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In vitro diffusion cell design and validation. I. A stability-indicating high-performance liquid chromatographic assay for betamethasone 17-valerate in purified isopropyl myristate receptor phase

  • Authors: Smith, Eric W , Haigh, John M
  • Date: 1989
  • Language: English
  • Type: text , Article
  • Identifier: vital:6431 , http://hdl.handle.net/10962/d1006595
  • Description: Introduction: The development of a reliable in vitro permeation system necessitates the use of a precise and accurate method of quantifying the amount of permeant partitioning from the membrane into the cell receptor phase. Aqueous donor and receptor chamber fluids have been used in the majority of reported investigations, which makes quantitative permeant analysis relatively facile. Alternatively, radiolabelled diffusants have been used and flux rates monitored by scintillation counting, obviating the need for chromatographic separation of the receptor-phase components. However, this technique is not applicable when nonlabelled compounds or commercial dosage forms are to be evaluated by a cell system. Furthermore, several studies indicate that aqueous receptor phases may not present an optimal partitioning environment for certain lipophilic permeants (1-4), thereby impairing accurate flux monitoring due to limited diffusant solubility. Several attempts have therefore been made to improve the partitioning environment within these systems, by the addition of surfactants for example (4). A lipophilic receptor environment appears beneficial for corticosteroid partitioning, and thus, the use of isopropyl myristate has been investigated because of its bipolar properties that tend to mimic the biochemical composition of the skin (5,6). Betamethasone 17-valerate and its 21-valerate degradation product are highly soluble in isopropyl myristate and this nonaqueous solvent will not augment C-17-to-C-21 ester degradation reactions.
  • Full Text:
  • Date Issued: 1989

In vitro systems for the assessment of drug release from topical formulations and trans-membrane permeation

  • Authors: Smith, Eric W , Haigh, John M
  • Date: 1989
  • Language: English
  • Type: Book chapter
  • Identifier: vital:6441 , http://hdl.handle.net/10962/d1006628
  • Description: Numerous experimental methods have been developed to investigate drug release from vehicles and the percutaneous absorption of topically applied chemicals. The objective of this research is often to find correlation between laboratory results and the transdermal absorption experienced by living subjects so that in vivo experimentation may be curtailed. In many instances, the diverse experimental techniques tend to obscure absorption-controlling factors and complicate inter study comparisons, rather than clarify the complex transdermal absorption process. Moreover, lack of agreement between results may occasionally be ascribed to shortcomings in the in vitro methodology employed. The benefits of using an in vitro cell system for the preliminary testing of drug permeation in the laboratory are obvious. The environmental and diffusion variables may be controlled in an attempt to elucidate specific factors affecting the kinetic processes and drug bioavailability. Investigations are complex because of the multiple, interrelated events underlying the processes of drug partitioning from the applied vehicle and diffusion through the portals of the stratum corneum to the myriad of metabolic, binding, and clearance activities in the lower epidermal and dermal strata.
  • Full Text:
  • Date Issued: 1989

Interactions between ants, herbivorous insects and bracken (Pteridium aquilinum), a fern with extrafloral nectaries

  • Authors: Rashbrook, Vanessa Karin
  • Date: 1989
  • Subjects: Arthropod pests -- South Africa Ants -- South Africa Ferns -- South Africa
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:5592 , http://hdl.handle.net/10962/d1002042
  • Description: Bracken (Pteridium aquilinum) is a cosmopolitan species of fern which possesses extrafloral nectaries. A survey of the arthropod fauna associated with the plant throughout its range in South Africa identified the most widespread and damaging bracken herbivores and those species most likely to be influenced by ants visiting the extrafloral nectaries. Seventeen herbivorous arthropods were found to be definitely feeding on bracken and a further thirteen species with a less certain status were recorded. In addition, several species of ants were observed on the fronds and feeding at the extrafloral nectarie. On the basis of their widespread distribution and abundance, four bracken herbivores emerged as being particularly detrimental to the plant in South Africa. They were an eriophyid gall mite, a leafhopper and two moths. The biology of the two lepidopterans, Appana cinisigna and Panotima sp., suggested that they were potentially vulnerable to ants at various stages of their life histories. Laboratory experiments were undertaken to observe ant-lepidopteran interactions under controlled conditions. The ant Crematogaster peringueyi rapidly removed exposed A. cini igna eggs, but did not appear to regard Panotima eggs as food items. Small instar larvae of both species proved vulnerable, but the larger larvae appeared capable of escaping ant predation. Ant exclusion experiments in the field, using natural and artificially augmented ant densities, were carried out at two sites near Grahamstown. The dominant ant species was C. peringueyi. Neither the numbers of lepidopterans nor levels of herbivory were significantly reduced by the presence of ants . Despite the implications of the laboratory tests, the results of these field experiments did not support the hypothesis that ants which visit bracken extrafloral nectaries benefit the plant. Ant-bracken field studies on other continents also reported no significant ant-related effects, though marginal reductions in the abundance of certain herbivores have been noted at one site in the U.K. Since ant protection does not appear to be an inevitable consequence of having extrafloral nectaries, their value to bracken is in some doubt. The most likely situation where effective protection will occur is when high densities of vulnerable herbivores are preyed upon by large numbers of aggressive ants. However, even under these conditions, enhancement of plant fitness is not inevitable. This raises the question of why extrafloral nectaries have been retained in a plant that is as successful and widespread as bracken.
  • Full Text:
  • Date Issued: 1989

Investigation of the causative agents of the 1982 Gazankulu poliomyelitis outbreak, using four biochemical techniques

  • Authors: Gibson, Katherine Margaret
  • Date: 1989
  • Subjects: Poliomyelitis -- Analysis , Poliomyelitis -- History -- South Africa , Poliomyelitis vaccine -- Analysis
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:3878 , http://hdl.handle.net/10962/d1001612
  • Description: Comparison of poliovirus strains was carried out to determine the origin of the virus in two isolates obtained during the 1982 outbreak of poliomyelitis in Gazankulu. Comparisons of the outbreak isolates with vaccine and wild-type strains of the same poliovirus type were carried out using four biochemical techniques. SDS-polyacrylamide gel electrophoresis (SDS-PAGE), two-dimensional thin-layer chromatography (TLC) and reversed-phase high-performance liquid-chromatography (RP-HPLC) were used for comparing viral capsid proteins. Comparison of poliovirus strains at a genetic level was carried out using two-dimensional oligonucleotide mapping of viral RNA. Results showed the type 1 poliovirus isolate, 5061, to be a novel wild-type poliovirus. The type 2 isolate, 5068, was closely related to the poliovirus type 2 Sabin vaccine strain, P712. It was concluded that the intrinsic variability of poliovirus strains was responsible for the appearance of isolate 5068
  • Full Text:
  • Date Issued: 1989

Isolation, purification and effect of ligands on the nicotinic cholinergic receptor

  • Authors: Kapp, Eugene Anthony
  • Date: 1989
  • Subjects: Ligands (Biochemistry) , Nicotinic receptors
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:4550 , http://hdl.handle.net/10962/d1018235
  • Description: The nicotinic cholinergic receptor protein of the fish electric organ, Torpedo fuscomaculata, has been isolated, purified and shown to represent a true model for the nAChR from other species and higher vertebrates. It is an integral membrane protein composed of four different subunits, tightly associated with other functional, but non-specific proteins. Purification of the nicotinic cholinergic receptor by chromatofocusing demonstrates an improved method over that of affinity and ion-exchange chromatography. Gel chromatography and SDS-polyacrylamide gel electrophoresis show evidence of four subunits; a(40-44 kDa), 6(53 kDa ),'Y(63 kDa) and 6(66 kDa) despite some degradation of receptor molecules by intracellular proteases. Spectrophotometric and fluorimetric studies of receptor-ligand interactions, show the functional and chemical integrity of the receptor to remain intact after solubilisation. The effect of cholinergic ligands on purified receptor preparations indicate quenching of the intrinsic fluorescence of the receptor. Agonists, like acetylcholine, bind and cause local conformational transitions, changing the active region from a hydrophobic to a hydrophilic environment. This phenomenon is illustrated by the 10-fold increase in fluorescence when the receptor is in a desensitised state. Antagonists, such as d-Tubocurarine, block this conformational transition. In vitro rectus abdominis muscle preparations . show the nitrosamines, dimethylnitrosamine and diphenylnitrosamine, to be true agonists of the nAChR. However their low affinity and specificity for the receptor precludes them as photoaffmity labelling agents. Photoactivation of dimethylnitrosamine occurs when associated with an acidic hydrogen at the active site of the receptor, suggesting energy-transfer labelling to be more facile than photoaffmity labelling. The membrane-bound receptor, in the presence of these nitrosamines, undergoes conformational transitions regulating the opening and closing of the ion-channel. Desensitisation and receptor activation are shown to involve one and the same molecular transition.
  • Full Text:
  • Date Issued: 1989

It's a long way to go to heaven

Jean Dubuffet : a study of his concepts pertaining to the alienation of the artist

  • Authors: Mather-Pike, Richard
  • Date: 1989
  • Language: English
  • Type: Thesis , Masters , MFA
  • Identifier: vital:21086 , http://hdl.handle.net/10962/6290
  • Description: I decided on an investigation into the nature of Dubuffet's remarks concerning the plight of the artist in modern societies, believing that the difficulties facing the artist are, at the time of this writing, still in force, and perhaps even more so now than they were in his day. These difficulties I believe, arise in the form of curtailments on personal and aesthetic freedoms brought about as the result of the artist's position in, and conformity to, the norms and values of his society. The problem is I believe, that these value systems not only censor or curb artistic freedom but actually restrict all individual enterprises by demanding that the indi vidual conform to the greater wish of the group, at the expense of his own creative and individual potential.
  • Full Text:
  • Date Issued: 1989

Jesus is coming over and over

Ka dijo tsa gago tsa Moya

Ka mponwane

Ka Tsholetsa

Ke ipolela

Ke lo naya taola entsha

Ke lone lerato la Jesu

Ke Tsepile

Kea Dumela

Kea Dumela

Kgosi lona ke mang

Khumbula Ukwenza Isabatha

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