INDEX tracer methods

Unlike direct reference assays, indirect index methods use two separate tests to estimate the free hormone concentration a total serum T4 (or T3) measurement and an assessment of either the serum TBG concentration or the fraction of T4 (or T3) that is free m serum the latter is traditionally derived using equilibrium tracer dialysis or T uptake methods. Results of these tests are then combined mathematically to give estimates of the free hormone concentration. Indirect index-based methods have essentially fallen out of favor in deference to the direct immunoassay methods. 

In some doublet reactions the same products may be obtained from the same reactants but in different ways. Such reactions were referred to as olistomeric and the structural conditions of their appearance were determined on the basis of the multiplet theory (348). Thus, theoretically two cases of bond fission can take place in esterification, HO—COR + H—OR and H—OCOR HO—R. The tracer method shows that the first case is realized as a rule. The half-doublet scheme expresses such experiments. The doublet indexes for the reactions in solutions disintegrate into such schemes see Balandin (37). A complete system of doublet reactions for C, H, N, 0, S, and Cl (without their isotopes) has been obtained by the author (345). It is much more detailed than Table VII and amounts to 1500 types. It was obtained by exhaustive variation of atoms and bonds in the index by means of a specially developed method based on matrix algebra and combinatorial analysis. The significance of the obtained classification for organic catalysis is similar to that of the complete system of forms in crystallography, which was derived from the groups of symmetry by Fedorov and covers all possible forms (349). 

It was observed that hydrodynamics plays an important role in circulation time (Table 1). The increase in flow velocity reduces t. It is important to note in Table 1 that both techniques resulted in similar values for for Newtonian and non-Newtonian fluids. Taking the tc obtained by the tracer method as reference, the difference with 4 by thermal method ranges from 11 to 25%. Table 1 shows that depends on flow properties as flow index reduces, increasing at the same time the consistence index, tc increases. 

The movement of individual particles in a liquid-solid fluidised bed has been measured by Handley et a/.(40) Carlos(41,42), and Latif(43). In all cases, the method involved fluidising transparent particles in a liquid of the same refractive index so that the whole system became transparent. The movement of coloured tracer particles, whose other physical properties were identical to those of the bed particles, could then be followed photographically. 

Quantitative measurement of diffusional uptake and carrier-mediated transport of nutrients and drugs in experimental animals was greatly facilitated with the introduction of Olden dorfs brain uptake index (BUI) [42].Test and reference tracers are injected as an intraarterial bolus into the carotid artery of the anaesthetized animal. After 5 s the animal is killed and the brain is removed for radioactivity counting. This method measures the ratio of the unidirectional brain extraction, E, of the test substance and of the reference ([ H]-water, [ " C]-butanol), which are labelled with different isotopes, during a single passage through the brain capillary bed ... 

Analysis. There are five important methods for measuring the ratios of isotopes, making use respectively of—the spectrograph, the mass spectrograph, density measurements, atomic weight measurements and refractive index measurements. Any of these methods must be pushed to the present limits of accuracy or beyond in order to meet the requirements for tracer experiments. If, for example, an increase in concentration of C13 is effected from 1 per cent to 1.1 per cent and an accuracy of five per cent in the increase is required the determination must be accurate to one part in 20,000. 

Methods. The diffusion experiments were performed at room temperature (23 C) utilizing a glass diffusion cell consisting of two compartments each with a volume of 175 ml. Each chamber was stirred at a constant rate to reduce boundary layer effects. Solute concentrations were monitored by h or C tracers, refractive index, or U.V. spectroscopy. Partition coefficients, defined as the ratio of the concentrations in the membrane and in the bulk aqueous phase were determined by solution depletion technique. 

All of the above-mentioned methods only measure certain indexes of relative permeability for the drug uptake to brain since they cannot determine the driving force for the efflux. Because it is hard to measure the BBB permeability in brain parenchyma, the microvessels in pia dura at the surface of brain (Figure 14.1) are often used in in vivo BBB permeability study. Although pial microvessels do not have the entire ensheathment of astrocytes as those cerebral microvessels in the parenchyma, the pial and cerebral microvessels appear to have many morphophysiological properties in common. These include ultrastructural characteristics, permeability of cell junctions to electron-dense tracers, transendothelium electrical resistance, and molecular properties of endothelium. For these reasons, pial microvessels are often used in the BBB permeability studies [58],... 

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