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Kinetic studies on the sorption of radioactiveSe (IV)ion onAmberlite MB9Lhave been carried out under a wide range of temperature, pH, initial concentration, and resin weight. Analyses of the experimental data by two theoretical models commonly used to explain the ion exchange kinetics and shrinking core model (SCM), and homogeneous diffusion model (HDM) against exponential diffusion decay model (EDM) show a greater preference of EDM over HDM and SCM at all reaction conditions. The obtained regression coefficient values in case of HDM and SCM are in general not high enough to give a satisfactory fit for the experimental data. The estimated values for EDM parameters provides a good satisfactory fit for the yielded adsorption results as the corresponding linear regression values are high. The sorption process is found to be accompanied with fast film diffusion and slow diffusion between the reacted layer and the shrinking un-reacted core within the ion exchange resin. It also shows that ion exchange as the controlling step offers the lowest probability due to the highest obtained diffusion parameters over the normal tested reaction conditions. [ABSTRACT FROM AUTHOR]

Background: Histamine was found to stimulate melanogenesis in cultured human melanocytes specifically mediated by histamine H 2 receptors via protein kinase A activation. Based on this finding, the effect of topically applied H 2 antagonist on UVB-irradiated Guinea pigs' skin was examined and found to be suppressive on the post-irradiation melanogenesis.Aims: In this study, we tried to explore the role of topically applied H 1 and H 2 receptor antagonists, in inhibition of UVB-induced melanization.Methods: The effect of topically applied H 1 and H 2 receptor antagonists in inhibition of melanization was done clinically and histochemically using Fontana Masson and DOPA reactions compared with placebo.Results: The post-irradiation pigmentation was found to be brownish/black instead of the original light brown color. This color change occurred below the shaved orange-red fur suggesting a switch of melanogenesis from pheomelanin to eumelanin. The induced pigmentation was suppressed by topically applied H 2 antagonist while both H 1 antagonist and vehicle had no effect. The microscopic examination showed that the keratinocytes in the H 2 antagonist-treated areas contained few melanosomes while the nearby dendrites are full of them.Conclusion: H 2 antagonists' inhibition of UVB-induced pigmentation is not only due to suppression of melanization but also due to a specific action on melanosomes' transfer. [ABSTRACT FROM AUTHOR]