The relaxant property of local prostaglandin E-2 on the non-pregnant uterus - a cyclic triphasic response

Cyclo-oxygenase (COX) inhibitors for preventing preterm labour

BACKGROUND

Preventing preterm labour is the most important step in preventing preterm birth. Prostaglandins play an important role in labour and birth. Prostaglandin production can be obstructed by inhibition of the cyclo-oxygenase (COX) enzyme and this may arrest uterine contraction. A Cochrane review on COX inhibitors for the treatment of preterm labour found insufficient data to draw conclusions about its effectiveness.

OBJECTIVES

To assess the effectiveness and safety of COX inhibitors for preventing preterm labour in high-risk women.

SEARCH METHODS

We searched the Cochrane Pregnancy and Childbirth Group's Trial Register (30 June 2012).

SELECTION CRITERIA

All published and unpublished randomised trials evaluating administration of any COX inhibitor for prevention of preterm labour in pregnant women at gestational age less than 36 weeks at risk of, but not experiencing, preterm labour. Cluster-randomised trials were eligible for inclusion. Quasi-randomised trials and studies with cross-over designs were excluded.

DATA COLLECTION AND ANALYSIS

Two review authors (T Khanprakob and U Sangkomkamhang) independently assessed all potential studies for inclusion. Disagreement was resolved by discussion and, where necessary, by consultation with a third review author. Two review authors independently assessed trial quality and extracted data. Data were checked for accuracy.

MAIN RESULTS

We included one randomised trial (involving 98 women) that evaluated the effectiveness of one type of COX inhibitor (rofecoxib) for preventing preterm birth. The included study did not report any data for one of our primary outcomes: preterm labour. Rofecoxib use was associated with an increased risk for preterm birth and preterm premature rupture of membranes (PPROM). Rofecoxib was associated with a higher risk of oligohydramnios and low fetal urine production but the effects were reversible after stopping treatment. There were no differences in the number of women who discontinued treatment before 32 weeks of gestation. There was no difference in neonatal morbidities and admission to neonatal intensive care unit. There were no maternal adverse effects or perinatal mortalities in either group.

AUTHORS' CONCLUSIONS

There was very little evidence about using COX inhibitors for preventing preterm labour. There are inadequate data to make any recommendation about using COX inhibitor in practice to prevent preterm labour. Future research should include follow-up of the babies to examine the short-term and long-term effects of COX inhibitors.

The effect of aspirin administration and parity on plasma salicylate concentrations and postpartum reproductive parameters in Brahman cows

Forty pluriparous (M) and 20 primiparous (P) suckled Brahman cows were used to evaluate the effect of aspirin and parity on plasma 13,14-dihydro-15-keto-prostaglandin F2alpha (PGFM) and progesterone (P4) concentrations and some reproductive parameters. On Day 7 after calving (PP), the cows were allocated within parity into 2 groups: the aspirin group received concentrate containing aspirin at a rate of 100 mg/kg of body weight every 12 h until Day 13 PP; and the control received concentrate every 12 h for the same interval. Blood samples were collected after first and last aspirin feeding and daily from Day 1 PP to Day 6 PP and from Day 14 PP to Day 21 PP, twice daily from Day 7 PP to Day 13 PP, and weekly until first non-return to estrus. Plasma salicylate concentrations in the aspirin group cows were affected by parity (P < 0.01) and time after feeding (P < 0.0001). P cows showed higher plasma salicylate concentrations with a later peak and slower decrease than M cows. Aspirin-treated P cows had longer PP intervals than either control P, control M, or aspirin-treated M cows. Cows receiving aspirin had a lower pregnancy rate, an increased incidence of abnormal estrous cycles, and a decline in the presence of corpora lutea after estrus. Cows that formed a corpora lutea and had received aspirin had higher P4 release between Day 6 and 14 after estrus. Aspirin-treated cows that did not form corpora lutea had lower P4 release between Days 9 and 14 after estrus. A treatment by parity interaction affected mean PGFM proportions (P < 0.01) during the treatment period. Aspirin-fed P cows increased PGFM release as measured by mean proportion of Day 6 PP values. Aspirin-fed M cows showed a decrease in mean PGFM proportions. Aspirin feeding during the early PP showed different effects on some reproductive parameters in P and M Brahman cows, indicating differences in PP physiology between parities.

Modulation of human myometrial PGE2 receptor by GTP characterization of receptor subtype

We studied PGE2 specific binding sites in human myometrial microsomes prepared from uterine specimens obtained by hysterectomy (women between 38 and 55 years of age). Competition experiments showed that the potency order for various prostaglandins (PGs) was: PGE2 > or = PGE1 >> PGF2 alpha > Iloprost > or = Carbacyclin >> ZK 110841 (PDG2 analogue). These relative affinities indicated that the receptor was of the EP type. In kinetic experiments GTP, GppNHp and GTP gamma S increased the rate of PGE2 binding (steady state was reached more rapidly in the presence of nucleotides) but maximal specific binding was not significantly different. Complete dissociation could not be obtained, even in the presence of GTP. Only 50% of maximal binding was readily dissociable. The dissociation rate was 4.56.10(-4) sec-1 (half time of about 660 sec) and in the presence of GTP analogues it was slightly increased (k-1 = 7.16 10(-4) sec-1, half time 420 sec.). Scatchard analysis of saturation curves showed an increase in ligand receptor affinity in the presence of GTP or nucleotide analogues: the Kd shifted from 9.66 +/- 2.8.10(-9) M to 4.96 +/- 1.25.10(-9) M, but the number of binding sites did not change significantly (310 +/- 37 to 350 +/- 17 fmol/mgP). The effect of GTP was observed at a concentration of 5.10(-4)M. GppNHp and GTP gamma S were effective at 1.10(-5) M. Pretreatment of myometrial membranes with pertussis or cholera toxins had no effect on PGE2 binding to membrane sites. Our conclusion is that GTP induced conversion of a population of low affinity sites into a population of higher affinity sites. This effect of guanine nucleotides was described in adipocytes and kidney medulla. Competition studies with PGE2 analogues (sulprostone, 17-phenyl-omega-trinor PGE2, M&B 28,767, misoprostol, butaprost) showed that this receptor mediates a contractile response and is probably an EP3 subtype.

Arbaprostil's [15(R)-15-methyl PGE2] effects on intrauterine pressure in the nonpregnant and pregnant human female--a report of four clinical trials

Four clinical trials evaluating arbaprostil's effects on the human uterus are reported. The initial two trials measured intrauterine pressures in nonpregnant and pregnant human females following arbaprostil doses of 10, 25, and/or 50 mcg. No statistical differences were found at any dosage level in either study for average uterine resting pressures, average peak pressures, the number of contractions or Montevideo units. Subsequently, two trials determined the abortifacient potential of arbaprostil in pregnant women during the first trimester. The first utilized total daily doses of 400 and 800 mcgs. while the second used total daily doses of 1200 and 1600 mcgs. Vaginal spotting was noted in one woman receiving 400 mcgs, three receiving 1200 mcgs. and in two receiving 1600 mcgs. One episode of moderate bleeding was seen in the latter study. Based on these studies, arbaprostil exhibits little potential for inducing abortifacient activity at these dosages in these patient populations.

Effect of human menopausal gonadotrophin on the non-pregnant uterine response to intrauterine administration of prostaglandin E2

The effect of intrauterine instillation of 50 micrograms of prostaglandin E2 (PGE2) on the non-pregnant human uterus was evaluated in 10 volunteers, before and after systemic administration of human menopausal gonadotrophin (HMG). The cases were either in the early proliferative (n = 5) or late secretory (n = 5) phases of the cycle. Before HMG administration, the uterus responded to local PGE2 by stimulation in all the cases. After HMG treatment, no response to PGE2 was detected in eight cases and a decrease in uterine tonus was observed in two cases. The implications of these findings in certain physiological and pathological conditions relating to reproduction are discussed.

Is prostaglandin F2 alpha involved in the increased myometrial contractility of primary dysmenorrhoea?

The concentrations of prostaglandin F2 alpha (PGF2 alpha) and E2 (PGE2) in menstrual fluid collected daily from 13 women with primary dysmenorrhoea and 11 matched controls, were compared with the pattern of uterine contractility during the hour following the menstrual fluid collection. The intra-uterine pressure (IUP) was measured using a micro-transducer catheter and the tracings analysed. On Day 2 the concentration of PGF2 alpha correlated with the peak area, but not with amplitude, duration or rate of contraction. These findings add additional support to the hypothesis that increased production of PGF2 alpha could contribute to the increased uterine contractility in primary dysmenorrhoea.

[Prostaglandins in reproductive physiology (author's transl)]

Up to the present time, the most extensive knowledge in prostaglandin research has been achieved in the field of reproductive physiology. It seems now certain that prostaglandins are involved in each phase of the reproductive process although their precise physiological functions cannot yet be completely explained. For example they are thought to play an important role in the hypothalamic -- pituitary system in the liberation of LHRH and in the ovary in steroid genesis, ovulation and luteolysis; also, in the non-pregnant uterus in the onset of menstruation while at conception both sperm and ovum transport are influenced by prostaglandins. In pregnancy, a prostaglandin function has been demonstrated in the uterus in initiating labour in cases of abortion and in birth at term. Further, they appear to be involved in regulating the blood circulation in placenta, cord and fetus. Already, because of their established physiological functions, the prostaglandins have been introduced successfully into clinical use.

Aberrant uterine response to prostaglandin E2 as a possible etiologic factor in functional infertility

The clinical entity of functional infertility still remains unexplained and largely lacking a line of proper management. The uterine response to prostaglandin E2 (PGE2) and prostaglandin F2alpha (administered by intravenous and intrauterine routes) was evaluated during different phases of the menstrual cycle in five functionally infertile women. The results (quantitative and qualitative) were compared with those elicited among 20 fertile women. There were no apparent differences between the two groups with respect to either compound (systemic or local) when given during the proliferative or luteal phase of the cycle. However, at midcycle, about the time of ovulation (days 13 to 18), there was a salient deviation in the type of response following local instillation of PGE2; in the normal fertile group there was a definite inhibition of motility, while uteri in the functionally infertile group showed marked stimulation. The possible role of this aberrant uterine response in the etiology of functional infertility is discussed.