This review focuses on current knowledge of leptin biology and the role of leptin in various physiological and pathophysiological states. Leptin is involved in the regulation of body weight. Serum leptin can probably be considered as one of the best biological markers reflecting total body fat in both animals and humans. Obesity in man is accompanied by increased circulating leptin concentrations. Gender differences clearly exist. Leptin is not only correlated to a series of endocrine parameters such as insulin, glucocorticoids, thyroid hormones, testosterone, but it also seems to be involved in mediating some endocrine mechanisms (onset of puberty, insulin secretion) and diseases (obesity, polycystic ovary syndrome). It has also been suggested that leptin can act as a growth factor in the fetus and the neonate., R. Janečková., and Obsahuje bibliografii
Lipid peroxidation of rat cerebral cortex membranes was induced by Fe2+/ADP and ascorbate. The rate of Na+/K+-ATPase inhibition was correlated with the increase of thiobarbituric acid-reactive substances (TBARS) and conjugated dienes (CD) and with membrane fluidity changes. Our data showed that membrane fluidity changes (evaluated by fluorescence steady-state anisotropy measurements) can participate in Na+/K+-ATPase inhibition during the initial period of lipid peroxidation process, whereas during the following period the enzyme inhibition correlates only with TBARS and CD production., H. Rauchová, Z. Drahota, J. Koudelová., and Obsahuje bibliografii
Pterygosoma livingstonei sp. n. collected from the Kenyan lizard Agama caudospinosa Meek shows morphological affinities with other South African congener species parasitizing lizards of the genus Agama, especially with P. triangulare Lawrence, 1936, but it differs in having glabrous genua II and III. P. livingstonei shows affinities with the Lawrence's hispida species group in the characters of genital and peripheral setae. This new species was found concentrated in a nuchal ''mite pocket-like structure'', a behaviour previously unreported among species belonging to the genus Pterygosoma. Mite pockets (or acarodomatia, acarinaria) of lizards typically house damaging chigger mites, and are usually interpreted as the evolutionary host's response to limit damage caused by parasites. Because scale mites are permanent ectoparasites and less damaging than seasonally occurring larval trombiculids, the heavy infestation by P. livingstonei in the nuchal skin folds of its host is interpreted as a consequence of the best utilisation of an available protected site by these mites that spend their entire life cycle on their host and whose primitive body shape prevents them from seeking shelter beneath the scales of their lizard host.
Aging is a process drawing attention of many researchers, and at present many theories exists, which try to explain this chain of inevitable events leading to death of organism. In this article we focused our attention on a theory explaining the degenerative changes occurring during aging by the effect of oxygen free radicals. These highly reactive radicals are produced during oxidative phosphorylation in mitochondria. All cellular components appear to be sensitive to oxygen-radical damage. Lipids, proteins and nucleic acids are probably the most susceptible to this injury. Lipoperoxidation of lipids together with cross-linking of proteins with phospholipids and nucleic acids caused changes in membrane fluidity. Mitochondrial DNA coding several subunits of respiratory chain enzymes can be also damaged by these radicals. All these changes together have negative impact on mitochondrial metabolism resulting progressive decrease of the efficiency of oxidative phosphorylation and thus of the whole organism.
Endothelial dysfunction may be considered as the interstage between risk factors and cardiovascular pathology. An imbalance between the production of vasorelaxing and vasoconstricting factors plays a decisive role in the development of hypertension, atherosclerosis and target organ damage. Except vasorelaxing and antiproliferative properties per se, nitric oxide participates in antagonizing vasoconstrictive and growth promoting effects of angiotensin II, endothelins and reactive oxygen species. Angiotensin II is a potent activator of NAD(P)H oxidase contributing to the production of reactive oxygen species. Numerous signaling pathways activated in response to angiotensin II and endothelin-1 are mediated through the increased level of oxidative stress, which seems to be in casual relation to a number of cardiovascular disturbances including hypertension. With respect to the oxidative stress, the NO molecule seems to be of ambivalent nature. On the one hand, NO is able to reduce generation of reactive oxygen species by inhibiting association of NAD(P)H oxidase subunits. On the other hand, when excessively produced, NO reacts with superoxides resulting in the formation of peroxynitrite, which is a free radical deteriorating endothelial function. The balance between vasorelaxing and vasoconstricting substances appears to be the principal issue for the physiological functioning of the vascular bed., O. Pecháňová, F. Šimko., and Obsahuje bibliografii
Dihydrotestosterone (DHT) originates via irreversible reduction of testosterone by catalytic activity of 5α-reductase enzyme and it is demonstratively the most effective androgen. Androgens influence adipose tissue in men either directly by stimulation of the androgen receptor or indirectly, after aromatization, by acting at the estrogen receptor. DHT as a non-aromatizable androgen could be responsible for a male type fat distribution. The theory of non-aromatizable androgens as a potential cause of a male type obesity development has been studied intensively. However, physiological levels of DHT inhibit growth of mature adipocytes. In animal models, substitution of DHT in males after gonadectomy has a positive effect on body composition as a testosterone therapy. Thus, DHT within physiological range positively influences body composition. However, there are pathological conditions with an abundance of DHT, e.g. androgenic alopecia and benign prostatic hyperplasia. These diseases are considered as ri sk factors for development of metabolic syndrome or atherosclerosis. In obese people, DHT metabolism in adipose tissue is altered. Local abundance of non- aromatizable androgen has a nega tive effect on adipose tissue and it could be involved in pathogenesis of metabolic and cardiovascular diseases. Increased DHT levels, compared to physiological levels, have negati ve effect on development of cardiovascular diseases. Difference between the effect of physiological and increased level brings about certain paradox., M. Dušková, H. Pospíšilová., and Obsahuje bibliografii a bibliografické odkazy
Oxygen can afFect the photosynthetic processes in two antagonistic (protective and destructive) ways. The protection is represented by draining off of the electron transport systém, by utilisation of NADPH and ATP, and production of carbon dioxide in the process of photorespiration, oxygen reduction in the Mehler reaction, and also by regeneration of monodehydroascorbate, one of the fmal products of the Mehler-peroxidase reaction. The subsequent building up of the proton gradient in the Mehler and Mehler-peroxidase reactions also helps protéct the photosynthetic apparatus. The production of harmful oxygen radicals is accompanied by the Mehler reaction. This is in contrast to the fact that the Mehler reaction can also protéct the photosynthetic apparatus. Nevertheless, the scavenging mechanisms in plants are efficient enough for protection against the active oxygen species. In some cases the disproportion between the production and scavenging of active oxygen can result in the destruction of thylakoid membrane. Singlet oxygen, another toxic form of oxygen, can also significantly increase the inhibition of photosynthesis in the presence of oxygen. None of these processes works alone or independently, they are in a dynamic equilibrium and each of them contributes to the regulation of photosynthesis.