INDEX mannitol

An alternative method for assessing cell layer integrity is through the use of hydrophilic paracellular transport markers (e.g., radiolabeled D-mannitol or fluorescein-Na+), which passively traverse cells by the paracellular route. Small amounts of compound required for in vitro conjunctival cell culture transport experiments make this approach well suited for screening purposes. Relative absorption index of a series of pharmacologically active molecules can be ranked against known markers for the identification of candidates with potential absorption problems, which is a reliable tool to select drug candidates with optimal characteristics. 

Figure 14.3 Integration plot of the initial uptake of [3H]adenosine by the retina after intravenous administration (A) and retinal uptake index (RUI) of [3H]adenosine and [3H]D-mannitol (B). A [3H]Adenosine (10 //.Ci/head) was injected into the femoral vein. B A test compound, [3H]adenosine or [3H]D-mannitol (10 //Ci/head), and a reference compound, [14C]n-butanol (0.1 //Ci/head), were injected into the common carotid artery in the presence or absence of 2 mM inhibitors. p < 0.05, significantly different from the control. Data from Biochimica et Biophysica Acta, 1758, Nagase et al., Functional and molecular characterization of adenosine transport at the rat inner blood-retinal barrier. 13-19, 2006, with permission from Elsevier.

Ethyl orthoborate has a boiling point of 120°, a density of 0.86426, and a refractive index (n ) of 1.3721. It is readily hydrolyzed to ethanol and orthoboric acid. The ester may be analyzed for boron by dissolving a weighed sample in water, adding mannitol (about ten times the weight of sample taken), and titrating the boric acid to the phenolphthalein end point. This determination works best if the solution is protected from atmospheric carbon dioxide in the region of the end point. 

This ingenious method gave a rough index of blood flow through the kidneys. It was subsequently greatly developed by my old friend and former associate, Homer Smith. Measurements of discrete function of glomerular filtration rate and renal blood flow using mannitol, creatinine, and p-aminohippurate were developed later. 

Hot water extraction of soil boron (B) (Berger Truog 1939) has been used widely to obtain an index of soil B status. The method presents difficulties for routine analysis as it is often difficult to prepare water extracts free of colloidal material. Dilute salt solutions have largely overcome this limitation, two examples being the use of 0.01 M CaCl2-0.05 M mannitol (Cartwright etal. 1983) and hot 0.01 M CaCl2 (Aitken etal. 1987). The empirical method described is based on the use of hot water reflux for soil extraction, with alternative analytical finishes based on a colour reaction and ICPAES. 

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