No abstract

To investigate the possible direct involvement ofangiotensin II (Ang II) in ovulation and oocyte maturation, Ang II ill lOOor IOyg was administered at 2-h intervals in the in-vitro perfused rabbit ovaries. The addition of Ang II in the pcrfusate induced ovulation in vhro in the absence of gonadotropin, while ovulation did not occur in any contralaleral control ovaries. I-Iowcver, the ovulatory eflicicncy in the Ang II-trcatcd ovaries was signiiicantly lower than in hCG-treated ovaries. Ang II signilicantly stimulated the meiolic maturation of ovulated ova and follicular oocytes. Concomitant addition of lhe specific receplor antagonist of Ang II. saralasin, 30 min before the onset of Ang II administrdlion blocked Ang ILinduced ovulation in a complete manner. Although suralasin did not inhibit completely hCG-induced ovulation and oocytc muturalion, these rcsulls suggest that Ang II produced in the ovary may act locally in the process of ovulation.

The present study was undertaken to investigate the effects of GH on follicular growth, oocyte maturation, ovulation, and production of insulin-like growth factor-I (IGF-I) in the in vitro perfused rabbit ovaries. Ovulation did not occur in any ovaries perfused with GH at a concentration of 1, 10, 100, or 200 ng/ml, but the addition of GH to the perfusate increased the follicle diameter in a dose-dependent manner. The production of IGF-I by ovaries perfused with medium alone was very low throughout the perfusion period. The addition of 100 ng/ml GH to the perfusate significantly increased ovarian production of IGF-I at 4, 6, 8, and 12 h compared with the contralateral control ovaries. Changes in the tissue concentrations of IGF-I in ovaries perfused with 100 ng/ml GH paralleled those triggered by exposure to 50 IU human CG (hCG). When the effect of GH on the tissue concentration of IGF-I was determined at 4 h, GH stimulated the tissue concentration of IGF-I in perfused rabbit ovaries in a dose-dependent manner. The percent increase in follicle diameter in ovaries treated with GH was significantly correlated with the intraovarian IGF-I content. The mean number of ovulations per ovary and the ovulatory efficiency were significantly reduced in ovaries perfused with 5 IU hCG, compared with those in ovaries perfused with 50 IU hCG. The addition of 100 ng/ml GH to the perfusate significantly increased the ovulatory efficiency and follicle diameter in the 5 IU hCG-treated ovaries. Exposure to GH significantly stimulated the resumption of meiosis in the follicular oocytes compared with that in ovaries perfused with medium alone. Furthermore, GH significantly stimulated the resumption of meiosis in ovulated ova and follicular oocytes in ovaries treated with 5 IU hCG. Thus, exposure to GH-stimulated follicular growth, oocyte maturation, and production of IGF-I in the in vitro perfused rabbit ovaries, which indicates that the ovary is in fact a site of GH reception and action. Additionally, GH enhanced the effects of gonadotropins, acting synergistically to promote the ovulatory process. These observations suggest that GH may amplify gonadotropin actions in the process of follicular development and ovulation, at least in part, by stimulating ovarian IGF-I production.

The role of integrins in the processes of adhesion and migration makes them attractive potential participants in the complex events of embryo implantation and placentation. Recently, the role of the alpha(v)beta(3)-integrin pathway was shown in the insulin-like growth factor-I (IGF-I)-stimulated migration of extravillous trophoblast (EVT) cells. This study was designed to investigate the role of alpha(5)beta(1)-integrin in this respect. Using cultured EVT cells, migration assays were carried out for IGF-I-treated or untreated cells in the presence or absence of the GRGDSP and GRGESP hexapeptides, alphaIR3, and a blocking antibody against alpha(5)beta(1)-integrin. Immuno-electron microscopy and immunofluorescent staining were performed to localize the distribution of alpha(5)beta(1)- and alpha(v)beta(3)-integrins, Rab5a, paxillin, phospho-FAK (pFAK), and vinculin. The results showed that IGF-I-induced migration of EVT cells was abolished following treatment with GRGDSP hexapeptide, alphaIR3, and a blocking antibody against alpha(5)beta(1)-integrin. Further, statistical analysis showed that the area-related numerical density of the alpha(5)beta(1)-integrin in the perinuclear regions was significantly higher than in the cell extensions. Immunocytochemical experiments demonstrated an up-regulation in internalization rate of alpha(5)beta(1)-integrin in IGF-I-stimulated EVT cells. Furthermore, alpha(5)beta(1)-integrin exhibited co-localization with Rab5a, but not with alpha(v)beta(3)-integrin, pFAK, paxillin, and vinculin at the focal adhesions of the EVT cells. Taken together, these findings suggest an essential role for alpha(5)beta(1)-integrin in IGF-I-promoted migration of EVT cells. It is possible therefore that IGF-I-induced internalization of alpha(5)beta(1)-integrin may be an important event during the migration of EVT cells in the complex processes of implantation and placentation.

The present study was undertaken to investigate the role of exogenous and endogenous angiotensin II (Ang II) in ovarian steroidogenesis and production of prostaglandin (PG) in in vitro perfused rabbit ovaries. The addition of 100 or 10 micrograms Ang II at 2-h intervals to the perfusate did not stimulate progesterone production, but significantly stimulated estradiol (E2) production by perfused rabbit ovaries. When the specific antagonist of Ang II, saralasin at 2 x 10(-6) M, was added to the perfusate 30 min before the onset of Ang II administration, Ang II-stimulated production of E2 was significantly blocked. Ang II also significantly stimulated both PGE2 and PGF2 alpha production, while the addition of saralasin to the perfusate significantly inhibited the Ang II-stimulated production of PG. The levels of PGs in ovaries perfused with saralasin plus 100 micrograms Ang II did not differ significantly from those in control ovaries perfused with medium alone. Exposure to human CG (hCG) significantly stimulated production of progesterone and E2 by perfused rabbit ovaries, while the concomitant administration of 2 x 10(-6) M saralasin significantly reduced only E2 production. Addition of saralasin to the perfusate inhibited hCG-stimulated PG production in a dose-dependent manner. The ovulatory efficiency in ovaries treated with hCG alone or hCG plus saralasin was significantly correlated with PG production by perfused rabbit ovaries at 12 h after exposure to hCG. The production of PG stimulated by Ang II was completely reduced by indomethacin treatment during the entire perfusion period. Indomethacin completely blocked Ang II-induced ovulation, but not Ang II-stimulated oocyte maturation. Concurrent administration of staurosporine, a protein kinase C inhibitor, at 10(-6) M significantly inhibited Ang II-stimulated meiotic maturation of ovulated ova and follicular oocytes. In conclusion, these results indicate that Ang II has a direct role in ovarian production of E2 and PG. An intrinsic renin-angiotensin system in the rabbit ovary may act as an intermediary of gonadotropin-stimulated PG production. Locally produced Ang II may induce ovulation in the rabbit ovary, at least in part, by stimulating PG production.