Shigetatsu Shiokawa

Integrins and reproductive physiology: expression and modulation in fertilization, embryogenesis, and implantation

OBJECTIVE To review the available information regarding the role of integrins in reproductive physiology and to discuss their potential clinical implications. DESIGN Studies that specifically relate to the expression and modulation of integrins in fertilization, embryogenesis, and implantation were identified through the literature and Medline searches. RESULT(S) Integrins are a class of adhesion molecules that participate in cell-to-cell and cell-to-substratum interactions and are present on essentially all human cells. All mammalian eggs express integrins at their surface, and the integrin alpha 6 beta 1 serves as a sperm receptor that mediates sperm-egg binding. In addition, certain integrin moieties appear to be regulated within the cycling endometrium. Specifically, the expression of beta 1 integrins in the early proliferative phase is restricted to the glandular epithelium, whereas stromal cells also express beta 1 integrins in the midsecretory phase. The expression of beta 1 integrins increases at the time of implantation and remains elevated in the decidua during early pregnancy. A disruption of integrin expression is associated with certain types of infertility in women. The apical surface of the mural trophectoderm does indeed possess functional integrins, and trophoblast interactions with extracellular matrix proteins largely depend on the integrin family of adhesion receptors. CONCLUSION(S) Integrins play particularly important roles in both fertilization and embryogenesis, including the process of implantation.

Angiotensin II directly induces follicle rupture and oocyte maturation in the rabbit

To investigate the possible direct involvement of angiotensin II (Ang II) in ovulation and oocyte maturation, Ang II at 100 or 10 μg was administered at 2‐h intervals in the in‐vitro perfused rabbit ovaries. The addition of Ang II in the perfusate induced ovulation in vitro in the absence of gonadotropin, while ovulation did not occur in any contralateral control ovaries. However, the ovulatory efficiency in the Ang II‐treated ovaries was significantly lower than in hCG‐treated ovaries. Ang II significantly stimulated the meiotic maturation of ovulated ova and follicular oocytes. Concomitant addition of the specific receptor antagonist of Ang II, saralasin, 30 min before the onset of Ang II administration blocked Ang II‐induced ovulation in a complete manner. Although suralasin did not inhibit completely hCG‐induced ovulation and oocyte maturation, these results suggest that Ang II produced in the ovary may act locally in the process of ovulation.

Gonadotropin stimulates ovarian renin-angiotensin system in the rabbit

The present study was undertaken to assess the role of ovarian renin-angiotensin system (RAS) in the preovulatory cascade induced by gonadotropin exposure. In the in vitro perfused rabbit ovaries, exposure to human chorionic gonadotropin (hCG) enhanced the secretion rate of angiotensin II (Ang II) within 1 h. The secretion rate reached maximal levels at 6 h and then declined thereafter. The intrafollicular Ang II content and renin-like activity were also significantly increased at 2 and 4 h after exposure to hCG, compared with control ovaries perfused with medium alone. The level of intrafollicular Ang II after hCG exposure significantly exceeded the concentration of Ang II in an equivalent volume of plasma. The addition of 1 microM captopril to the perfusate significantly inhibited the secretion rate of Ang II stimulated by hCG; however, captopril affected neither the ovulatory efficiency nor prostaglandin production in ovaries treated with hCG. Captopril significantly inhibited the resumption of meiosis in the ovulated ova and follicular oocytes stimulated by hCG. The administration of 100 micrograms Ang II at 2-h intervals to the perfusate reversed the inhibitory effects of captopril on hCG-induced oocyte maturation. In conclusion, these data indicate that gonadotropin stimulates renin-like activity and Ang II production in the rabbit ovary. Ovarian renin-angiotensin system may play an important role in the process of oocyte maturation after exposure to gonadotropin.

Direct effect of gonadotropin-releasing hormone agonists on the rabbit ovarian follicle

OBJECTIVE To determine if gonadotropin-releasing hormone agonist (GnRH-a)-induced oocyte maturation and degeneration can be attributed to the direct actions on the follicle. DESIGN Mature rabbit follicle culture. INTERVENTIONS The mature follicles were cultured with human chorionic gonadotropin (hCG) (100 ng/mL), buserelin acetate (10(-9) to 10(-6) M), leuprolide acetate (10(-9) to 10(-6) M), or buserelin acetate (10(-7) M) with a GnRH antagonist (10(-8) to 10(-6) M) for 14 hours. MAIN OUTCOME MEASURES The percentage of oocytes achieving germinal vesicle breakdown, the oocyte degeneration rate, prostaglandins (PG) production by mature follicles, and the frequency of fertilization and embryonic development. RESULTS Gonadotropin-releasing hormone agonist induced the meiotic maturation of follicle-enclosed oocytes in a dose-dependent manner while concomitantly increasing oocyte degeneration. The simultaneous addition of GnRH antagonist inhibited significantly GnRH-a-induced oocyte maturation and PG production by the mature follicles. Furthermore, a GnRH antagonist reversed the oocyte degeneration rate that had been increased by GnRH-a. The rates of normal fertilization and early embryonic development were significantly reduced in the oocytes matured by GnRH-a as compared with those matured by hCG. CONCLUSIONS Gonadotropin-releasing hormone agonist acts directly on mature rabbit follicles to trigger the oocytes to undergo meiotic maturation, but oocytes matured in vitro by GnRH-a are not necessarily cytoplasmically mature.

Effects of Beta-1 Integrins in the Process of Implantation

The expression and function of beta 1 integrins on human decidual cells were investigated. Flow cytometric analysis revealed that the cultured decidual cells expressed a high level of the beta 1 subunit on the cell surface. Mouse blastocysts attached to and spread onto cultured human decidual cells. Attachment of the blastocysts was a necessary prerequisite for the further outgrowth of trophoblasts. The addition of a monoclonal antibody recognizing the beta 1 subunit to the cultured decidual cells did not affect the rates of hatching and attachment of blastocysts. The outgrowth of embryos on decidual cells was inhibited by the addition of the anti-beta 1-subunit antibody in a dose-dependent manner. Furthermore, exposure of decidual cells to the anti-beta 1-subunit antibody significantly inhibited the extent of outgrowth of trophoblasts, implying that blastocyst attachment and outgrowth is mediated by different mechanisms. These observations suggest that beta 1 integrins on decidual cells may be involved in the process of blastocyst development and differentiation after attachment.

Comparative study of hormonal dynamics in pregnant and nonpregnant cycles during pulsatile subcutaneous administration of human menopausal gonadotropin in anovulatory infertile women.

OBJECTIVE To assess the clinical relevance of daily hormonal changes for achieving a successful pregnancy in anovulatory infertile women. DESIGN A comparative study of hormonal dynamics in pregnant and nonpregnant cycles during the pulsatile subcutaneous administration of hMG. Subjects received subcutaneous injection of either 9.375 IU or 14.0625 IU of hMG diluted in 50-microL physiological saline (total daily dose, 150 or 225 IU) at 90-minute intervals by means of a portable peristaltic pump. SETTING Kyorin University Hospital and Ichikawa General Hospital. PATIENTS We analyzed 18 pregnant and 42 nonpregnant cycles in 17 patients with secondary hypothalamic/pituitary amenorrhea who conceived after receiving pulsatile hMG treatment. Another 14 women with normal spontaneous ovulation, including 14 pregnant and 15 nonpregnant cycles, served as controls. MEASUREMENTS Serum concentrations of LH, FSH, E2, and P were measured, and the P:E2 ratio was determined. RESULTS Serum concentrations of LH and FSH did not differ significantly between the pregnant and nonpregnant cycles. Serum levels of P and E2 were significantly higher during the hMG treatments than those of the spontaneous ovulatory cycles throughout the follicular and luteal phases. Up to the midluteal phase, the P and E2 values in the nonpregnant cycles during the hMG treatments did not differ significantly from those in the pregnant cycles. The P:E2 ratios were comparable between the pulsatile stimulatory cycles and the normal spontaneous ovulatory cycles. However, the P:E2 ratio in the early and midluteal phases was significantly greater in the pregnant cycles than in the nonpregnant cycles. CONCLUSION The P:E2 ratio in the early and midluteal phases is a more important indicator of hormonal function for implantation than the absolute levels of either P or E2.

Possible Involvement of Lipoxygenase Products in Human Corpora lutea

The present study was undertaken to determine the ability of cultured luteal cells from human corpora lutea to secrete progesterone (P4) and prostaglandins (PGs), and to assess the effects of the products of the lipoxygenase pathway on luteal P4 production. Luteal cells responded to human chorionic gonadotropin (hCG) with a significant increase (2- to 7-fold) in P4 production. Arachidonic acid significantly stimulated PGE2 synthesis by luteal cells in a dose-dependent manner. Both basal PGE2 production and the responsiveness to arachidonic acid were maintained for 8 days. In contrast, both PGF2 alpha and 6-keto-PGF1 alpha production abruptly declined as the culture proceeded. However, the addition of hCG did not further stimulate the accumulation of the 3 PGs assayed. In the subsequent experiment, 5-hydroxyeicosatetraenoic acid (5-HETE) and the reaction products of soybean lipoxidase of arachidonic acid (AA-LIP) were utilized for evaluating the involvement of the lipoxygenase pathway in luteolysis. The addition of 5-HETE dose-dependently inhibited P4 production by the cultured luteal cells. Although treatment with either arachidonic acid or lipoxidase alone had no effect on P4 production, AA-LIP significantly reduced P4 production in the presence or absence of hCG. These results suggest that the products of the lipoxygenase as well as of the cyclo-oxygenase pathway may be important in regulating the life span and function of human corpora lutea.