On the mechanism of midtrimester abortions induced by prostaglandin "impact"

Using Csapo's technique, a single dose of 24.3 +or- 1.1 mg prostaglandin F2alpha (PGF2alpha) had been delivered intraamniotically to 20 sedated pregnant patients (15.9 +or- 0.6 weeks pregnant) in order to provoke a PG impact (PGI), a consequent progesterone (P) withdrawal, and a conversion of the pharmacologically refractory normal pregnant uterus into a reactive organ. The side effects were occasional and acceptable and no further PGF2alpha treatment was needed except in 4 cases (5-10 mg). Only after the Oxytocin test showed that the uterus is becoming reactive, was 50 mU/minute oxytocin infused intravenously to facilitate the evolution of IUP to 93 +or- 3 mmHg and thus promote clinical progress. All the 20 patients aborted both the fetus and the placenta in 16.5 +or- 2.1 hours, but 8 women retained small placental residues to be removed by curettage. The Csapo score was a high 92 +or- 2. As early as 3 hours after PGI, the plasma P levels already decreased significantly. They continued to decline throughout the IAT and reached a 72% withdrawal when the fetus was aborted. 15 patients whose P withdrawal was rapid, aborted before the mean IAT, while those 5 women whose P withdrawal was slow aborted after this time. Thus, the rate of P withdrawal was direct while parity and gestational age indirectly related to the IAT. Studies are in progress to elucidate further the abortifacient action of PGF2alpha and through this knowledge promote predictable therapy.     

Reassessment of systemic administration of prostaglandins for induction of midtrimester abortion

This investigation was conducted to evaluate the abortifacient efficacy of vaginal and intramuscular administration of different dose schedules of the 15-methyl analogues of prostaglandin F2 alpha. Both 15-methyl PGF2 alpha and 15-methyl PGF methyl ester can be absorbed from the vagina in sufficient amounts to induce abortion. The potency of the methyl ester was approximately twice that of the free acid. The most successful treatment schedule consisted of an initial dose of 0.5 mg of the methyl ester followed by 1.0 or 2.0 mg every third hour. On this treatment all patients aborted within 24 hours. Initially 200 ug of 15-methyl-PGF2 alpha was given. The dose was increased to 400 ug or occassionally to 500 ug depending on the effect and tolerance of the patient and repeated every third hour. The treatment schedule resulted in a 100% abortion rate and the mean induction-abortion interval was 16.1 hours. Both routes were associated with a higher frequency of side effects than that reported for intraamniotic administration of 15-methyl-PGF2 alpha. It seems justified to conclude that the intraamniotic route is preferable after the 14th week when the uterine cavity is easy to puncture, but that vaginal or intramuscular injections of the compounds could be an alternative in late first trimester and early second trimester cases.     

Single intraamniotic injections of prostaglandin F-2-alpha as an abortifacient agent: size of effective dose and effect of parity

This report discusses the authors' experience with intraamniotic administration of single doses of the prostaglandin PGF2alpha as an abortifacient agent. 98 healthy women between the 12th and 26th week of pregnancy admitted to the Clinical Research Unit of the North Carolina Memorial Hospital were given a single intraamniotic dose of PGF2a administered through an indwelling polyethelene catheter inserted either transabdominally or transvaginally. The drug was given as Tham salt with the first 5 mg of any dose being given at the rate of 1 mg/minute for 5 minutes, followed by more rapid administration of the balance of the dose. Abortion which did not occur within 48 hours was considered a failure. Each patient received 1 of the following dosages: 25, 40, 50, and 75. 9 (64%) of 14 patients given 25 mg PGF2a aborted within the 48-hour period. The percentages of abortion in the doses 40, 50, and 75 mg were 88.9% (9 patients), 96.7% (60 patients) and 93.3% (15 patients) respectively. As these figures were almost similar, the 84 patients were combined as a single group (84 patients) relative to the injection-abortion time, effect of parity, and stage of gestation at which the abortion was carried out. Half of the patients in this combined group aborted in approximately 21 hours; more than 90% at the end of 32 hours; and 95% at the end of the 48 hours post-injection. For comparison, the cumulative abortion curve of 552 patients who had intraamniotic saline for abortion showed that 50% of the women aborted within 31 hours, 84% within 48 hours, and 97% within 72 hours. Prostaglandin induced abortions thus are shown to reach the 50% level 10 hours before the saline patients, and the 90% level about 21 hours before the saline patients. Significant side effects (presented elsewhere) were observed in all groups, with the incidence increasing at higher dosages. Mean induction-abortion time for nulliparas at all dosages was 17.4 hours; for multiparas, 20.4 hours. There was no clear relationship between gestational age and parity. The study shows that the effective dose for inducing abortion with PGF2a lies within the 40 to 50 mg dose range.     

The effect of a 10 cm2, 0.5% 15-ME-PGF2α methyl ester intravaginal silastic device on abortion and plasma prostaglandin concentration

Intravaginal insetion of a 10 cm² silastic device with an 0.5% concentration of 15(S)-15-methyl-prostaglandin F_2α methyl ester alone successfully induced abortion in 27 of 48 patients in the midtrimester and in an additional 11 patients with a concomitant infusion of oxytocin. The mean abortion time for the 38 successful induction was 15.35 hours. In 8 of the 10 patients who failed to abort even with concomitant oxytocin therapy, abortion was induced by serial intramuscular injections of 15-ME-PGF_α; the remaining 2 failures underwent surgical evaccution. The plasma levels of 15-ME-PGF_2α methyl ester in the 11 patients studied varied widely over the first 2 hours after insertion of the device. The maximum mean level was achieved at 2 hours, maintained at 4 hours and then dropped sharply at 8 hours and declined over the abortion period in undelivered patients. Vomiting and diarrhea were the most common side effects and in general well tolerated by the patients. However, there was an adverse reaction in a single patient who experienced almost constant nausea, vomiting and diarrhea. The device was removed 1 hour 50 minutes after insertion and the patient aborted spontaneously 7 hours later. Intravaginal insertion of a silastic device is an effective means of prostaglandin abortion, but their investigation is required to determine the most effective device which would provide a slow, continuous release of the prostaglandin.     

Cervical dilatation with prostaglandin analogues prior to vaginal termination of first trimester pregnancy in nulliparous patients.

Dilatation of the cervix with prostaglandin analogues prior to vaginal termination of pregnancy was attempted in 125 nulliparous women in the first trimester of pregnancy. The patients were divided into five groups (25 in each group) and given a single extra-amniotic dose of one of the following prostaglandin analogues 14-16 hours prior to the evacuation of the uterus by vacuum aspiration. (Group A) 15 (S) 15 methyl PGE2 (free acid); (Group B) 15 (S) 15 methyl PGE2 methyl ester; (Group C) 15 (S) 15 methyl PGF2alpha (free acid); (Group D) 15 (S) 15 methyl PGF2alpha methyl ester and(Group E) a mixture of 15 (S) 15 methyl PGE2methyl ester and 15 (S) 15 methyl PGF2alpha methyl ester. Evacuation of the uterus without mechanical dilatation of the cervix was possible in 111 (90%) of the patients. In an additional 10 patients (8%) there was some degree of cervical dilatation and further mechanical dilatation could be performed easily. With the combination of 15 (S) 15 methyl PGE2 methyl ester and 15 (S) 15 methyl PGF2alpha methyl ester the incidence of gastrointestinal side effects and pyrexia were considerably reduced.     

The efficacy and acceptability of the "prostaglandin impact" in inducing complete abortion during the second week after the missed menstrual period

Clinical research was undertaken using PGF2a (prostaglandin) to induce abortion in 22 pregnant women at 12 +/- 1 days following their missed menstrual period. The PG was administered in a 5 mg single intrauterine dose through the cervix for a 10-minute period. The PG administration caused increased uterine contraction within 20 minutes and raised intrauterine pressure which was sustained for 2 hours. During the initiation of the intrauterine pressure, bleeding started and progesterone and estradiol levels decreased and continued to do so. In those patients who had been sedated, side effects were minimal. At 24 hours following the PG administration, progesterone had been withdrawn at a rate of 44%, bleeding was continuing, and cervical dilatation was at approximately 1 cm. Complete abortion was achieved in 20 out of the 22 women. It is believed that the abortion was effected through the action of endogenous PG, due to the withdrawal effect on progesterone of the exogenously-administered PG.     

Changes in estrogen levels in maternal venous plasma after intra-amniotic infusion of prostaglandin F2 for therapeutic abortion

Peripheral plasma levels of estrone, estradiol-17beta and estriol were measured by the method of Shutt and Cox in 10 women following intra-amniotic infusion of prostaglandin F2alpha (PGF2a) for therapeutic abortion. Initial dose was 30 mg, followed if necessary, by doses of 15 mg at 24 hours and 42 hours. Gestational age of pregnancies ranged from 14 to 19 weeks, with a mean of 16 weeks. All 10 women completely aborted. Mean induction-abortion interval was 24 + or - 12 hours. The mean estrone, estradiol 17beta and estriol levels declined to about half of the pre-infusion levels after 80% of the induction-abortion interval had elapsed. The main decline in estrogen levels occurred in individual women either during the 1st quarter or during the last quarter of the induction-abortion interval. There were no significant relationships between changes in estrogen levels and the interval from 1st administration of PGF2a to subsequent abortion.     

Laminaria augmentation of intra-amniotic prostaglandin F2α for the induction of mid-trimester abortion

From interpretation of 24-hour dose-response curves, it is improbable that mid-trimester abortion rates greater than about 80% can be accomplished with any one dose schedule of Prostaglandin F2α (PGF2α). To determine whether augmentation of intra-amniotic PGF2α with laminaria would improve the abortion rate, the results of a group of 22 gravidas treated with intra-amniotic PGF2α were compared to those of a group of 21 subjects treated with laminaria and an identical dose schedule of PGF2α. Patients with laminaria not only had a shorter mean abortion time (14.6 hours), but 95% aborted within 24 hours and all patients aborted within 24.5 hours of the initial PGF2α injection. Patients without laminaria had a longer mean abortion time (18.9 hours); only 68% aborted within 24 hours and one failed to abort within the 48-hour trial period. No significant differences in the frequency or severity of complications between the two groups were observed. Uterine contractility over the initial 6 hours of the induction was similar in the two groups. Therefore, augmenting the intra-amniotic PGF2α method with laminaria appears practicable.     

Mid-trimester abortion with intra-amniotic prostaglandin F2 alpha and intravenous oxytocin infusion

Induction of abortion in mid-trimester pregnancies were performed on 26 patients. The first 12 patients were treated by intra-amniotic instillation of Prostaglandin F2 alpha, with a mean dosage of 40.2 mg. and mean abortion time of 24 hours and 41 minutes (ten patients). Fourteen additional mid-trimester abortions were performed using identical protocol plus the addition of oxytocin by intravenous infusion two hours after injection of the prostaglandin. All patients aborted, with mean dosage of PGF2 alpha of 28.2 mg. and mean abortion time of 15 hours and 37 minutes.     

Comparison of intra-amniotic prostaglandin F2 alpha and hypertonic saline for induction of second-trimester abortion.

The efficacy and safety of intra-amniotic prostaglandin (PG) F2 alpha (25 mg repeated in six hours) and hypertonic saline (200 ml 20% NaC1) were compared in an international multicentre randomised study organised by the World Health Organisation''s prostaglandin task force. Both hypertonic saline and PGF2alpha were found to be effective in terminating second-trimester pregnancy. The main advantage of PGF2alpha however, was its greater efficacy, with significantly higher success rates in the first 48 hours. Out of 717 women given PGF2alpha 614 (85-6%) aborted within 48 hours; by 24 hours 439 (61-2%) had aborted, and by 36 hours 574 (80-1%) had aborted. Out of 796 women given hypertonic saline 641 (80-5%) aborted within 48 hours; however, by 24 and 36 hours, respectively, only 161 (20-2%) and 462 (58%) had aborted. Although PGF2alpha was associated with a somewhat higher frequency of minor side effects than hypertonic saline, notably vomiting and diarrhoea, these were within acceptable limits. Only 59 women (8-2%) in the prostaglandin group had more than four episodes of vomiting and 11 (1-5%) more than four episodes of diarrhoea. Ohter side effects occurred only occasionally. No difference was found between the two groups in the frequency of incomplete abortion or excessive bleeding.     

Induction of midtrimester abortion by serial intravaginal administration of 15(S)-15-methyl-prostaglandin F2α (THAM) suppositories

Midtrimester abortion was successfully induced in 13 of 22 patients by serial intravaginal administration of 15(S)-15-methyl-prostaglandin F_2α (THAM) suppositories. Nine patients, 4 nulliparas and 5 multiparas, failed to abort after 24 hours of prostaglandin administration and a concomitant infusion of oxytocin was initiated. Seven of the nine patients aborted within 7 hours of the combined therapy and one patient on methadone maintainence aborted after 17.5 hours of combined therapy, 41.5 hours after the first dose of prostaglandin. A single patient failed to abort, despite the concomitant prostaglandin-oxytocin administration and underwent surgical evacuation. The mean abortion time for the 21 successful abortions was 22.56 hours. Nulliparous patients aborted somewhat faster, mean 21.79 hours, than multiparous patients, mean 23.80 hours, but this difference was not statistically significant. In this study, one patient aborted in less than 12 hours, and 62% of the successful cases aborted within 24 hours. The plasma levels of 15-ME-PGF_2α were analyzed by radioimmunoassay in 10 patients. Plasma prostaglandin levels rose significantly 30 minutes after the insertion of the first suppository, but there was a wide variation in levels from patient to patient. It was observed that the 2 patients with the highest levels had the fastest abortion times and episodes of gastro-intestinal side effects appeared related to a rise in prostaglandin levels. Sixty-four percent of the patients in this study had no gastro-intestinal side effect related to prostaglandin administration.     

Induction of midtrimester abortion by serial intravaginal administration of 15(S)-15-methyl-prostaglandin F2alpha (THAM) suppositories.

Midtrimester abortion was successfully induced in 13 of 22 patients by serial intravaginal administration of 15(S)-15-methyl-prostaglandin F2alpha (THAM) suppositories. Nine patients, 4 nulliparas and 5 multiparas, failed to abort after 24 hours of prostaglandin administration and a concomitant infusion of oxytocin was initiated. Seven of the nine patients aborted within 7 hours of the combined therapy and one patient on methadone maintainence aborted after 17.5 hours of combined therapy, 41.5 hours after the first dose of prostaglandin. A single patient failed to abort, despite the concomitant prostaglandin-oxytocin administration and underwent surgical evacuation. The mean abortion time for the 21 successful abortions was 22.56 hours. Nulliparous patients aborted somewhat faster, mean 21.79 hours, than multiparous patients, mean 23.80 hours, but this difference was not statistically significant. In this study, one patient aborted in less than 12 hours, and 62% of the successful cases aborted within 24 hours. The plasma levels of 15-ME-PGF2alpha were analyzed by radioimmunoassay in 10 patients. Plasma prostaglandin levels rose significantly 30 minutes after the insertion of the first suppository, but there was a wide variation in levels from patient to patient. It was observed that the 2 patients with the highest levels had the fastest abortion times and episodes of gastro-intestinal side effects appeared related to a rise in prostaglandin levels. Sixty-four percent of the patients in this study had no gastro-intestinal side effect related to prostaglandin administration.     

Serial intramuscular injections of 15(S)-15-methyl-prostaglandin F2alpha in the induction of abortion.

Abortion was successfully induced in 62 of 68 patients in the 9th to the 26th week of pregnancy be serial intramuscular administration of 15(S)-15-methyl-prostaglandin F2alpha (15-ME-PGF2alpha). In 6 patients who failed to abort after 24 hours of prostaglandin administration, a concomitant infusion of oxytocin was initiated; 5 of these patients aborted within 12 hours of the combined therapy. A single patient failed to abort, even with the combined therapy, and underwent surgical evacuation. The mean abortion time in the 67 successful inductions was 14.56 hours. Parous patients aborted somewhat fasteter, mean 13.98 hours, as compared to nulliparous patients, mean 15.02 hours, but this difference was not statistically significant. In this study initial intramuscular injection of 100 mug 15-ME-PGF2alpha was followed in 1 hour by 250 mug and then 250 mug every 2 hours with concomitant oxytocin therapy initiated after 24 hours. The results with this dose schedule were compared to the results obtained in a previous study with a higher dose schedule, an initial dose of 100 mug 15-ME-PGF2alpha, followed in 1 hour by 250 mug then 500 mug every 2 hours. There was significant difference in the mean abortion time and the incidence of side effects between the 2 dose schedules. The mean abortion time for patients with gestational ages 16 weeks and less was the same with both dose schedules, however patients with gestational ages of 17 weeks and higher aborted somewhat faster with the higher dose schedule. It might therefore be advisable for patients with gestations of 17 weeks and higher to be treated with the higher dose schedule. In earlier gestations patients could be started on the lower schedule, and if abortion had not occurred within 15 hours the dose of 15-ME-PGF2alpha could then be increased to 500 mug every 2 hours.     

Trilostane but not prostaglandin F2alpha (PGF2alpha) or cortisol aborts 90-day-pregnant lutectomized sheep

Ewes were lutectomized and treatments were started 72 h later. Pregnant ewes were treated with vehicle; prostaglandin F2alpha (PGF2alpha); cortisol (C); trilostane (TR), a 3beta-hydroxy-steroid dehydrogenase inhibitor; PGF2alpha + C; TR + PGF2alpha; TR + C, or TR + PGF2 + C. TR, TR + PGF2alpha, TR + C, and TR + PGF2alpha + C aborted (P < or = 0.05) all ewes receiving TR. One ewe treated with PGF2alpha aborted (P > or = 0.05). The average time to abortion of TR-treated ewes was 50.8 h (P < or = 0.05) after initiation of treatments. All aborted ewes had retained placentas (P < or = 0.05) except one ewe in the TR + PGF2alpha, treatment group. TR was given every 12 h starting at 72 h postlutectomy until 96 h postlutectomy. TR reduced (P < or = 0.05) progesterone. Estradiol-17beta was increased (P < or = 0.05) 2 h after the first two TR treatments and declined 2 h later and was followed by a sustained increase (P < or = 0.05) in estradiol-17beta, which was coincident with the onset of abortions. Estradiol-17beta was increased (P < or = 0.05) by PGF2alpha but did not decrease (P > or = 0.05) placental secretion of progesterone. It is concluded that TR but not PGF2alpha is an abortifacient in 90-day-pregnant lutectomized ewes and that abortion occurs only when there is a decrease in circulating progesterone and an increase in circulating estradiol-17beta.     

Late midtrimester medical pregnancy terminations: three different procedures with prostaglandin F2 alpha and laminaria tents

One hundred twenty eight women underwent midtrimester induced abortion with: 1) combined regimen of intramniotic prostaglandin (PG) F2a injection and intracervical laminaria tents (group A, 50 women), 2) intramniotic PGF2a injection only (group B, 51 women) and 3) laminaria tents followed by intracervical PGF2a tablets insertion (group C, 27 women). The mean induction-abortion time (+/- SE) was 24.9 +/- 1.7 hours for group A, 28.2 +/- 2.2 hours for group B (p greater than 0.05) and 42.1 +/- 3.4 hours for group C, significantly longer than goup A and B (p less than 0.001 and p less than 0.01 respectively). In 48 hours 98% of the patients of group A, 90% of group B (p less than 0.05) and 59% of group C (p less than 0.001) completed the abortion procedure. Parous women of group A and B presented similar induction - abortion time, while in nulliparous the use of laminaria shortened the abortion procedure significantly (p less than 0.05). The complications rate was low. In conclusion, the intracervical PGF2a insertion is a simple but very slow abortion procedure with high failure rates. The intramniotic PGF2a injection is a successful method for late midtrimester medical pregnancy termination and the concurrent use of laminaria tents shortens the abortion procedure, particularly in nulliparous, reduces the number of prostaglandins' reinjections and increases the incidence of successful abortion within 48 hours.     

Peripheral plasma levels of progesterone in pregnant goats and in pregnant goats treated with prostaglandin F2a

Prostaglandin or prostaglandin analogues have been shown to be luteolytic in the pregnant goat. In this study the temporal changes in the plasma concentrations of progesterone during pregnancy and after administration of PGF2a to pregnant goats are described. PGF2a administration to pregnant goats at 30 and 65 days after breeding induced abortion within 34 to 75 hours. These abortions were accompanied by estrus and profuse muco-hemorrhagic discharges. When PGF2a was administered to pregnant goats 140 or 142 days after breeding, premature parturition occurred within 42 to 76 hours. Live kids were delivered in all cases. The plasma levels of progesterone in all pregnant goats showed dramatic decreases within 24 hours after the prostaglandin injections and continued to decrease gradually until abortions or premature parturition. Thereafter, the progesterone levels remained low for several days.     

Luteolytic action of 15-keto prostaglandin F2alpha in the rhesus monkey.

The naturally-occurring metabolite of prostaglandin F2alpha, 15-keto prostaglandin F2alpha (15-keto PGF2alpha), elicited rapid and sustained declines in serum progesterone concentrations when administered to rhesus monkeys beginning on day 22 of normal menstrual cycles. Evidence for luteolysis of a more convincing nature was obtained in studies where a single dose of 15-keto PGF2alpha was given on day 20 of ovulatory menstrual cycles in which intramuscular injections of hCG were also given on days 18-20; serum progesterone concentrations fell precipitously in monkeys within 24 hours following intramuscular administration of 15-keto PGF2alpha. However, corpus luteum function was impaired in only 4 of 11 early pregnant monkeys when 15-keto PGF2alpha was administered on days 30 and 31 from the last menses, a time when the ovary is essential for the maintenance of pregnancy. Gestation failed in 2 additional monkeys 32 and 60 days after treatment with 15-keto PGF2alpha, but progressed in an apparently normal manner in the remaining 5 animals. Two pregnant monkeys treated with 15-keto PGF2alpha on day 42 from the last menstrual period, a time when the ovary is no longer required for gestation, continued their pregnancies uneventfully. Corpus luteum function was not impaired in 9 control monkeys which received injections of vehicle or hCG at appropriate times during the menstrual cycle or pregnancy.     

Midtrimester abortion induced by single intra-amniotic instillation of two dose schedules of 15(S)-15-methyl-prostaglandin F2alpha.

Midtrimester abortion was successfully induced in a series of 20 patient by intraamniotic instillation of 15(S)-15-methyl-prostaglandin F2alpha with a mean abortion time of 17.78 hours. The patients in this study was divided into two groups, Groups 1 received an initial dose of 2.5 mg 15-ME-PGF2alpha and aborted in a mean time of 16.26 hours. The patients in Group II received 3.0 mg 15-ME-PGF2alpha and aborted in a mean time of 18.94 hours. There was no significant difference in the abortion time, occurrence of side effects or the initiation of uterine activity between Group I and Group II. Parous patients aborted somewhat faster than nulliparous patients but this difference was not significant. In this study 80% of the patients aborted in 24 hours or less, and the intra-amniotic instillation of 15-ME-PGF2alpha was an effective abortifacient technique from the 15th to the 23rd week of gestation. The uterine response to intra-amniotic instillation of 15-ME-PGF2alpha was characterized by the gradual appearance of low amplitude, high frequency contractions accompanied by a rise in baseline intrauterine tonus. Uterine activity developed gradually and peaked at 1:50 hours after intraamniotic instillation of 15-ME-PGF2alpha. In this small series 15-ME-PGF2alpha administered via intra-amniotic instillation did not appear to have a distinct advantage over the naturally occuring PGF2alpha administered by the same method for the induction of midtrimester abortion; a large series in indicated to define the advantage of either technique.     

The effect of progesterone and human interferon alpha-2 on the release of PGF2 alpha and PGE from epithelial cells of human proliferative endometrium.

Progesterone and interferon-like trophoblastic proteins modulate prostaglandin (PG) synthesis from endometrium in early ovine and bovine pregnancy. Enriched epithelial cells were prepared from human endometrium removed in the proliferative phase of menstrual cycle (n = 8). Progesterone at a concentration of 1 microM suppressed PGE release from the cells during the first 24 hours in culture. After 48 hours in culture progesterone at a dose of 100 nM and 1 microM suppressed both the release of PGF2 alpha and PGE from the cells and this suppression was maintained for a further two days. Addition of exogenous 30 microM arachidonic acid (AA) abolished this effect of progesterone on both PGF2 alpha and PGE release. Interferon alpha-2 did not suppress the basal release of PGF2 alpha nor PGE. In the presence of progesterone, interferon alpha-2 attenuated the progesterone mediated suppression of PGF2 alpha but not PGE release from endometrial cells. These findings suggest that progesterone suppresses the basal release of PGs from human endometrium, but unlike the sheep, interferon alpha-2 does not exert this action on human endometrium.     

Response of the midpregnant human uterus to systemic administration of 15(S)-15-methyl-prostaglandin F2alpha

The contractile response of the midpregnant human uterus to a new (PG) prostaglandin analogue, 15(S)-methyl-PGF2alpha (15-me-PGF2alpha), was investigated and compared to the effect of natural PGF2alpha. It was found that the threshold dose of 15-me-PGF2alpha was around 10 mcg when given as a single intravenous injection, which is approximately 1/10 of the corresponding dose of PGF2alpha. It was also found that higher intravenous doses of 15-me-PGFalpha resulted in a uterine response of longer duration than that following PGF2alpha. Intramuscular injection of the analogue at doses of 1.0-1.5 mg induced a marked uterine stimulation sustained for 5-7 hours without causing local reaction. Intravenous infusion of 5 mcg/min of 15-me-PGF2alpha stimulated a level of uterine activity equivalent to that of 75 mcg/min of PGF1alpha. The incidence of gastrointestinal side effects was the same in the 2 treatment groups. However, there seemed to be a tendency toward a significantly higher abortion rate with the analogue.