The effects of prostanoids on estrogen-dominated rat myometrial longitudinal muscle in vitro

The purpose of these experiments was to characterize the contractile response of longitudinal muscle from the estrogen-dominated rat uterus to natural and synthetic prostanoids. The biological significance is 1) to provide evidence for or against a physiological role for each natural prostanoid in the regulation of myometrial activity, 2) to determine if each prostanoid has pharmacological potential for the manipulation of myometrial activity, and 3) to understand the structural requirements for prostanoid action on the myometrium. All analogs tested produced excitation of the myometrium in vitro through what appeared to be a direct action on the muscle. The order of potency of the natural prostanoids was prostaglandin (PG) F2 alpha = PGD2 = PGE2 = PGE1 greater than PGA2 = PGB2 = 6-keto-PGF1 alpha. This order of potency was not consistent with any single currently recognized prostanoid receptor. Furthermore, PGF2 alpha had an EC50 (effective concentration that produces 50% of the maximal response) of 0.5 microM, which was low in comparison to other PGF2 alpha-sensitive tissues. There were large differences in the maximum tension developed in response to the prostanoids tested, only PGF2 alpha, PGE2 and 6-keto PGF1 alpha were full agonists. Although the simplest explanation of these data was that the rat uterus contains a single novel type of prostanoid receptor, the existence of multiple receptor subtypes could not be disproved. Evidence from the effect of synthetic analogs suggested that neither thromboxane A2 nor PGI2 are physiological regulators of activity in this tissue.     

Prostaglandins potentiate U-46619-induced pulmonary microvascular dysfunction.

The induction of cyclooxygenase is an important event in the pathophysiology of acute lung injury. The purpose of this study was to examine the synergistic effects of various cyclooxygenase products (PGE(2), PGI(2), PGF(2alpha)) on thromboxane A(2) (TxA(2))-mediated pulmonary microvascular dysfunction. The lungs of Sprague-Dawley rats were perfused ex vivo with Krebs-Henseleit buffer containing indomethacin and PGE(2) (5 x 10(-8) to 1 x 10(-7) M), PGF(2alpha) (7 x 10(-9) to 5 x 10(-6) M), or PGI(2) (5 x 10(-8) to 2 x 10(-5) M). The TxA(2)-receptor agonist U-46619 (7 x 10(-8) M) was then added to the perfusate, and then the capillary filtration coefficient (K(f)), pulmonary arterial pressure (Ppa), and total pulmonary vascular resistance (RT) were determined. The K(f) of lungs perfused with U-46619 was twice that of lungs perfused with buffer alone (P = 0.05). The presence of PGE(2), PGF(2alpha), and PGI(2) within the perfusate of lungs exposed to U-46619 caused 118, 65, and 68% increases in K(f), respectively, over that of lungs perfused with U-46619 alone (P < 0.03). The RT of lungs perfused with PGE(2) + U-46619 was approximately 30% greater than that of lungs exposed to either U-46619 (P < 0.02) or PGE(2) (P < 0.01) alone. When paired measurements of RT taken before and then 15 min after the addition of U-46619 were compared, PGI(2) was found to attenuate U-46619-induced increases in RT (P < 0.01). These data suggest that PGE(2), PGI(2), and PGF(2alpha) potentiate the effects of TxA(2)-receptor activation on pulmonary microvascular permeability.     

Effects of EP-receptor subtype specific agonists and other prostanoids on adenylate cyclase activity of duodenal epithelial cells.

Rank order of agonist potency for activation of adenylate cyclase by the naturally occurring prostanoids PGE2, PGF2 alpha, PGD2, the stable PGI2 analogue iloprost, and the TXA2 mimetic U 46619, provides evidence for the existence of a distinct PGE-receptor on guinea-pig duodenal enterocytes. The PGE-receptor is likely to be of the EP2-subtype since the specific EP2-agonist 11-deoxy-PGE1 stimulated adenylate cyclase activity with a 20-fold higher potency than the EP1-agonist 17-phenyltrinor-PGE2 and the EP3-agonists MB 28767 and GR 63799. In addition, sulprostone (acting on both EP1- and EP3-receptors) was ineffective. Since the specific EP1-antagonist SC 19220 did not inhibit PGE2-stimulated adenylate cyclase activity, the involvement of EP1-receptors could be further excluded. The synthetic prostaglandin E-analogues misoprostol and nocloprost stimulated adenylate cyclase almost identically, though they were about 10-fold less potent than the natural PGE2.     

Characterisation of the prostanoid receptors mediating contraction of guinea-pig isolated trachea

The receptors mediating prostanoid-induced contraction of guinea-pig isolated trachea have been characterised in terms of a recently proposed general classification of prostanoid receptors. Results obtained on the trachea were compared with those obtained on guinea-pig fundus, which contains a sub-type of PGE2-sensitive (EP-) receptor termed the EP1-receptor, and guinea-pig lung strip, which contains a thromboxane-sensitive or TP-receptor. The following agonists were studied, PGE2, PGF2 alpha and the thromboxane-like agonists U-46619 and Wy17186. The antagonists studied were SC-19220 which selectively blocks EP1-receptors, and AH19437 which selectively blocks TP-receptors. On guinea-pig fundus the rank order of agonist potency was PGE2 greater than PGF2 alpha greater than Wy-17186 approximately equal to U-46619, and responses to all agonists were antagonised by SC-19220 but not by AH19437. On guinea-pig lung strip the rank order of potency was U-46619 greater than Wy17186 much greater than PGF2 alpha greater than PGE2 and responses to all agonists tested were blocked by AH19437 but not by SC-19220. On the trachea, the rank order was PGE2 = U-46619 greater than Wy17186 = PGF2 alpha. SC-19220 antagonised responses to PGE2 and PGF2 alpha, but not those to U-46619 or Wy17186. Conversely, AH19437 antagonised responses to U-46619 and Wy17186 but not those to PGE2 or PGF2 alpha. It is concluded that prostanoid-induced contractions of guinea-pig trachea can be mediated by both EP1- and TP-receptors.     

Stimulation of cytosolic free calcium and inositol phosphates by prostaglandins in cultured rat mesangial cells

We studied the effects of four products of arachidonate cyclo-oxygenation on a phospholipase C-dependent signal transduction system in cultured rat glomerular mesangial cells. PGF2 alpha, PGE2 and the thromboxane A2/endoperoxide analogue U-46619 rapidly increased cytosolic free Ca2+, measured in monolayers loaded with the fluorescent intracellular probe fura-2. Peak responses were dose-dependent and unaffected by chelation of extracellular Ca2+, indicating release from internal stores. The thromboxane A2-receptor antagonist SQ 27,427 selectively inhibited responses to U-46619. The PGI2 analogue Iloprost had no effect on cytosolic Ca2+. PGF2 alpha, PGE2 and U-46619 also stimulated accumulation of total inositol phosphates during 15 min incubations. We conclude that phospholipase C activation mediates the effects of certain eicosanoids on the glomerular mesangium.     

Cerebrovascular effects of prostanoids: in-vitro studies in feline middle cerebral and basilar artery

The effect of prostaglandin (PG) E2, F2 alpha, the thromboxane-A2 mimetic U46619 (9,11-dideoxy-9 alpha,11 alpha-methanoepoxy-prostaglandin F2 alpha) and the prostacyclin mimetic iloprost was investigated in cat middle cerebral and basilar arteries in vitro precontracted with 5-hydroxytryptamine (5-HT) (50nM) in the absence and presence of the cyclooxygenase inhibitor indomethacin or the thromboxane receptor blocker AH23848B [1 alpha (z),2 beta,5 alpha]-(+)-7-[5-[1,1'-(biphenyl)-4-yl] methoxy]-2-(4-morpholinyl)-3-oxocyclopentyl]-4-heptenoic acid). PGF2 alpha and U46619 both produced further concentration-related contractions of basilar and middle cerebral artery, U46619 being approximately 1,000 times more potent than PGF2 alpha. Iloprost produced concentration-related relaxations of precontracted basilar and middle cerebral artery, the mean maximum relaxations produced at a concentration of 1.3 microM being 57.3% and 80.6%, respectively of the contraction produced by 50nM 5-HT. PGE2, 100nM relaxed the basilar and middle cerebral artery, 46.7% and 38.5% respectively. However, at 1 microM, PGE2 caused contraction. Indomethacin, 2.8 microM had no effect on contractile or relaxant responses to any of the prostanoids. Oxyhaemoglobin inhibited the relaxation of both arterial preparations but had no effect on responses to PGE2 or iloprost. The thromboxane-receptor blocker AH23848B antagonised the contractile responses to U46619, PGF2 alpha and PGE2 and had no effect against relaxant responses to PGE2 or iloprost. It is concluded that both contraction- and relaxation-inducing prostanoid receptors are present in the in vitro preparation of feline basilar and middle cerebral artery. Under sustained tension conditions, endothelial factors do not appear to be involved in the responses to dilating prostanoids.     

Arachidonic acid metabolites in pregnant rat uterus

Production of prostaglandin E2 (PGE2), F2 alpha (PGF2 alpha) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) by pregnant rat uterus were measured in vitro. At mid-pregnancy, myometrium incubated with decidua attached released more prostanoids into the culture medium than when incubated without. As pregnancy progressed to 21 days more prostanoids were detected in the culture medium. However, no significantly increased conversion of exogenous arachidonic acid (AA) by myometrium was found.     

Placental lactogen as a regulator of luteal cells function during pregnancy in sheep

The luteotropic activity of ovine placental lactogen (oPL) on different days of gestation in ewes was assessed using in vitro methods. Corpora lutea (CL) harvested on Days 45, 70, 95, 120 and 135 of gestation and during parturition were enzymatically dispersed and plated on multiwell plates. After 48 h of incubation, all cultures were terminated and media were frozen for further steroid analysis. Cells were cultured in control medium, with addition of oPL alone, or in combination with PGE2 or PGF2alpha. Supplementation of culture media with oPL increased basal progesterone secretion by cells isolated on Days 45 and 70 of gestation. There was no effect on progesterone secretion by cells isolated on other days of gestation; PGE2 added to the culture media increased progesterone production only by cells isolated on Day 70 of pregnancy. Simultaneous oPL treatment with PGE2 had a statistically significant and stimulatory effect on progesterone production by luteal cells collected on Days 70 and 95 of pregnancy. In contrast, PGF2alpha alone in culture media decreased progesterone secretion by cells isolated on Days 45, 70 and 95 of gestation, while oPL plus PGF2alpha on Days 70 and 95 of gestation protected against luteolytic action of PGF2alpha. The results showed 1) a direct effect of the oPL on luteal cells isolated on Days 45 and 70 of gestation; 2) synergism between PL and PGE2 in progesterone production; by cells isolated on Day 70; 3) and a luteoprotective effect of oPL against the luteolytic action of prostaglandin F (PGF2alpha) observed on Days 70 and 95 of gestation.     

A common binding site for primary prostanoids in vascular smooth muscles: a definitive discrimination of the binding for thromboxane A2/prostaglandin H2 receptor agonist from its antagonist

Differences in binding characteristics between agonists and antagonists for the thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptor were examined in rat cultured vascular smooth muscle cells (VSMC). Scatchard analysis indicated the existence of two binding sites for the TXA2/PGH2 agonist, whereas a single class of recognition sites for the receptor antagonists were observed with approximately the same maximum binding capacity (Bmax) as a high-affinity binding site of the agonist. Weak binding inhibition by approx. 100 nM of primary prostanoids (PGE1, PGF2 alpha and PGD2) was detected only with the TXA2/PGH2 agonist, and not with the antagonist. Primary prostanoids as well as TXA2/PGH2 agonists (U46619 and STA2) suppressed the [3H]PGF2 alpha and [3H]PGE1 binding with almost the same potency, whereas TXA2/PGH2 antagonists (S-145, SQ29,548 and ONO3708) did not. The Bmax value of the binding sites was roughly identical in PGF2 alpha, PGE1 and a low-affinity binding site of U46619. These results suggest the existence of two binding sites for TXA2/PGH2 in VSMC, i.e., a high-affinity binding site corresponding to that of the TXA2/PGH2 antagonists and a low-affinity binding site in common with primary prostanoids.     

Prostacyclin and thromboxane formation in human umbilical arteries following stimulation with vasoactive autacoids

The formation of prostacyclin (PGI2) and thromboxane A2 (TXA2) (measured as the stable metabolites 6-keto-PGF1 alpha and TXB2) during stimulation with vasoactive autacoids was registered in human umbilical arteries perfused in vitro. Responses were registered within 3-4 minutes after addition of the substances. Both angiotensin I and II were found to increase the formation of PGI2 while depressing that of TXA2. Serotonin increased the formation of TXA2 but not that of PGI2. Both PGE2 and PGF2 alpha stimulated the PGI2 formation. The TXA2 mimetic U46619, increased PGI2 production, whereas PGI2 slightly increased the formation of TXA2. All responses were found to be completely inhibited by indomethacin.     

Receptors for prostaglandins F2 alpha and E2 in ovine corpora lutea during maternal recognition of pregnancy.

Plasma membrane receptors for prostaglandins (PG) F2 alpha and E2 were quantified in ovine corpora lutea obtained from nonpregnant and pregnant ewes on Days 10, 13, and 15 post-estrus, and from additional ewes on Days 25 and 40 of pregnancy. Regardless of reproductive status or day post-estrus, concentrations of luteal receptors for PGF2 alpha were 7- to 10-fold greater than those for PGE2. In pregnant ewes the concentration of receptors for PGF2 alpha was highest on Day 10 (35.4 +/- 2.8 fmol/mg) and lowest on Day 25 (22.3 +/- 2.5 fmol/mg). A difference in the concentration of luteal receptors for PGF2 alpha between pregnant and nonpregnant ewes was apparent only on Day 15 post-estrus, at which time the concentration of receptors for PGF2 alpha was higher in pregnant ewes than in nonpregnant ewes (27.1 +/- 2.7 vs. 17.7 +/- 2.7 fmol/mg). Concentrations of receptors for PGE2 in pregnant ewes were similar (p > 0.05; 2.8 +/- 0.3 to 3.7 +/- 0.2 fmol/mg) between Days 13 and 40 but were higher (p < 0.05) than in corpora lutea obtained from nonpregnant ewes on Days 10 (5.0 +/- 0.4 vs. 4.1 +/- 0.2 fmol/mg) and 15 (3.7 +/- 0.2 vs. 2.0 +/- 0.4 fmol/mg) post-estrus. Although concentrations of receptors for both PGF2 alpha and PGE2 were lowest in corpora lutea obtained from nonpregnant ewes on Day 15, this was not due to luteal regression since the weights and concentrations of progesterone in corpora lutea on Day 15 were not lower than those for corpora lutea obtained on Days 10 and 13.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of effects of oxytocin and prostaglandin F2-alpha on circular and longitudinal myometrium from the pregnant rat

Previous studies showed that circular (CM) and longitudinal myometrium (LM) have different physiological and pharmacological characteristics. To determine if such differences also exist with respect to the actions of oxytocin and prostaglandin F2-alpha (PGF2 alpha), we compared the effects of these agents on the spontaneous contractions of CM and LM from rats on Days 15, 17, and 21 (term) of pregnancy. Both agents stimulated CM and LM on all gestation days, but the responses differed as follows: 1) the CM response to oxytocin was all-or-nothing on Days 15 and 17, to PGF2 alpha on Day 15, and was graded to both agents only at term; 2) the LM response to both agents was always graded; 3) the maximum response to oxytocin was always less in CM than in LM, and to PGF2 alpha was less in CM except at term, when it was greater than in LM; 4) the EC50 (effective concentration that produced 50% of the maximum response) for PGF2 alpha in CM was greater than in LM, indicating a lesser sensitivity of CM for this agent. Therefore, the heterogeneity between CM and LM extends to the effects of oxytocin and PGF2 alpha, further emphasizing the importance of distinguishing between the two muscle layers in studies of uterine activity.     

Cyclooxygenase and lipoxygenase pathways in the preimplantation rabbit uterus and blastocyst

We have measured by radioimmunoassay the concentration and production of 5(S)-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE), a metabolite in the lipoxygenase pathway, and PGs in different uterine compartments, and blastocysts during the preimplantation period in the rabbit. The production is defined as the synthesis minus the metabolism for a defined period of time. The pattern of uterine PGF production on days 5-6.5 was quite similar for the whole uterus and the myometrium showing a peak production on Day 6. The concentration and production of PGF were always higher in the endometrium. While significant production of PGE was noticed in the whole uterus on days 5-6 and in the myometrium on Day 6, the endometrium showed some production on these days. On the contrary, absolutely no production of this PG was observed in the endometrium on Day 6.5. The concentration and production of 6-keto-PGF1 alpha were always lower in the endometrium than those observed in the myometrium or the whole uterus. While highest production of this PG was found to be on Day 6.5 in the whole uterus and on Day 5 in the endometrium, the production in the myometrium remained constant on all days examined. The production of 5-HETE in the endometrium was noticeable on Days 5-6.5, in the whole uterus on Days 5 and 6.5, and in the myometrium only on Day 6.5. However, the concentrations of 5-HETE showed a tendency to be higher at 2 h than at 0 h in these compartments on Days 5-6.5. Furthermore, a linear increase in 5-HETE levels both at 0 h and 2 h was observed in the endometrium on Days 5-6.5; no such difference in mean 5-HETE level was noted in the whole uterus or myometrium on any of these days. The production of 5-HETE in the blastocyst was noted only on Day 5. The results not only demonstrate the presence of both the cyclooxygenase and the lipoxygenase pathways in the preimplantation rabbit uterus and blastocyst, their differential operation in various compartments of the uterus on various days of early pregnancy suggests an integrated role for these mediators in embryo-uterine interaction during implantation.     

Conceptus-derived prostaglandins regulate endometrial function in sheep

In sheep, the trophectoderm of the elongating conceptus secretes interferon tau (IFNT) and prostaglandins (PGE2, PGF2alpha, PGI2). The PGs are derived from PG synthase 2 (PTGS2), and inhibition of PTGS2 in utero prevents conceptus elongation. IFNT increases expression of many genes in the endometrial epithelia that regulate conceptus elongation. This study tested the hypothesis that PGs secreted by the conceptus regulate endometrial functions that govern conceptus elongation. Cyclic ewes received intrauterine infusions of control vehicle or early pregnancy levels of IFNT, PGE2, PGF2alpha, or PGI2 from Days 10-14 postestrus. Expression levels of endometrial GRP, IGFBP1, and LGALS15, whose products stimulate trophectoderm cell migration and attachment, were increased by PGE2, PGI2, and IFNT. All PGs and IFNT increased expression of the HEXB protease gene, but only IFNT increased the CST6 protease inhibitor gene. Differential effects of PGs were observed for expression of the CTSL protease gene and its inhibitor, CST3. IFNT, PGF2alpha, and PGI2 increased ANGPTL3 expression, but only IFNT and PGE2 increased HIF1A expression, both of which regulate angiogenesis. For glucose transporters, IFNT and all PGs increased SLC2A1 expression, but only PGs increased SLC2A5 expression, whereas endometrial SLC2A12 and SLC5A1 expression levels were increased by IFNT, PGE2, and PGF2alpha. Infusions of all PGs and IFNT increased the amino acid transporter SLC1A5, but only IFNT increased SLC7A2 expression. In the uterine lumen, only IFNT increased glucose levels, and only PGE2 and PGF2alpha increased total amino acids. These results indicate that PGs and IFNT from the conceptus coordinately regulate endometrial functions important for growth and development of the conceptus during the peri-implantation period of pregnancy.     

Increase in uterine prostaglandin E2, F2 alpha, prostacyclin and stability in thromboxane A2 production during late pregnancy in streptozotocin-induced diabetic rats

This experiment was conducted to determine the effect of diabetes on uterine prostanoids production in near-term rats. The incidence of an insulin therapy was also studied. On the 21st day of pregnancy, uterine PGE2, PGF2 alpha and PGI2 levels showed a significant increase (respectively p less than 0.05, p less than 0.01 and p less than 0.05) in diabetic rats compared to controls whereas TxA2 production remained unchanged. The insulin therapy restored PGE2 levels, the most potent stimulatory factor of the myometrial fiber at control values, whereas it enhanced significantly PGI2 concentrations (p less than 0.05) and had no effect on PGF2 alpha production; TxA2 levels remaining always unchanged. It is suggested that the increase in uterine protanolds production during diabetes could induce a myometrial hypertonicity and play a role in the disturbances of the fetal development. The maintenance of PGE2 levels to control values by the insulin therapy might contribute to a normal delivery.     

Prostaglandin release by zygotes and endometria of pregnant rabbits

When 4-day rabbit zygotes were incubated for 1 h at 37 degrees C in vitro, very little prostaglandin (PG) was released into the medium, and the concentration of PGs in the zygotes after incubation was also low. The release of prostaglandin E (PGE) and prostaglandin F (PGF) into the medium, and their concentration in the zygotes after incubation, increased sharply on Days 6 and 7 of pregnancy, reaching, by Day 7, values close to 200 ng of each PG released in 1 h per mg of protein. By contrast, endometrial samples on Days 4 and 5 of pregnancy released more PGF and less PGE than the zygotes of the same ages on a per mg of protein basis, and on Days 6 and 7, less of both PGs. Furthermore, endometrial concentrations of PGs after incubation, except for PGF on Day 4, were always lower than values for zygotes. Endometrial concentrations of PGs on Day 6 were lower before than after incubation. Although there was a slight upward trend in PG release by endometrial samples with increasing length of pregnancy, the changes were minimal and, in the case of PGE, none of the mean values exceeded 1 ng per mg of protein. In 7-day blastocysts, high levels of both PGF and PGE were found in the blastocoelic fluid, and these did not change during the 1-h incubation. The release of PGF and PGE during in vitro incubation of ruptured and washed Day 6 blastocysts was stimulated by arachidonic acid, and that of PGF, but not PGE, inhibited by indomethacin. The release of PGE, but not of PGF, from Day 6 blastocysts was inhibited by low temperature, and the same conditions inhibited release of both PGF and PGE from endometrial cell suspensions. It seems that both blastocysts and endometria have capability to synthesize PGs, the blastocysts being particularly active in this regard on Days 6 and 7 of pregnancy. It is hypothesized that, in vivo, Day 6 and 7 blastocysts release large quantities of PGs which trigger some of the local endometrial changes associated with pregnancy.     

Prostaglandin release from the guinea-pig uterus superfused in vitro. Effect of stage of estrous cycle, progesterone, estradiol, oxytocin and A23187

Prostaglandin (PG) E2 was the major PG released from the superfused guinea-pig uterus on Day 7, followed by in descending order 6-oxo-PGF1 alpha, thromboxane (TX) B2 and PGF2 alpha. However, the outputs of all four substances were low and were very similar. By Day 15, PGF2 alpha output from the superfused uterus had increased 21.9-fold, whereas the outputs of PGE2, 6-oxo-PGF1 alpha and TXB2 had increased only 1.8-, 2.9- and 1.2-fold, respectively. A mechanism is apparently "switched on" between Days 7 and 15 which causes a fairly specific increase in the release of PGF2 alpha from the uterus. Progesterone and/or estradiol had no effect on PG or TX release when superfused over the uterus on Day 7, nor did they have any effect on PG and TX release from the Day 15 uterus when administered separately. When administered together, however, they significantly inhibited PGF2 alpha, PGE2 and 6-oxo-PGF1 alpha, but not TXB2, release from the Day 15 uterus. Oxytocin had no effect on PG release from the Day 7 or Day 15 uterus, while A23187 stimulated PGF2 alpha, 6-oxo-PGF1 alpha and, to a lesser extent, PGE2 release from the uterus on both Days 7 and 15. Oxytocin is apparently not important for stimulating PGF2 alpha release from the guinea-pig uterus in relation to luteolysis, whereas increasing intracellular free Ca++ levels may be part of the mechanism for "switching on" uterine PG synthesis. Furthermore, changes in intracellular free Ca++ levels in the endometrium may be responsible for the pulsatile nature of PGF2 alpha release from the uterus.     

Concentrations of prostaglandins E2, F2 alpha and 6-keto-prostaglandin F1 alpha in the utero-ovarian venous plasma of nonpregnant and early pregnant ewes

The effect of pregnancy on concentrations of prostaglandins E2, F2 alpha and 6-keto-prostaglandin F1 alpha (PGE2, PGF2 alpha and 6-keto-PGF1 alpha) in utero-ovarian venous plasma was examined in ewes on Days 10 through 14 after estrus, an interval which includes the critical period for maternal recognition of pregnancy. The utero-ovarian vein ipsilateral to a corpus luteum was catheterized on Day 9 or 10 in 6 pregnant and 8 nonpregnant ewes. Five blood samples were collected at 30-min intervals for 2 h beginning at 0500 and 1700 h daily. Sampling began at 0500 h on the day after catheterization. The mean and variance within each 2-h collection period were calculated for each ewe. The natural logarithm of the variance in each collection period (ln variance) was used as an estimate of the fluctuations in secretory activity by the endometrial-conceptus complex. Patterns of the mean concentrations of PGE2 were different between pregnant and nonpregnant ewes (P less than 0.01); PGE2 being higher in the pregnant ewes beginning on Day 13. There was a trend for the patterns of ln variance in PGE2 to differ (P less than 0.1) with pregnancy status over the entire period; ln variance was greater in pregnant ewes beginning on Day 13. The patterns of the mean concentrations and ln variances for PGF2 alpha and 6-keto-PGF1 alpha did not differ between pregnant and nonpregnant ewes. There were significant increases in both of these prostaglandins over time, independent of pregnancy status (P less than 0.01). The association of higher concentrations of PGE2 in utero-ovarian venous plasma with early pregnancy is consistent with the hypothesis that PGE2, originating from the uterus and/or conceptus, is one factor involved in maintenance of the corpus luteum of pregnancy.     

Effect of oestradiol 17 beta on prostaglandin biosynthesis by the uterus of ovariectomized rat and guinea pig

In vitro prostaglandin biosynthesis by uteri of ovariectomized rats and guinea pigs treated or untreated with oestradiol 17 beta, administered subcutaneously, was measured by R.I.A. of PGF2 alpha and PGE2. Incubations with [1-14C] arachidonic acid were also performed and labelled metabolites were analyzed by TLC. The main metabolite in rats was 6 keto PGF1 alpha and in decreasing order of magnitude, PGF2 alpha and PGE2. In guinea pig PGF2 alpha was the main product. Ovariectomy in rats completely changed the pattern of synthetized prostanoids : PGI2 production was doubled when compared to cycling rats and PGE2 increased 10 fold. PGF2 alpha values were similar to the mean value measured during the cycle. OE2 treatment almost completely inhibited PGI2 synthesis and reduced PGE2 by half. Total PG synthesis in OE2 treated animals was decreased by 5 fold when compared to spayed rats. Endogenous PGF2 alpha synthesis was slightly stimulated. In the guinea pig OE2 treatment of ovariectomized animals increased the total synthesis from 50 per cent. PGF2 alpha was always the main metabolite. In conclusion OE2 regulation of uterine PG synthesis is depending on the animal species and cannot be explained by a unique effect on the cyclooxygenase, but rather by an interplay on the various enzymes of the arachidonic acid cascade.