In Vitro Reconstruction of Xenopus Oocyte Ovulation

Progesterone is widely used to induce maturation of isolated fully grown oocytes of the African clawed frog, Xenopus laevis. However, the hormone fails to release oocytes from the layer of surrounding follicle cells. Here, we report that maturation and follicle rupture can be recapitulated in vitro by treating isolated follicular oocytes with progesterone and low doses of the matrix metalloproteinase (MMP), collagenase, which are ineffective in the absence of the steroid. Using this in vitro ovulation model, we demonstrate that germinal vesicle breakdown (GVBD) and oocyte liberation from ovarian follicles occur synchronously during ovulation. Inhibition of the MAPK pathway in these experimental settings suppresses both GVBD and follicular rupture, whereas inhibition of MMP activity delays follicular rupture without affecting GVBD. These results highlight importance of MAPK and MMP activities in the ovulation process and provide the first evidence for their involvement in the release of oocytes from ovarian follicles in frogs. The in vitro ovulation model developed in our study can be employed for further dissection of ovulation.

Clinical relevance in present day hormonal contraception

The contraceptive pill is an effective and very safe method to control pregnancies. It was developed 60 years ago, and despite that the composition has been the same since it was first developed (estrogen and progestogen), over the years the concentration of ethinyl estradiol has been reduced to improve tolerability. Nevertheless, progestogens are the basic active agent of hormonal contraception. The mechanism of progestogens is a multimodal one and basically three modes of contraceptive action can be distinguished: (a) A strong antigonadotrophic action leading to the inhibition of ovulation. The necessary dosage of ovulation inhibition per day is a fixed dosage that is intrinsic to each progestogen and independent of the dosage of estrogen used or the partial activities of the progestogen or the mode of application. (b) Thickening of the cervical mucus to inhibit sperm penetration and (c) desynchronization of the endometrial changes necessary for implantation. The on the market available progestogens used for contraception are either used in combined hormonal contraceptives (in tablets, patches or vaginal rings) or as progestogen only contraceptives. Progestogen only contraceptives are available as daily oral preparations, monthly injections, implants (2–3 years) and intrauterine systems (IUS). Even the long-acting progestogens are highly effective in typical use and have a very low risk profile. According to their introduction into the market, progestogens in combined hormonal contraceptives, have been described as 1st, 2nd, 3rd and 4th generation progestogens. The different structures of progestogens are derivatives from testosterone, progesterone and spironolactone. These differences in the molecular structure determine pharmacodynamic and pharmacokinetic differential effects which contribute to the tolerability and additional beneficial or therapeutic effects whether used in combined oral contraceptive (COC) or as progestogen only drugs. These differences enhance the individual options for different patient profiles. The new development of polymers for vaginal rings allowed on the one hand, the improvement of the estrogen/progestogen combination in these rings especially regarding the comfort of use for women (e.g. avoiding the use of cold chains or packages with up to 6-month rings) and on the other hand, the development of progestogen only formulations. Another future development will be the introduction of new progestogen only pills that will provide effective contraceptive protection with more favorable bleeding patterns and a maintenance of ovulation inhibition after scheduled 24-h delays in pill intake than the existing progestogen only pill (POP) with desogestrel (DES).

Abdominal pain mimicking dysmenorrhea in luteal phase

We treated four patients with severe abdominal pain in the luteal phase that showed a remarkable resemblance to dysmenorrhea. The symptoms began when the patients were in their twenties and thirties, and the pain was identical to the high phase of basal body temperature. No other abnormal findings were revealed in physical examinations, except for leiomyoma in two patients. Oral contraceptive use led to symptom exacerbation, while gonadotropin-releasing hormone agonist administration completely inhibited the pain. One patient underwent a hysterectomy for leiomyoma, with ovulation later confirmed, though luteal phase abdominal pain completely disappeared. Based on our findings, the postulated mechanism for the pain is uterine contractions induced by progesterone through various mechanisms. The symptoms in our patients were successfully treated by ovulation inhibition obtained with cyclic administration of conjugated estrogen.