Study on the action of D-norgestrel as a postcoital contraceptive agent

Uterine flushings from women treated with levonorgestrel affect sperm functionality in vitro

Levonorgestrel (LNG), a synthetic 19 nor-testosterone derivative, is widely used for emergency contraception. It is well known that LNG prevents ovulation only when given prior to the surge of serum luteinizing hormone (LH) during the periovulatory phase of the menstrual cycle. This observation suggests that LNG, given its contraceptive efficacy, has additional effects other than those affecting ovulation. In this study, we have evaluated the effects on human sperm functionality of uterine flushings (UF) obtained from women at day LH + 1 of a control cycle (CTR-LH + 1) and after receiving LNG (LNG-LH + 1) two days before the surge of LH. Human sperm from normozoospermic donors were incubated with UF and protein tyrosine phosphorylation, sperm motility, acrosome reaction as well as zona pellucida (ZP) binding capacity were assessed. A significant decrease in total motility and tyrosine phosphorylation accompanied by an increase on spontaneous acrosome reaction was observed when sperm were incubated in the presence of LNG-LH + 1. None of these effects were mimicked by purified glycodelin A (GdA). Moreover, the addition of UF obtained during the periovulatory phase from LNG-treated women or the presence of purified GdA significantly decreased sperm-ZP binding. The data were compatible with changes affecting sperm capacitation, motility and interaction with the ZP. These results may offer evidence on additional mechanisms of action of LNG as an emergency contraceptive.

Does levonorgestrel emergency contraceptive have a post-fertilization effect? A review of its mechanism of action

BACKGROUND

Recent studies have identified that levonorgestrel administered orally in emergency contraception (LNG-EC) is only efficacious when taken before ovulation. However, the drug does not consistently prevent follicular rupture or impair sperm function.

OBJECTIVE

The present systematic review is performed to analyze and more precisely define the extent to which pre-fertilization mechanisms of action may explain the drug's efficacy in pregnancy avoidance. We also examine the available evidence to determine if pre-ovulatory drug administration may be associated with post-fertilization effects.

CONCLUSION

The mechanism of action of LNG-EC is reviewed. The drug has no ability to alter sperm function at doses used in vivo and has limited ability to suppress ovulation. Our analysis estimates that the drug's ovulatory inhibition potential could prevent less than 15 percent of potential conceptions, thus making a pre-fertilization mechanism of action significantly less likely than previously thought. Luteal effects (such as decreased progesterone, altered glycodelin levels, and shortened luteal phase) present in the literature may suggest a pre-ovulatory induced post-fertilization drug effect.

LAY SUMMARY

Plan B is the most widely used emergency contraceptive available. It is important for patients and physicians to clearly understand the drug's mechanism of action (MOA). The drug was originally thought to work by preventing fertilization. Recent research has cast doubt on this. Our review of the research suggests that it could act in a pre-fertilization capacity, and we estimate that it could prevent ovulation in only 15 percent or less of cases. The drug has no ability to alter sperm function and limited ability to suppress ovulation. Further, data suggest that when administered pre-ovulation, it may have a post-fertilization MOA.

Update on emergency contraception

Emergency contraception (EC) is any method used after sexual intercourse to prevent pregnancy. This article provides an overview of the history of EC methods and describes the current availability of oral and intrauterine EC. Oral forms include the Yuzpe regimen (combining ethinyl estradiol and levonorgestrel), levonorgestrel-only pills, and ulipristal acetate, which is a new emergency contraceptive drug recently approved by the US Food and Drug Administration. The copper T-380A intrauterine device can also be used for EC. Information about dosing, timing, access, and other considerations in the provision of EC is covered. Clinicians should be aware of all available options in order to counsel women in need of EC appropriately.

Levonorgestrel administration in emergency contraception: bleeding pattern and pituitary-ovarian function

BACKGROUND

This study was conducted to evaluate the effects of levonorgestrel administration for emergency contraception (EC) on bleeding pattern and pituitary-ovarian function.

STUDY DESIGN

In 69 women with a reported stable menstrual cycle length of 24-34 days, we investigated bleeding patterns following EC administration in the follicular (n=26), periovulatory (n=14) and luteal (n=29) phase. In a subgroup of 8 women, hormonal evaluation and ultrasonography were performed.

RESULTS

EC taken in the follicular, but not in the periovulatory or luteal phase, significantly shortened cycle length by 10.9+/-1 days. The subsequent cycle was not affected. EC taken in the late preovulatory phase, prior to the gonadotrophin surge, suppressed ovulation (n=7), while ovulation was not blocked when EC was given during an ongoing luteinizing hormone (LH) pulse (n=1).

CONCLUSIONS

Our data indicate that EC given before the onset of the luteinizing hormone (LH) surge inhibits ovulation and hastens the end of the current menstrual cycle. Subsequently, the length of the following menstrual cycle returned as prior to treatment. By contrast, levonorgestrel administered after the expected ovulation has no effect on menstrual cycle length.

The effects of levonorgestrel on various sperm functions

Two doses of 750-microg levonorgestrel at 12 h apart is one of the regimens for emergency contraception. The mechanism of action of this regimen is not fully known. We investigated whether levonorgestrel influences sperm functions and thereby, exerts contraceptive activity. The motility, acrosome reaction, zona binding capacity, and oocyte fusion capacity of human spermatozoa treated with 1, 10, and 100 ng/mL levonorgestrel for 3 h were evaluated. Levonorgestrel decreased the curvilinear velocity of the treated spermatozoa in a dose-dependent manner. A significant decrease in straight-line velocity, average path velocity and linearity were also found with 100 ng/mL levonorgestrel treatment. This concentration of levonorgestrel, but not others, also marginally decreased (p = 0.045) the zona binding capacity of the treated spermatozoa. The steroid had no effect on acrosome reaction but had a dose-dependent inhibition on spermatozoa-oocyte fusion. These data show that levonorgestrel affects sperm function only at high concentration and the contribution of these effects to emergency contraception is unlikely to be significant.

On the mechanisms of action of short-term levonorgestrel administration in emergency contraception

The effects of short-term administration of levonorgestrel (LNG) at different stages of the ovarian cycle on the pituitary-ovarian axis, corpus luteum function, and endometrium were investigated. Forty-five surgically sterilized women were studied during two menstrual cycles. In the second cycle, each women received two doses of 0.75 mg LNG taken 12 h apart on day 10 of the cycle (Group A), at the time of serum luteinizing hormone (LH) surge (Group B), 48 h after positive detection of urinary LH (Group C), or late follicular phase (Group D). In both cycles, transvaginal ultrasound and serum LH were performed from the detection of urinary LH until ovulation. Serum estradiol (E2) and progesterone (P(4)) were measured during the complete luteal phase. In addition, an endometrial biopsy was taken at day LH + 9. Eighty percent of participants in Group A were anovulatory, the remaining (three participants) presented significant shortness of the luteal phase with notably lower luteal P4 serum concentrations. In Groups B and C, no significant differences on either cycle length or luteal P4 and E2 serum concentrations were observed between the untreated and treated cycles. Participants in Group D had normal cycle length but significantly lower luteal P4 serum concentrations. Endometrial histology was normal in all ovulatory-treated cycles. It is suggested that interference of LNG with the mechanisms initiating the LH preovulatory surge depends on the stage of follicle development. Thus, anovulation results from disrupting the normal development and/or the hormonal activity of the growing follicle only when LNG is given preovulatory. In addition, peri- and post-ovulatory administration of LNG did not impair corpus luteum function or endometrial morphology.

The effects of peri-ovulatory administration of levonorgestrel on the menstrual cycle☆

Levonorgestrel (LNG) 0.75 mg administered 12 h apart within 72 h of unprotected coitus, is an established method of emergency contraception (EC). The mechanism of action of LNG used in this manner is unknown. We administered LNG 0.75 mg twice immediately before ovulation, to test the hypothesis that LNG acts as an emergency contraceptive by abolishing the pre-ovulatory lutenizing hormone (LH) surge and thereby delaying ovulation. Twelve women took LNG on or before the day of the first significant rise in urinary LH in 12 cycles. In four women, the LH peak and the onset of next menses were significantly delayed (delay of 16.8 days (SD +/- 8.7) from the day of mean LH peak in placebo cycles). One woman did not ovulate at all, despite a normal LH peak and cycle length. In the remaining eight women, LNG did not affect ovulation or the cycle length, but the length of the luteal phase and the total luteal phase LH concentrations were significantly reduced. We suggest that LNG acts as an emergency contraceptive by other mechanisms as well as delaying the LH surge and interfering with ovulation.

The mechanism of action of hormonal contraceptives and intrauterine contraceptive devices

Modern hormonal contraceptives and intrauterine contraceptive devices have multiple biologic effects. Some of them may be the primary mechanism of contraceptive action, whereas others are secondary. For combined oral contraceptives and progestin-only methods, the main mechanisms are ovulation inhibition and changes in the cervical mucus that inhibit sperm penetration. The hormonal methods, particularly the low-dose progestin-only products and emergency contraceptive pills, have effects on the endometrium that, theoretically, could affect implantation. However, no scientific evidence indicates that prevention of implantation actually results from the use of these methods. Once pregnancy begins, none of these methods has an abortifacient action. The precise mechanism of intrauterine contraceptive devices is unclear. Current evidence indicates they exert their primary effect before fertilization, reducing the opportunity of sperm to fertilize an ovum.

The effect of levonorgestrel administered in large doses at different stages of the cycle on ovarian function and endometrial morphology

In a pharmacokinetic study, levonorgestrel (L-NOG) 0.75 mg was administered orally to 10 swedish women in the early follicular phase of the menstrual cycle. L-NOG levels were measured after L-NOG administration. A peak level of 16 nmol/l was reached after 2 hours, T 1/2 was estimated to be 14.5 hours (8.5-18.5) in the 24-48-hour interval after dosing. Seventy-two women (in Stockholm, Bombay and Shanghai) were assigned to 4 treatment groups and studied during a control cycle, a treatment cycle and a posttreatment cycle when 0.75 mg L-NOG was administered orally for 4 days in the follicular phase, periovulatory period or luteal phase. Peripheral blood was drawn 3 times weekly during the entire study for the assay of estradiol and progesterone. In 22 women in Stockholm, an endometrial biopsy was obtained on cycle day 20-22 in all 3 cycles studied. When L-NOG was administered on periovulatory days 9, 11, 13, and 15, 3 women showed follicular activity only, 7 exhibited follicular activity followed by insufficient luteal function and 7 women ovulated normally. When L-NOG was administered on periovulatory days 11, 12, 16 and 19, 7 women ovulated during treatment, 6 women exhibited follicular activity followed by insufficient luteal function and 5 exhibited follicular activity only. When L-NOG was administered in the follicular or luteal phase, no effect on ovarian function was seen. No significant prolongation of the cycle lengths was seen when L-NOG was taken during the follicular phase. Only minor effects in the endometrium were observed during treatment.

Pharmacokinetic study of levonorgestrel used as a postcoital agent

The pharmacokinetics and pharmacodynamics of levonorgestrel (LNG) were studied in six women given 0.75 mg LNG orally for seven days during the periovulatory phase of the menstrual cycle. Steady-state concentrations of LNG were reached within three days and serum LNG concentrations at various times on day 7 were generally lower than on day 1, presumably due to a reduced serum level of SHBG. On day 7 the volume of distribution was significantly increased and Co significantly decreased and both the clearance and elimination half-life were higher on day 7 than on day 1. Half-lives varied from 5.6 to 25.1 hours. The day-to-day intra-subject variations in serum LNG concentrations ranged from 23% to 80%. Serum concentrations of pituitary and ovarian hormones suggested that ovulation was not inhibited in four of the six subjects and was delayed in the remaining two. No significant changes in serum prolactin levels were observed.

A possible mechanism of action of danazol and an ethinylestradiol/norgestrel combination used as postcoital contraceptive agents

Twenty-seven women requesting postcoital contraception were randomly allocated to take an ethinylestradiol/dl-norgestrel combination or danazol. Urine specimens were assayed for luteinising hormone (LH) and pregnanediol-3-glucuronide (P3G) levels from the day of the postcoital treatment to the next period. In addition, the urine samples of these recruits and 12 additional women were assayed for the Beta-subunit of human chorionic gonadotropin (B-hCG). A consistent pattern of alteration in urinary steroids was lacking, indicating a heterogeneous effect on ovarian function. There was no evidence of early pregnancy in successfully treated cases. We suggest that the main mechanism of action of these drugs is at the endometrial level.

Mode of action of dl-norgestrel and ethinylestradiol combination in postcoital contraception. III. Effect of preovulatory administration following the luteinizing hormone surge on ovarian steroidogenesis

A combination of 1.0 mg dl-norgestrel and 0.1 mg ethinylestradiol was administered orally at 18 hours after the detection of luteinizing hormone rise and again at 30 hours in five healthy volunteers with normal menstrual cycles. The effects on ovarian function were studied by comparing the daily serum levels of progesterone (P), 17 alpha-hydroxyprogesterone, and estradiol (E2) measured in a control (placebo) cycle with those in two consecutive treatment cycles. Treatment did not alter the steroid levels in one subject. P was suppressed in one or both treatment cycles of four subjects. E2 was suppressed in both treatment cycles of one subject and produced widely fluctuating patterns in another. The hormonal patterns in the two consecutive treatment cycles of the same individual were similar in all but one instance, where only the P level in the second treatment cycle was diminished. These results showed that this treatment can elicit steroidogenic responses of varying degrees and duration. The contraceptive action may lie in the altered P and/or E2 level at certain points in the menstrual cycle.

Mode of action of dl-norgestrel and ethinylestradiol combination in postcoital contraception. II. Effect of postovulatory administration on ovarian function and endometrium

A combination of 1.0 mg dl-norgestrel and 0.1 mg ethinylestradiol (EE) was administered orally at 36 hours after the detection of the luteinizing hormone peak and again at 48 hours in 12 healthy volunteers with normal menstrual cycles. The effects on ovarian function were studied by comparing the daily serum levels of progesterone (P), 17 alpha-hydroxyprogesterone, and estradiol (E2) in control (placebo) and treatment cycles. Five subjects showed no significant change in the levels of these steroids but had a shortened luteal phase. The treatment significantly decreased both P and E2 levels in three subjects, while two subjects showed diminished E2 levels only. The remaining two subjects had lower P levels and fluctuating E2 patterns. Endometrial biopsies from both study cycles indicated asynchronous development of the epithelial and stromal components in the treatment cycle. These findings (abnormal luteal phase steroid levels and duration and outphased endometrial development) indicate that corpus luteum function was variously affected by the action of norgestrel-EE treatment.

Mode of action of DL-norgestrel and ethinylestradiol combination in postcoital contraception

Possible mechanisms of action of a combination of ethinylestradiol (EE) and dl-norgestrel as a postcoital contraceptive agent were studied in 12 healthy female volunteers. An oral dose of 0.1 mg of EE and 1.0 mg of dl-norgestrel was given at the predicted time of ovulation and again 12 hours later. Serum luteinizing hormone, prolactin, progesterone, 17 alpha-hydroxyprogesterone, and estradiol were measured by specific radioimmunoassays in blood samples obtained daily from the 8th day of the menstrual cycle to the 1st day of menses. Hormone profiles suggested that the medication elicited a range of individual variations in pituitary and/or ovarian responses. Histologic examination of the endometrium consistently showed significant alteration in endometrial development with a dissociation in maturation of glandular and stomal components. This postcoital contraceptive acts either by (1) suppressing ovulation or (2) disrupting luteal function by acting directly on the corpus luteum or by interfering with appropriate endometrial responses to ovarian steroids.

Effect of short-term cyclic administration of cyproterone acetate on pituitary-ovarian function in the human

Short courses of cyproterone acetate, a compound with progestational and antiandrogenic activities, were administered to normally menstruating women during different phases of the menstrual cycle to suppress growth and maturation of the follicles and corpus luteum function. Postovulatory administration of 20 mg of the drug daily for 8 days to two women delayed menstruation by 4 to 6 days, followed by prolonged bleeding and short post-treatment cycles. Plasma levels of progesterone were suppressed temporarily during therapy, but increased immediately after cessation of treatment. Administration of 10 mg of the drug for 8 days during the early follicular phase to two women resulted in irregular bleeding, short cycles, and decreased plasma levels of progesterone throughout the cycle. Reduction of the dose to 2.5 mg during the early follicular phase in two other women also resulted in irregular cycles. When the 2.5-mg dose was administered to three women from the 8th to the 15th days of the cycle, vaginal bleeding and cycle length were normal. Plasma levels of luteinizing hormone and progesterone were suppressed during therapy. In one subject, cervical mucus was found to be hostile to sperm penetration in all three treatment cycles. The results indicate that, with cyclic administration of low doses of cyproterone acetate to women during the late follicular phase, it may be possible to interrupt pituitary-ovarian function, as well as sperm transport through the cervical mucus.

Luteinizing hormone and progesterone in women under postcoital contraception with D-norgestrel

Luteinizing hormone (LH) and progesterone (Pg) levels in blood were measured simultaneously by radioimmunoassay during 53 menstrual cycles in order to investigate the effect of 400 mug of D-norgestrel, administered postcoitally, on pituitary and ovarian function. Of 31 control cycles, 2 appeared to be anovulatory, since the LH peak and subsequent Pg elevation were absent. Twenty-nine cycles showed typical LH surges in the middle of the cycle, followed by a manifold Pg increase. Twelve women received 5 to 13 tables of D-norgestrel. A total absence or at least marked suppression of LH and Pg elevations was observed. In a third group, D-norgestrel was administered on scheduled days. Each woman ingested one to four tablets between the 6th and 18th days of the cycle. Two or more tablets disturbed LH and Pg ovulatory patterns. Of four women who received a tablet on day 10, one failed to show characteristic ovulatory patterns and three exhibited a delay in the time of the LH and Pg increase. These results demonstrate that D-norgestrel in a postcoital regimen alters pituitary and ovarian function, strongly suggesting an antiovulatory effect.