5 oocytes were retrieved vs 6.7 when FSH was greater than the median. Comparable values using the median of the RIA assay were 17.5 vs 8.1 oocytes. Similar analysis for serum LH failed to show any relationship between baseline LH and the number of oocytes retrieved. This study thus demonstrates that at least one non-isotopic method is equal to a specific RIA method in distinguishing good from average or poor responders.

Adult↗