Search PubMed⌕ Search

Biomedical subjects

R A Webster

Publications and source records attributed to R A Webster.

At least 73 records · Page 4Linked to original sources
PubMed1977

Convulsant-anticonvulsant interactions on seizure activity and cortical acetylcholine release.

The effects of leptazol and bicuculline on the efflux of endogenous acetylcholine (ACh) from the surface of the cerebral cortex have been related to EEG activity in urethane-anaesthetised rats. During seizure activity there was a calcium dependent increase in ACh efflux which was related to increase EEG activity and clonic muscle movements. ACh release and EEG activity were reduced during convulsive activity by trimethadione but not phenytoin. Phenobarbitone reduced convulsive EEG activity but left ACh release relatively unaffected. Blood pressure changes induced by convulsant and anticonvulsant drugs were not consistently related to EEG activity or ACh release. It is suggested that ACh efflux from the cerebral cortex is closely related to the activity of neurones within the cortex where it is released from nerve endings. Comparison of EEG changes induced by anticonvulsants and urethane during control and convulsant activity showed that only trimethadione produces anticonvulsant activity unaccompanied by general CNS depression.

Acetylcholine↗
PubMed1976

Progesterone binding to hen oviduct genome: specific versus nonspecific binding.

Data are presented to explain discrepancies in the literature involving the in vitro binding of steroid receptor complexes to isolated nuclei and chromatin. The type of binding in vitro of the progesterone-receptor complex to nuclei, chromatin, or DNA of hen organs is largely determined by the ionic strength of the medium. Low ionic conditions (0.01 to 0.05 molar potassium chloride) result in a nonspecific, nonsaturable binding, while high ionic conditions (0.15 to 0.20 molar potassium chloride) create a tissue-specific, saturable binding. Pure DNA binds the steroid receptor complex extensively in low salt but very little in the higher salt conditions.

Animals↗
PubMed1976

Nuclear binding of progesterone in hen oviduct. Binding to multiple sites in vitro.

Steroid hormones, including progesterone, are known to bind with high affinity (Kd approximately 1x10(-10)M) to receptor proteins once they enter target cells. This complex (the progesterone-receptor) then undergoes a temperature-and/or salt-dependent activation which allows it to migrate to the cell nucleus and to bind to the deoxyribonucleoproteins. The present studies demonstrate that binding the hormone-receptor complex in vitro to isolated nuclei from the oviducts of laying hens required the same conditions as do other studies of bbinding in vitro reported previously, e.g. the hormone must be complexed to intact and activated receptor. The assay of the nuclear binding by using multiple concentrations of progesterone receptor reveals the presence of more than one class of binding site in the oviduct nuclei. The affinity of each of these classes of binding sites range from Kd approximately 1x10(-9)-1x10(-8)M. Assays using free steroid (not complexed with receptor) show no binding to these sites. The binding to each of the classes of sites, displays a differential stability to increasing ionic concentrations, suggesting primarily an ionic-type interaction for all classes. Only the highest-affinity class of binding site is capable of binding progesterone receptor under physioligical-saline conditions. This class represent 6000-10000 sites per cell nucleus and resembles the sites detected in vivo (Spelsberg, 1976, Biochem. J. 156, 391-398) which cause maximal transcriptional response when saturated with the progesterone receptor. The multiple binding sites for the progesterone receptor either are not present or are found in limited numbers in the nuclei of non-target organs. Differences in extent of binding to the nuclear material between a target tissue (oviduct) and other tissues (spleen or erythrocyte) are markedly dependent on the ionic conditions, and are probably due to binding to different classes of sites in the nuclei.

Animals↗
PubMed1976

Nuclear binding of progesterone in hen oviduct. Role of acidic chromatin proteins in high-affinity binding.

The multiple classes of binding sites for the progesterone-receptor complex in hen oviduct muclei were found to be of chromatin origin. The highest-affinity, and presumably most physiologically important class, is localized in oviduct chromatin and contains approx. 6000-10000 sites per nucleus. None of these sites is detected in spleen chromatin. Two new techniques were used for assaying rapidly the binding of steroid-receptor complexes to soluble deoxyribonucleoproteins in vito. The extent of high-affinity binding by the nucleo-acidic protein fraction from spleen chromatin is as great as that by the nucleo-acidic protein from oviduct chromatin. Consequently the tissue-specific nuclear binding of the progesterone receptor is found not to be a consequence of the absence of the nuclear binding sites (acceptors) from chromatin of non-target tissue (spleen), but rather a result of complete masking of these sites. In the target-tissue (oviduct) chromatin, approx. 70% of the high-affinity acceptor sites are also masked. Acidic proteins, and not histones, appear to be responsible for the masking of these acceptor sites. In addition, acidic proteins represent (or at least are an essential part of) these high-affinity sites in the oviduct nucleus. Pure DNA displays a few high-and many low-affinity binding sites. In support of previous work with immature chicks, the acidic protein fraction of the nucleo-acidic results thus support the hypotheis that protein complexed with DNA, and not DNA alone, represent the high-affinity binding sites for the steroid-receptor complexes in nuclear chromatin. The lower-affinity classes of binding sites may represent DNA and/or other nuclear components.

Animals↗
PubMed1976

Separation and characterization of transcriptionally active and inactive nuclear subfractions of AKR mouse embryo cells.

This study was initiated with the objective of separating and characterizing two or more nuclear subfractions, which could then be compared with respect to their relative propensity for binding carcinogenic polycyclic aromatic hydrocarbons. Nuclei were isolated from cloned AKR-2B mouse embryo cells, which are susceptible to transformation by chemical carcinogens. The nuclei were mechanically sheared and subfractions were separated by sedimentation through a 0.17 to 1.7 M sucrose gradient. When the cells were treated with [3H]uridine for 30 min, most of the label incorporated into RNA was recovered in the top region of the gradients, which represented Nuclear Subfraction I. The majority of the chromatin DNA, however was localized in the bottom region (Subfraction II) and the pellet (Subfraction III). Precipitation (with CaCl2) of the rapidly labeled RNA of Subfraction I along with the chromatin DNA suggested that the label was present in nascent RNA chains still attached to the chromatin. Thus, the transcripitionally active chromatin seemed to be localized in Nuclear Subfraction I. The chromatin of Subfraction I was also the best template for RNA synthesis in vitro with exogenous bacterial polymerase. The protein and RNA content of subfraction I was greater than that of the other two subfractions and whole chromatin. Electron microscopy revealed the presence of membrane material in Subfraction I and II, with little such material in Subfraction III. Subfraction I differed from Subfractions II and II and whole chromation with respect to thermal denaturation of the DNA and histone composition (as determined by gel electrophoresis). The acidic protein composition (as determined by gel electrophoresis) differed for the chromatin of all three nuclear subfractions.

Binding Sites↗
PubMed1976

Binding of polycyclic aromatic hydrocarbons to transcriptionally active nuclear subfractions of AKR mouse embryo cells.

The objective of this study was to examine the binding of carcinogenic polycyclic aromatic hydrocarbons in well-characterized nuclear subfractions from transformable cells in culture. A cloned line of AKR mouse embryo cells was exposed to culture medium containing [3H]-3-methyl-cholanthrene (MC) (0.4 mug/ml) 670 Ci/mole). Cellular uptake and nuclear binding were determined after 4 hr of exposure. The addition of unlabeled MC up to 10 mug/ml did not cause reduction of [3H]MC cellular uptake or nuclear binding. From 2 to 5% of the total cellular MC was localized in the nuclei. All nuclear subfractions obtained from mechanically sheared nuclei and separated on sucrose gradients showed some MC binding; however, a high-affinity, high-specific-activity binding of MC was associated only with the slower-sedimenting component shown to represent that fraction of nuclear chromatin that is transcriptionally active. Conditions that caused the precipitation of this chromatin also resulted in the precipitation of the radioactive compound, thus suggesting that the MC was physically bound to the chromatin. Unlabeled MC (10 mug/ml) saturated this high-affinity MC binding to the transcripitionally active chromatin but did not saturate the binding to the other nuclear fractions. The binding of another potent carcinogen, [3H]-1,2,5,6-dibenzanthracene, and the "weak" carcinogen, [3H]-1,2,3,4-dibenzanthracene (3,4-DBA), to whole nuclei and nuclear subfractions was also determined. The concentration, specific activity, and time of treatment were identical with those used for MC. The level of binding of [3H]-1,2,5,6-dibenzanthracene was approximately 3-fold greater in whole nuclei on a per mass DNA basis than in those of either the MC or the 3,4-DBA. The binding of MC and 3,4-DBA to whole nuclei was approximately equal. As with MC, the [3H]-1,2,5,6-dibenzanthracene demonstrated a peak of high specific activity binding to the slower-sedimenting fraction of chromatin while the 3,4-DBA displayed considerably less binding to this fraction.

Benz(a)Anthracenes↗
PubMed1974

Second report on the organization of pharmacology in Great Britain.

1 A questionnaire was sent to 150 departments employing pharmacologists including all those academic departments teaching pharmacology, in Great Britain and Northern Ireland, and all industrial firms and research institutes engaged in pharmacological (27) and toxicological (38) work. All questionnaires were completed. The returns refer to the situation on 1st January 1972.2 There were 1,104 pharmacologists, of whom 652 were established staff, 383 were research staff and students, and 29 visiting workers. Of the staff in established posts, 192 were in medical schools, 81 in other university departments, 75 in other non-university departments and 28 in toxicology departments. Forty pharmacologists were established in other research units.3 Since 1964, 11 B.Sc. (Pharmacology) courses have been started. In 1971-72 there were 69 students in the final year of all B.Sc. Pharmacology courses. By 1974-75, 134 students are expected in the final year of these courses.4 Of 413 students specializing in pharmacology who graduated in 1971, 74% had taken a pharmacy qualification. Overall, 26% continued in academic courses, 11% went into industry, 56% into hospital or retail pharmacy. Only 1% were unemployed.5 Of 68 students completing postgraduate courses in pharmacology in 1971, 20% went into university teaching, 26% into industry and only 1% were unemployed. At present there are 260 students in postgraduate training in pharmacology departments.6 During 1970 and 1971 appointments exceeded losses in all sections giving an overall annual gain of 58.5. The total demand was estimated at 73 per year over this time. The predicted size of pharmacology departments in 1974-75 could lead to a maximum annual demand of 95 per year for these next three years.7 Up to January 1972, the supply of, and demand for pharmacologists seems to have been near balance from the unemployment and vacancy rates reported.However, in 1971, the supply of pharmacologists exceeded significantly the identifiable demand from pharmacology and toxicology departments. Thus there was a considerable demand from unknown employers. In the future there will be a considerable increase in the supply of specialist pharmacologists. We cannot predict if this will be balanced by demand in the absence of information about the growth in demand from the unknown employers.8 Taking the number of professors as an index of academic status, pharmacology has improved its standing, especially in the non-medical school departments. Now there are 40 professors in 51 departments compared with 25 in 42 departments in 1964.9 Overall, the composition of departments has not changed much since 1964. Academic departments still draw on each other for their pharmacologists whereas industrial departments draw equally from other industrial departments and academic departments. The total proportion of medically qualified pharmacologists has fallen to 14% (from 25% in 1964) and these pharmacologists are still concentrated heavily in medical school departments. In industrial departments, only 3% have a medical qualification.10From the replies of 94 out of 410 recent graduates specializing in pharmacology, the courses are in general interesting and effective. However, both students and employers considered that not enough statistics and mathematics as applied to pharmacology were taught. Of the respondents, 84% also wanted more teaching on the clinical use of drugs.

Education, Pharmacy↗