Effects of onapristone, tamoxifen and ICI 182780 on uterine prostaglandin
`production and luteal function in nonpregnant guinea-pigs
`N. L. Poyser
`Department of Pharmacology, University of Edinburgh Medical School, 1 George Square,
`Edinburgh EH8 9]Z, UK
`
`Onapristone (a progesterone antagonist) or ICI 182780 (an oestrogen antagonist) adminis-
`tered to guinea-pigs on days 11\p=n-\14of the cycle significantly reduced uterine PGF2\g=a\output
`on day 15. Concentrations of progesterone in plasma of onapristone-treated and ICI 182780\x=req-\
`treated guinea-pigs were still high on day 15 indicating that luteal regression had been
`prevented. These findings indicate that progesterone and oestradiol are necessary for
`increased PGF2\g=a\production by the uterus towards the end of the cycle, and support the
`hypothesis that oestradiol acting on a progesterone-primed uterus is the physiological stimu-
`lus for increased uterine PGF2\g=a\synthesis and release in guinea-pigs. The capacity of the
`endometrium to synthesize PGF2\g=a\on day 15 was reduced by treatment with ICI 182780
`and, unexpectedly, by treatment with onapristone, indicating that onapristone may also be
`antagonizing the release or action of oestradiol in some way. Tamoxifen was an agonist in
`guinea-pigs since it induced vaginal opening. It had no inhibitory effect on uterine PGF2\g=a\
`output and did not delay luteal regression when administered between days 11 and 14 of the
`it redirected PG synthesis in homogenates of endometrium and myo-
`cycle. However,
`metrium from PGI2 (as indicated by 6-keto-PGF1\g=a\) to PGF2\g=a\. The output of 6-keto-PGF1\g=a\
`from the uterus of day 15 guinea-pigs was reduced following tamoxifen treatment, but the
`high output of PGF2\g=a\from the uterus was not affected.
`
`Introduction
`Prostaglandin F2a (PGF2a) produced by the uterus is responsible
`for regression of the corpora lutea in the ovary of guinea-
`pigs (see Horton and Poyser, 1976; Poyser, 1981). Oestradiol
`administered to ovariectomized guinea-pigs maintained on pro¬
`(Blatchley and
`gesterone stimulates uterine PGF2a output
`Poyser, 1974; Poyser, 1983a). During the oestrous cycle, oestra¬
`diol secretion from the ovary increases from day 10 (Joshi et al,
`this precedes the increase in PGF2a secretion from
`1973);
`the uterus by 24 h (Blatchley et al, 1972; Earthy et al, 1975;
`Antonini et al, 1976). Oestradiol acting on a progesterone-
`primed uterus therefore appears to be the physiological
`stimulus for increased PGF2a production by guinea-pig uterus
`(particularly the endometrium) towards the end of the oes¬
`trous cycle, especially as oxytocin has no stimulatory effect
`on endometrial PGF2a synthesis in guinea-pigs (Poyser and
`Brydon, 1983; Riley and Poyser, 1987). If this is so, appropri¬
`ate steroid receptor antagonists should prevent
`the stimu¬
`lation of uterine PGF2u synthesis and release towards the end
`the cycle, and thereby should delay luteal
`regression.
`of
`Consequently, the effects of onapristone (a progesterone an¬
`tagonist), tamoxifen and ICI 182780 (oestrogen antagonists)
`on uterine PGF2U production and luteal function in guinea-
`pigs were investigated.
`Received 20 October 1992.
`
`Materials and Methods
`Twenty-five virgin guinea-pigs, weighing 650-850 g, were
`examined daily and a vaginal smear was taken when the vagina
`was perforate. Day 1 of the cycle was defined as the day preced¬
`ing the post-ovulatory influx of leucocytes when cornification
`was at a maximum. All guinea-pigs had exhibited at least two
`cycles of normal duration (16 to 17 days) before being treated
`as described in the following experiments. The animals were
`killed by stunning and incising the neck on the day after the last
`day of treatment.
`Experiment h effects of onapristone and tamoxifen
`Guinea-pigs were injected s.c. once a day from days 11 to 14
`of the cycle with 1 ml peanut oil containing 5% benzyl alcohol
`(control vehicle), 10 mg onapristone, or 10 mg tamoxifen (five
`animals per treatment). The uteri were removed on day 15.
`One uterine horn from each uterus was superfused with Krebs
`solution (5 mlmin^1; for composition see Mitchell et al, 1977)
`at 37°C and pre-gassed with 5% C02-95% 02. Samples of
`superfusate were collected for 10-min periods between 0—10
`and 60-70 min of superfusion. The other uterine horn was
`divided into endometrium and myometrium by cutting away
`small pieces of endometrium from the myometrium. This tech¬
`nique separates the two tissues by > 85% (Leaver and Poyser,
`1981). Both tissue types were homogenized separately in 10 ml
`
`MYLAN PHARMS. INC. EXHIBIT 1016 PAGE 1
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`

`
`,
`
`Krebs solution and were incubated at 37°C for 60 min. After
`superfusion or incubation, the pH of the samples of superfusates
`and of the incubates were lowered to 4.0 with 1 mol HC1 I
`and the PGs were extracted by shaking twice with ethyl acetate
`(50 and 20 ml for the superfusates and incubates, respectively).
`The two ethyl acetate extracts obtained from each sample were
`combined and evaporated to dryness at 50°C on a rotary
`evaporator. The recoveries of PGF2a and PGE2 are >90%
`and the recovery of 6-keto-PGF,a is >80% by this method
`(Poyser and Scott, 1980; Swan and Poyser, 1983). The results
`are not corrected for recovery. The amounts of PGF2a, PGE2
`and 6-keto-PGF10 present
`in each sample were measured by
`radioimmunoassay using antibodies raised in this laboratory;
`the crossreactivities have been reported elsewhere (Poyser,
`1987). The inter- and intra-assay coefficients of variation were
`< 11.8%. The detection limit was 10-30 pg per assay tube.
`At the time of removing the uterus, a sample of peripheral
`blood was collected into a heparinized (20 U ml"1) syringe. The
`blood was centrifuged at 2500g for 15 min, and the plasma was
`20°C. Progesterone in the plasma
`withdrawn and stored at
`samples was measured as described by Poyser and Horton
`(1975), using an antibody raised in this laboratory; the cross-
`reactivities have been reported elsewhere (Poyser, 1983b,
`1984). The intra-assay coefficient of variation was 9.5%, and all
`the samples were measured in one assay. The detection limit
`was 40 pg per assay tube.
`
`—
`
`Experiment 2: effects of ICI 182780
`Guinea-pigs were injected s.c. once a day from days 11 to 14
`of the cycle with 0.8 ml 5% benzyl alcohol in peanut oil alone
`(controls) or containing 4 mg ICI 182780 (five animals per
`group). The uteri were removed on day 15 and treated as in
`Expt 1. The amounts of PGF2a, PGE2 and 6-keto-PGFIa present
`in the extracts obtained were measured by radioimmunoassay.
`The inter- and intra-assay coefficients of variation were < 12%,
`and the detection limits were 20-30 pg PG per assay tube.
`Progesterone was measured in a peripheral plasma sample,
`the time of removing the
`obtained from each guinea-pig at
`uterus, by radioimmunoassay as outlined in Expt 1. The intra-
`the samples
`assay coefficient of variation was 10.1%, and all
`were measured in one assay. The detection limit was 40 pg per
`assay tube.
`
`Statistical tests
`Results were analysed by the Student's I
`if
`the
`test or,
`variances of the two groups were significantly different by the
`variance ratio F test, by a modified I test for unequal variances
`(see Steel and Torrie, 1980).
`
`Results
`
`PGF2a was the major PG released, together with lesser quanti¬
`ties of PGE2 and 6-keto-PGFla, from the uterus superfused in
`vitro from day 15 control guinea-pigs. These outputs of PGF2a,
`PGE2 and 6-keto-PGFIa fell significantly (P < 0.05) between
`
`0-10 min
`60-70 min
`Fig. 1. Mean ( + SEM, = 5) outputs of (a) PGF2a, (b) PGE2 and (c)
`6-keto-PGFla from the day 15 uterus of (D) control, ( ) onapristone-
`treated and (0) tamoxifen-treated guinea-pigs when superfused in
`vitro during the periods (i) 0-10 min and (ii) 60-70 min. fSignificantly
`(P < 0.05) lower than the control output of the same PG during the
`same period.
`
`the first (0-10 min) and second (60-70 min) periods of super-
`fusion (Figs 1 and 2). The treatment of guinea-pigs with ona¬
`pristone between days 11 and 14 of the cycle significantly
`(P < 0.05) reduced the outputs from the uterus of PGF2a on day
`15 during both periods of superfusion, and of PGE2 during the
`first period of superfusion. Onapristone had no significant effect
`on the output of 6-keto-PGFla during either superfusion period
`(Fig. 1). Tamoxifen administered to guinea-pigs between days
`11 and 14 of the cycle had no effect on the uterine outputs on
`day 15 of PGF2a and PGE2, but significantly (P < 0.05) reduced
`the output of 6-keto-PGFIa during the first but not the second
`period of superfusion (Fig. 1).
`The treatment of guinea-pigs with ICI 182780 on days 11 to
`14 of the cycle significantly (P < 0.05) reduced the outputs of
`PGF2a and PGE2 from the day 15 uterus during both periods of
`superfusion. ICI 182780 treatment had no effect on the output
`of 6-keto-PGFIa from the day 15 uterus during either period of
`superfusion (Fig. 2).
`PGF2o and 6-keto-PGFla were the major PGs synthesized by
`homogenates of day 15 endometrium and myometrium, respect¬
`ively, although the endometrium also synthesized significant
`quantities of 6-keto-PGFIa. PGE2 was synthesized in smaller
`quantities by both tissues (Figs 3 and 4). Onapristone adminis¬
`tered between days 11 and 14 of
`the cycle significantly
`reduced the amount of PGF2a synthesized by
`(P < 0.05)
`homogenates of the day 15 endometrium, without significantly
`affecting the amounts of PGE2 and 6-keto-PGFla synthesized
`
`MYLAN PHARMS. INC. EXHIBIT 1016 PAGE 2
`
`

`
`300-1
`
`240-
`
`180
`
`á 120
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`
`BO
`
`
`
`40-, (b)
`
`20
`
`<"
`
`200
`
`100-
`
`Endometrium
`Myometrium
`Fig. 4. Mean ( ± SEM, = 5) amounts of (a) PGF2a, (b) PGE2 and (c)
`6-keto-PGFla synthesized during 1 h by homogenates of endometrium
`and myometrium from (D) control and ( ) ICI 182780-treated
`guinea-pigs on day 15 of the cycle. fSignificantly (P < 0.05) lower
`than the control value for the same PG in the same tissue.
`
`60
`
`50-
`
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`60-70 min
`Fig. 2. Mean ( ± SEM, = 5) amounts of (a) PGF2a, (b) PGE2 and (c) 6-
`keto-PGFI(1 from the day 15 uterus of (D) control and ( ) ICI 182780-
`treated guinea-pigs when superfused in vitro during the periods (i)
`0-10 min and (ii) 60-70 min. fSignificantly (P < 0.05) lower than the
`control value for the same PG during the same time period.
`
`M
`
`(b)
`
`(O 0-10 min
`
`10
`
`Fig. 5. Mean ( + SEM, = 5) concentrations of progesterone in the
`peripheral plasma of (D) control, ( ) onapristone-treated and (0)
`'Significantly
`tamoxifen-treated guinea-pigs on day 15 of the cycle.
`(P < 0.05) higher than the control and tamoxifen-treated values.
`
`(although the synthesis of both PGs tended to be reduced; Fig.
`3). Onapristone treatment had no effect on the amounts of the
`three PGs synthesized by homogenates of day 15 myometrium
`(Fig. 3). Tamoxifen administered between days 11 and 14 of the
`cycle significantly (P < 0.05) increased the amount of PGF2a
`synthesized and significantly (P < 0.05) decreased the amount
`of 6-keto-PGFIa synthesized by homogenates of the day 15
`endometrium, without affecting PGE2 synthesis (Fig. 3).
`Tamoxifen administration significantly (P < 0.05) increased the
`amount of 6-keto-PGFla synthesized by homogenates of day
`15 endometrium, without significantly affecting the amounts of
`
`Endometrium
`
`Myometrium
`Fig. 3. Mean ( + SEM, = 5) amounts of (a) PGF2a, (b) PGE2 and (c)
`6-keto-PGFIa synthesized during 1 h by homogenates of day 15 endo¬
`metrium and myometrium from ( ) control, (I) onapristone-treated
`fSignificantly (P < 0.05)
`and (0) tamoxifen-treated guinea-pigs.
`lower than the control value for the same PG in the same tissue.
`'Significantly (P < 0.05) higher than the control value for the same PG
`in the same tissue.
`
`MYLAN PHARMS. INC. EXHIBIT 1016 PAGE 3
`
`

`
`30
`
`(a)
`
`— 2-5-
`
`20-
`
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`
`£ 1-5
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`(a) concentrations of progesterone in
`Fig. 6. Mean ( + SEM, = 5)
`peripheral plasma, and (b) uterine horn weight in ( ) control and ( )
`ICI 182780-treated guinea-pigs on day 15 of the cycle. 'Significantly
`(P < 0.05) higher than the corresponding control value. fSignificantly
`(P < 0.05) lower than the corresponding control value.
`
`PGE2 and 6-keto-PGFla synthesized (although these were
`slightly depressed).
`Treatment with ICI 182780 from days 11 to 14 of the cycle
`significantly (P < 0.05) reduced the amounts of PGF20, PGE2
`and 6-keto-PGFIa synthesized by homogenates of the day 15
`endometrium, with PGF2a synthesis being particularly affected
`(Fig. 4). ICI 182780 treatment had no significant effect on the
`amounts of PGF2(I, PGE2 and 6-keto-PGFla synthesized by
`homogenates of day 15 myometrium (Fig. 4).
`Concentrations of progesterone in peripheral plasma were
`typically low ( < 1 ng ml"1) on day 15 in control and tamoxifen-
`treated guinea-pigs, but were significantly (P < 0.05) increased
`in guinea-pigs treated with onapristone and ICI 182780 (Figs 5
`and 6a). Tamoxifen caused the vagina to open after 2—3 days of
`treatment, which is in agreement with a previous report (Furr
`and Jordan, 1984).
`Mean ( + SEM, = 5) uterine horn weights of the guinea-pigs
`used in Expt 1 were 0.662 ± 0.094,0.509 ± 0.018, and 0.636 ±
`0.022 g in the control, onapristone-treated, and tamoxifen-treated
`animals, respectively. These values did not differ significantly. In
`Expt 2, the uterine hornweight was significantly (P < 0.05) lower
`in ICI 182780-treated guinea-pigs than in control guinea-pigs
`(Fig. 6b).
`
`Discussion
`If oestradiol acting on aprogesterone-primed uterus is thephysio¬
`logical stimulus for increasing uterine PGF2(I synthesis and release
`in guinea-pigs, inhibiting the effect of each steroid with a receptor
`antagonist should reduce uterine PGF2(I output and delay luteal
`regression. Onapristone (a progesterone antagonist) adminis¬
`tered to guinea-pigs between days 11 and 14 of thecycle inhibited
`uterine PGF2a output and extended luteal lifespan (as indicated by
`peripheral plasma progesterone concentrations) when examined
`on day 15. Consequently, endogenous progesterone appears to
`be essential for the increase in uterine PGF20 synthesis and release
`after day 11 of the cycle. However, since maximum uterine PGF2(1
`output occurs when plasma progesterone concentrations are at
`their lowest, this inverse correlation supports a 'priming role' for
`progesterone. Onapristone also reduced uterine PGE2 output
`
`(which indicates that PGE2 may be a by-product of PGF2a synthe¬
`sis), but had no significant effect on6-keto-PGF1(1 output. This is in
`agreement with previous findings (Riley and Poyser, 1987, 1990)
`which showed that endometrial PGF2a and PGI2 (as indicated by
`6-keto-PGFla) syntheses are controlled independently.
`The decrease in uterine PGF2a output induced by onapristone
`is not due to increased PG metabolism, since the increases in
`peripheral plasma concentrations of 13,14-dihydro-15-keto-
`PGF2(1 in guinea-pigs towards the end of the cycle (and which are
`indicative of increased uterine PGF2a secretion) are prevented by
`onapristone treatment. Luteal function is also prolonged (Qing
`et al, 1989).
`During the cycle,
`the amounts of PGF2a synthesized by
`homogenates of guinea-pig endometrium increase 2.2-fold
`between days 7 and 13 of the cycle as ovarian oestradiol output
`the end of the
`increases, but this increase reaches 4.4-fold at
`cycle after plasma progesterone concentrations have fallen
`In ovariectomized guinea-pigs, oestradiol
`(Poyser, 1983b).
`administered alone increases endometrial PGF2a synthesizing
`capacity 3.2-fold, but when progesterone treatment precedes
`oestradiol administration the capacity of the endometrium to
`synthesize PGF2a increases only 1.7-fold (Poyser, 1983b). These
`differences are not due to changes in PG metabolism since, in
`the absence of NAD+, metabolism of PGs by the guinea-pig
`uterus is low ( < 5%; Poyser, 1979), nor are they due to lack of
`arachidonic acid since, during the homogenization process,
`large amounts of free arachidonic acid are released (Mitchell
`et al, 1977). As prostaglandin endoperoxide synthase exhibits a
`self-catalysed destruction during the synthesis of PGs within
`the period studied (Lands et al, 1973),
`the increases in the
`amounts of PGF2a synthesized by homogenates of guinea-pig
`endometrium during the cycle or following oestradiol treatment
`are due to an increase in the amounts of enzymes that synthe¬
`size PGs that are present. Oestradiol stimulates the synthesis
`of these enzymes, but progesterone attenuates this stimulatory
`effect. However, oestradiol acting on a progesterone-primed
`uterus stimulates endometrial synthesis and release from the
`intact tissue, so this increase is not directly due to an increase
`in the amounts of PGF2a synthesizing enzymes present in the
`endometrium. Consequently in the present study, whereas
`onapristone prevents the stimulation of endometrial PGF2a syn¬
`it might be expected to increase the
`thesis and secretion,
`amounts of enzymes that synthesize PGF2a in the endometrium
`as the attenuating effect of progesterone on this stimulatory
`action of oestradiol should be prevented. However, this did not
`reduced the amounts of
`occur since onapristone treatment
`PGF2a synthesized by the day 15 endometrial homogenates by
`68%. The amounts of PGE2 and 6-keto-PGFla synthesized by
`homogenates of day 15 endometrium following onapristone
`treatment tended also to be reduced, so that in these animals the
`total amount of PGF2a, PGE2 and 6-keto-PGF,a synthesized by
`endometrial homogenates was reduced by 50%.
`It would seem that onapristone may also be inhibiting the
`action of oestradiol either by reducing ovarian oestradiol out¬
`put (possibly as a consequence of maintaining plasma pro¬
`gesterone concentrations at a high value), or by some action
`of onapristone on the uterus. Onapristone did not reduce the
`uterine horn weight of day 15 guinea-pigs, which suggests that
`it is not inhibiting the action of oestradiol directly (i.e. at the
`oestrogen receptor level). In ovariectomized rabbits treated with
`
`MYLAN PHARMS. INC. EXHIBIT 1016 PAGE 4
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`

`
`oestradiol alone or with onapristone, there is a dose-dependent
`inhibition by onapristone of oestradiol-induced gland formation
`in the endometrium, and also degenerative changes occur in the
`glandular epithelial cells within the endometrium. These
`changes produced by onapristone appear to be mediated by
`progesterone receptors since the additional administration of
`progesterone prevents these actions of onapristone (Chwalisz
`et al, 1991). Since many studies in a variety of species have
`indicated that the glandular epithelial cells are the main source
`of PGF2a and are the cells acted upon by steroid hormones, and
`if similar inhibitory and degenerative changes affect glandular
`epithelial cells in the endometrium of guinea-pigs as in rabbits
`following onapristone treatment, this may explain why onapris¬
`tone has an inhibitory effect on the amounts of PGF2a synthe¬
`sized by homogenates of the endometrium at the end of the
`cycle. However, as plasma concentrations of progesterone
`remained high in the onapristone-treated guinea-pigs and pro¬
`gesterone prevented the degenerative changes induced in rabbit
`endometrium by onapristone, another reason may have to be
`sought to explain why onapristone reduced the PG synthesizing
`capacity of guinea-pig endometrium. The mechanism by which
`onapristone reduces endometrial PG synthesizing capacity merits
`further study.
`Tamoxifen was an agonist in guinea-pigs as it induced vaginal
`opening within 2 to 3 days after the start of treatment, and it did
`not decrease uterine weight. Tamoxifen had no inhibitory effect
`on uterine PGF2a output, and did not prevent luteal regression
`time. Tamoxifen significantly
`the normal
`from occurring at
`increased the amounts of PGF2a synthesized by homogenates of
`the endometrium and myometrium, and significantly reduced the
`amount of 6-keto-PGF]a synthesized by homogenates of the
`endometrium. The amount of 6-keto-PGFla synthesized by
`homogenates of the myometrium also tended to be reduced after
`tamoxifen treatment. However, the total amounts ofPGF2a, PGE2
`and 6-keto-PGFIa synthesized by homogenates of endometrium
`and myometrium, respectively, did not differ between the control
`and tamoxifen-treated guinea-pigs. This indicates that tamoxifen
`switches uterine PG synthesis away from PGI2 (as indicated by
`6-keto-PGFIa) and towards PGF2a. Although there was a
`reduction in uterine 6-keto-PGFIa output following tamoxifen
`treatment, there was no corresponding increase in PGF2(I output,
`although uterine PGF2a synthesis and release was high.
`The administration of ICI 182780 significantly reduced uterine
`horn weight by approximately 50%, indicating that ICI 182780
`is an anti-oestrogen in guinea-pigs. The treatment of guinea-
`pigs with ICI 182780 between days 11 and 14 of the cycle
`significantly reduced uterine PGF2a output when measured on
`day 15. Luteolysis was therefore prevented in ICI 182780-
`treated guinea-pigs as indicated by the high plasma progester¬
`one concentrations. ICI 182780, like onapristone, also reduced
`PGE2 output without significantly affecting the output of 6-
`keto-PGFla. ICI 182780 treatment also prevented the increase
`in endometrial PGF2a synthesizing capacity normally observed
`by day 15 of the cycle, which agrees with the hypothesis that
`this increase is under the control of endogenous oestradiol
`(Poyser, 1983b). The amounts ofPGE2 and 6-keto-PGFIa synthe¬
`sized by homogenates of day 15 endometrium were also reduced
`by ICI 182780, but the extents of these reductions were not as
`large as for PGF20. This indicates that it is endometrial PGF2a
`synthesis which is largely controlled by oestradiol. The amounts
`
`of PGF2a, PGE2 and 6-keto-PGFIa synthesized by homogenates
`of myometrium were unaffected by treatment with ICI 182780.
`Thus, PG production by the myometrium is apparently not
`controlled by oestradiol.
`Overall, the findings with onapristone and ICI 182780 indi¬
`cate that endogenous progesterone and oestradiol are necessary
`for the stimulation of uterine PGF2a synthesis and secretion,
`the hypothesis that oestradiol acting on a
`and they support
`progesterone-primed uterus is the stimulus for increased PGF2(I
`production by the endometrium. Surprisingly, onapristone, like
`reduced the amounts of PGF2a synthesized by
`ICI 182780,
`homogenates of the endometrium, but not of the myometrium,
`which suggests that in some way onapristone is also inhibiting
`the release or the action of oestradiol. Tamoxifen proved to
`be an agonist in guinea-pigs, so it had no inhibitory effect on
`uterine PGF2a synthesis and release. However,
`tamoxifen did
`reduce uterine 6-keto-PGFm synthesis apparently by causing a
`switch to PGF2a synthesis. The treatment with a pure oestrogen
`receptor antagonist may be beneficial in preventing an increase
`in uterine PG production when such an increase is not desirable,
`e.g. (i) inearly pregnancy in non-primate mammalian species when
`uterine PGF2a synthesis has not been suppressed sufficiently so
`that luteal function is inadequate (see Poyser, 1981), and (ii) in
`disorders of menstruation such as dysmenorrhoea (Lundström
`et al, 1976). Progesterone receptor antagonists may also have a
`similar use in menstrual disorders.
`The technical assistance of L. Marshall is much appreciated. This study
`was supported by a grant from The Wellcome Trust. Onapristone was a
`generous gift from Schering AG, Berlin, Germany, and tamoxifen and ICI
`182780 were generous gifts from ICI Pharmaceuticals, Alderley Park,
`Macclesfield, Cheshire, UK.
`
`References
`
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`Blatchley FR and Poyser NL (1974) The effect of oestrogen and progesterone on
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`Blatchley FR, Donovan BT, Horton EW and Poyser NL (1972) The release of
`prostaglandins and progestin into the utero-ovarian venous blood of guinea-
`pigs during the oestrous cycle and following oestrogen treatment fournal of
`Physiology 222 69-88
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`Inhibition of the estradiol-mediated endometrial gland formation by the anti-
`relationship to uterine estrogen receptors
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`concentrations in utero—ovarian venous plasma of cyclic guinea-pigs Journal
`of Endocrinology 64 IIP—12P
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`Pharmacology and Therapeutics 25 127—205
`Horton EW and Poyser NL (1976) Uterine luteolytic hormone: a physiological
`role for prostaglandin F2a Physiological Reviews 55 595-651
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`oestrone, 20-dihydroprogesterone and progesterone during the oestrous
`cycle of the guinea-pig fournal of Reproduction and Fertility 35 177—182
`Lands WEM, LeTellier PR, Rome LH and Vanderhoek JY (1973) Inhibition of
`prostaglandin synthesis Advances in the Biosciences Vol. 9, pp 15—28 Ed.
`S Bergström. Pergamon Press, Braunschweig
`Leaver HA and Poyser NL (1981) Distribution of arachidonic acid and other
`fatty acids in the lipids of guinea-pig uterus and plasma in relation to uterine
`prostaglandin synthesis Journal of Reproduction and Fertility 61 325—333
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`Lundström V, Green and Wiqvist (1976) Prostaglandins, indomethacin and
`dysmenorrhoea Prostaglandins 11 893-904
`Mitchell S, Poyser NL and Wilson NH (1977) Effect of p-bromophenacyl bromide,
`an inhibitor of phospholipase Az, on arachidonic acid release and prostaglandin
`synthesis by the guinea-pig uterus British Journal of Pharmacology 59
`107-113
`Poyser NL (1979) Effects of actinomycin D on uterine prostaglandin production
`and oestrous cycle length in guinea-pigs Journal of Reproduction and Fertility
`56 559-565
`Poyser NL (1981) Prostaglandins in Reproduction John Wiley and Sons, Chichester
`Poyser NL (1983a) Effect of treating ovariectomised guinea-pigs with estradiol
`and progesterone on basal and A23187-stimulated release of prostaglandins
`from the uterus superfused in vitro Prostaglandins, Leukotrienes and Medicine
`11 345-360
`Poyser NL (1983b) Differential stimulation of prostaglandins and thromboxane
`synthesising capacities in guinea-pig uterus and ovary Prostaglandins,
`Leukotrienes and Medicine 10 163—177
`Poyser NL (1984) Prostaglandin production by the early pregnant guinea-pig
`uterus in relation to implantation and luteal maintenance, and the effect of
`oestradiol Journal of Reproduction and Fertility 72 117—127
`Poyser NL (1987) Effects of various factors on prostaglandin synthesis by the
`guinea-pig uterus Journal of Reproduction and Fertility 81 269—276
`Poyser NL and Brydon LJ (1983) Prostaglandin release from the guinea-pig
`uterus superfused in vitro. Effect of stage of estrous cycle, progesterone,
`estradiol, oxytocin and A23187 Prostaglandins 25 443-456
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`Poyser NL and Horton EW (1975) Plasma progesterone levels in guinea-pigs
`actively immunised against prostaglandin F2u, hysterectomised or treated
`with intra-uterine indomethacin Journal of Endocrinology 67 81—88
`Poyser NL and Scott FM (1980) Prostaglandin and thromboxane production
`by the rat uterus and ovary in vitro during the oestrous cycle Journal of
`Reproduction and Fertility 60 33—40
`Qing SS, Fähnrich M, Chwalisz , Hasan HS and Elger W (1989) PGFM and sex
`steroid concentrations throughout the oestrous cycle and pregnancy in the
`guinea-pig: effects of treatment with the progesterone antagonist ZK.98,299.
`In Hormone Antagonists for Fertility Regulation, pp 87-97 Eds CP Puri and PFA
`van Look. Indian SSRF, Bombay
`Riley SC and Poyser NL (1987) Effects of oestradiol, progesterone, hydro-
`cortisone and oxytocin on prostaglandin output
`from the guinea-pig
`endometrium maintained in tissue culture Prostaglandins 34 535—552
`Riley SC and Poyser NL (1990)
`Is the inhibitory effect of progesterone
`on endometrial prostaglandin F2a production due to an inhibition of
`protein synthesis? Prostaglandins, Leukotrienes and Essential Fatty Acids 39
`189-196
`Steel RBD and Torrie JH (1980) Principles and Procedures of Statistics
`A Bio-
`metrical Approach (2nd Edn) pp 106—107. McGraw-Hill Kogakusha Ltd,
`Tokyo
`Swan CG and Poyser NL (1983) Prostaglandin synthesis by, and the effects of
`prostaglandins and prostaglandin analogues on,
`the vas deferens of the
`rabbit and rat in vitro Journal of Reproduction and Fertility 69 91-99
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