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Biomedical subjects

C Becker

Publications and source records attributed to C Becker.

At least 379 records · Page 21Linked to original sources
PubMed1985

Avarol, a cytostatically active compound from the marine sponge Dysidea avara.

A main metabolic product of the sponge Dysidea avara was isolated and purified and subsequently identified as avarol by applying a series of analytical techniques, e.g. [13C]NMR, [1H]NMR and i.r. spectroscopy. This sesquiterpenoid hydroquinone was found to possess strong cytostatic activity. Using the L5178y mouse lymphoma cell system in vitro (roller tube assays) avarol reduced cell growth to 50% at a concentration of 0.9 microM. Avarol treated cells did not show "unbalanced growth". Avarol interfered with mitotic processes, preventing telophase formation. Incorporation studies with precursors for DNA, RNA, protein and glycoprotein syntheses revealed increased incorporation rates in response to avarol treatment. From these results and further autoradiographical experiments it is suggested that inhibition of cell growth is due to changes of the intracellular pools and/or alterations of the permeability properties of the cell membrane for the precursors. Avarol diacetate caused the same cytostatic effect as avarol.

Animals↗
PubMed1985

[Peripheral nerve repair: value of biological glues and epiperineural suture in late interventions. Experimental study in rats].

In order to approximate as close as possible genuine clinical conditions, the sciatic nerve of the rat was divided and then repaired after a delay of one or seven days either by application of a biological glue or by an epiperineural suture technique. The metabolic activity of the sciatic nerve Schwann cells - whether located in the distal or the proximal ends - and that of the (fast acting) white gastrocnemius and (slow acting) red soleus muscle were assessed using 32P-radiolabeled acid-soluble phosphates. Delayed repair, as judged by our biochemical criteria, was equivalent whatever method, biological glue or suture, was used. The frozen and lyophilized forms of the biological glue provided similar results.

Animals↗
PubMed1985

In vitro combination-effect of temocillin with ticarcillin and aminoglycosides on gram-negative and gram-positive bacteria.

The in vitro efficacy of temocillin in combination with ticarcillin and with gentamicin, tobramycin, amikacin and netilmicin against 80 Gram-negative and 20 Gram-positive bacterial strains was compared by use of the checkerboard agar dilution technique. No synergistic or additive effect was seen on the Gram-positive strains. Great variations occurred between the different bacterial species, and the temocillin-ticarcillin combination had only little effect against the Pseudomonas strains tested. On average, only 12% of all strains tested were inhibited synergistically by temocillin-gentamicin combinations, and only 7 to 10% by combinations of temocillin with the other aminoglycosides. However, 25% of Gram-negative strains were inhibited synergistically and 40% of Gram-negative strains were inhibited additively by the combination of temocillin-gentamicin.

Aminoglycosides↗
PubMed1985

Commentary on 2,3,7,8-tetrachlorodibenzo-para-dioxin (TCDD).

There is deep concern about the long term health effects of exposure to phenoxy herbicides and the contaminant TCDD; however, there is considerable scientific and medical uncertainty regarding the health effects from exposure to these chemicals. There are at least ten ongoing studies on reproduction, morbidity and mortality as well as studies of tissue concentrations of TCDD that are attempting to determine the health effects of these chemicals (see Table 2). Appropriate efforts should be made to prevent human and environmental exposure and to decontaminate the environment while awaiting the results of these investigations. Animal toxicity studies show such wide variations that extrapolations from a different species to humans are tenuous. Human studies on exposed workers and nonoccupational exposures are difficult to interpret because the exposure has not been quantified and because workers were exposed to mixtures of chemicals. Chloracne appears to be an important specific clinical marker of TCDD exposure, however, it can be caused by structurally similar compounds. Many of the past studies on human health effects of 2,4,5-T and TCDD are controversial. Since the scientific data are not firm, no specific statements can be made regarding the long term health effects at this time. Any individual who has had a significant exposure to TCDD should see his/her physician and have appropriate consultation. Long term follow up will be required. Physicians should be instructed regarding the possible manifestations of TCDD exposure to look for chloracne, soft tissue masses, muscle pain, fatigue, peripheral neuropathy, tender hepatic enlargement, enlargement, elevated liver enzymes, elevated lipids, prolonged prothrombin time, hemorrhagic cystitis and hirsutism.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Inhibition of mitosis by avarol, a natural product isolated from the sponge Dysidea avara.

Avarol, a sesquiterpenoid hydroquinone, is a cytostatic agent, isolated from the sponge Dysidea avara. Autoradiographic studies show that in vivo (L5178y mouse lymphoma cells) avarol changes the labelling index in favour of the fraction of unlabelled cells (from 1.24 to 1.04). At concentrations below the 50% inhibition dose, the mitotic index increases from 6.5 +/- 0.5 to 10.4 +/- 0.8; at higher concentrations the formation of mitotic figures is almost completely suppressed. In vitro studies applying the methods of viscosimetry and electron microscopy demonstrate that avarol inhibits assembly of brain microtubule protein at an at least stoichiometric concentration ratio. Moreover, evidence is presented that the new antimitotic agent avarol inhibits protofilament elongation rather than lateral association of tubulin during protofilament formation. The results suggest that avarol interferes with polymerization of tubulin both in interphase and during mitosis.

Animals↗
PubMed1984

Recovery of beta-adrenoceptors and cyclic AMP response after long term treatment of intact heart cells with beta-blockers.

We have studied the recovery of receptor binding and of isoprenaline-stimulated cyclic AMP responses after chronic (2-5 days) exposure of tissue-cultured living rat heart cells to several beta-adrenoceptor antagonists. Most experiments were performed with [3H]- (+/-)-carazolol and [3H]-(+/-)-CGP 12177, as prototypes of high affinity lipophilic and hydrophilic ligands respectively. Chronic antagonist treatment did not alter the total number of receptors nor did it cause intracellular accumulation of the ligands. At the end of the treatment, radiolabelled antagonists were displaced either by 'infinite' dilution of the incubation medium or by competitive displacement with the non-labelled ligand (-)-timolol. In dilution assays dissociation of carazolol from specific sites was biphasic with t 1/2 values of 41 +/- 14 and 219 +/- 15 min. Dissociation of CGP 12177 was monophasic with t 1/2 of 102 +/- 2 min. Timolol enhanced the dissociation rates of both radioligands and suppressed the slow phase of carazolol dissociation. Isoprenaline-stimulated cyclic AMP formation did not recover in parallel with the release of the two antagonists from receptor binding sites. To reach about 80% of control values for receptor availability or cyclic AMP response required 3 h and 24 h washout periods, respectively, after carazolol (0.2 nM) treatment, or 1.5 and 12 h washout periods after CGP 12177 (4 nM) treatment. Such a 'decoupling' effect was not observed during recovery from chronic exposure to the antagonists, timolol and propranolol. We conclude that some antagonists cause a novel form of desensitization that is not linked to their partial agonistic potency. Moreover, carazolol-type drugs seem to induce an additional isomeric form of the beta-receptor that is not recognized by other antagonists. These observations could explain the well known discrepancy between long duration of action and rapid removal from the circulation of several antagonists in current therapeutic use.

Adrenergic beta-Antagonists↗
PubMed1984

In vitro combination effects of cefotetan with four aminoglycosides, piperacillin and mezlocillin on gram-positive and gram-negative nosocomial bacteria.

The in vitro efficacy of cefotetan in combination with gentamicin, tobramycin, amikacin, netilmicin against Staphylococcus aureus, Staphylococcus epidermidis and Enterobacter cloacae and with piperacillin and mezlocillin against Escherichia coli, Klebsiella pneumoniae, Serratia marcescens and Enterobacter cloacae was compared by use of the checkerboard agar dilution technique. On average, 60% of the gram-negative and 46% of the gram-positive strains were inhibited by additive, but only 22% of the gram-negative and 2% of the gram-positive bacteria were inhibited by synergistic cefotetan-aminoglycoside combinations. Netilmicin combinations were least active. On gram-negative bacteria, 63% of the cefotetan-penicillin combinations were additive and 11% synergistic. No antagonism occurred with any of the combinations.

Aminoglycosides↗
PubMed1984

The relationship of airways responsiveness to cold air, cigarette smoking, and atopy to respiratory symptoms and pulmonary function in adults.

The response to eucapnic hyperventilation with subfreezing air was studied in a population based sample of 171 adults, all of whom also completed a respiratory questionnaire, spirometry, and skin testing. A positive response to the cold air challenge was defined as [initial FEV1-post-challenge FEV1)/initial FVC) X 100) greater than or equal to 9%. Cigarette smoking was with a positive cold air response: 12 of 128 current and ex-smokers (9.4%) versus 1 of 43 nonsmokers (2.3%) (p = 0.095). Among current and ex-smokers, a positive response to the cold air challenge was significantly associated with asthma (p = 0.046). Using a logistic regression model, both current smoking and response to cold air were significant predictors of the presence of "persistent wheeze" or asthma. A positive skin test to any of the 4 environmental antigens used (ragweed, housedust, trees, and grasses) was significantly associated with cigarette smoking (p = 0.018) and hay fever (p = 0.003 among current and ex-smokers) but not with wheezing or asthma. Though not statistically significant, cold air responders had a lower percentage of positive skin test reactivity than nonreactors. The findings of this cross-sectional analysis suggest that in adults, both airways responsiveness and cigarette smoking are important predictors of wheezing and asthma. Furthermore, the data suggest that airway hyperresponsiveness and atopy are independent traits. However, in adults, these traits are associated with cigarette smoking, a common environmental exposure.

Child↗
PubMed1984

Action of botulinum A toxin and tetanus toxin on synaptic transmission.

Intracellular recordings of the spontaneous activity from mammalian spinal cord neurons in culture demonstrated different sensitivities of excitatory and inhibitory synaptic transmission for the action of tetanus toxin (Tetx) and botulinum toxin type A (Botx). The effects of Tetx and Botx on spontaneous and nerve-evoked transmitter release were compared under identical experimental conditions in experiments on in vitro poisoned mouse diaphragms. At 37 degrees C completely paralyzed endplates are characterized by a very low frequency of spontaneous miniature endplate potentials (m.e.p.p.s) and by a 100% failure to evoke endplate potentials (e.p.p.s) in response to single nerve stimuli. Striking differences in the action of both toxins have been observed when the very low transmitter release probabilities of paralyzed nerve-muscle preparations were increased by tetanic nerve stimulation and/or application of potent K+-channel blockers and/or by reduction of temperature to 25 degrees C. While Botx did not change the short latency between nerve impulse and postsynaptic response, Tetx produced a temporal dispersion of the quantal release suggesting that the toxins act at different sites in the chain of events that result in transmitter release. To find further evidence to support the different actions of the toxins the spontaneous transmitter release was studied in more detail. Tetx blocked preferentially the release of so-called large mode m.e.p.p.s without affecting the frequency of the small mode ones. In contrast, Botx strongly inhibited both the small and large mode m.e.p.p.s.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1983

An assessment of the potential testicular toxicity of 10 pesticides using the mouse-sperm morphology assay.

Dinitrobutylphenol, chlorbenzilate, atrazine, Ordram, Telone (dichloropropene), pentachlorophenol (technical and reagent grades), Benomyl, DBCP (dibromochloropropane), and carbaryl were tested over a range of 7 doses in the mouse to assess their testicular toxicity. Measures of potential toxicity were sperm morphology, sperm counts and testicular weights. Each pesticide was injected intra-peritoneally in a single dose on each of 5 days. Testicular toxicity was assessed at 35 days. None of the pesticides tested, including the known human male testicular toxin, DBCP, produced statistically significant differences in the parameters from vehicle-injected controls.

Animals↗
PubMed1982

Competitive and non-competitive interactions between specific ligands and beta-adrenoceptors in living cardiac cells.

We have used primary cultures of hearts from newborn rats to study beta-adrenoceptor properties in living myocardial cells. Receptors were labelled with the lipophilic antagonists 3H-(+/-)-carazolol and 125I-(+/-)-cyanopindolol (CYP) or with the hydrophilic antagonist 3H-(+/-)-CGP 12177. Under equilibrium conditions all ligands bound to a saturable homogeneous class of specific sites with a maximal binding capacity of approximately 100 fmol/mg protein (corresponding to approximately 5000 sites/cell). After 90-180 min preincubation of intact cells with 3H-carazolol or 3H-CGP 12177 only 80% of these antagonists could be displaced from specific binding sites by competing ligands. In the simultaneous presence of the antagonist (-) timolol 100% of specifically bound radiolabelled ligand remained displaceable. In competitive displacement experiments the radioligands did not affect the apparent affinity of the displacing nonlabelled antagonists timolol and CGP 12177, but agonist affinity was markedly changed. The apparent KD values for (-)-isoprenaline were 1560 and 2720 nmol/l in the presence of carazolol and CYP, but only 32 nmol/l in the presence of CGP 12177. This antagonist-dependent difference in agonist KD values was observed only in intact cells but not in membrane particles prepared from heart homogenates of newborn rats, where high agonist affinity was seen during displacement of all radioligands. The KA value for isoprenaline-stimulated cAMP accumulation in living cells was 30 nmol/l in 5-day cultures. A direct proportionality existed between agonist receptor occupation and cAMP accumulation in the presence of CGP 12177 as estimated by the KA/KD ratio. In the presence of carazolol the KA/KD ratio decreased from 1 to 0.02 suggesting that low affinity receptors were not coupled functionally to adenylate cyclase. These results indicate that some lipophilic antagonists which appear to be inert competitive ligands in fragmented membranes, alter receptor binding properties in intact cells. These antagonists seem to promote the transformation of receptor sites into a new "inactivated" state where competitive interactions between different ligands are inhibited.

Animals↗