Effect of prostaglandins on in vitro synthesis of progesterone and oestradiol-17β in placenta from early human pregnancy

In vitro synthesis of progesterone and estradiol-17β from endogenous precursors was studied in the placenta from women in early stage of gestation (< 7 weeks). Radioimmunoassay techniques were used to measure progesterone and estradiol-17β.It was shown that placental tissue from as early as six weeks of gestation can synthesize both progesterone and estradiol-17β in vitro. Prostaglandins F_2α and E₂ in concentration of 100 μg/ml of the incubation media did not have any significant effect on the in vitro synthesis of progesterone and estradiol-17β in the placental tissue.It seems unlikely that the abortifacient effect of natural prostaglandins PGE₂ and PGF_2α is due to their direct action on the synthesis of progesterone and estradiol-17β in the placenta.     

What regulates placental steroidogenesis in 90-day pregnant ewes?

By day-90, the placenta secretes half of the circulating progesterone and 85% of the circulating estradiol-17beta [Weems YS, Vincent D, Tanaka Y, et al. Effects of prostaglandin F(2alpha) on sources of progesterone and pregnancy in intact, ovariectomized, and hysterectomized 90-100 day pregnant ewes. Prostaglandins 1992;43:203-22; Weems YS, Vincent DL, Nusser K, et al. Effects of prostaglandin F(2alpha) (PGF(2alpha)) on secretion of estradiol-17beta and cortisol in 90-100 day hysterectomized, intact, or ovariectomized pregnant ewes. Prostaglandins 1994;48:139-57]. Ovariectomy (OVX) or prostaglandin (PG) F(2alpha) (PGF(2alpha)) does not abort intact or OVX 90-day pregnant ewes and PGF(2alpha) regresses the corpus luteum, but does not affect placental progesterone secretion in vivo [Weems YS, Vincent D, Tanaka Y, et al. Effects of prostaglandin F(2alpha) on sources of progesterone and pregnancy in intact, ovariectomized, and hysterectomized 90-100 day pregnant ewes. Prostaglandins 1992;43:203-22]. Luteal progesterone secretion in vitro at day-90 of pregnancy in ewes is regulated by PGE(1)and/or PGE(2), not by ovine luteinizing hormone (LH; 3). Concentrations of PGE in uterine or ovarian venous plasma averaged 6 ng/ml at 90-100 days of pregnancy in ewes [Weems YS, Vincent DL, Tanaka Y, Nusser K, Ledgerwood KS, Weems CW. Effect of prostaglandin F(2alpha) on uterine or ovarian secretion of prostaglandins E and F(2alpha) (PGE; PGF(2alpha)) in vivo in 90-100 day hysterectomized, intact or ovariectomized pregnant ewes. Prostaglandins. 1993;46:277-96]. Ovine placental PGE secretion is regulated by LH up to day-50 and by pregnancy specific protein B (PSPB) after day-50 of pregnancy [Weems YS, Kim L, Humphreys V, Tsuda V, Weems CW. Effect of luteinizing hormone (LH), pregnancy specific protein B (PSPB), or arachidonic acid (AA) on ovine endometrium of the estrous cycle or placental secretion of prostaglandins E(2) (PGE(2)) and F(2alpha) (PGF(2alpha)), and progesterone in vitro. Prostaglandins Other Lipid Mediators 2003;71:55-73]. Indomethacin (INDO), a prostaglandin synthesis inhibitor [Lands WEM. The biosynthesis and metabolism of prostaglandins. Annu Rev Physiol 1979;41:633-46], lowers jugular venous progesterone [Bridges PJ, Weems YS, Kim L, et al. Effect of prostaglandin F(2alpha) (PGF(2alpha)), indomethacin, tamoxifen or estradiol-17beta on pregnancy, progesterone and pregnancy specific protein B (PSPB) secretion in 88-90 day pregnant ewes. Prostaglandins Other Lipid Mediators 1999;58:113-24] and inferior vena cava PGE of pregnant ewes with ovaries by half at day-90 [Bridges PJ, Weems YS, Kim L, LeaMaster BR, Vincent DL, Weems CW. Effect of prostaglandin F(2alpha) (PGF(2alpha)), indomethacin, tamoxifen or estradiol-17beta on prostaglandin E (PGE), PGF(2alpha) and estradiol-17beta secretion in 88-90 day pregnant sheep. Prostaglandins Other Lipid Mediators 1999;58:167-78]. In addition, treatment of 90 day ovine diced placental slices with androstenedione in vitro increased placental estradiol-17beta, but treatment with PGF(2alpha)in vitro did not decrease placental progesterone secretion, which indicates that ovine placenta progesterone secretion is resistant to the luteolytic action of PGF(2alpha) [Weems YS, Bridges PJ, LeaMaster BR, Sasser RG, Vincent DL, Weems CW. Secretion of progesterone, estradiol-17beta, prostaglandins (PG) E (PGE), F(2alpha) (PGF(2alpha)), and pregnancy specific protein B (PSPB) by day 90 intact or ovariectomized pregnant ewes. Prostaglandins Other Lipid Mediators 1999;58:139-48]. This also explains why ovine uterine secretion of decreased around day-50 [Weems YS, Kim L, Humphreys V, Tsuda V, Weems CW. Effect of luteinizing hormone (LH), pregnancy specific protein B (PSPB), or arachidonic acid (AA) on ovine endometrium of the estrous cycle or placental secretion of prostaglandins E(2) (PGE(2)) and F(2alpha) (PGF(2alpha)), and progesterone in vitro. Prostaglandins Other Lipid Mediators 2003;71:55-73], when placental estradiol-17beta secretion is increasing [Weems C, Weems Y, Vincent D. Maternal recognition of pregnancy and maintenance of gestation in sheep. In: Reproduction and animal breeding: advances and strategies. Enne G, Greppi G, Lauria A, editors, Elsevier Pub., Amsterdam 1995. p. 277-93]. Treatment of 90 day pregnant ewes with estradiol-17beta+ PGF(2alpha), but not either treatment alone, caused a linear increase in both estradiol-17beta and PGF(2alpha) and ewes were aborting [Bridges PJ, Weems YS, Kim L, Sasser RG, LeaMaster BR, Vincent DL, Weems CW. Effect of prostaglandin F(2alpha) (PGF(2alpha)), indomethacin, tamoxifen or estradiol-17beta on pregnancy, progesterone and pregnancy specific protein B (PSPB) secretion in 88-90 day pregnant ewes. Prostaglandins Other Lipid Mediators 1999;58:113-24; Bridges PJ, Weems YS, Kim L, LeaMaster BR, Vincent DL, Weems CW. Effect of prostaglandin F(2alpha) (PGF(2alpha)), indomethacin, tamoxifen or estradiol-17beta on prostaglandin E (PGE), PGF(2alpha) and estradiol-17beta secretion in 88-90 day pregnant sheep. Prostaglandins Other Lipid Mediators 1999;58:167-78]. Pregnant ewes OVX on day 83 of pregnancy and placental slices cultured in vitro secretes 2-3-fold more estradiol-17beta, PSPB, PGE, and progesterone than placental slices from 90 day intact pregnant ewes, but placental PGF(2alpha) secretion by placental slices from intact or OVX ewes did not change [Denamur R, Kann G, Short R V. How does the corpus luteum of the sheep know that there is an embryo in the uterus? In: Pierrepont G, editor. Endocrinology of pregnancy and parturition, vol. 2. Cardiff, Wales, UK: Alpha Omega Pub Co.; 1973. p. 4-38]. The objective of these experiments was to determine what regulates ovine placental progesterone and estradiol-17beta secretion at day-90 of pregnancy, since the hypophysis [Casida LE, Warwick J. The necessity of the corpus luteum for maintenance of pregnancy in the ewe. J Anim Sci 1945;4:34-9] or ovaries [Weems CW, Weems YS, Randel RD. Prostaglandins and reproduction in female farm animals. Vet J 2006;171:206-28] are not necessary after day-55 to maintain pregnancy. In Experiment 1, diced placental slices from day-90 intact or OVX pregnant ewes that were ovariectomized or laparotomized and ovaries were not removed on day 83 were collected on day-90 and incubated in vitro in M-199 with Vehicle, ovine luteinizing hormone (oLH), ovine follicle stimulating hormone (oFSH), ovine placental lactogen (oPL), PGE(l), PGE(2), PGD(2), PGI(2), insulin-like growth factor (IGF) 1 or 2 (IGF(l); IGF(2)), leukotriene C(4) (LTC(4)), platelet activating factor (PAF) 16 or 18 (PAF-16; PAF-18) at doses of 0, 1, 10, or 100ng/ml for 4h. In Experiment 2, placental slices from day-90 intact and OVX (intact or OVX laporotomized 7 days earlier) pregnant ewes were incubated in vitro with vehicle, INDO, Meclofenamate (MECLO), PGE(l), PGE(2), INDO+PGE(1), MECLO+PGE(l), INDO+PGE(2), or MECLO+PGE(2) for 4h. Media were analyzed for progesterone, estradiol-17beta, PGE, or PGF(2alpha) by RIA. Hormone data in media were analyzed in Experiment 1 by a 2x3x13 and in Experiment 2 by a 2x9 Factorial Design for ANOVA. In Experiment 1, placental progesterone, PGE, or estradiol-17beta secretion were increased (P< or =0.05) two-fold by OVX. Progesterone was not increased (P> or =0.05) by any treatment other than OVX and only FSH increased (P< or =0.05) estradiol-17beta secretion by placental slices in both OVX and intact ewes 90-day pregnant ewes. In Experiment 2, INDO or MECLO decreased (P< or =0.05) placental progesterone secretion by 88% but did not decrease (P> or =0.05) placental estradiol-17beta secretion from intact or OVX ewes. PGE(l) or PGE(2) increased (P< or =0.05) progesterone secretion only in ewes treated with INDO or MECLO. It is concluded that FSH probably regulates day-90 ovine placental estradiol-17beta secretion, while PGE(l) or PGE(2) regulates day-90 placental progesterone secretion.     

Secretion of progesterone, estradiol-17beta, PGE, PGF2alpha, and pregnancy-specific protein B by 90-day intact and ovariectomized pregnant ewes

Ninety-day pregnant ewes were either laparotomized, ovaries left in situ or bilaterally ovariectomized, and a jugular venous catheter and an inferior vena cava catheter via the saphenous vein were installed. Seven days later, placenta slices were collected and incubated in vitro for 4 h. Secretions of progesterone, PGE, estradiol-17beta and pregnancy-specific protein B (PSPB) in vitro by placenta from ovariectomized ewes were increased (P < or = 0.05) by 2.7-, 3.6-, 2.2-, and 2.4-fold, respectively, when compared to placenta slices from intact 90-day pregnant ewes. Secretion of PGF2alpha in vitro was unchanged (P > or = 0.05). Ovariectomy decreased (P < or = 0.05) jugular venous progesterone for 78 h followed by a quadratic increase (P < or = 0.05), whereas progesterone remained unchanged (P > or = 0.05) in intact ewes over the 162-h sampling period. Ovariectomy increased (P < or = 0.05) PGE in inferior vena cava plasma over the last half of the 162-h sampling period, whereas concentration of PGF2alpha did not change (P > or = 0.05). Increases in PGE occurred before the increase in progesterone. Concentrations of PSPB in inferior vena cava plasma of ovariectomized pregnant ewes increased (P < or = 0.05) during the last half of the 162-h sampling period, but not in intact ewes (P > or = 0.05). PSPB increased before PGE and progesterone. Concentrations of estradiol-17beta in jugular venous plasma of ovariectomized pregnant ewes increased (P < or = 0.05) during the last half of the sampling period, but not in intact ewes (P > or = 0.05). Increases in estradiol-17beta occurred before increases in PSPB. It is concluded that these data support the hypothesis that estradiol-17beta may control placental secretion of PSPB; PSPB may regulate placental secretion of PGE; and PGE may regulate placental secretion of progesterone.     

Hormone changes occurring during second trimester abortion induced with 15 (S)-15-methyl prostaglandin F2alpha.

Changes in progesterone, human placental lactogen (HPL), cortisol and estradiol-17B were measured during second trimester abortion induced by I.M. 15-methyl PGF2alpha. A rapid decline in progesterone and HPL was found, indicating perhaps an initial effect on the placenta. A rapid rise in cortisol was found, but it is not clear if this is due to stress or part of the termination mechanism. The changes of estradiol were not as distinct and may reflect opposite effects of the prostaglandin on the placenta and adrenals. Similar hormonal changes were observed regardless of the duration of gestation.     

Effect of the aromatase inhibitor CGS-16949A on pregnancy and secretion of progesterone, estradiol-17beta, prostaglandins E and F2alpha (PGE; PGF2alpha) and pregnancy specific protein B (PSPB) in 90-day ovariectomized pregnant ewes

The aromatase inhibitor CGS-16949A was used to determine whether CGS-16949A altered secretion of progesterone, estradiol-17beta, PGE (PGE1 + PGE2), PGF2alpha and PSPB. Ninety day pregnant ewes were ovariectomized and received vehicle, PGF2alpha, CGS-16949A or PGF2alpha+CGS-16949A. None of the ewes treated with PGF2alpha, CGS-16949A or PGF2alpha+CGS-16949A aborted (P > or = 0.05) during the 108-h experimental period. Treatment with CGS-16949A lowered (P < or = 0.05) progesterone in jugular venous plasma but concentrations of progesterone were not affected (P > or = 0.05) by treatment with PGF2alpha. Concentrations of estradiol-17beta and PSPB in jugular venous plasma and PGE in inferior vena cava plasma were decreased (P < or = 0.05) by treatment with CGS-16949A. Concentrations of PGF2alpha in inferior vena cava plasma were not affected (P > or = 0.05) by treatment with CGS-16949A. Decreases in estradiol-17beta occurred before decreases in PSPB, which was then followed by decreases in PGE (P < or = 0.05). It is concluded that these data support the hypothesis that estradiol-17beta regulates placental secretion of PSPB; PSPB regulates placental secretion of PGE; and PGE regulates placental secretion of progesterone during mid-pregnancy in ewes.     

Interrelationships among plasma progesterone concentrations, luteal anatomy and function, and placental ontogeny during gestation in a viviparous lizard (Niveoscincus metallicus: Scincidae)

Plasma progesterone concentrations were measured at six stages of gestation in the viviparous lizard Niveoscincus metallicus. Anatomical and functional parameters of luteal activity were also investigated. The diameter of the corpus luteum (CL) decreased gradually though gestation, as did the diameter of the luteal cells. Major degenerative changes were observed in CLs post-partum. Plasma progesterone concentrations were basal both prior to, and just after, ovulation; a rapid increase occurred in early gestation. Plasma progesterone concentrations remained elevated until late gestation, but fell some 2 weeks before parturition. In vitro production of progesterone was greater in CLs in mid- than in late-gestation, and the addition of prostaglandin F(2alpha) to the incubation medium had no effect on progesterone production. Non-luteal ovarian tissue and adrenals produced progesterone, but at approximately one-tenth the rate of production by CLs. Temporal correlations between the plasma progesterone profile and stages of placental development were also assessed. The rise in plasma progesterone concentrations occurs before differentiation of the chorioallantoic placenta, but progesterone is still high when it degenerates. We conclude that the CLs are the major source of gestational progesterone in N. metallicus.     

PGE2 induces its own secretion in vitro by bovine 270-day placenta but not by 200-day placenta.

Two separate experiments were conducted to determine whether prostaglandin (PG) E2 stimulates the secretion of progesterone by 270- or 200-day Brahman placentas in vitro. Secretion of progesterone, PGF2alpha, pregnancy specific protein B, or estradiol-17beta by 270-day Brahman placentas was not affected (p > or = 0.05) by PGE2, during the 4-h incubation period at the doses tested. Indomethacin or meclofenamic acid decreased (p < or = 0.05) 270-day Brahman placental secretion of PGE and PGF2alpha by 98 and 60%, respectively. However, PGE2 induced (p < or = 0.05) its own secretion, but not the secretion of PGF2alpha (p > or = 0.05), by 270-day Brahman placentas, even in the presence of indomethacin or meclofenamic acid at a dose of 100 ng/mL. Also, secretion of 8-Epi-PGE2 by Day 270 Brahman placentas was increased (p < or = 0.05) by PGE2. Secretion of progesterone, estradiol-17beta, or pregnancy specific protein B by 200-day Brahman placentas was not affected by PGE2, 8-Epi-PGE2, PGF2alpha, estradiol-17beta, or trichosanthin during the 4- or 8-h incubation period (p > or = 0.05). Secretion of estradiol-17beta at 8 h was lower (p < or = 0.05) in all treatment groups and did not differ (p > or = 0.05) among the 8-h incubation treatment groups. Secretion of PGE by 200-day Brahman placentas was reduced (p < 0.05) by indomethacin 72 and 82% and by meclofenamic acid 72 and 96%, respectively, at 4 and 8 h when compared to controls. Secretion of PGF2alpha was reduced (p < or = 0.05) 71 and 86% by indomethacin or 89 and 89% by meclofenamic acid at 4 and 8 h, respectively, and did not differ (p > or = 0.05) between 4 and 8 h of incubation. PGE2 did not (p > or = 0.05) induce secretion of PGE above what was added in any treatment group. PGE in culture media was increased (p < or = 0.05) by 8-Epi-PGE2, pregnancy specific protein B, and the 100 ng/mL PGF2alpha dose (p < or = 0.05), but not by PGE2, progesterone, estradiol-17beta, 8-Epi-PGF2alpha, or trichosanthin. Secretion of PGF2alpha by 200-day Brahman placentas was not affected (p > or = 0.05) by 8-Epi-PGE2, progesterone, or estradiol-17beta, but PGF2alpha secretion was increased (p < or = 0.05) by trichosanthin or PGE2, even in the presence of indomethacin or meclofenamic acid. It is concluded that PGE does not affect secretion of progesterone by 200- or 270-day bovine placentas, but, pregnancy specific protein B may regulate placental secretion of PGE. Also, indomethacin and meclofenamic may affect enzymes converting PGH to PGE rather than acting only on cyclooxygenase because indomethacin and meclofenamic acid lowered PGE secretion by 270-day Brahman placentas more than they lowered PGF2alpha. In addition, it is concluded that PGE2 can induce bovine placental secretion of PGE, but this is dependent upon the stage of gestation.     

Effect of PGF2alpha, indomethacin, tamoxifen, or estradiol-17beta on incidence of abortion, progesterone, and pregnancy-specific protein B (PSPB) secretion in 88- to 90-day pregnant sheep

One objective of this experiment was to evaluate our hypotheses that estradiol-17beta regulates secretion of pregnancy specific protein B (PSPB) and that secretion of progesterone during pregnancy is regulated by a prostanoid by examining the effects of prostaglandin F2alpha (PGF2alpha), a luteolyic agent; indomethacin, a prostanoid synthesis inhibitor; tamoxifen, an estrogen receptor antagonist; estradiol 17-beta; and interaction of these factors on the incidence of abortion and progesterone and PSPB secretion. Another objective was to determine if there is a luteal source of PSPB. Weights of corpora lutea were decreased (P < or = 0.05) by PGF2alpha, indomethacin, PGF2alpha + tamoxifen, PGF2alpha + indomethacin, and PGF2alpha + estradiol-17beta but not (P > or = 0.05) by tamoxifen or estradiol-17beta alone. No ewe treated with PGF2alpha alone aborted (P > or = 0.05). Forty percent of ewes treated with PGF2alpha + estradiol-17beta aborted (P < or = 0.05), but ewes were not aborted by any other treatment within the 72-h sampling period. Profiles of progesterone in jugular venous blood differed (P < or = 0.05) among control, indomethacin-, tamoxifen-, and PGF2alpha + indomethacin-treated ewes. Progesterone in jugular venous blood of control ewes decreased (P < or = 0.05) by 24 h, followed by a quadratic increase (P < or = 0.05) from 24 to 62 h. Progesterone in jugular venous blood of indomethacin-, PGF2alpha-, PGF2alpha- + tamoxifen-, PGF2alpha + indomethacin-, PGF2alpha + estradiol-17beta-, and tamoxifen-treated ewes was reduced (P < or = 0.05) by 18 h and did not vary (P > or = 0.05) for the remainder of the 72-h sampling period. Progesterone in vena cava and in uterine venous blood was reduced (P < or = 0.05) at 72 h in PGF2alpha-, indomethacin-, tamoxifen-, PGF2alpha + indomethacin-, PGF2alpha + tamoxifen-, and PGF2alpha + estradiol-17beta-treated ewes. Weights of placentomes did not differ among treatment groups (P > or = 0.05). Profiles of PSPB in inferior vena cava blood differed (P < or = 0.05) among control, estradiol-17beta-, indomethacin-, tamoxifen-, PGF2alpha + indomethacin-, and PGF2alpha + tamoxifen-treated 88- to 90-day pregnant ewes. Concentrations of PSPB in inferior vena cava blood were increased (P < or = 0.05) in indomethacin-, estradiol-17beta-, tamoxifen-, PGF2alpha + tamoxifen-, and PGF2alpha + indomethacin-treated 88- to 90-day pregnant ewes within 6 h and did not vary (P > or = 0.05) for the remainder of the 72-h sampling period. Concentrations of PSPB in uterine venous blood of indomethacin-, tamoxifen-, PGF2alpha + tamoxifen-, and PGF2alpha + indomethacin-treated ewes were greater (P < or = 0.05) at 72 h than at 0 h. PSPB in ovarian venous blood did not differ (P > or = 0.05) adjacent or opposite to the ovary with the corpus luteum. It is concluded from these data that estrogen regulates placental secretion of PSPB and that a prostanoid, presumably prostaglandin E, regulates placental secretion of progesterone during 88-90 days of gestation in sheep and that there is no luteal source of PSPB.     

Kinetic analysis of human placental, ovarian, and adrenal 3 beta-hydroxysteroid dehydrogenase inhibition by epostane in vitro

The effect of epostane [(2 alpha,4 alpha,5 alpha,17 beta)-4,5-epoxy-17-hydroxy-4,17-dimethyl-3-oxo- androstane-2-carbonitrile] on the conversion of pregnenolone to progesterone and of dehydroepiandrosterone (DHA) to androstenedione was studied in human term placental microsomes and in comparison with human ovarian and adrenal microsomes. Using pregnenolone as substrate, 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activity in the three tissues had a similar Km (3-6 microM) but Vmax ranged from 1.3 nmol/mg protein per min in ovary to 10 nmol/mg protein per min in placenta. Epostane inhibited 3 beta-HSD activity in all three tissues with the characteristics of a pure competitive inhibitor: mean Ki values were 1.7 microM for placenta, 0.5 microM for adrenal and 0.1 microM for ovary. Moreover, in placental microsomes epostane inhibited the conversion of DHA to androstenedione with a Ki of 0.6 microM. The mechanism of action of epostane explains its effectiveness in blocking progesterone synthesis during the luteal phase and in pregnancy in women, and its strong anti-steroidogenic effect in other endocrine tissues in vitro.     

Oxytocin-stimulated production of prostaglandin F2alpha by isolated endometrium of rabbit: modulation by ovarian steroids

To test the hypothesis that ovarian steroid hormones modulate oxytocin-induced release of prostaglandin F2alpha (PGF2alpha) from uterine endometrium, 2 ovariectomized rabbits were pretreated with progesterone (5 mg/day for 10 days), 2 with estradiol-17 beta (25 microgram/day for 10 days), 2 with both steroids, and one with sesame oil only. On the last day of treatment, endometrial fragments were excised and incubated in vitro with or without oxytocin (100 muU/ml). Although endometrium from rabbits pretreated with combined steroids released more PGF2alpha immediately after excision than did tissue from animals pretreated with either steroid by itself, endometrium from animals pretreated with estradiol-17 beta alone released the most PGF2alpha during sustained incubation in vitro. Moreover, only this tissue exhibited significant oxytocin-dependent release of PGF2alpha. At the dosages used, progesterone completely antagonized both of these effects of estradiol-17 beta. The results support the hypothesis that ovarian steroid hormones regulate oxytocin-dependent release of PGF2alpha from endometrial cells. A posible mechanism of action is suggested.     

Dexamethasone inhibition of cyclooxygenase expression in bovine term placenta.

Since both prostaglandin (PG) F2 alpha and corticosteroids are elevated in mammals before the onset of parturition, we studied the effect of the synthetic corticosteroid dexamethasone on PGF2 alpha accumulation and cyclooxygenase (prostaglandin synthase, PGS) expression in the bovine fetal placenta. Cultures were prepared from cotyledons at different stages of gestation. The effect of dexamethasone on PGF2 alpha accumulation and PGS expression was determined by radioimmunoassay and [35S]methionine metabolic labeling followed by immunoprecipitation with specific anti-cyclooxygenase antibodies, respectively. Data demonstrate that in fetal placental cells at term, both PGF2 alpha accumulation and cyclooxygenase expression are significantly inhibited after 18 hours of dexamethasone treatment (150 nM). In contrast, neither first nor second trimester cells were sensitive to dexamethasone treatment. Dexamethasone inhibition of PGF2 alpha synthesis in fetal cells at term was abolished in the presence of RNA or protein synthesis inhibitors (actinomycin D or puromycin, 10 micrograms/ml each). Neither progesterone nor 17 beta-estradiol accumulation were affected by dexamethasone treatment at any stage of gestation. Data suggest that corticosteroids play a role in parturition through PGF2 alpha synthesis regulation by fetal placental cells. Since abnormalities during parturition e.g. retained placenta, are common following dexamethasone induction of labor in cows, we postulate that the local inhibition of PGF2 alpha accumulation by cotyledon cells after corticosteroid administration, may be involved in placental retention.     

Hormone changes occurring during second trimester abortion induced with 15(S)-15-methyl prostaglandin F2α

Changes in progesterone, human placental lactogen (HPL), cortisol and estradiol-17β were measured during second trimester abortion induced by I.M. 15-methyl PGF2α. A rapid decline in progesterone and HPL was found, indicating perhaps an initial effect on the placenta. A rapid rise in cortisol was found, but it is not clear if this is due to stress or part of the termination mechanism. The changes of estradiol were not as distinct and may reflect opposite effects of the prostaglandin on the placenta and adrenals. Similar hormonal changes were observed regardless of the duration of gestation.     

Norethisterone acetate and ethinylestradiol in early human pregnancy

In a double-blind randomized trial, 25 women (8-9 weeks pregnant) received 20 mg norethisterone acetate (NET-AC) and 0.04 mg ethinylestradiol (EE2), 25 women receiving placebo. The patients were followed by ultrasound and the products at curettage studied macroscopically and microscopically. In an open trial, ten patients (5-9 weeks pregnant) received NET-AC + EE2, 11 serving as controls. The concentrations of plasma progesterone, estradiol-17 beta, 17 alpha-hydroxyprogesterone, norethisterone, and FSH were followed. The frequency of intrauterine hemorrhage in early pregnancy was not affected by NET-AC + EE2. Ultrasound was not reliable when studying the occurrence of decidual hemorrhages during early pregnancy. The pharmacokinetics and bioavailability of NET remain unchanged during early pregnancy. The treatment with NET-AC + EE2 had no effect on the heights and the time courses of the mean plasma values of progesterone, estradiol-17 beta, 17 alpha-hydroxyprogesterone, and FSH. No differences were found between treated and nontreated patients in the pathology of the placenta or decidua as determined by both macroscopic and microscopic examinations. The hypothesis of Papp and Gardo, that decidual hemorrhages may be induced in early pregnancy as a consequence of a "withdrawal effect" of hormonal pregnancy tests, is not supported by the results of this investigation.     

Inhibition of progesterone synthesis in placenta by administration of dexamethasone to pregnant rats

Glucocorticoid receptors have been detected in placenta from several species, including the rat, although the biological function of corticoids is unknown in placenta from the latter species. The present experiments examined the effect of glucocorticoid treatment on placental progesterone biosynthesis from endogenous precursors by incubated basal zone trophoblast and labyrinthine zone of placentas from adrenalectomized-ovariectomized rats at the end of pregnancy. It was found that a higher proportion of synthesized progesterone was retained in the tissue than that released into the incubation medium. Treatment of rats on the 17th-18th day of pregnancy with 10 micrograms/ml of dexamethasone in the drinking saline for 3 days, produced a significant inhibition of progesterone detected in tissue and medium of incubated placental zones. In vitro addition of dexamethasone (10(-4) M) was also effective in reducing progesterone in the placental zone studied (LZ). Serum progesterone of intact rats was in the range of rats near parturition (approx 25 ng/ml) and dropped to almost undetectable levels in rats with adrenalectomy and ovariectomy, with or without dexamethasone treatment, suggesting that in late pregnancy the rat placenta does not contribute significantly to circulating levels of progesterone. This glucocorticoid effect could not be extended to estrogens, as we, in accord with the work of other groups, failed to detect estrogen synthesis in rat placenta. It is suggested that a function for glucocorticoid receptors in rat placenta may be the inhibition of local progesterone production.     

Effect of trilostane on PGE, PGF2alpha, estradiol-17beta, and progesterone secretion and pregnancy of 90-day ovariectomized pregnant ewes

Ninety-day pregnant sheep were ovariectomized and received vehicle or trilostane every 12 h through 132 h, starting at 72 h postovariectomy. All trilostane-treated ewes aborted (P < or = 0.05) between 36 and 50 h after initiation of treatment. Profiles of progesterone in jugular venous blood differed (P < or = 0.05) and was lower (P < or = 0.05) in trilostane-treated ewes. Profiles of estradiol-17beta in jugular venous plasma of trilostane-treated ewes differed (P < or = 0.05) from controls. Estradiol-17beta increased after the first two treatments, followed by a return 2 h later to pretreatment levels (P > or = 0.05), which was followed by a sustained increase (P < or = 0.05) in estradiol-17beta. Profiles of PGF2alpha in inferior vena cava plasma of trilostane-treated ewes differed and were greater (P < or = 0.05) and occurred with the sustained increase in estradiol-17beta and the onset of most of the abortions. Profiles of PGE in inferior vena cava plasma between control and trilostane-treated 90-day pregnant ewes did not differ (P > or = 0.05). It is concluded that abortions occur at midpregnancy in sheep when the estradiol-17beta : progesterone ratio changes sufficiently to cause a sustained increase in estradiol-17beta and PGF2alpha but without changing placental secretion of PGE.     

Gonadotropin-releasing hormone effects on placental hormones during gestation: II. Progesterone, estrone, estradiol and estriol

The release of progesterone (P), estrone (E1), estradiol (E2) and estriol (E3) from human placental tissue in vitro was found to be related to the gestational age of the placenta. The basal release of P, E1 and E2 on Day 1 of culture was highest from placentas of early gestation (9-13 wk). The release of P then declined, reaching a nadir by 15 wk, and continued at that level. The release of E1 and E2, reached a nadir at 17 weeks, and then again increased by term. In contrast, the basal release of E3 increased with increasing gestational age of the placenta. Thus, it appears that differing factors may influence placental P, E1, E2 and E3 production. In addition, the effect of synthetic gonadotropin-releasing hormone (GnRH) on these hormonal releases was studied. The stimulation of P by GnRH was greatest in placentas of 16 and 17 wk of gestation after extended culture when the basal release of P had declined. As much as a 240-fold increase was observed on the eighth day of culture. A large stimulation of P (32-fold) was also observed in the term placental cultures. A stimulation of E1 and E2 by GnRH was observed during the initial days of culture and in mid-gestational placental cultures (16-17 wk). A stimulation of E2 only was also observed at 13-15 wk and at term. A stimulation of E3 was observed in certain individual placentas. A correlation of the P and human chorionic gonadotropin (hCG) response to GnRH stimulation was noted, as well as an inverse relation of estrogens and hCG stimulation by GnRH. These data demonstrate that steroidogenic competence of the placenta differs with gestational age and that GnRH can influence steroid release. The degree and pattern of response to GnRH varied with the gestational age of the placenta and its endocrine milieu.     

Do calcium-mediated cellular signalling pathways, prostaglandin E2 (PGE2), estrogen or progesterone receptor antagonists, or bacterial endotoxins affect bovine placental function in vitro?

The major objective of this experiment was to determine whether the bovine placenta could be stimulated to secrete progesterone, since the bovine placenta secretes little progesterone when the corpus luteum is functional. Secondly, we wanted to determine whether reported abortifacients or progesterone or estrogen receptor antagonists affected bovine placental prostaglandin secretion. The ovine placenta secretes half of the circulating progesterone at day 90 of pregnancy and PGE2 appears to regulate ovine placental progesterone secretion. Calcium has been reported to regulate placental progesterone secretion in cattle. Diced 186-245-day placental slice explants from six Brahman and six Angus cows were incubated in vitro at 39.5 degrees C under 95% air: 5% CO2 at pH 7.2 in 5 ml of M-199 for 1 h in the absence of treatments and for 4 and 8 h in the presence of treatments. Treatments were: vehicle; R24571; compound 48/80; IP3; PGE2; CaCl2; cyclosporin A; lipopolysaccharide (endotoxin) from Salmonella abortus equi., enteriditis, and typhimurium; monensin; ionomycin; arachidonic acid; mimosine; palmitic acid; progesterone, androstenedione; estradiol-17beta; A23187; RU-486; or MER-25. Jugular and uterine venous plasma and culture media were analyzed for progesterone, PGE2 and PGF2alpha by radioimmunoassay (RIA). Plasma hormone data were analyzed by a One-Way Analysis of Variance (ANOVA). Hormone data in culture media were analyzed for breed and treatment effects by a Factorial Design (2 breeds, 2-range of days, 21 treatments) for ANOVA (2 x 2 x 21). Since hormone data secreted by placental tissue in vitro did not differ (P > or = 0.05) by breed or range of days of pregnancy, data were pooled and analyzed by a One-Way ANOVA. Concentrations of PGE2 in uterine venous blood were two-fold greater (P < or = 0.05) in Angus than Brahman cows. PGE2 and PGF2alpha in vehicle controls increased from 4 to 8h (P < or = 0.05), but not progesterone (P > or = 0.05) Progesterone in culture media treated with RU-486 increased (P < or = 0.05) at 4 and 8 h compared to vehicle controls and was not affected by other treatments (P > or = 0.05). Concentrations of PGE2 in media at 4 and 8 h were lower (P < or = 0.05) when compared to controls except treatment with PGE2 at 4 and 8h and RU-486 at 8h (P > or = 0.05). PGF2alpha was increased (P < or = 0.05) by RU-486 at 8h and no other treatment affected PGF2alpha at 4 or 8 h (P < or = 0.05). In conclusion, modulators of cellular calcium signalling pathways given alone do not affect bovine placental progesterone secretion at the days studied and progesterone receptor-mediated events appear to suppress placental progesterone, PGF2alpha, and PGE2 secretion in cattle. In addition, PGE2 does not appear to regulate bovine placental progesterone secretion when the corpus luteum is functional and bacterial endotoxin does not appear to affect bovine placental secretion of PGF2alpha or PGE2.     

Estradiol-17 beta interference with meiotic maturation in Rana pipiens ovarian follicles: evidence for inhibition of 3 beta-hydroxysteroid dehydrogenase.

Increasing doses of estradiol-17 beta added to in vitro incubations inhibited pregnenolone-induced germinal vesicle breakdown in Rana pipiens ovarian follicles. The inhibition was reversed with increasing concentrations or pregnenolone added to the medium. Because no evidence of estradiol-17 beta inhibition or interaction with progesterone-induced GVBD was observed, the effect of estradiol-17 beta on the conversion of 3H-pregnenolone to 3H-progesterone was investigated. Estradiol-17 beta in doses as low as 10(-7) M significantly inhibited the conversion of 3H-pregnenolone to 3H-progesterone in follicles incubated in vitro. It is suggested that estradiol-17 beta is a feedback inhibitor of 3 beta-hydroxysteroid dehydrogenase-isomerase, the enzyme complex that converts pregnenolone to progesterone, a necessary step in the initiation of GVBD.     

Imbalanced synthesis of human choriogonadotropin alpha and beta subunits reflects the steady state levels of the corresponding mRNAs

Previous studies have demonstrated an imbalance in placental levels of the human choriogonadotropin (hCG) alpha and beta subunits. Free alpha subunit was present in first trimester placentae, and the imbalance was accentuated as gestation approached parturition. Two sets of experiments were performed to assess the control on production levels of each subunit. Synthesis of the alpha and beta subunits was assessed by labeling the nascent chains of polysomes derived from first trimester placenta. The products of these reactions were immunoprecipitated with subunit-specific antisera and the labeled subunits were quantitated; the ratio of alpha to beta subunit synthesized was 1.7. To examine whether this imbalanced synthesis reflected differences in the amount of subunit mRNAs, or differing mRNA translational efficiencies, the ratio of the steady state levels of these mRNAs was also determined. Total first trimester placental RNA was hydrolyzed with alkali, 5'-end-labeled with 32P, and hybridized in DNA excess to cloned alpha and beta cDNAs. These experiments demonstrated the presence of twice as much hCG-alpha mRNA as hCG-beta mRNA. In term placenta, the amounts of excess alpha subunit are greater than at first trimester; the ratio of alpha to beta mRNAs in term RNA was about 12:1. Thus, the subunit mRNA levels are independently regulated and their imbalance accounts for differences in the quantities of alpha and beta subunits seen in placental tissue.     

Progesterone and estradiol-17beta in the peripheral plasma of Brahman cows with single and twin pregnancies

Peripheral plasma samples from Brahman cows with single and twin pregnancies were assayed for progesterone and estradiol-17beta throughout pregnancy. The twin pregnancies were obtained by transfer of Friesian embryos to inseminated single-ovulating Brahman cows. The twin-bearing cows had significantly higher levels of progesterone at 8 and 36 weeks of pregnancy. There were no differences in estradiol-17beta levels until the pre-parturient rise which occurred earlier in twin pregnancies. Intra-muscular injection of progesterone had no measurable effect on peripheral plasma levels of estradiol-17beta in Charolais cows 31 - 32 weeks pregnant.