Dose response curve, sigmoid

The absorbance values obtained are plotted on the ordinate (linear scale) against the concentration of the standards on the abscissa (logarithmic scale), which produces a sigmoidal dose-response curve (Figure 5). The sigmoidal curve is constructed by... 

Cyclic cascades can propagate a sigmoidal dose-response curve showing how an increasing concentration of allosteric effector manifests itself in activity changes of the target enzyme. 

The quantal dose-response curve is actually a cumulative plot of the normal frequency distribution curve. The frequency distribution curve, in this case relating the minimum protective dose to the frequency with which it occurs in the population, generally is bell shaped. If one graphs the cumulative frequency versus dose, one obtains the sigmoid-shaped curve of Figure 22A. The sigmoid shape is a characteristic of most dose-response curves when the dose is plotted on a geometric, or log, scale. 

In this type, the response is quantal or all or none type. If dose-response curve is plotted, no significant response is observed till a certain steady or threshold level is attained. The dose with which it is obtained is called ceiling dose. Beyond this point, there is no further increase in the therapeutic effect which remains unchanged even after increasing the dose of the drug. This type of response gives a sigmoid type dose-response curve. 

Therapeutic Efficacy. The therapeutic efficacy of risperidone for schizophrenia has been well established in several controlled trials conducted worldwide ( 74, 75). The clinical efficacy trials performed to support approval of risperidone by regulatory agencies have all been published. Therefore, it is appropriate to combine these data using meta-analytic techniques to explore the efficacy of risperidone compared with neuroleptics. For most drugs, the relationship of dose and response is defined by the classic sigmoidal curve. Thus, as the dose (or plasma level) increases beyond a threshold and reaches the linear portion of the curve, response increases. Once the dose is high enough to produce maximal clinical response, the dose-response curve then levels off. 

Finally, note that the quantal dose-effect curve and the graded dose-response curve summarize somewhat different sets of information, although both appear sigmoid in shape on a semilogarithmic plot (compare Figures 2-15 and 2-16). Critical... 

A bifunctional sex-aggregation pheromone system may also exist with unidentified Caloglyphus sp. sasagawa, in which the major component, rosefuran (24), acts as a female sex pheromone with a sigmoidal dose-response curve (unpublished data), and /i-phenylelhanol (30), a minor component, functions as an aggregation pheromone. 

The number of receptor sites and the position of the equilibrium (Eq. 1) as reflected in KT, will clearly influence the nature of the dose response, although the curve will always be of the familiar sigmoid type (Fig. 2.4). If the equilibrium lies far to the right (Eq. 1), the initial part of the curve may be short and steep. Thus, the shape of the dose-response curve depends on the type of toxic effect measured and the mechanism underlying it. For example, as already mentioned, cyanide binds very strongly to cytochrome a3 and curtails the function of the electron transport chain in the mitochondria and hence stops cellular respiration. As this is a function vital to the life of the cell, the dose-response curve for lethality is very steep for cyanide. The intensity of the response may also depend on the number of receptors available. In some cases, a proportion of receptors may have to be occupied before a response occurs. Thus, there is a threshold for toxicity. With carbon monoxide, for example, there are no toxic effects below a carboxyhemoglobin concentration of about 20%, although there may be... 

Those animals or patients responding at the lowest doses (Fig. 2.5) are more sensitive (hypersensitive) and those responding at the highest doses are less sensitive than the average (hyposensitive). The median point of the distribution is the dose where 50% of the population has responded and is the midpoint of the dose-response curve (Fig. 2.6). If the frequency distribution of the response is plotted cumulatively, this translates into a sigmoid curve. The more perfect the Gaussian curve, the closer to a true sigmoid curve will the dose-response curve be. 

Indeed, in the experiment described above with the carcinogen DMBA, the production of papillomas in mice shows a sigmoid dose-response curve when plotted against the concentration of TPA. The dose-response curve for the interaction between the TPA and its receptor mirrors this dose-response curve almost exactly. 

Evaluated from sigmoidal dose-response curve fitted to G-bead assembly data, Gas-bead for /ijAR-GFP and Gsy-bead for FPR-GFP. 

Figure 11.3 The dose-response relationship, (a) Five segments of the sigmoidal dose-response curve as described in the text, (b) Linearized dose-response relationship through log (dose)-probit (effect) transformations. Locations of the LD50 and LD05 are depicted.

Data are recorded using e.g. TIDA software (HEKA Electronics, Lambrecht, Germany) and the results are typically expressed as fraction of baseline current. Concentration-response data can be fitted to an equation of the following form 1/10 = 1/(1 + flcom-poundl/ICso)) such that the IC50 can be calculated with a sigmoidal dose-response curve model. 

DeLean A, Munson PJ, Rodbard D (1978) Simultaneous analysis of families of sigmoidal curves Application to bioassay, radioligand assay, and physiological dose-response curves. Am J Physiol 235 E97-E102... 

Haanstra L, Doelman P, Oude Voshaar JH. 1985. The use of sigmoidal dose response curves in soil ecotoxicological research. Plant Soil 84 293-297. 

Figure 19.4. Plot of fractional occupancy (FO) versus the [ligand] and the log [ligand]. This provides the theoretical basis for the utility of semilog plots a sigmoidal curve results that allows maximal visual extrapolation of information from the most biologically meaningful part of the dose-response curve.

Fig. 14,1. Basic competitive and non-competitive immunoassay designs. (A) Non-competitive immunoassays use paired antibodies directed against different parts of the analyte molecule. The first antibody is used to capture the analyte from the sample and the second, labelled antibody to measure the amount of analyte bound, resulting in a response directly related to the concentration of analyte in the sample. (B) Competitive immunoassays use labelled antigen to measure unoccupied sites, resulting in a sigmoidal dose-response curve where the signal is inversely related to the concentration of analyte in the sample.

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