1,721,384 research outputs found
Signal transduction mechanism for LH in the cumulus-oocyte complex
No full textThe paper reviews recently described signalling mechanisms by which cumulus cells exposed to peak levels of gonadotropins, activate oocyte maturation. Cumulus cells react to LH with a prompt Ca raise which diffuses through gap junctions in a few minutes also into the oocyte where a local amplification system spreads the signal all over the cell. Few h later, still as a consequence of LH stimulation, cumulus cells undergo aprogressive depolarisation of their plasma membrane potential. Due to the electric coupling with these cells the oocyte depolarises too and this open specific voltage gated Ca channels responsible for a second wider and more sustained intracellular Ca rise. As a result of changes throughout maturation with a consequent modification of the size and charge of the molecules that can diffuse from one cell compartment to the other. This cell to cell interaction is further modified with cumulus expansion that leads to a progressive uncoupling of outer cumulus cells while the inner cell layer, corona radiata, remains in oocyte maturation by addressing to the oocyte nutrients and instructions in a well-orchestrated sequence. The identification of these mechanisms are a fundamental prerequisite for the development of in vitro systems suitable to produce oocytes matured in vitro with normal developmental competence[...
Oocyte maturation involves important changes required for activation competence
No full textThe Authors studied the influence of the culture conditions on the ability of oocytes matured in vitro to activate in response to parthenogenetic activation (7% ethanol, etOH, for 5 min). Sheep oocytes were matured as cumulus enclosed oocytes (COCs) or as COCs cocultured with suspended granulosa cells in the presence or absence of gonadotropins. The reactivity of the eggs was evaluated at three different levels. First, intracellular calcium (Ca) was evaluated with the fluorescent dye Indol at the time of exposure of the eggs to the activating stimulus, parthenogenetic development was then ascertained 5h after etOH by recording the formation of pronuclei (PN), and 4 days later by recording early embryo development. Intracellular Ca levels after etOH were significantly higher in oocytes matured in the presence of granulosa cells than in COCs cultured alone. The presence of gonadotropins throughout maturation further increased the amount of Ca released after etOH and FSH was significantly more effective than LH. Culture conditions similarly influenced the formation of IN (Fig 4) and the subsequent development of parthenogenetic embryos (Table 2) These results demonstrate that: a) culture conditions throughout maturation affect the ability of the egg to activate, b) follicle somatic cells in coculture are required for the acquisition of activation competence, c) gonadotropins and FSH in particular improves the reactivity of the oocytes, d) the different reactivity of the eggs are due to the different ability to release Ca following parthenogenetic stimulation.[...
REGENERATIVE MEDICINE IN ‘FUTURE MEDICINE’: The amniotic membrane as a source of stem cells in tendon regenerative therapy
No full text
Ram-induced ovulation to improve artificial insemination efficiency with frozen semen in the sheep
No full textRam effect, defined as shortening of seasonal anestrus in ewes by exposure to the ram, is now well recognized but the underlying mechanisms are still unclear. Little information also exists whether the ram is able to influence the estrus cycle and ovulation. Three experiments were conducted to investigate endocrine response, time of ovulation and pregnancy rate of ewes in proestrus, exposed to the ram (treated) or an adult ewe (control). In the first experiment, ewes (n = 20) were treated with fluorgestone acetate pessaries for 12 days and were given eCG and cloprostenol one day before withdrawal of pessaries. On the day after removal of the pessaries ewes in the treated group (n = 10) were exposed to the sam and those in the control group (n = 10) were exposed to an adult ewe. Blood samples were taken for LH assay every 20 min from 2 h before to 24 h after ram exposure. In the second experiment, ewes (n = 120) were induced into proestrus and on the day after removal of the pessaries were exposed to either a ram (n = 60) or a ewe (n = 60) as described above and were laparoscoped 50, 60 or 70 h after pessary withdrawal (n = 20 at each time interval). In the third experiment ewes (n = 90) were induced and exposed to the ram (n = 45) or an adult ewe (n = 45) and inseminated via a laparoscope whit frozen-thawed semen at 50 or 60 h after pessary removal, respectively. Exposure to the ram was followed in 2 h by a marked rise in LH, equivalent to a preovulatory surge in duration and amplitude. It was also followed by concentrated ovulation within 25 to 30 h and by an increased pregnancy rate in exposed ewes (73.3 vs. 53.3%). [...
Membrane depolarisation triggers maturation in meiotically arrested pig oocyte by activating P type Ca channels on the oolemma
No full text- …
