Assays TOPICAL

The difficulty in relating resistance gene frequencies, the presence of resistant phenotypes and the level of resistance to field control indicates a need for monitoring techniques that sample significant numbers of a population and more accurately reflect the field situation (23-24). For example, in many cases, the standard topical assay may not adequately reflect the situation in the field. The efficacy of the pyrethroids seems to depend on many factors other than just contact activity. In cases where topical assays indicate high levels of resistance but no corresponding field failures, contact activity may not be the only factor affecting susceptibility. The repellency and antifeedant attributes of the pyrethroids may also contribute to their efficacy in the field (25-31). These behavioral attributes may also affect the evolution of resistance in field populations (22). The type of exposure in the field to the pyrethroids may also affect field control more than previously considered (33). 

The compounds were tested in a topical assay. Each set of assays include the standard permethrin to help account for inter-... 

For the topical assay, the test compound was dissolved in acetone at a known concentration. One microliter of this solution was placed on the mid-dorsal region of early 3 instar southern armyworm larvae. During the four day holding period the larvae were provided with an artifical casein diet. Following this period, the number of dead and living insects were recorded. This test simulates field conditions in which larvae do not ingest treated plant material. 

Compound Artificial diet assay Topical assay ... 

Mortality was determined six days after treatment. Artificial diet assay at 500 ppm Topical assay at 25 g insect ... 

Many groups throughout the world tried to repeat the experiments using similar in vitro assays and other test systems, but without success. Current experimental data suggest additive interactions do occur between EDs, but the issue of interactive effects, and synergism in particular, will undoubtedly remain a topic of intense debate for some time to come. 

We have already stressed the potential importance of lipid-rich membranes in the skin as potential targets for ROS-induced damage and ageing of human skin is morphologically identical to changes found by peroxidative processes (Serri et al., 1977). The involvement of AA metabolites in skin disease, and in particular psoriasis, has been the subject of much recent interest. Studies have included topical and intradermal administrations of AA metabolites, and assay of such products in clinical specimens. Results show that concentration of AA, 12-hydroxy-eicosatetraenoic acid (12-HETE), PG and leu-kotrienes are increased in psoriatic lesions (Hammarstrom etal., 1975 Camp etal., 1983 Brain etal., 1984 Duell et al., 1988) and also that full-thickness epidermis from normal and diseased skin has the enzymatic capacity to convert AA to some of the same metabolites (Hammarstrom etal., 1975, 1979 Camp etal., 1983 Brain etal., 1984 Ziboh et al., 1984 DueU et al., 1988). The biological effect of both 12-HETE and leukotrienes was confirmed by both topical application and intradermal injection, which caused epidermal inflammation and... 

Several considerations influence the suitability of the immunoassay as a qualitative or quantitative tool for the determination of tissue residues. These include the assay format, the end user (on-farm or laboratory use), effects of sample matrix on the analysis, cross-reactivity considerations, detection levels required of the assay, target tissues to be used in the assay, and the use of incurred or fortified tissues for validation of the immunoassay against accepted instrumental methods. Although these variables are often interrelated, each topic will be discussed in further detail below. 

The discussion above was concerned with the effects of solution conditions on enzyme activity, hence reaction velocity. Equally important for the purpose of assay design is the influence of specific solution conditions on the detection method being used. This latter topic is beyond the scope of the present text. Nevertheless, this is an important issue for screening scientists whose job is often to balance the needs of biochemical rigor and assay practicality in development of an HTS assay. An... 

Assay preparation Transfer an accurately weighed portion of topical powder, equivalent to about 20 mg of miconazole nitrate, to a stoppered 50-mL centrifuge tube. Add 25 mL of methanol, and shake by mechanical means for 30 min to dissolve the miconazole nitrate. Centrifuge to obtain a clear supernatant liquid. Transfer 5 mL of this solution to a test tube, add 2 mL of Internal standard solution and evaporate at a temperature not higher than 40 °C with the aid of a current of nitrogen to dryness. Dissolve the residue in 2 mL of a mixture of chloroform and methanol (1 1). 

Procedure Separately inject equal volumes (about 5 pL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. The relative retention times for cholestane and miconazole nitrate are about 0.5 and 1, respectively. Calculate the quantity, in mg, of Ci8H14Cl4N2OHN03 in the portion of topical powder given by the formula ... 

Many methods are available for determining food antioxidant capacity, which is an important topic in food and nutrition research. However, there is a great need to standardize these methods because the frequent lack of an actual substrate in the procedure, the system composition, and the method of inducing oxidation could limit their accuracy. In fact, antioxidant activities in complex systems cannot be evaluated satisfactorily using a single test, and several test procedures may be required. The search for more specific assays that can be more directly related to oxidative deterioration of foods and biological systems should be the objective of future investigations. 

The antiinflammatory properties of such topical agents as halcinonide are usually determined by a vasoconstrictor assay. Topically applied corticosteroids cause a blanching at the site of application, which can be the forearm or the upper back of healthy adults where stratum corneum is removed with cellophane tape. ° The test areas, containing various concentrations of halcinonide, are occluded with plastic wrap and are evaluated on an all-or-none basis. Percutaneous absorption studies with 0.1%... 

Strongly basic antibiotics may be precipitated by formation of the coloured reineckate salt which may then be determined spectrophotometri-cally 65. Bickfordl66 dissolved the precipitated neomycin reineckate in acetone and has successfully used this procedure to assay neomycin extracted from topical formulations. Roushdi et al 73 preferred to oxidise the precipitate with potassium permanganate and then colorimetrically estimate the chromate produced with diphenylcarbazide. 

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