Secretion Of Prostaglandin F2α Research Articles

Conceptus signals for establishment and maintenance of pregnancy

Establishment and maintenance of pregnancy results from signaling by the conceptus (embryo/fetus and associated extraembryonic membranes) and requires progesterone produced by the corpus luteum. In most mammals, hormones produced by the trophoblast maintain progesterone production by acting directly or indirectly to maintain the corpus luteum. In domestic animals (ruminants and pigs), hormones from the trophoblast are antiluteolytic in that they act on the endometrium to prevent uterine release of luteolytic prostaglandin F2α. In cyclic and pregnant sheep, progesterone negatively autoregulates progesterone receptor gene expression in the endometrial luminal and superficial glandular epithelium. In cyclic sheep, loss of the progesterone receptor is closely followed by increases in epithelial estrogen receptors and then oxytocin receptors, allowing oxytocin to induce uterine release of luteolytic prostaglandin F2α pulses. In pregnant sheep, the conceptus trophoblast produces interferon tau that acts on the endometrium to inhibit transcription of the estrogen receptor alpha gene directly and the oxytocin receptor gene indirectly to abrogate development of the endometrial luteolytic mechanism. Subsequently, sequential, overlapping actions of progesterone, interferon tau, placental lactogen, and growth hormone comprise a hormonal servomechanism that regulates endometrial gland morphogenesis and terminal differentiated function to maintain pregnancy in sheep. In pigs, the conceptus trophoblast produces estrogen that alters the direction of prostaglandin F2α secretion from an endocrine to exocrine direction, thereby sequestering luteolytic prostaglandin F2α within the uterine lumen. Conceptus estrogen also increases expression of fibroblast growth factor 7 in the endometrial lumenal epithelium that, in turn, stimulates proliferation and differentiated functions of the trophectoderm, which expresses the fibroblast growth factor 7 receptor. Strategic manipulation of these physiological mechanisms may improve uterine capacity, conceptus survival, and reproductive health.

Effect of ovarian steroids on basal and oxytocin-induced prostaglandin F2alpha secretion from pig endometrial cells.

These studies were undertaken to determine how treatment with 100 nM progesterone and/or 10 nM oestradiol-17beta acutely (3 h; Experiment 1) or chronically (72 h; Experiments 2-4) influenced basal and oxytocin (OT)-stimulated prostaglandin (PG) F(2alpha) secretion, in enriched cultures of pig endometrial luminal epithelial, glandular epithelial and stromal cells obtained on Day 16 (Experiments 1, 2 and 4) or Day 12 (Experiment 3) after oestrus. In Experiment 1, acute treatment with progesterone stimulated PGF(2alpha) secretion from each cell type on Day 16, whereas acute oestradiol treatment inhibited the stimulatory action of progesterone on PGF(2alpha) secretion only in glandular epithelial cells. In Experiment 2, OT stimulated phospholipase (PL) C activity in luminal epithelial cells on Day 16 only in the presence of chronic oestradiol treatment. For glandular epithelial cells on Day 16, OT stimulated PLC activity only in the presence of chronic treatment with steroid. In stromal cells on Day 16, OT stimulated PLC activity in the absence of steroids and the response to OT was further enhanced by oestradiol. In the absence of chronic treatment with steroid, OT did not stimulate PGF(2alpha) secretion from luminal epithelial cells, but oestradiol induced a response to OT. For glandular epithelial cells, OT-induced PGF(2alpha) secretion was not altered by steroids, whereas the stimulatory response to OT was inhibited by oestradiol or progesterone in stromal cells. For endometrial cells obtained on Day 12 after oestrus in Experiment 3, OT only stimulated PGF(2alpha) release from glandular epithelial and stromal cells. For luminal epithelial cells obtained on Day 16 after oestrus and cultured under polarizing conditions in Experiment 4, secretion of PGF(2alpha) occurred preferentially from the basolateral surface and was stimulated by OT more from the basolateral surface than from the apical surface. Oxytocin-induced PGF(2alpha) secretion from the apical surface was enhanced by chronic treatment with oestradiol, whereas that from the basolateral surface was enhanced by chronic treatment with progesterone. In summary, oestradiol enhanced OT-induced PGF(2alpha) secretion from the apical surface of luminal epithelial cells and reduced the response of stromal cells to OT, actions that may contribute to the reorientation of PGF(2alpha) from endocrine secretion (i.e. towards the uterine vasculature) to exocrine secretion (i.e. towards the uterine lumen) during pregnancy recognition in pigs.

Direct inhibitory effect of progesterone on oxytocin-induced secretion of prostaglandin F(2alpha) from bovine endometrial tissue.

The effect of progesterone on oxytocin-induced secretion of prostaglandin (PG) F(2alpha) from bovine endometrial tissue explants was examined. Endometrial tissue from the late luteal phase were preincubated for 20 h in control medium. Explants were then treated for 6 h with control medium, oxytocin (10(-7) M), progesterone (10(-5) M), or both hormones. Oxytocin increased the medium concentration of 13,14-dihydro-15-keto-PGF(2alpha), whereas progesterone completely suppressed the stimulatory effect of oxytocin. In experiment 2, isolated endometrial epithelial cells were incubated with progesterone (10(-5) M), oxytocin (10(-7) M), and combinations of these hormones with or without actinomycin D (1 ng/ml). Only oxytocin stimulated secretion of PGF(2alpha), and this response was suppressed by progesterone. Oxytocin induced a rapid increase in intracellular concentrations of Ca(2+) detected within 1 min of exposure of epithelial cells from the same cows. Progesterone pretreatment diminished this response. In experiment 3, direct effects of progesterone (2 nM-20 microM) on binding of (3)H-oxytocin to the membrane preparation from epithelial cells were determined by saturation analysis. Oxytocin binding was suppressed by progesterone at every dosage tested. Progesterone is capable of suppressing the ability of oxytocin to induce endometrial secretion of PGF(2alpha). This effect appears to be mediated through a direct interference in the interaction of oxytocin with its own receptor.

Angiotensin II increases intracellular calcium concentration in pig endometrial stromal cells through type 1 angiotensin receptors, but does not stimulate phospholipase C activity or prostaglandin F2alpha secretion.

Although the presence of endometrial receptors for angiotensin (Ang) II has been demonstrated, a specific function for AngII in the uterus has not been identified. Cytosolic free Ca2+ concentration [Ca2+]i, phospholipase C (PLC) activity and prostaglandin (PG) F2alpha secretion in response to AngII and oxytocin (OT) were measured in pig endometrial stromal cells collected 16 days after oestrus. Treatment with 100 nM OT or AngII increased (P<0.001) [Ca2+]i in stromal cells similarly (720 +/- 34 v. 690 +/- 33 pM, respectively). Subsequent administration of OT or AngII to the same cells induced smaller [Ca2+]i increases (25% or 35% of the initial responses, respectively) that occurred only if the second exposure to the same agent took place at least 5 min after the first. When administered sequentially, OT and AngII each induced a full response within 1 min of the previous treatment, regardless of which peptide was applied first. Whereas OT increased PLC activity and PGF2alpha secretion in stromal cells (P<0.01), AngII did not increase either PLC activity or PGF2alpha secretion. Type I AngII (AT1) receptors were present on stromal cells, whereas AT2 receptors were absent. Therefore, the effect of AngII in stromal cells was mediated via AT1 receptors. That AngII increased [Ca2+]i in stromal cells, but did not increase PLC or PGF2alpha secretion, indicates that either AngII releases a pool of Ca2+ through a mechanism that is not mediated by PLC and is not involved in PGF2alpha secretion or that a mechanism for PGF2alpha production other than one involving Ca2+ may exist.

Oxytocin-stimulated phosphoinositide hydrolysis and prostaglandin F2α secretion by luminal epithelial, glandular epithelial and stromal cells from pig endometrium. II. Responses of cyclic, pregnant and pseudopregnant pigs on Days 12 and 1

In pigs, the exact mechanism for the shift in endometrial PGF2alpha secretion from an endocrine to an exocrine mode during pregnancy recognition is not known. The objective of this study was to examine whether this shift involved a change in the responsiveness of luminal epithelial, glandular epithelial and stromal cells to 0 or 100 nM oxytocin. Luminal epithelial cells, glandular epithelial cells and stromal cells were isolated from cyclic, pregnant or oestrogen-induced pseudopregnant gilts on Day 12 (Experiment 1) or Day 16 (Experiment 2) post oestrus (oestrus = Day 0). For cells obtained on Day 12, oxytocin stimulated PGF2alpha secretion by stromal cells (P<0.01) similarly for each reproductive status, whereas oxytocin stimulated PGF2alpha secretion from luminal and glandular epithelial cells (P<0.05) from pregnant and pseudopregnant gilts but not from cyclic gilts. For both concentrations of oxytocin, mean PGF2alpha secretion was less (P<0.05) from stromal cells of pregnant than cyclic gilts. For cells obtained on Day 16, oxytocin stimulated PGF2alpha release from stromal cells of cyclic gilts but not from stromal cells of pregnant gilts. Mean PGF2alpha secretion also was less (P<0.05) from stromal cells of pregnant gilts than cyclic gilts. Oxytocin tended to stimulate PGF2alpha release (P<0.07) from glandular epithelial cells of cyclic but not pregnant or pseudopregnant gilts. Luminal epithelial cells from all reproductive statuses were similarly unresponsive to oxytocin. In conclusion, the increased PGF2alpha secretory response to oxytocin of luminal and glandular epithelial cells from pregnant gilts on Day 12, combined with the decreased response of stromal cells from pregnant gilts on Days 12 and 16, may contribute, in part, to the shift in endometrial PGF2alpha secretion from an endocrine to an exocrine direction during early pregnancy in pigs.

Effect of an oxytocin antagonist on prostaglandin F2 alpha secretion and the course of luteolysis in sows.

The role of oxytocin (OT) in the regulation of prostaglandin F2 alpha (PGF2 alpha) secretion during luteolysis in gilts was studied using a highly specific OT antagonist (CAP-581). In Experiment 1 gilts on Days 14 to 19 of the oestrous cycle in Latin square design were used, to determine the dose and time of application of OT and CAP. In Group I (n = 6) gilts were treated intravenously with saline or with 10, 20 and 30 IU of OT. Concentrations of the main PGF2 alpha metabolite i.e. 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) were measured in blood samples as uterine response to the treatment. Twenty IU of OT was the most effective to stimulate PGFM release and this dose was used after CAP treatment in gilts of Groups II, III and IV. Gilts of Group II (n = 3) were injected into the uterine horns (UH) with saline (5 ml/horn) or CAP (2 mg, 3 mg and 4 mg; half dose/horn) and OT was injected (i.v.) 30 min thereafter. Any of the CAP doses given into the UH affected PGFM plasma concentrations stimulated by OT. In Group III (n = 4) gilts were infused (i.v.) for 30 min with CAP (9 mg, 14 mg and 18 mg/gilt) followed by 20 IU of OT. All doses of CAP effectively inhibited OT-stimulated PGF2 alpha release, therefore 9 mg was selected for the further studies. Gilts of Group IV (n = 4) received OT 4, 6 and 8 h after CAP to define how long CAP blocks the OT receptors. Concentrations of PGFM increased after any of this period of time. Thus, we concluded that 9 mg of CAP infused every 4 h will effectively block OT receptors. In Experiment 2, gilts (n = 4) received CAP as a 30-min infusion every 4 h on Days 12-20 of the oestrous cycle. Control gilts (n = 3) were infused with saline. CAP infusions diminished the height of PGFM peaks (P < 0.05). Frequency of the PGFM (P < 0.057) and OT (P < 0.082) peaks only tended to be lower in the CAP-treated gilts. Peripheral plasma concentrations of progesterone (P4) and oestradiol-17 beta (E2) and the time of luteolysis initiation as measured by the decrease of P4 concentration were the same in CAP- and saline-treated gilts. The macroscopic studies of the ovaries in gilts revealed lack of differences between groups. We conclude that OT is involved in the secretion of luteolytic PGF2 alpha peaks but its role is limited to controlling their height and frequency. Blocking of OT receptors did not prevent luteolysis in sows.

Reproductive placental corticotropin-releasing hormone and its clinical implications

The hypothalamic-pituitary-adrenal axis and the reproductive system exhibit a complex relationship in both nonpregnant and pregnant women.1,2 The hypothalamic-pituitary-adrenal axis exerts profound, mostly inhibitory, effects on the reproductive axis, with corticotropin-releasing hormone and corticotropin-releasing hormone–induced pro-opiomelanocortin peptides inhibiting hypothalamic gonadotropin-releasing hormone secretion and with glucocorticoids inhibiting pituitary luteinizing hormone and ovarian estrogen and progesterone secretion and rendering estrogen-target tissues, such as the endometrium, resistant to the gonadal steroid. Conversely, estrogen directly stimulates the hypothalamic corticotropin-releasing hormone gene, which may explain the slight hypercortisolism seen in women and the preponderance of depression, anxiety disorders, and anorexia nervosa among women.3 Interestingly, several components of the hypothalamicpituitary-adrenal axis and their receptors are present in reproductive tissues as autacoid regulators of their various functions2, 4-7 (Table I). These include ovarian and endometrial corticotropin-releasing hormone, which may participate in the regulation of steroidogenesis and the inflammatory processes of the ovary (ovulation and luteolysis) and of the endometrium (blastocyst implantation and menstruation), and placental corticotropin-releasing hormone, which is secreted mostly in the latter half of pregnancy and is responsible for the physiologic hypercortisolism seen during this period (Fig 1). Most circulating corticotropin-releasing hormone is neutralized by corticotropin-releasing hormone binding protein produced by the liver. Between weeks 34 and 35 of gestation, however, the concentrations of this protein fall by about 60%, leading to elevations of free corticotropin-releasing hormone. Subsequently plasma free corticotropin-releasing hormone concentrations rise further, to peak at labor and delivery. In addition to the hypercortisolism of pregnancy, placental corticotropin-releasing hormone causes vasodilation of the fetoplacental circulation by activating nitric oxide synthase and participates in labor by stimulating secretion of prostaglandin F2α and prostaglandin E2 by the fetal membranes and by promoting constriction of myometrial cells. Placental corticotropin-releasing hormone secretion is stimulated by glucocorticoids, inflammatory cytokines, and anoxic conditions and therefore by noninflammatory or inflammatory stress, including the stress of preeclampsia or eclampsia.2,6 Premature elevation of placental corticotropin-releasing hormone level has been associated with premature labor and birth. Potent corticotropin-releasing hormone antagonists are in the making and could be tested as labor retardants. The hypercortisolism of pregnancy is followed by a transient suppression of hypothalamic corticotropin-releasing hormone secretion in the postpartum period, which may explain the blues or depression and autoimmune phenomena seen during this period.2,7 Estrogen administration has been shown to ameliorate postpartum depression, probably by returning to normal the secretion of the suppressed corticotropin-releasing hormone neuron. From Section on Pediatric Endocrinology, Developmental Endocrinology Branch, National Institute of Child Health and Development, National Institutes of Health. Reprint requests: G. P. Chrousos, MD, Section on Pediatric Endocrinology, National Institutes of Health, Bethesda, MD 20892-1862. Am J Obstet Gynecol 1999;180:S249-50. 0002-9378/99 $8.00 + 0 6/0/90865 Table I. Reproductive corticotropin-releasing hormone and its potential physiologic functions

Oxytocin modulates the pulsatile secretion of prostaglandin F2αin initiated luteolysis in cattle

Subluteolytic doses of prostaglandin F2αanalogue (oestrophan) given i.m. and oxytocin (OT) antagonist (CAP) and noradrenaline (NA) infused into the abdominal aorta were used to test the importance of lutealOTin pulsatile secretion of prostaglandin F2α(PGF) during luteolysis in heifers (n = 17). In experiment 1, heifers were pre-infused for 30 minutes with saline on either day 17 of the oestrous cycle (group 1; n = 4) or on day 18 of the oestrous cycle (group 2; n = 3), and with CAP (8 mg per animal) on day 17 of the oestrous cycle (group 3; n = 4). Next, heifers were injected with oestrophan (30 μg per animal). Injection of oestrophan in Group 3 increasedOTconcentrations (P < 0.001) to values similar to those observed during spontaneous luteolysis (50 to 70 pg ml–1).PGFMconcentrations in this group also increased (P < 0.001), but were lower (P < 0.05) than the values in groups 1 and 2.CAPgiven prior to oestrophan decreased bothPGFMelevation (P < 0.06) and its area under the curve (P < 0.01), compared to the saline pretreated heifers. In experiment 2NA(4 mg) was infused twice for 30 minutes at five hour intervals to releaseOTon day 17 of the oestrous cycle (n = 6). However, during hormone analysis it appeared that three of six heifers had elevatedPGFMconcentrations (group 1) and three others did not (group 2).NAcaused the correlated increase of progesterone andOTsecretion (r = 0.68; P < 0.05) in both groups but it only influencedPGFsecretion in group 1 only (P < 0.05).We postulate thatOTcan amplify and modulate the course of induced luteolysis as a regulator of the amplitude of pulsatilePGFsecretion.PGFanalogue stimulates secretion of endogenousPGFfrom the uterus in cattle and this may be an important component of the luteolytic response to exogenousPGF.

Uterine secretion of prostaglandin F2alpha stimulated by different doses of oxytocin and released spontaneously during luteolysis in cattle.

The objectives were to determine the involvement of oxytocin (OT) in the stimulation of prostaglandin F2alpha (PGF) secretion during luteolysis in cattle. On days 16-17 of the oestrous cycle, catheters were inserted into the aorta abdominalis of heifers for OT or saline infusion and into the jugular vein for blood sample collection. The following day, heifers were assigned to one of three experimental groups (Gr): Gr I - 10 IU OT (n=4); Gr II - 20 IU OT (n=4); Gr III - 50 IU OT (n=4). Blood samples were collected every 10 min during a 1-h control period before treatment and every 5-10 min for 2 h after OT treatment. In Gr IV (n=5), a catheter was inserted into the jugular vein on day 15 of the cycle and blood samples were collected every 15 min for 12 h on days 16-19. Plasma concentrations of progesterone, PGF metabolite, 13, 14-dihydro-15-keto-prostaglandin F2alpha (PGFM) and OT were determined. Within 5 min of infusion of 10 or 20 IU OT, peripheral concentrations of OT (7-12 pg/mL) increased by about 200 and 350-500 pg/mL, respectively. These doses did not affect plasma concentrations of PGFM or progesterone within 1.5 h. Fifty IU of OT increased its maximal peripheral concentration to 1500 pg/mL, which is over 20 times greater than that observed physiologically. Concentrations of plasma PGFM in Gr III increased from basal concentrations (5065 pg/mL) to 150-250 pg/mL (P < 0.01) within 10-30 min. During luteolysis, PGFM pulses ranged between 250 and 600 pg/mL on days 16-19 of the cycle (Gr IV), whereas coincident pulses of OT, and those appearing between spikes of PGFM, were never above 75 pg/mL. Only 50% of OT pulses coincided with pulses of PGFM, and 54 % of PGFM pulses coincided with a pulse of OT. Results indicate that luteolytic PGF secretion in cattle is not directly dependent upon ovarian OT.

Down-Regulation of Oxytocin Receptors and Secretion of Prostaglandin F2α after Chronic Treatment of Ewes with Estradiol-17β1

Experiments were conducted to investigate the mechanisms through which chronic treatment with estradiol-17beta (E2) prolongs the estrous cycle in the ewe. To determine whether treatment with estradiol maintained the corpus luteum (CL), mature ewes were assigned randomly to two groups receiving s.c. injections of either 500 microg E2 in corn oil or vehicle alone for 20 days beginning on Day 4 of the cycle (n = 5 per group). Laparotomy of E2-treated ewes on Day 24 revealed the presence of CL previously marked with India ink on Day 7 of the cycle. Treatment increased the mean interestrous interval for 4 of 5 animals compared with that of controls (p < 0.001). Therefore, to determine whether the increase in the interestrous interval was due to an effect on the function and/or concentration of uterine oxytocin receptors (OTr), ewes (n = 5 per group) were injected with 500 microg E2 or vehicle as described above from Days 4 to 14 of the cycle. On Day 15, a jugular blood sample was collected for progesterone (P4) analysis, after which ewes were given an i.v. injection of oxytocin (OT; 20 IU USP) or saline, and blood samples were collected at frequent intervals for 60 min to determine plasma concentrations of 13,14-dihydro-15-ketoprostaglandin F2alpha (PGFM). Laparotomies were performed after blood collection to remove uterine endometrium for OTr analysis. Mean serum concentrations of P4 were greater in treated than in control ewes on Day 15 (p < 0.05). Treatment of ewes with E2 prolonged luteal function and resulted in reduced uterine concentration of OTr compared with that of controls (p = 0.002). Treatment with E2 reduced OT-induced plasma concentrations of PGFM compared with controls (p < 0.01). Collectively, these data suggest that chronic treatment of ewes with estradiol during the cycle can prolong the interestrous interval by reducing uterine concentration of OTr and hence OT-induced secretion of prostaglandin.

Influence of estradiol and progesterone withdrawal on the secretion of and the temporal correlation between pulses of oxytocin and prostaglandin F2(alpha) in ewes.

The primary objective was to examine the effects of estradiol and the progesterone receptor antagonist onapristone on the pulsatile secretion of prostaglandin F(2alpha) (PGF(2alpha)) and ovarian and pituitary oxytocin. A 2 x 2 factorial arrangement of estradiol and onapristone treatments was administered to groups of 5 ewes after destruction of ovarian follicles on Day 8 of the cycle. Estradiol treatments consisted of the administration of a silicone elastomer implant, either containing or not containing estradiol, on Day 8 plus 50 microg of estradiol or corn oil on Days 11 and 12. Onapristone (2 mg/kg) or its vehicle were administered on Day 13, immediately preceding the simultaneous collection of blood samples from the carotid artery, jugular vein, and vena cava at 7.5-min intervals for 7 h. Ewes were immediately killed for measurements of uterine oxytocin receptor concentrations and phosphatidylinositide turnover. More oxytocin pulses were detected in the jugular vein than in the carotid artery (p < 0.01), suggesting that the pituitary is a source of oxytocin. A similar number (p > 0.1) of PGF(2alpha) pulses were correlated with oxytocin pulses as were not. The linked PGF(2alpha) pulses were longer in duration (p = 0.01) with a tendency toward a higher amplitude (p = 0.08). The corresponding vena caval oxytocin pulses had a longer duration (p = 0.02) than those not linked to PGF(2alpha). Estradiol increased oxytocin receptor concentrations and the turnover of phosphatidylinositides (p = 0.02) without affecting PGF(2alpha) pulse characteristics. Onapristone increased (p = 0.03) PGF(2alpha) pulse amplitude. Although a lower than expected temporal correlation between oxytocin and PGF(2alpha) pulses was observed, the distinguishing characteristics of linked pulses may be indicative of their physiological significance.

Corpus Luteum and Its Control by Intra-Luteal Regulators

It is well documented that the corpus luteum is required for a successful pregnancy. The primary function of the corpus luteum is to secrete progesterone, which has several biological effects on target tissues in the reproductive system to prepare them for support of pregnancy or to provide nourishment to the conceptus. In most domestic species including cattle, three organ systems regulate the function of the corpus luteum. The anterior pituitary gland secretes LH, which is the primary hormone responsible for stimulating the secretion of progesterone. The uterus has a luteolytic effect during the late luteal phase of the estrous cycle. This luteolytic effect of the uterus is mediated via secretion of prostaglandin F2α. Finally, the conceptus has either direct luteotropic or antiluteolytic effects. However, there is increasing evidence for the existence of substances in luteal tissue which are able to act locally, either alone or by modulating the action of the gonadotropins, thus modifying the functions of corpus luteum. The intra-luteal regulators consist of peptides, eicosanoids, growth factors, cytokines, and neurotransmitters. Available data suggest an important role for these substances in the control of luteal function during not only pregnancy but the estrous cycle as well.

Effects of progesterone withdrawal on uterine secretion of prostaglandin F2 alpha in response to oxytocin in ewes.

Two experiments were conducted to determine if withdrawal of progesterone during the luteal phase of the oestrous cycle affected the ability of the ovine uterus to secrete prostaglandin F2 alpha (PGF2 alpha) in response to oxytocin. In Experiment 1, 18 ewes were ovariectomized on Day 9 and Day 12 after oestrus. Ewes were subdivided into three treatment groups (n = 6 per group): Group-1 ewes underwent sham surgery; Group-2 ewes received oestradiol (OVX + O); and Group-3 ewes received oestradiol + progesterone (OVX + O,P). Oxytocin was administered to each ewe on Days 10, 13 and 15 after oestrus. Concentrations of 13, 14-dihydro-15-keto-PGF2 alpha (PGFM) were determined in samples of jugular venous blood for 2 h after oxytocin challenge. The magnitude of the PGFM response 24 h after ovariectomy was greater (P < 0.1) in ewes from which progesterone had been withdrawn (OVX + O) than in ewes in which progesterone was maintained (intact controls and OVX + O,P). Therefore, progesterone appears to exert an inhibitory effect on uterine secretory responsiveness to oxytocin which is removed by progesterone withdrawal. In Experiment 2, ewes were ovariectomized on Day 11 and assigned to 1 of 4 treatment groups (n = 6 per group): Group 1, no steroid replacement (OVX); Group 2, oestradiol replacement (OVX + O); Group 3, progesterone replacement (OVX + P); or Group 4, progesterone + oestradiol replacement (OVX + O,P). Ewes received oxytocin on Day 12 and Day 15. On Day 12, uterine secretory responsiveness to oxytocin was greatest in ewes in the OVX + O group (P < 0.1). Responsiveness was low in ewes in the OVX group, as it was in ewes in both groups that received progesterone replacement. Therefore, the increase in uterine secretory responsiveness to oxytocin following progesterone withdrawal is dependent on oestradiol replacement.

Effect of progesterone on prostaglandin F2α secretion and outcome of pregnancy during cloprostenol-induced abortion in mares

Abstract Objectives To determine the role of progesterone in the regulation of endogenous prostaglandin F2α (PGF2α) secretion during cloprostenol-induced abortion and to investigate use of progestins to prevent prostaglandin-associated abortion. Animals 16 pregnant mares. Procedure To induce abortion, cloprostenol (250 μg/d) was administered daily until fetal expulsion or for up to 5 days. In experiment 1, 8 mares, 98 to 153 days’ pregnant, received progesterone (300 mg/d) at 24-hour intervals for 5 days, starting 18 hours after the first cloprostenol administration. In experiment 2, 8 mares, 93 to 115 days’ pregnant, received altrenogest (44 mg/d) at 24-hour intervals, starting 12 hours after the first cloprostenol administration. Historic control mares, 82 to 102 days’ pregnant, received cloprostenol (250 μg/d) daily until fetal expulsion. Results In control mares, fetal expulsion occurred after 2 to 3 cloprostenol administrations and was associated with significant increases in PGF2α secretion. Abortion did not occur in 5 of 8 progesterone-treated mares and 8 of 8 altrenogest-treated mares, and endogenous PGF2α secretion was inhibited, compared with values in aborting mares. Conclusion Circulating progestogen concentrations may have a role in the outcome of pregnancy during prostaglandin-induced abortion. Altered prostaglandin secretion may be a reflection of a direct effect of progesterone or may be caused by the abortion process. Clinical Relevance Progestogens might be useful for prevention of abortion in mares in which pregnancy is at risk owing to diseases that are associated with excess prostaglandin secretion. (Am J Vet Res 1996;57:1331-1337)

Placental interferons.

Trophectoderm of ruminant conceptuses (embryo and associated membranes) secrete tau interferons (IFN tau) as the pregnancy recognition signal. Secretion of IFN tau on gestational days 12-13 for sheep and gestation days 14-17 for cows and goats is critical for pregnancy recognition. IFN tau acts on uterine epithelium to suppress estrogen receptor and oxytocin receptor gene expression, which prevents uterine release of luteolytic pulses of prostaglandin F2 alpha (PGF). Expression of the progesterone receptor (PR) gene in uterine endometrium is not affected by oIFN tau. Maintenance of progesterone secretion by the corpus luteum (CL) ensures establishment of pregnancy. Pig conceptuses secrete both IFN alpha and IFN gamma between days 15-21 of gestation, but their role(s) in early pregnancy is unknown. Estrogen secreted by pig trophoblast between gestational days 11-13 and 15-25 increases endometrial receptors for prolactin and causes exocrine secretion of PGF into the uterine lumen to prevent luteolysis. Shared cell-signaling mechanisms by IFNs and lactogenic hormones through Janus kinases (JAK) 1 and 2 may provide a common pathway to abrogate luteolytic mechanisms to ensure establishment of pregnancy. The role(s) of IFNs produced by human and rodent placentae is not known.

Effect of flunixin meglumine on endogenous prostaglandin F2α secretion during cloprostenol-induced abortion in mares

Abstract Objective To determine the relative role of endogenous prostaglandin F2α (pgf2α secretion in cloprostenol-induced abortion in mares that no longer require luteal progesterone secretion for maintenance of pregnancy, and to evaluate the ability of a prostaglandin cyclooxygenase inhibitor (flunixin meglumine) to prevent cloprostenol-induced abortion. Design The effect of flunixin meglumine on pgf2α secretion and outcome of pregnancy was compared between mares treated with cloprostenol only and mares treated with cloprostenol plus flunixin meglumine. Animals Five pregnant mares, aged 4 to 15 years, of light-horse type. Procedure Cloprostenol (250 μg) was administered at 24-hour intervals to 5 pregnant mares. Flunixin meglumine (500 mg, iv) was administered at 8-hour intervals starting 15 minutes before the first cloprostenol administration. Hourly blood samples were analyzed for 15-ke-todihydro-pgf2α, progesterone, and estrogen concentrations. Previously reported data on cloprostenol-induced abortion in 6 pregnant mares treated daily with cloprostenol only were used as historic controls. Results The mean (± sem) interval from first cloprostenol administration to fetal expulsion 56.4 (± 13.7) hours and number of cloprostenol administrations 3.2 (± 0.6) in the 5 flunixin meglumine-treated mares were not significantly different, compared with values for 6 pregnant mares treated daily with cloprostenol only, 48.6 (± 5.6) hours and 2.8 (± 0.2) cloprostenol administrations. Flunixin meglumine did not inhibit endogenous pgf2α secretion. Prostaglandin F2α secretion rates on the day before and day of fetal expulsion were similar in both groups. Conclusion Flunixin meglumine at a dosage of 500 mg/animal, administered iv every 8 hours, is ineffective in modulating uterine pgf2α secretion during cloprostenol-induced abortion. Clinical Relevance Flunixin meglumine is ineffective in the modulation of prostaglandin-induced uterine pgf2αsecretion and, therefore, does not offer a viable alternative for the prevention of abortion in mares at risk of abortion because of systemic illness.

Extension of Corpus Luteum Lifespan and Reduction of Uterine Secretion of Prostaglandin F2α of Cows in Response to Recombinant Interferon-τ

Two experiments tested the effect of recombinant ovine and bovine interferon-τ on corpus luteum lifespan, interestrous interval, and oxytocin-induced uterine secretion of prostaglandin F2α. Cows received intrauterine injections of 100μg of recombinant ovine interferon-τ plus 1.4mg of BSA or of 1.5mg of BSA alone in Experiment 1 and 200μg of recombinant bovine interferon-τ plus 1.3mg of BSA or 1.5mg of BSA alone in Experiment 2. Twice daily injections (0700 and 1900h) were split evenly between the uterine horns from d 14 to 24 of the experimental estrous cycle via an AI pipette in Experiment 1 and via intrauterine catheters in Experiment 2. On d 17, cows were injected with 100 IU of oxytocin, and plasma was collected for analysis of 13,14-dihydro-15-keto-prostaglandinF2α. Recombinant ovine interferon-τ extended the lifespan of the corpus luteum (27.5 vs. 19.2 d) and interestrous interval (30.5 vs. 20.6 d) and abolished the oxytocin-induced increase in 13,14-dihydro-15-keto-prostaglandinF2α, which peaked at 30min for the BSA control group (210.8 pg/ml). Recombinant bovine interferon-τ also extended the lifespan of the corpus luteum (29.0 vs. 21.4 d) and interestrous interval (31.5 vs. 22.6 d) and abolished the oxytocin-induced increase in 13,14-dihydro-15-keto-prostaglandin F2α, which peaked at 30min for the BSA control group (205.6 pg/ml). In conclusion, recombinant ovine interferon-τ and recombinant bovine interferon-τ were effective antiluteolytic agents in cattle.

Endocrine changes, with emphasis on 13, 14–dihydro–15–keto–prostaglandin F2α and corticosteroids, before and during parturition in dromedary camels (Camelus dromedarius)

SUMMARYA study was conducted on eight preparturient camels which were kept in individual stalls adjacent to the Cairo abattoir during 1989. Four novel phenomena are described in this paper: (i) a significant (P &lt; O·05) prepartum decrease in plasma concentrations of progesterone evident over the 48 h preceding parturition; (ii) a remarkably consistent increase in total plasma unconjugated oestrogens, commencing 2–4 days prior to parturition and peaking in excess of 200 pg/ml for c. 2 h before delivery; (iii) a tenfold increase to 5·4±0·19 ng/ml (mean±S.E.) in plasma concentrations of 13, 14-dihydro-15-keto-prostaglandin F2α (PGFM) between days –10 and – 1, showing a sudden and large increase during the 5 h prior to delivery; and (iv) three peaks of total plasma corticosteroids during the 4 h preceding delivery, with the third peak showing the greatest magnitude (24·0±3·11 ng/ml). These results suggest that the dromedary camel is an example of a species in which luteal secretion of progesterone, especially 3α-dihydroprogesterone, is required throughout pregnancy and in which cessation of luteal function, associated with a rapid increase in the oestrogen: progesterone ratio and the secretion of prostaglandin F2α (PGF2α), is a requirement for parturition.

Relationships among endometrial oxytocin receptors, oxytocin-stimulated phosphoinositide hydrolysis and prostaglandin F2 alpha secretion in vitro, and plasma concentrations of ovarian steroids before and during corpus luteum regression in cyclic heifers.

Oxytocin stimulates secretion of endometrial prostaglandin (PG) F2 alpha and induces endometrial phosphoinositide hydrolysis around the time of regression of the corpus luteum (CL) in cows. This study investigated the relationship between endometrial oxytocin receptors, oxytocin-stimulated phosphoinositide hydrolysis and PGF 2 alpha secretion in vitro, and plasma concentrations of ovarian steroids before and during CL regression in cyclic heifers (i.e., Days 13-19 post-estrus). Reproductive tracts were collected from 16 cyclic heifers on Days 13 (n = 5), 16 (n = 5), and 19 (n = 6). Decreases in mean CL weight (4.7, 4.6, and 3.0 +/- 0.6 g for Days 13, 16, and 19, respectively; p < 0.05) and plasma progesterone (12.2, 10.5, and 4.3 +/- 1.5 ng/ml for Days 13, 16, and 19, respectively; p < 0.01) were detected between Days 16 and 19, indicating that CL regression had been initiated in the group of Day 19 heifers. Mean concentration of plasma estradiol (3.4, 3.8, and 5.6 +/- 1.7 pg/ml for Days 13, 16, and 19, respectively) did not differ significantly (p > 0.5) among days of the estrous cycle. Concentration of endometrial oxytocin receptors increased (p < 0.06) during the estrous cycle (36, 49, and 789 +/- 234 fmol/mg protein on Days 13, 16, and 19, respectively), but the greatest increase (p < 0.05) occurred between Days 16 and 19. Similarly, incorporation of [3H]inositol into endometrial inositol phosphates induced in vitro with 100 nM oxytocin also increased (p < 0.01) during the estrous cycle (5121 vs. 5819, 4529 vs. 7239, and 5888 vs 68,096 +/- 18,564 dpm/g tissue for control vs. oxytocin-treated endometrium on Days 13, 16, and 19, respectively) with the greatest increase (p < 0.01) in responsiveness to oxytocin occurring between Days 16 and 19.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in progesterone and oestrogen receptor mRNA and protein and oxytocin receptors in endometrium of ewes after intrauterine injection of ovine trophoblast interferon.

This study determined whether twice-daily intrauterine injections of ovine conceptus secretory proteins (oCSP) containing type-I trophoblast interferon (25 micrograms/uterine horn) from day 11 to day 15 post-oestrus (oestrus = day 0) could alter the binding capacities of endometrial receptors for oxytocin, progesterone and oestrogen in cyclic ewes when compared with control ewes receiving serum protein (SP) injections. Injections of oCSP on days 11-15 post-oestrus decreased concentrations of oestrogen receptors (P < 0.06), oestrogen receptor mRNA (P < 0.05) and progesterone receptors (P < 0.08) in endometrium on day 16 when compared with SP-infused control ewes, which were undergoing corpus luteum regression on days 14-16. Injection of oCSP also decreased the number (P < 0.10) and affinity (P < 0.06) of oxytocin receptors. Inositol phosphate formation induced in the endometrium on day 16 by 100 nM oxytocin in vitro was highly correlated with the concentration (r > or = 0.93, P < 0.001) and Kd (r = -0.91, P < 0.01) of oxytocin receptors in SP-infused ewes, but was not as highly correlated with concentration (r < or = 0.83, P < 0.06) and Kd (r < or = 0.40, P > 0.40) of oxytocin receptors in oCSP-infused ewes. This indicates that oCSP disrupted the relationship between oxytocin receptor binding and oxytocin-induced activation of its second messenger system. These results indicate that antiluteolytic type-I trophoblast interferon may prevent oxytocin-induced luteolytic pulsatile secretion of prostaglandin F2 alpha during maternal recognition of pregnancy in sheep, by reducing the synthesis and affinity of endometrial oxytocin receptors.(ABSTRACT TRUNCATED AT 250 WORDS)