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The effect of pineal melatonin on insulin production
Hovorková, Adéla ; Bendová, Zdeňka (advisor) ; Horníková, Daniela (referee)
Both production and secretion of insulin depend on the circadian rhythms. These are set by the internal circadian clock reacting to the external stimuli such as the light or the darkness. The central clock synchronization of the rhythmic processes in the organism is formed by the structure so-called suprachiasmatic nucleus. Secretion of melatonin, aka "hormone of the night," is controlled by the central clock and serves to align them with the peripheral clocks. Peripheral clocks are located, for example, in pancreas, liver or other body organs. Langerhans' islets in pancreas consist of -, - and -cells. These play an important role in maintaining glucose homeostasis as they produce hormones insulin and glucagon, key blood glucose level regulators. This text describes how the corruption of circadian system by a light pulse at night impacts insulin secretion. A phase shift results in melatonin secretion anomaly (increase), which inhibits insulin levels and thus gives rise to elevated glucose levels. Hyperglycaemia and insulin resistance because of a long-term rhythm corruption may result in type 2 diabetes. Key words: circadian rhythm, SCN, melatonin, MT1 receptor, MT2 receptor, β-cell, insulin, glucagon, insulin resistance, type 2. diabetes
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Optimization of flavin monooxygenase activity assay
Hovorková, Adéla ; Dračínská, Helena (advisor) ; Heidingsfeld, Olga (referee)
Flavin monooxygenases, biotransformation enzymes catalyzing the oxidation of broad spectrum of xenobiotics, have long been overlooked compared to cytochromes P450, a larger group of biotransformation enzymes. Liver microsomes containing both flavin monooxygenases and cytochrome P450 are often used to study metabolism of xenobiotics. The catalytic aktivity of both enzymes may overlap due to the need of identical cofactors and it is therefore necessary to differentiate them appropriately. This bachelor thesis deals with the optimization of the method for the determination of enzyme activity of flavin monooxygenases in rat liver microsomes. Model reaction for optimization of the method was the oxidation of methyl p-tolyl sulfide to methyl p-tolyl sulfoxide. To determine the activity, the most suitable conditions were set: sample buffer with pH 9.5, 2 mM methyl p-tolyl sulfide and a 10 minute incubation time. It has been found that in the oxidation of methyl p-tolyl sulfide cytochromes P450 are also involved, mostly isoform 1A1. Various inhibitors of both of the above mentioned biotransformation enzymes (lipoic acid, methimazole, Brij 35 and Triton X-100) have also been tested. Brij 35 was selected as a suitable inhibitor of the catalytic action of cytochromes P450, because it had no effect on the rate...
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