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Background. Ghrelin, a newly discovered hormone is involved mainly in the regulation of body energy homeostasis. It has also been proved that ghrelin affects many other processes including the control of the hypothalamo-pituitary-gonadal axis in vertebrates. Ghrelin interacts also with other peptides and neurotransmitters, which are involved in gonadotropin release, such as endogenous opioid peptides. The aim of the experiment was to compare the effects of ghrelin and naltrexone, an opioid antagonist, on LH secretion by pituitary cells of mature female and male common carp, Cyprinus carpio L. Materials and methods. In the in vitro experiment the time-dependent (10 and 24 h) action of ghrelin (10-7 or 10-6 M) and naltrexone at 10-6 M added alone or in combination on LH secretion by enzymatically dispersed pituitary cells of mature female and male carp (Cyprinus carpio L.) was studied. Results. Ghrelin alone at a dose of 10-6 M stimulated LH secretion after 10 h of female- but not male-derived cell incubations. Ghrelin at 10-7 M had no effect on LH secretion from either female or male cells. Naltrexone alone stimulated LH secretion only after 24 h of female cell culture. In male cells no significant changes in LH secretion in response to naltrexone alone were found after 10 or 24 h incubation period. Combined treatment (ghrelin 10-7 or 10-6 M and naltrexone) stimulated LH secretion in female and male cell incubations at 10 and 24 h: LH levels were significantly higher in comparison to control, to ghrelin alone (in cells of both sexes) and to naltrexone alone (in male cells only). Conclusion. The results suggest that opioids and ghrelin may control LH secretion in carp acting synergistically, probably through the same receptor type. The concept of opioid and ghrelin interaction in the gonadal steroid feedback on LH release is also discussed.
The effects of naltrexone on the in vitro luteinizing hormone (LH) secretion from whole pituitary glands as well as from dispersed pituitary cells of common carp (Cyprinus carpio L.)in primary cell culture were studied. The perifusion of whole pituitary glands with naltrexone at a concentration of 10⁻⁴ M caused a significant increase of LH secretion compared to the control. This finding suggests that opioid peptides can indirectly affect LH secretion at the pituitary level, probably through the nerve terminals containing GnRH and/or DA present in the pituitary. In the perifusion of dispersed pituitary cells with naltrexone at concentrations of 10⁻⁶ or 10⁻⁴ M, significant increases of LH levels were found. Similar results were observed in static culture of dispersed carp pituitary cells: after 4 or 24 hours of culture in the medium containing naltrexone at concentrations of 10⁻⁶, 10⁻⁴ or 10⁻² M,a dose-dependent, statistically significant increase of LH secretion to the culture medium was found. The results from dispersed pituitary cell perifusions or cell culture with naltrexone indicate that this antagonist directly affects the pituitary cells and stimulates LH release from carp gonadotrophs.
The effect of different cadmium concentrations on sperm motility in common carp was investigated. The motile activity of spermatozoa was evaluated by means of computer assisted sperm analysis (CASA) using three major parameters characterizing sperm movement - VCL, VAP and VSL. Moreover, subjective microscopic observations were performed in order to evaluate the average time of sperm movement. The following cadmium concentrations were tested: 10,50 100, 200, 500, 1.000 and 2.000 ppm. Computer assisted analysis and microscopic observations both showed that cadmium decreases the motility of carp spermatozoa in all tested concentrations, and that lethal effects were detectable at a concentration of 500 ppm (as determined by CASA) or 1.000 ppm (when manual microscopic observations were performed). Additionally, it was shown that low cadmium concentrations have the most negative influence on straight line velocity, which suggests the possible negative influence of cadmium on the ability of sperm to fertilize female gametes.
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