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Biomedical subjects

D Palm

Publications and source records attributed to D Palm.

At least 19 recordsLinked to original sources
PubMed1995

Choroid plexus electrolytes and ultrastructure following transient forebrain ischemia.

A temporal profile of lateral and fourth ventricle rat choroid plexus (LVCP and 4VCP, respectively) tissue injury and recovery was determined using alterations in K, Na, and H2O content and ultrastructure after 10 min of transient forebrain ischemia (TFI). At 0.5 h postischemia the LVCP displayed a maximum reduction in K content by 32% and a significant increase in Na content by 85% and H2O content by 22%. LVCP tissue K, Na, and H2O content returned to sham values by 24 h postischemia. Ultrastructural changes appeared more severe between 0.5 and 12 h postischemia, whereas by 24 h, normal ultrastructure was restored. Elevations in 4VCP tissue Na (P < 0.05) and H2O content, which were less than those in LVCP, gradually reached a maximum by 24 h compared with sham. No change in 4VCP tissue ultrastructure was observed. These results indicate that the LVCP tissue is more vulnerable than 4VCP in the bilateral carotid artery occlusion model but that it recovers in a timely manner after TFI. Furthermore, the ability of the LVCP tissue to rapidly recover suggests its functional importance in helping to restore brain homeostasis.

Animals↗
PubMed1995

Beta 1-adrenoceptor subtype selective antagonism of esmolol and its major metabolite in vitro and in man. Investigations using tricresylphosphate as red blood cell carboxylesterase inhibitor.

Esmolol (CAS 103598-03-4, ASL-8052, Brevibloc) is an ultrashort acting beta-adrenoceptor antagonist which is rapidly hydrolyzed by a red blood cell esterase. In order to investigate the affinity profile of esmolol and its acid metabolite at beta-adrenoceptor subtypes in plasma and in whole blood in radioligand binding studies a potent esterase inhibitor was needed to prevent hydrolysis of esmolol and--in contrast to sodium fluoride--without influencing binding of the drugs at the receptor site. Tricresylphosphate was found to be a potent inhibitor of hydrolysis of esmolol which did not affect the parameters of radioligand binding. During an incubation time of 15 min at 25 degrees C in whole blood no significant metabolism of esmolol took place whereas without addition of inhibitor about 20% were inactivated. Thus, for the first time exact determinations of plasma concentrations of esmolol by ligand binding studies could be carried out. In vitro in radioligand binding studies esmolol had a 34 fold higher affinity for beta 1-adrenoceptors than for beta 2-adrenoceptors. Its acid metabolite had a very low and nonselective affinity for both adrenoceptor subtypes: Compared with esmolol it was 400fold less potent at beta 1-adrenoceptors. When plasma concentrations of esmolol and its metabolite after i.v. administration of esmolol to healthy volunteers (3000 micrograms/kg as a bolus and consecutively 500 micrograms/kg/min for 70 min) were determined in parallel by a beta 1-selective radioreceptor assay and an HPLC-method the following conclusions could be drawn from the direct correlation between the respective results: 1. (ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-1 Receptor Antagonists↗
PubMed1994

The cognition-enhancing drug tenilsetam is an inhibitor of protein crosslinking by advanced glycosylation.

Non-enzymatic glycosylation of proteins, also called Maillard reaction, which occurs at an accelerated rate in diabetes, can lead to the formation of advanced glycosylation endproducts (AGEs). Tenilsetam (CAS 997: (+/-)-3-(2-thienyl)-2-piperazinone), a cognition-enhancing drug successfully used for treatment of patients suffering from Alzheimer's disease, when included in the Maillard reaction apparently inhibits protein crosslinking by AGEs in vitro. According to the mechanism proposed, Tenilsetam acts via covalent attachment to glycated proteins, thus blocking the reactive sites for further polymerisation reactions. A beneficial effect of Tenilsetam in Alzheimer's disease could come from the interference with AGE-derived crosslinking of amyloid plaques and a decreased inflammatory response by diminished activation of phagocytosing microglia.

Aging↗
PubMed1992

Pyridoxal 5'-phosphate as a 31P reporter observing functional changes in the active site of Escherichia coli maltodextrin phosphorylase after site-directed mutagenesis.

Changes in the active site of Escherichia coli maltodextrin phosphorylase created by substituting residues Lys533, Arg534, Tyr538, and Glu637 were monitored in the absence and presence of arsenate as substrate analogue using pyridoxal-P as 31P NMR reporter. The chemical shift of the cofactor phosphate group of wild-type E. coli phosphorylase is pH dependent with an apparent pK of 5.6 and limiting delta values of 0.71 and 3.6 ppm for the low- and high-pH values, respectively. The apparent pK value of 5.6 indicates that the phosphate group of the cofactor is in hydrogen bond linkage to Lys533. In all mutant enzymes in which the enzymatic activity was significantly reduced, effects on the 31P chemical shift pattern of pyridoxal-P were observed. The K533S, R534Q, E637D, and E637Q mutant enzymes show 0.6, 0.01, 0.2, or 0.1% residual activity, and the apparent pK values of the cofactor phosphate transition of E637D and E637Q mutant enzymes are altered. The Y538F mutant enzyme is a remarkable exception, displaying 12% activity and an environment of the cofactor quite similar to that in wild-type enzyme. This finding suggests that Tyr538, although involved in substrate binding and specificity, is not functionally essential. One crucial aspect of catalysis is the close contact of the phosphates of pyridoxal-P and of substrate rendered by a cluster of positively charged amino acids, Lys533, Lys539, and Arg534. The similar apparent pK values of wild-type and K533S mutant phosphorylase suggest that the cofactor phosphate and the hydroxyl group of Ser533 are linked by a hydrogen bond.(ABSTRACT TRUNCATED AT 250 WORDS)

Arsenates↗
PubMed1992

Characteristic EEG findings in childhood moyamoya syndrome.

Moyamoya syndrome-specific alterations of EEG recordings are only observed in children. These consist of a gradual frequency decrease and amplitude activation after hyperventilation. This is referred to as re-build-up phenomenon. Thus, a tentative diagnosis of Moyamoya syndrome in children can be based on the EEG finding. This should be radiologically confirmed by angiography.

Cerebral Angiography↗
PubMed1991

Chemical and functional analysis of components of adenylyl cyclase from human platelets treated with phorbolesters.

Human platelets, prelabeled with [32P]phosphate were treated with tetradecanoylphorbol acetate (TPA) for 5 min at 37 degrees C. Phosphorylation of the components of adenylyl cyclase was determined in membranes using specific antibodies against G-proteins and the catalytic moiety. Less than 0.01 mol of [32P]phosphate/mol could be detected in immunoprecipitates using antibodies against sequences within the alpha-subunit of the GTP binding protein Gi. TPA, however, caused the incorporation of 0.67-1.1 mol of [32P]phosphate per mol of catalyst while 0.13-0.2 mol were found in the absence of TPA. Lack of modification of the alpha-subunit of Gi was also indicated by the results of reconstitution experiments with purified Gi alpha from bovine brain: adenylyl cyclase in membranes from untreated platelets was significantly more inhibited by added G1 alpha, than that from TPA treated cells. While beta, gamma-subunits were like-wise inhibitory no difference dependent on platelet-pretreatment could be observed.

Adenylyl Cyclase Inhibitors↗
PubMed1991

Multisite contacts involved in coupling of the beta-adrenergic receptor with the stimulatory guanine-nucleotide-binding regulatory protein. Structural and functional studies by beta-receptor-site-specific synthetic peptides.

Synthetic peptides, 12-22 amino acid residues long, comprising the presumed coupling sites of the beta-adrenergic receptor with the stimulatory guanine-nucleotide-binding regulatory protein (Gs), were examined for their ability to modulate Gs activation in turkey erythrocyte membranes. Three peptides corresponding to the second cytoplasmic loop, the N-terminal region of the third cytoplasmic loop, and the N-terminal region of the putative fourth cytoplasmic loop, compete synergistically with the hormone-stimulated receptor for Gs activation with median effector concentrations of 15-35 microM, or 3-4 microM for combinations of two peptides. One peptide, corresponding to the C-terminal region of the third cytoplasmic loop, carries the unique ability to activate the Gs-adenylate-cyclase complex independent of the signalling state of the receptor. These observations are consistent with a dynamic model of receptor-mediated G-protein activation in membranes, where domains composed of the second, third and fourth intracellular loop of the receptor bind to and are interactive with the G-protein heterotrimer, resulting in ligand-induced conformational changes of the receptor. In response to hormone binding, the extent or the number of sites involved in interaction with Gs may be readjusted using a fourth site. Modulation of coupling sites may elicit congruent conformational changes within the Gs heterotrimer, with qualitatively different effects on GTP/GDP exchange in the alpha subunit of Gs and downstream effector regulation. This model corroborates and expands a similar model suggested for activated rhodopsin-transducin interaction [König, B., Arendt, A., McDowell, J. H., Kahlert, M., Hargrave, P. A. & Hofmann, K. P. (1989) Proc. Natl Acad. Sci. USA 86, 6878-6882].

Aluminum↗
PubMed1991

Monoclonal antibodies against various forms of the adenylyl cyclase catalytic subunit and associated proteins.

Monoclonal antibodies against partially purified adenylyl cyclase from bovine brain cortex were raised in mice. Three types of antibody were obtained. Type 1 was specific for the calmodulin-sensitive enzyme. Type II also recognized this enzyme, but recognized the calmodulin-insensitive enzymes from a variety of species and tissues as well. Type I antibodies precipitated their antigens in both the native and denatured forms, while type II strongly favored the denatured forms. Type III antibodies precipitated adenylyl cyclase activity, but as shown by Western blot analysis, were directed against 38-kDa and 45-kDa glycoproteins. The 38-kDa protein was identified as synaptophysin.

Adenylyl Cyclases↗
PubMed1991

AF-DX 116, a cardioselective muscarinic antagonist in humans: pharmacodynamic and pharmacokinetic properties.

Effects of AF-DX 116, a cardioselective antagonist, on M cholinergic receptors (M-ChR) were studied in healthy volunteers. Occupancy of M-ChR subtypes by drug present in plasma samples (radioreceptor assay) was compared with these effects. After an intravenous dose of AF-DX 116 saturating greater than 90% of cardiac M2-ChR, an increase in heart rate by 25 beats/min was observed. This cardiac receptor occupancy and effect wore off with a parallel time course within 10 hours. No inhibition of salivary flow was observed, coinciding with a lack of M3-ChR blockade in the radioreceptor assay. Beta-adrenergic receptor blockade by propranolol did not affect either of the effects. No indication for active metabolites or stereoselective drug metabolism was found comparing HPLC and receptor assay for drug concentrations in plasma. We conclude that AF-DX 116 may be a useful drug for the treatment of bradycardia. Its lack of troublesome side effects is the result of its selectivity for cardiac M-ChR.

Adult↗
PubMed1991

Bioequivalence of two atenolol formulations in healthy volunteers. Evaluation and prediction of effect kinetics at beta-adrenoceptors in vivo by means of a radioreceptor assay.

Pharmacokinetic and pharmacodynamic effects of single oral doses of 200 mg of two atenolol formulations (Tenormin, atenolol (T) and Duraatenolol, atenolol (D)) were assessed in eight male healthy volunteers for 48 h (double-blind crossover design). Both formulations were bioequivalent in terms of pharmacokinetic parameters (AUC, tmax, Cmax, t1/2) as detected by gas liquid chromatography. By means of a radioreceptor assay (RRA) any significant contribution of beta 2-adrenoceptors and active metabolites to effects observed in vivo was ruled out. Based on parameters derived from RRA a prediction of the time course of any beta 1-adrenoceptor-mediated effect in vivo was made. During the first 12 h after intake of atenolol (T) and atenolol (D) effect kinetics simulated from RRA data corresponded very well to the inhibition of exercise-induced tachycardia observed in vivo. Thus, RRA is an in vitro method enabling assessment and prediction of relative bioequivalence of 2 atenolol formulations in vivo. Moreover, it enables establishment of a causal relationship between pharmacodynamic and pharmacokinetic parameters.

Adolescent↗
PubMed1990

Escherichia coli maltodextrin phosphorylase: contribution of active site residues glutamate-637 and tyrosine-538 to the phosphorolytic cleavage of alpha-glucans.

The role of Escherichia coli maltodextrin phosphorylase (EC 2.4.1.1) active site residues Glu637 and Tyr538 which line the sugar-phosphate contact region of the enzyme was investigated by site-directed mutagenesis. Substitution of Glu637 by an Asp or Gln residue reduced kcat to approximately 0.2% of wild-type activity, while the Km values were affected to a minor extent. This indicated participation of Glu637 in transition-state binding rather than in ground-state binding. 31P NMR analysis of the ionization state of enzyme-bound pyridoxal phosphate suggested that Glu637 is also involved in modulation of the protonation state of the coenzyme phosphate observed during catalysis. Despite loss of proposed hydrogen-bonded substrate contacts, the Tyr538Phe mutant enzyme retained more than 10% activity; the apparent affinity of all substrates was slightly decreased. Mutations at either site affected the error rate of the enzyme (ratio of hydrolysis/phosphorolysis). Besides a role in substrate binding, the hydrogen-bond network of Tyr538 supports the exclusion of water from the active site.

Amino Acid Sequence↗
PubMed1990

Identification of a Gs-protein coupling domain to the beta-adrenoceptor using site-specific synthetic peptides. Carboxyl terminus of Gs alpha is involved in coupling to beta-adrenoceptors.

Competition between Gs-protein and the synthetic peptide, GSA 379-394, derived from the carboxyl-terminal region of the alpha s-subunit, led to complete inhibition of receptor-mediated adenylate cyclase activation in turkey erythrocyte membranes. Related peptides corresponding to the homologous carboxyl-terminal region of alpha t-, alpha il- or alpha o-subunits did not interfere with beta-receptor-Gs coupling. The direct coupling between Gs and adenylate cyclase was not influenced by any of these peptides. These results emphasize the important role of the carboxyl-terminus of G-protein alpha-subunits for the specific recognition of their corresponding receptors and for signal transduction.

Adenylyl Cyclases↗
PubMed1990

Sensorineural hearing loss owing to deficient G proteins in patients with pseudohypoparathyroidism: results of a multicentre study.

Pseudohypoparathyroidism (PHP) is a rare disorder that might be caused by an hereditary defect in the G protein system. These membrane-bound proteins are responsible for the transduction of biological signals through the outer cell membrane. The investigation of 22 patients with PHP showed a symmetric sensorineural hearing loss in 63.6% of the subjects. In erythrocyte membrane preparations from blood samples of 15 of these patients, we measured the concentration of the stimulatory Gs protein and the inhibitory Gi protein by means of the Western blot analysis using selective antibodies against alpha-subunits of G proteins. In nine of the 15 cases (60%), we found a distinct decrease in the amount of the Gs protein with a partial preponderance of the Gi protein. These patients had a considerable symmetric sensorineural hearing loss. Pathophysiological mechanisms and the possible role of G proteins in the inner ear are discussed.

Adolescent↗
PubMed1990

[Decreased vagal tone in hyperkinetic heart syndrome?].

Increasing amounts of atropine (0.03 mg + 0.07 mg + 0.01 mg + 0.25 mg + 0.5 mg + 1.0 mg + 1.5 mg; sigma = 3.5 mg, interval between injections: 30 min) were injected intravenously in a cumulative manner in five patients with hyperkinetic heart syndrome and in seven healthy volunteers. The heart rate increased from 93 to 127 beats per min in patients, and from 63 to 104 beats per min. in controls. The diastolic blood pressure slightly increased in both groups, whereas the systolic blood pressure did not change significantly. The accommodation diminished from 6 to 2 dioptries in patients, and from 8 to 5 dioptries in controls. Salivary flow fell from 1.6 to 0.1 g/min in patients with hyperkinetic heart syndrome, and from 1.3 to 0.1 g/min in control persons, respectively. The maximum occupancy of muscarinic receptors (m2-glandular), as measured in plasma specimens by means of a radioreceptor assay, reached more than 80% in each group. The dose-response-curves of atropine were highly comparable in patients and controls. It is concluded that the effects of atropine are essentially the same in patients with hyperkinetic heart syndrome and in healthy control persons. There is no evidence for a diminished vagal tone in such patients.

Adult↗
PubMed1989

Mapping of beta-adrenoceptor coupling domains to Gs-protein by site-specific synthetic peptides.

Peptides corresponding to the known sequence of turkey erythrocyte beta 1-adrenergic receptor were synthesized and the effects on receptor-mediated cyclase activation were measured. Peptides corresponding to the first and second intracellular loops (T61-71 and T138-159) inhibited at micromolar concentrations the hormone-dependent cyclase activation in turkey erythrocyte membranes. In contrast, the peptide corresponding to the C-terminal part of the third intracellular loop (T284-295) increased the cyclase activity in a hormone-independent manner. Peptides T338-353 and T2-10 and a number of synthetic peptides unrelated to the beta-adrenoceptor had no effect.

Adenylyl Cyclases↗