The gonadotropin surge in human reproduction: endocrine and biochemical mechanisms

The role of aromatase inhibitors in ameliorating deleterious effects of ovarian stimulation on outcome of infertility treatment

Clinical utilization of ovulation stimulation to facilitate the ability of a couple to conceive has not only provided a valuable therapeutic approach, but has also yielded extensive information on the physiology of ovarian follicular recruitment, endometrial receptivity and early embryo competency. One of the consequences of the use of fertility enhancing agents for ovarian stimulation has been the creation of a hyperestrogenic state, which may influence each of these parameters. Use of aromatase inhibitors reduces hyperestrogenism inevitably attained during ovarian stimulation. In addition, the adjunct use of aromatase inhibitors during ovarian stimulation reduces amount of gonadotropins required for optimum stimulation. The unique approach of reducing hyperestrogenism, as well as lowering amount of gonadotropins without affecting the number of mature ovarian follicles is an exciting strategy that could result in improvement in the treatment outcome by ameliorating the deleterious effects of the ovarian stimulation on follicular development, endometrial receptivity, as well as oocyte and embryo quality.

Effects of hyperstimulation with gonadotrophins and age of females on oocytes and their metaphase II status in rats

The present study was undertaken to evaluate the effects of hyperstimulation and aging on the number and proportion of oocytes in the metaphase II stage in female Wistar rats. It explored the validity of the hypothesis that a combination of hyperstimulation with pregnant mare serum gonadotrophins (PMSG) and age could compromise, to a greater extent, the oocyte quality as indicated by the proportion of ovulated oocytes in the metaphase II stage. Female Wistar rats were stimulated with varying doses of PMSG and human chorionic gonadotrophins (hCG) and the number and proportion of ovulated oocytes in the metaphase II stage were examined and compared between different groups of young adult (8-10 weeks old) and aging (30-32 weeks old) female rats. While spontaneous ovulation occurred in all young adult rats, only 50% of the aging rats did. The ovulation rate in aging rats was increased from 50 to 93% when non-PMSG-stimulated rats were given a dose of 10 IU of hCG at proestrus. The lower number of ovulated oocytes noted, even in those hyperstimulated with high doses of PMSG/hCG, also indicated a reduction in fertility in aging rats. Under the influence of high doses of PMSG, all aging rats ovulated, but as with the young adult rats, a higher dose of hCG was needed to achieve the maximum number of ovulated oocytes from the PMSG-induced expanded pool of preovulatory follicles. However, the average number of ovulated oocytes in aging rats was, nevertheless, still significantly lower than in young adult rats even when approximation of weight was considered. No consistent significant difference in proportion of normal oocytes was noted within groups and between young adult and aging rats. A lower proportion of ovulated oocytes was arrested at the metaphase II stages when rats, whether they were young adult or aging, were hyperstimulated with 40 IU of PMSG. However, this proportion was restored to normal (about 100%) when a higher dose of hCG, which is a signal responsible for initiating oocyte maturation, was used. Results of the present study showed that there appears to be an age-related reduction of sensitivity of the preovulatory follicles to the ovulation induction signal of hCG and thus higher doses of hCG were needed to ovulate the PMSG-induced expanded pool of dominant follicles. In older rats, apart from the obvious depletion of the pool of follicles, the evidence from the present study suggests that some of these older rats do have follicles, but that these were unable to develop to preovulatory follicles, probably because of the absence of sufficiently high levels of gonadotrophins essential for the initiation of folliculogenesis. PMSG-hyperstimulation can affect nuclear maturation; the proportion of ovulated oocytes not arrested at the metaphase II stage was higher. However, the proportion of ovulated oocytes at the metaphase II was restored to normal by increasing the dose of hCG use. Hence, meiotic aberration in rats is not age-dependent but rather dependent on the amplitude of the luteinizing hormone (LH)/hCG surge present. The results from this study nullified the hypothesis that hyperstimulation in combination with aging would lead to a higher proportion of abnormality in ovulated oocytes with respect to their being at inappropriate meiotic stages.

Association of molecular variants of luteinizing hormone with menstrual disorders

OBJECTIVE

Luteinizing hormone (LH) promotes ovulation and luteinization of the ovarian follicle, and stimulates steroidogenesis in the ovaries. It is known to be present in different molecular forms, and secretion of abnormal LH has been implicated in menstrual disorders and infertility. The purpose of this study was to determine any association of two recently described LH variants with menstrual disorders in Singapore Chinese women. One of these variants had Trp8 to Arg8 and Ile15 to Thr15 replacements in the LH beta-subunit, while the second variant possessed Ser102 substitution for Gly102.

PATIENTS

One hundred and seventy six patients with menstrual disorders and two hundred normal ovulatory women were recruited and screened for the presence of these two LH variants.

METHODS

The polymerase chain reaction (PCR) products of patients were analysed by restriction fragment length polymorphism (RFLP) and the results were compared with those of normal ovulatory women and confirmed by DNA sequencing.

RESULTS

Twenty one (11.9%) patients with menstrual disorders and twenty (10%) normal ovulatory women were found to carry the first variant, but its occurrence did not show any significant statistical difference between the patient and control groups (P = 0.679). However, the second variant was only detected in seven (4%) patients with menstrual disorders, and none of the normal ovulatory subjects (P = 0.005).

CONCLUSIONS

the study showed that the first variant was not associated with menstrual disorders, whereas the second variant might be implicated in menstrual disorders in some Singapore Chinese women.