The role of nonsteroidal regulators in control of oocyte and follicular maturation

Effect of intraovarian factors on porcine follicular cells: cumulus expansion, granulosa and cumulus cell progesterone production

The role of granulosa cell conditioned media (CM) containing luteinization stimulator (LS), and the role of EGF in the cumulus expansion of oocyte-cumulus complexes (OCC) isolated from large antral follicles was investigated. The CM were prepared by incubation of granulosa cells isolated from large antral follicles. After 24h incubation, more than 61 or 64% of OCC expanded to the +3 and +4 stage in the presence of CM (50%) or EGF (10ng/ml), respectively. The stimulatory effect of LS and EGF on the cumulus expansion was accompanied by the enhanced hyaluronic acid synthesis. Complete suppression of cumulus expansion stimulated by LS and EGF was observed in the presence of 10 micromol/l genistein (tyrosine kinase inhibitor), in the presence of 10mmol/l LiCl (the inhibitor of inositol 1,4,5-trisphosphate metabolism), and 100 micromol/l gallopamil, verapamil and norverapamil (calcium channel blockers). Stimulatory effect of EGF on the cumulus expansion of OCC isolated from large follicles was accompanied by the increased cumulus cell progesterone production. However, EGF did not affect the progesterone production by OCC isolated from small follicles. To determine whether EGF could modulate the granulosa cell steroidogenesis also, the effect of EGF on granulosa cells isolated from large (LGC) and small (SGC) follicles was compared. EGF (10ng/ml) failed to affect the progesterone synthesis during 72h culture of SGC but significantly enhanced the LGC progesterone production. Our results indicate that luteinization factor stimulates the cumulus expansion and hyaluronic acid synthesis by the OCC isolated from large antral follicles. The mechanism of LS- and EGF-induced cumulus expansion may involve tyrosine kinase activation and calcium mobilization. In addition, these results indicate the different response of porcine cumulus and granulosa cells originating from small and large follicles on the stimulatory effect of EGF.

Regulation of murine oocyte meiosis: evidence for a gonadotropin-induced, cAMP-dependent reduction in a maturation inhibitor

We have developed an assay that can detect relative changes in the amount of a non-cAMP inhibitor of maturation present in cumulus cells (Eppig et al., 1983, Dev. Biol., 100:39-49). Using this assay in which accelerated maturation of a group of treated cumulus cell-oocyte complexes relative to untreated complexes indicates a decrease in the amount of inhibitor, results of the experiments described here suggest a possible relationship between elevation of cAMP levels and subsequent decreased amounts of a non-cAMP inhibitor. Mouse oocytes obtained from cumulus cell-oocyte complexes treated with luteinizing hormone (LH) resumed meiosis prior to oocytes obtained from untreated complexes; the degree of acceleration of maturation was dependent on LH concentration. A similar result was obtained with follicle-stimulating hormone (FSH). Correlated with LH- or FSH-acceleration of maturation was an LH- or FSH-induced elevation of cumulus cell cAMP levels. Inhibiting LH-induced elevation of cumulus cell cAMP levels inhibited LH-induced acceleration of maturation. An initial incubation of complexes in medium containing dibutyryl cAMP (dbcAMP) also promoted acceleration of maturation. In contrast, maturation of denuded oocytes was not altered by treatment with either LH, FSH, or dbcAMP. Complexes initially incubated in dbcAMP-containing medium still demonstrated acceleration of maturation after a subsequent 2 h incubation in dbcAMP-free medium. Relative to untreated complexes, none of these treatments disrupted intercellular communication between cumulus cells and the oocyte. Elevating follicle cAMP levels with cholera toxin induced maturation of follicle-enclosed oocytes when cumulus cell-oocyte coupling was still fully maintained. These results are interpreted to indicate that gonadotropin-mediated acceleration of maturation is via a cAMP-dependent reduction in the level of a maturation inhibitor present in granulosa/cumulus cells.

Decline of follicular oocyte maturation inhibitor coincident with maturation and achievement of fertilizability of oocytes recovered at midcycle of gonadotropin-treated women

To examine whether a decline in follicular oocyte maturation inhibitor (OMI) is associated with attainment of oocyte maturation and fertilizability, OMI was measured in follicular fluid (FF) of 39 follicles of 20 normal women given human menopausal gonadotrophin and human chorionic gonadotrophin to induce follicular growth and maturation. Oocytes were aspirated per laparoscope, the fluid was saved, and the egg was observed, incubated, and inseminated with the husband's sperm. Concepti that developed to the 4- to 8-cell stage were transferred to the uterus and the women were followed for pregnancy. OMI activity in each FF was measured by using cultured cumulus-enclosed porcine oocytes (30-40 oocytes per FF sample). Estrogen, progesterone, oocytes (30-40 oocytes per FF sample). Estrogen, progesterone, and delta 4-androstenedione were measured in FF by radioimmunoassay. The FF of 13 preovulatory follicles yielding oocytes that were mature and fertilizable had significantly less OMI activity (mean +/- SEM) (0.58 +/- 0.10 unit/ml) compared to follicles yielding immature oocytes (2.8 +/- 0.56 units/ml; n = 9), atretic oocytes (5.5 +/- 2.5 units/ml; n = 7), or preovulatory oocytes with fractured zonae (1.9 +/- 0.63 units/ml; n = 7). The estrogen concentration (mean +/- SEM) of preovulatory follicles yielding mature fertilizable eggs or mature eggs with fractured zonae was greater (396 +/- 34 ng/ml; n = 20) compared to follicles yielding immature or atretic eggs (203 +/- 59 ng/ml; n = 9 and 97 +/- 47 ng/ml; n = 7, respectively; P less than 0.05). Progesterone concentration (mean +/- SEM; ng/ml) of FF was generally elevated in all preovulatory follicles (635 +/- 53) compared to immature or atretic follicles (230 +/- 64 and 76 +/- 17, respectively; P less than 0.05). It may be concluded that in normal follicle maturation there is a decline in OMI in the follicle containing an oocyte that becomes mature and fertilizable. There is also an increase in estrogen, progesterone, and follicle size. It is also possible to have an abnormal follicle maturation when there is an increase in size as well as FF, estrogen, and progesterone, but withut a decline in OMI--a situation which can lead to production of a nonfertilizable oocyte.