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Feeding behavior is closely related to the circadian activity of humans and animals. The endocannabinoid system is known to affect the circadian changes in energy balance and gastrointestinal peptides were found to change the expression of CB1 receptor in vagal terminals in the alimentary tract. Therefore, we have examined whether the anorectic action of CB1 receptor antagonist, AM 251, may be modified by activation or blockade of GLP-1 receptor. Male Wistar rats were housed in individual cages and maintained on a 12:12 hour light-dark cycle with free access to standard, pelleted rat chow and water. Each rat received a preweighed amount of food every day throughout the experiment. The animals were injected intraperitoneally either with a CB1 receptor antagonist, AM251 (2 mg/kg bw.), followed 15 min later by a GLP-1 antagonist, exendin (9-39) (160 µg/kg bw.), or AM 251 (1 mg/kg bw.) followed 15 min later by a GLP-1 agonist, exendin 4 (1.5 µg/kg bw.). All injections were made 1 – 1.5 hour before lights off. 24-hour food intake was recorded two days before and two days after the injection. AM 251 at a dose of 2 mg/kg significantly reduced daily food intake and concomitant injection of exendin (9-39), at a dose found previously to prevent the action of other anorectic agents, had no effect on a AM 251-induced decrease in food consumption. On the other hand, either 1 mg/kg AM 251 or 1.5 µg exendin-4 administered alone had no significant effect on 24-hour food intake. When, however, these drugs were co-injected, a marked reduction in 24-hour food intake occurred. These results indicate that (1) the anorectic action of CB1 receptor antagonist is not mediated by GLP-1 and (2) the CB1 receptor antagonist and GLP-1 receptor agonist act synergistically to reduce the daily food consumption in the rat when injected before of the nocturnal feeding phase. This work was supported by the National Centre for Science (grant No. 0056/B/ P01/2011/40).
Both the endocannabinoids and glucagon-like peptide-1 (GLP-1) are known to control intake of highly palatable food. We have investigated whether WIN 55,212-2 (a cannabinoid receptor 1 agonist) and exendin-4 (Ex-4, a GLP-1 agonist) may interact to change feeding behavior in rats maintained on a free-choice, high-sucrose diet. The rats were presented with both their regular and highsucrose chow throughout the experiment. After 4 days, they were injected once daily for 3 days with either 1 mg/kg WIN 55,212-2, 3 µg/kg Ex-4 or both. Ex-4 and, unexpectedly, WIN 55,212-2 injected separately diminished the mean daily caloric intake. When both drugs were administered together, the daily caloric intake was further reduced, the consumption of high-sugar chow was almost completely inhibited but the intake of standard diet was increased and was significantly higher than that in either Ex-4-, WIN 55- 212-2- or saline-injected rats. These changes were associated with a marked reduction in body weight in both WIN-55,212-2- and Ex-4+WIN-55,212-2-treated animals wherein the difference between these groups was not significant. In conclusion, subchronic treatment with WIN 55-212-2 resulted in the reduced total caloric intake and Ex-4 enhanced this effect. Moreover, combined administration of WIN 55-212-2 and Ex-4 reversed food preferences (i.e., decreased sweet chow and increased standard chow consumption).
The study of human disorders known as premature aging syndromes may provide insight into the mechanisms of cellular senescence. The main feature of cellular senescence in vitro is cessation of cell proliferation. Down syndrome (DS) and neuronal ceroid-lypofuscinosis (NCL) are clinically characterized by the premature onset of numerous features normally associated with human aging. Phytohemagglu- tinin stimulated lymphocytes derived from DS subjects showed a statistically significant diminished proliferation capacity in comparison with lymphocytes derived from NCL and healthy individuals. We demonstrated, by applying the electrophoretic mobility shift assay, slightly impaired AP-1 DNA binding activity in NCL lymphocytes and strong in DS ones. Our results showed that the same molecular mechanisms of proliferation cessation could exist in fibroblasts characterized by replicative senescence and in lymphocytes derived from individuals with premature aging syndromes (Down).
Normal human T lymphocytes growing in culture undergo replicative senescence. Previously, we have shown that in our conditions polyclonal T cells cease proliferation after about three weeks (Radziszewska et al., 1999, Cell Biol. Int. 23, 97-103). Now we present results of a more detailed analysis of in vitro growth as well as phenotypic changes of T cells. Cell cycle analysis showed that about 20% of cells were in the S phase untill the 17th day of culture (young cells). The highest number of mitotic cells (phase G2/M; 10%) was observed during the first week of culture. All not dividing senescent cells were stopped in the G1 phase (after the 30th day of culture). The sub-G1 fraction which represents apoptotic cells did not exceed 8% during the whole period until the 30th day of culture. During in vitro T-cell growth, a rather rapid selection to CD3+CD8+ cells occurs. In the presenescent (between the 17th and 30th day) and senescent populations the majority of cells (above 90%) were CD8 positive. We also have checked the expression of alpha-chain interleukin-2 (IL-2) receptor (CD25). In young and presenescent cells about one third of cells was CD25 positive, but only 15% in the pool of senescent cells. Immunoblotting analysis of p16 protein recognized previously as a marker of senescent T cells, showed its highest and transient expression in presenescent cells. A critical review of the polyclonal T cell replicative senescence model is presented.
UVC-induced apoptotic symptoms such as morphological changes, DNA fragmentation, Bcl-2 and Bax protein expression were examined in primary splenocyte cultures from young (3 months) and old (24 months) rats. The activities of AP-1 and CRE transcription factors in UVC-irradiated splenocytes were also assessed. At 24 h after UVC irradiation 40% of cells derived from young rats were found to be apoptotic, which was twice as much as in splenocytes from old rats. Apoptosis in cells from old rats did not give typical symptoms like a DNA ladder and Bcl-2 protein downregulation, in contrast to splenocytes from young rats. No AP-1 transcription factor activity was found in UVC-irradiated splenocytes from old animals and only a trace activity in splenocytes from young animals. This indicates that, UVC-induced apoptosis in rat splenocytes is practically AP-1 independent and that cells from old rats are less sensitive to UVC irradiation than splenocytes from young rats.
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