Prostaglandins F in uterine tissue and venous plasma of ewes with intrauterine devices

A century of research on the uteroovarian pathway for uterine-induced luteolysis in mammals

Year 2023 is the 100-year anniversary of the discovery in guinea pigs that the lifespan of the corpus luteum (CL) is controlled by the uterus. The CL is the gatekeeper between two fundamental reproductive events - the estrous cycle and pregnancy. Uteroluteal research for the initial 33 years was productive but limited to laboratory species until the inclusion of farm animals in 1956. In the early 1960s, it was found that uterine luteolysin in sows travels unilaterally from a uterine horn to the adjacent CL which likely accounted for the heyday of uteroluteal research in the 1960s-70s. The luteolytic properties of PGF2α were demonstrated in rats in 1969. In 1971, (1) surgical separation of the lengthwise adherence between the uteroovarian vein and ovarian artery interfered with luteolysis in ewes, (2) species with primarily unilateral vs systemic uterine-induced luteolysis have a strong vs an absent or weak unilateral venoarterial transfer pathway, and (3) vascular infusions identified PGF2α as a uterine luteolysin. Vascular and PGF2α studies were beginning to merge. In 1973, a venoarterial pathway was firmly demonstrated in ewes and later in heifers by surgical anastomosis of a uterine vein or ovarian artery from a uterine-intact side to the corresponding vessel on the unilaterally hysterectomized side. More recent studies described how prostaglandins likely transfer through the walls of uterine and ovarian vessels using concentration gradients in sows and a prostaglandins transporter system in cows.

Prostaglandins and reproduction in female farm animals

Prostaglandins impact on ovarian, uterine, placental, and pituitary function to regulate reproduction in female livestock. They play important roles in ovulation, luteal function, maternal recognition of pregnancy, implantation, maintenance of gestation, microbial-induced abortion, parturition, postpartum uterine and ovarian infections, and resumption of postpartum ovarian cyclicity. Prostaglandins have both positive and negative effects on reproduction; they are used to synchronize oestrus, terminate pseudopregnancy in mares, induce parturition, and treat retained placenta, luteinized cysts, pyometra, and chronic endometritis. Improved therapeutic uses for prostaglandins will be developed when we understand better their involvement in implantation, maintenance of luteal function, and establishment and maintenance of pregnancy.

The oestrous cycle and early pregnancy – a new concept of local endocrine regulation

Facts discovered in recent decades have compelled us to revise long-established views on the physiological regulation of cyclic adjustments to the reproductive system in preparation for pregnancy in females. Evidence has been presented to show that changes in the uterine blood supply induced by the oestrogen/progesterone ratio in the blood and cytokines are important in the regulation of the secretory function of the endometrium. Progressive reduction in uterine blood flow during the luteal phase of the oestrous cycle causes regressive changes in endometrial cells and release of prostaglandin (PG) F(2 alpha), resulting in initiation of luteolysis. Retrograde transfer of PGF(2 alpha) in the area of the mesometrium vasculature is an important element in the mechanism protecting the corpora lutea against luteolysis before day 12 of the porcine oestrous cycle and during early pregnancy and pseudopregnancy. Results of many studies presented in this review indicate that PGF(2 alpha) pulses in uterine venous blood during the follicular phase of the oestrous cycle may not be due to PGF(2 alpha) secretion by endometrial cells, but occur due to remodeling of the endometrium and pulsatile exretion of PGF(2 alpha) in accordance with rhythmic uterine contractions caused by oxytocin.

Effects of estrous synchronization on response to nitric oxide donors, nitric oxide synthase inhibitors, and endothelin-1 in vitro

Two experiments were conducted to determine the effects of nitric oxide (NO) donors, endothelin-(ET-1), and NO synthase (NOS) inhibitors on bovine luteal function in vitro. In experiment 1, estrus in Brahman cows was synchronized with Synchro-Mate-B (SMB) and day-13-14 corpora luteal slices were weighed, diced and incubated in vitro. Treatments (100 ng/ml) were: vehicle, N[see symbol in text]-nitro-L-arginine-L-methyl ester (L-NAME), N(G)-monomethyl-L-arginine acetate (L-NMMA), diethylenetriamine (DETA), DETA-NONOate, sodium nitroprusside (SNP), or ET-1. In experiment 2, estrus was synchronized with Lutalyse, a Controlled Intravaginal Progesterone Releasing Device (CIDR), or cows were not synchronized. Corpora lutea were collected, weighed, and luteal slices were weighed, diced and incubated in vitro with treatments. Treatments (100ng/ml) were: vehicle, L- NAME, L-NMMA, DETA, DETA-NONOate, sodium nitroprusside, S-nitroso-N-acetylpenicillamine (SNAP) or endothelin-1. Tissues were incubated in M- 199 for 1 h without treatments and for 4 and 8 h in both experiments with treatments in both experiments. Media were analyzed for progesterone, prostaglandins E2 and F2alpha (PGE2, PGF2alpha) by radioimmunoassay (RIA). Hormone data in experiments 1 and 2 were analyzed by 2 x 7 and 3 x 2 x 8 factorial design for analysis of variance (ANOVA), respectively. Luteal weights in experiment 2 were analyzed by a one-way ANOVA. Concentrations of progesterone in media were similar (P > or = 0.05) among treatments within experiments. Concentrations of PGE2 in media in experiment 1 were undetectable in 90 and 57% of the samples at 4 and 8 h, respectively. PGF2alpha increased (P < or = 0.05) with time, but did not differ (P > or = 0.05) among treatments. Secretion of PGF2alpha was not affected by treatments (P > or = 0.05). In experiment 2, luteal weights of the induced estrous cycle were decreased (P < or = 0.05) by Lutalyse. Concentrations of PGE2 and PGF2alpha increased (P < or = 0.05) with time in control of all three synchronization regimens. DETA-NONOate, SNAP, sodium nitroprusside (NO donors) and ET-1 increased (P < or = 0.05) PGE2 except in the CIDR synchronized group (P > or = 0.05). No treatment increased (P > or = 0.05) PGF2alpha in any synchronization regimen. It is concluded that either SMB containing norgestomet or a CIDR containing progesterone alters luteal secretion of PGE2, Lutalyse lowers luteal weights in the induced estrous cycle, and NO or ET-1 given alone are not luteolytic agents. It is suggested that NO and ET-1 could have indirect antiluteolytic/luteotropic effects via increasing PGE2 secretion by luteal tissue rather than being luteolytic.

Uterine response to infectious bacteria in estrous cyclic ewes

PROBLEM

Luteal-phase uteri are susceptible to infections, and PGE2 and exogenous progesterone can down-regulate, whereas PGF2alpha can up-regulate, uterine immune functions.

METHOD OF STUDY

Uteri of follicular- or luteal-phase ewes were inoculated with either saline or bacteria (Arcanobacterium pyogenes and Escherichia colt). Vena caval blood was collected for the next 3 days, and progesterone, PGE2, and PGF2alpha were measured. The effects of 10(-7) M PGE2 (Experiment 1), 10(-7) M PGF2alpha (Experiment 2), 10(-7) M indomethacin (INDO), and diluent on proliferation of lymphocytes from the vena caval blood in response to mitogens was quantified.

RESULTS

Experiment 1: Progesterone was greater (P < 0.01) in luteal than in follicular ewes (3.4 versus 0.4 ng/mL), and only luteal ewes inoculated with bacteria developed infections.Lymphocyte proliferation was least (P = 0.08) in follicular ewes (2.6 versus 4.5 pmol for follicular and luteal, respectively). Concanavalin A (Con A)-stimulated proliferation was less (P < 0.05) for ewes inoculated with bacteria and for cells cultured with diluent (5.9 versus 3.1 pmol for saline and bacteria, respectively) or with INDO (6.6 versus 2.8 pmol for saline and bacteria, respectively). Also, Con A-stimulated lymphocytes from ewes inoculated with bacteria tended to proliferate less (P < 0.1) when cultured with PGE2 (4.9 versus 3.7 pmol for saline and bacteria, respectively) or PGE2 + INDO (5.5 versus 3.8 pmol for saline and bacteria, respectively). Experiment 2: Progesterone was greater (P < 0.01) in luteal than in follicular ewes (6.5 versus 1.2 ng/mL), and only luteal ewes inoculated with bacteria developed infections. Con A-stimulated lymphocyte proliferation was greater (P < 0.001) for follicular ewes (4.1 versus 3.1 pmol for follicular and luteal, respectively). Proliferation of lymphocytes collected from follicular ewes was greater (P < 0.01) when cells were cultured with PGF2alpha (3.5 versus 2.7 pmol for follicular and luteal, respectively), but INDO did not affect unstimulated or mitogen-stimulated proliferation.

CONCLUSIONS

Prostaglandin F2alpha enhanced lymphocyte proliferation, whereas bacterial inoculation and in vitro treatment with PGE2 suppressed lymphocyte proliferation. This may signify the involvement of bacterial products and prostaglandins in regulation of uterine immunity.

Modulation of the uterine response to infectious bacteria in postpartum ewes

PROBLEM

Exogenous progesterone and prostaglandin E2 (PGE2) can downregulate uterine immune functions and render the uterus susceptible to bacterial infection.

METHOD OF STUDY

Ewes were sham-ovariectomized (SHAM) or ovariectomized (OVEX) 9 days after parturition (day 0), and their uteri were inoculated with Arcanobacterium pyogenes and Escherichia coli on day 15. Vena caval blood was collected on day 14 and days 16-19, and uteri were collected on day 20. Ewes began receiving either canola oil (OIL) or progesterone in oil (PROG) on day 10. Lymphocytes from each blood sample were assigned to a 2 x 2 factorial array of in vitro treatments; 10(-7) M PGE2 and 10(-7) M indomethacin (INDO) were main effects. [3H]Thymidine incorporation (expressed in picomoles) was used to quantify proliferation.

RESULTS

Progesterone was greater (P = 0.001) in PROG than in OIL ewes (3.6 versus 0.7 ng/mL), and only PROG ewes developed infections. Lymphocyte proliferation was least (P = 0.02) in PROG-OVEX ewes (4.1 versus 5.4, 5.7, and 5.8 pmol for OIL-SHAM, PROG-SHAM, and OIL-OVEX, respectively). Concanavalin A (Con-A)-stimulated proliferation was less (P < 0.01) for PGE2- and PGE2 + INDO-treated lymphocytes (7.5 and 8.3 pmol, respectively) than for control or INDO-treated cells (12.9 and 14.7 pmol, respectively).

CONCLUSIONS

Progesterone treatment of postpartum ewes suppressed uterine immunity. In vitro PGE, treatment suppressed lymphocyte proliferation, regardless of PROG, and highlights a progesterone-independent level of regulation of uterine immune function.

In vitro response to oxytocin and interferon-Tau in bovine endometrial cells from caruncular and inter-caruncular areas

Caruncules are differentiated sites of the endometrium in which placentation occurs in ruminants. We investigated whether the response to agents involved at the time of recognition of pregnancy differed in the caruncular (CAR) and inter-caruncular (ICAR) areas of the endometrium in vitro. The specialization in prostaglandin (PG) production previously described in cells from whole endometrium was reproduced in the CAR and ICAR areas: PGF2alpha and PGE2 were produced in greater proportions, respectively, in epithelial and stromal cells. The relative production of PGE2 was equivalent in epithelial cells from CAR and ICAR regions, but the production of PGF2alpha was higher (p < 0.05) in the ICAR region (2.2 +/- 0.5 vs. 4.0 +/- 0.2 ng/ microg DNA, respectively). In stromal cells, the ICAR area produced more PGE2 than did the CAR area (3.4 +/- 0.4 vs. 2.1 +/- 0.4 ng/ microg DNA, p < 0.05), and the respective PGE2:PGF2alpha ratio was significantly higher in the ICAR area (p < 0.05). The production of PGs was measured first in response to oxytocin (OT, 10(-9) to 10(-5) M) and then to recombinant ovine interferon-tau (roIFN-tau, 0.02 to 20 microg/ml) in a separate set of experiments. In epithelial cells, OT stimulated the production of PGF2alpha 6.3-fold in the CAR area and more than 33.0-fold in the ICAR area (7.1 +/- 3.2 vs. 36.3 +/- 9.8 ng/ microg DNA, respectively, p < 0.05). Production of PGE2 was also increased in both regions and reached a plateau at 4.1 +/- 0.4 ng/ microg DNA. In epithelial cells from the ICAR but not the CAR region, the PGE2:PGF2alpha ratio was decreased in the presence of OT (p < 0.05). In separate experiments, addition of roIFN-tau stimulated PGE2 production significantly (p < 0.05), and no difference (p > 0.8) was observed between CAR and ICAR regions. An increase in PGE2:PGF2alpha ratio was observed in epithelial cells from both CAR and ICAR regions, but it was significant only in the CAR region (p < 0.05). In stromal cells, roIFN-tau stimulated PGE2 production significantly in cells from the CAR and ICAR regions (35.6 +/- 2.9 vs. 24.1 +/- 3.8 ng/ microg DNA, respectively, p < 0.05). In summary, the ICAR region seems to be the privileged site for regulation of PGF2alpha production by OT, but the caruncules may be a preferred site for recognition of the embryonic IFN-tau signal. Endometrial cells from the CAR and ICAR areas appear to exhibit specialized responses, with cells from the ICAR region more responsive to OT and those from the CAR region more sensitive to roIFN-tau.

Prostaglandin E2 levels in uterine tissues and its relationship with uterine and luteal progesterone during the estrous cycle in dairy cows

Endometrial tissue homogenates obtained at luteal and follicular stages of the estrous cycle were determined for prostaglandin E2 and progesterone contents by EIA and RIA, respectively. In Experiment 1, the concentrations and changes of PGE2 in uterine tissues collected by biopsy before slaughter and subsequent samples collected at 30, 60 and 90 min after slaughter were measured. No significant differences were observed in the concentration of PGE2 preslaughter or at 30 and 60 min post slaughter. However, there was a significant decrease (P<0.01) in PGE2 concentration 90 min post slaughter. In Experiment 2, the concentrations of PGE2 in the ipsilateral and contralateral horns in relation to corpus luteum function were compared. A significant (P<0.05) interaction was found between stages of estrous cycle (luteal vs follicular) based on CL progesterone content, and type of uterine horn (ipsilateral vs contralateral) on uterine PGE2 levels. The PGE2 concentration was significantly higher (P<0.01) at luteal phase than at follicular phase. During the luteal phase PGE2 concentrations in tissues of the uterine horn ipsilateral to the corpus luteum was significantly higher (P<0.01) than the contralateral horn. The PGE2 concentration was low and did not differ significantly between horns during follicular phase. A parallel increase (luteal: high) and decrease (follicular: low) in PGE2 and progesterone concentrations were observed. Correlations were observed for CL progesterone and uterine PGE2 concentrations as well as for PGE2 and progesterone concentrations in uterine tissues (r=0.70 and r=0.60, respectively). The results show that the increase in PGE2 concentrations in uterine tissues coincides with the high uterine progesterone concentrations during luteal phase.

Total content of prostaglandin F2 alpha in the endometrium and myometrium from various sections of the porcine uterine horn during the estrous cycle

The purpose of this study was to determine effects of various stages of the estrous cycle on the content and concentration of PGF2 alpha in endometrium and myometrium in different segment of the uterine horn and whether different methods of expressing PGF2 alpha data would affect interpretation of results. Total content of PGF2 alpha in the endometrium and myometrium of the entire uterine horn, and PGF2 alpha concentrations in five sections of uterine horn each of equal length (1 to 5 beginning from the ovarian end) were measured in gilts during three different phases of the estrous cycle: the early luteal phase (Days 3 to 6 of the estrous cycle), mid-luteal phase (Days 9 to 12), and during luteolysis (Days 15 to 18). The total content of PGF2 alpha in the early and mid-luteal phases was similar (P > or = 0.05) in both the endometrium and myometrium. During luteolysis the content of PGF2 alpha in the endometrium and myometrium increased 7-fold and 4-fold, respectively, when compared to the early luteal phase. The distribution of PGF2 alpha was similar throughout the length of the uterine horn and this did not change during the phases of the cycle studied. The PGF2 alpha concentrations during different phases of the estrous cycle differed with methods of expressing the data i.e. ng g-1 tissue, ng mg-1 DNA, ng mg-1 protein, but the relative differences were not appreciably altered.

Effect of prostaglandin F2 alpha on uterine or ovarian secretion of prostaglandins E and F2 alpha in vivo in 90-100 day hysterectomized, intact or ovariectomized pregnant ewes

Vehicle or 8 or 16 mg of PGF2 alpha per 58 kg body weight was given intramuscularly to intact, hysterectomized or ovariectomized 90-100 day pregnant ewes in three separate experiments. Both doses of PGF2 alpha increased PGF2 alpha in ovarian venous plasma compared with controls at 72 hr post treatment in intact (P < or = 0.05) but did not in hysterectomized (P > or = 0.05) 90-100 day pregnant ewes. Concentrations of PGE in ovarian venous blood of intact ewes did not differ (P > or = 0.05) between treatment groups and were equivalent to concentrations of PGE determined in uterine venous plasma. PGE was decreased in ovarian venous plasma by PGF2 alpha in hysterectomized ewes (P < or = 0.07). PGE in uterine venous plasma averaged 6 ng/ml over the 72-hr treatment period in intact and ovariectomized 90-100 day pregnant ewes and was 12 fold greater (P < or = 0.05) than PGF2 alpha which averaged 500 pg/ml in uterine venous plasma. Both PGF2 alpha and PGE increased (P < or = 0.05) by 64 hr in uterine venous plasma of the 8 mg PGF2 alpha-treated intact pregnant ewes. A significant quadratic increase (P < or = 0.05) was observed for PGF2 alpha and PGE in the vehicle and both PGF2 alpha treatment groups of intact ewes at the end of the 72-hr sampling period. It is concluded that the uterus and ovaries secrete significant quantities of PGF but little PGF2 alpha during midgestation. In addition, PGF2 alpha increased uterine secretion of PGE in vivo. PGE may be a placental stimulator of ovine placental secretion of progesterone or PGE may protect placental steroidogenesis from actions of PGF2 alpha.

Factors contributing to the formation of experimentally-induced ovarian cysts in prepubertal gilts

Manipulation of an ovary during the follicular phase in cycling gilts or prepubertal gilts treated with PMSG and hCG results in formation of cysts on manipulated ovaries and corpora lutea (CL) of normal appearance on nonmanipulated ovaries. In contrast, cysts did not form after manipulation in luteal phase gilts. In the present experiment, daily administration of 50 mg progesterone to prepubertal gilts treated with PMSG and hCG established luteal phase concentrations of progesterone but did not lessen the incidence of manipulated-induced cysts. Number of cysts formed was associated with the number of follicles > or = 5 mm at manipulation, which was inversely related to serum concentrations of progesterone. Number of receptors for LH/hCG in follicular tissues did not differ between manipulated and nonmanipulated ovaries but was greater in granulosa (P < .05) and theca (P < .08) from follicles with diameters > or = 7 mm compared to 5 and 6 mm. Contents of estradiol, androstenedione, testosterone, progesterone and prostaglandins E2 and F2 alpha in follicular fluid, granulosa and theca were not different between follicles > or = 5 mm destined to form cysts. Profiles of progesterone and estradiol in peripheral serum and duration of luteal phase concentrations of progesterone were not different for gilts with induced cysts and gilts with CL. In conclusion, manipulation of follicles resulted in a failure to ovulate. Subsequent formation of cysts did not result from or result in a loss of steroidogenic function or the ability to bind LH to follicular receptors. These results demonstrate that the mechanism for ovulation is independent of other follicular processes, since ovulation can be disrupted without altering follicular steriodogenesis or subsequent luteinization.

Effects of superovulation, arachidonic acid or endometrium on release of prostaglandins and synthesis of proteins by bovine trophoblast

This study was conducted in vitro to examine factors that may regulate prostaglandin release by bovine trophoblast and endometrial slices. Trophoblastic tissues and endometrial slices were recovered from superovulating and normally-ovulating cattle on day 16 or 20 of pregnancy and incubated for 24 h. Release of PGF2 alpha and 13,14-dihydro-15-keto-PGF2 alpha (PGFM), and incorporation of [14C]-leucine into proteins were quantified and expressed per microgram DNA, which gives a measure of cellular activity. Activity of trophoblastic tissue for synthesizing protein was decreased (P less than .05) and for releasing PGFM was increased (P less than .05) on day 20 compared to day 16 of pregnancy. Neither superovulation nor day of pregnancy altered trophoblastic activity for releasing PGF2 alpha. Superovulation increased (P less than .05) endometrial release of PGF2 alpha. Endometrial release of PGF2 alpha was less (P less than .05) on day 20 than on day 16 of pregnancy. When arachidonic acid (0, 100, 200 or 400 micrograms) was added at the start of incubation, trophoblastic release of PGF2 alpha changed (P less than .05) quadratically with dose of arachidonic acid. When arachidonic acid was added 8 h after the start of incubation, trophoblastic release of PGF2 alpha increased linearly (P less than .01) with dose of arachidonic acid. Adding arachidonic acid to incubation medium did not affect trophoblastic or endometrial protein synthesis. Endometrial slices suppressed (P less than .05) trophoblastic protein synthesis and release of PGF2 alpha. Apparently, endometrium can modulate trophoblastic release of prostaglandins and synthesis of proteins in vitro, and trophoblastic tissue from superovulated cattle 16 or 20 days pregnant can be used to study trophoblastic synthesis of prostaglandins and proteins.

Role of progesterone in regulating uteroovarian venous concentrations of PGF2 alpha and PGE2 during the estrous cycle and early pregnancy in ewes

The role of progesterone in regulation of uteroovarian venous concentrations of prostaglandins F2 alpha(PGF2 alpha) and E2 (PGE2) during days 13 to 16 of the ovine estrous cycle or early pregnancy was examined. At estrus, ewes were either mated to a fertile ram or unmated. On day 12 postestrus, ewes were laparotomized and a catheter was inserted into a uteroovarian vein. Six mated and 7 unmated ewes received no further treatment. Fifteen mated and 13 unmated ewes were ovariectomized on day 12 and of these, 7 mated and 5 unmated ewes were given 10 mg progesterone sc and an intravaginal pessary containing 30 mg of progesterone. Uteroovarian venous samples were collected every 15 min for 3 h on days 13 to 16 postestrus. Mating resulted in higher mean daily concentrations of PGE2 in the uteroovarian vein than in unmated ewes. Ovariectomy prevented the rise in PGE2 with day in mated ewes but had no effect in unmated ewes. Progesterone treatment restored PGE2 in ovariectomized, mated ewes with intact embryos. Mating had no effect on mean daily concentrations of PGE2 alpha or the patterns of the natural logarithm (1n) of the variance of PGF2 alpha. Ovariectomy resulted in higher mean concentrations and 1n variances of PGF2 alpha on day 13 and lower mean concentrations and 1n variances of PGF2 alpha on days 15 and 16. Replacement with progesterone prevented these changes in patterns of mean concentrations and 1n variances of PGF2 alpha following ovariectomy. It is concluded that progesterone regulates the release of PGF2 alpha from the uterus, maintaining high concentrations while also preventing the occurrence of the final peaks of PGF2 alpha which are seen with falling concentrations of progesterone. This occurs in both pregnant and non-pregnant ewes. Progesterone is also needed to maintain increasing concentrations of PGE2 in mated ewes.

Indomethacin inhibits the uptake of 22sodium by ovine trophoblastic tissue in vitro

Blastocysts from several species synthesize prostaglandins in vitro, but the exact functions of the prostaglandins are unknown. The purpose of this study was to determine if indomethacin, an inhibitor of prostaglandin synthesis, would inhibit the uptake of 22sodium ([22Na]) by ovine trophoblastic tissue. To determine the concentration of indomethacin that would inhibit the synthesis of PGF2 alpha and 13,14-dihydro-15-keto-PGF2 alpha (PGFM) by blastocysts, blastocysts were collected from ewes 16 days after mating, sliced into pieces approximately 2 mm in length and incubated for 48 h at 37 degrees C in 2 ml of medium containing either 0, 0.2, 0.4, 0.8 or 1.6 mM of indomethacin. Concentrations of indomethacin greater than or equal to 0.2 mM reduced (P less than .01) trophoblastic release (ng/micrograms DNA) of PGF2 alpha from 205 +/- 71.2 to less than or equal to 3.3 +/- 0.2, reduced PGFM from 0.7 +/- 0.1 to less than or equal to 0.17 +/- 0.01, and inhibited formation of trophoblastic vesicles. In a second experiment, blastocysts were recovered from ewes 16 days after mating and pieces of trophoblast were incubated with [22Na] and either 0 or 0.4 mM of indomethacin. Indomethacin reduced the uptake of [22Na], which is an indirect measure of the transport of water across epithelia, from 3680 +/- 1118 to 934 +/- 248 cpm/micrograms DNA (P less than .03) and prevented formation of trophoblastic vesicles. Prostaglandins produced by ovine blastocysts might be involved in controlling uptake of water, which is essential for expansion of blastocysts.

Prostaglandin E2 (PGE2) inhibits an IUD-induced premature luteolysis in sheep

Fifteen ewes were assigned as they came into estrus to one of three randomized treatment groups: 1. Sham IUD + Vehicle, 2. IUD + Vehicle, and 3. IUD + PGE2 in Vehicle. An IUD was inserted adjacent to the luteal-bearing ovary of unilaterally ovariectomized ewes on day 3 postestrus. Vehicle (Na2CO3) or PGE2 (500 micrograms) in vehicle was given every 4 hours intrauterine through an indwelling uterine cannula from day 3 postestrus until ewes returned to estrus. Luteolysis was advanced in both the Sham IUD and IUD groups receiving vehicle. An IUD-induced premature luteolysis was prevented by PGE based on daily concentrations of progesterone in peripheral blood and the extended interestrous interval. It is concluded that chronic intrauterine injections of PGE2 (500 micrograms) every four hours can prevent an IUD-induced premature luteolysis. It is also concluded that an IUD-induced premature luteolysis is not necessarily through uterine distention.

Inhibition of an IUD-induced precocious luteolysis by prostaglandin E1 (PGE1) in sheep

Fifteen ewes were assigned as they came into estrus to one of three randomized treatment groups: 1. Sham IUD + Vehicle, 2. IUD + Vehicle or 3. IUD + PGE1 in vehicle. An IUD was inserted adjacent to the luteal-bearing ovary on day 3 postestrus. Prostaglandin E1 (500 micrograms) in vehicle (Na2CO3) or vehicle was given intrauterine through an indwelling uterine cannula every four hours from day 3 postestrus until ewes returned to estrus. Precocious estrus was induced in both the sham IUD and IUD groups receiving vehicle. Prostaglandin E1 prevented an IUD-induced premature luteolysis based on daily concentrations of progesterone in peripheral blood and the interestrous interval. It is concluded that an IUD-induced premature luteolysis is not necessarily via physical distention by the IUD. It is also concluded that chronic intrauterine infusions of PGE1 can prevent an IUD-induced premature luteolysis.

Metabolism of arachidonic acid in vitro by ovine conceptuses recovered during early pregnancy

Metabolism of [3H] arachidonic acid ([3H] AA) and synthesis of prostaglandins were examined with ovine conceptuses and endometrial slices collected on various days after mating. Tissues were incubated for 24 hr with or without 5 microCi of [3H] AA and with 200 micrograms radioinert AA. In experiment 1, results of chromatography indicated that conceptuses collected on days 14 and 16 after mating metabolized [3H] AA to PGE2, PGF2 alpha, PGFM, 6-keto-PGF1 alpha, and to unidentified compounds in three chromatographic regions. One of these regions (region I) contained triglycerides. Endometrial slices metabolized only small amounts of the [3H] AA to prostaglandins. In experiment 2, results of radioimmunoassays indicated that day 14 conceptuses released somewhat similar amounts (ng/mg tissue) of PGF2 alpha (32.1 +/- 17.9), PGFM (8.4 +/- 6.2), PGE2 (12.3 +/- 7.5) and 6-keto-PGF1 alpha (41.4 +/- 4.8), whereas day 16 conceptuses released more (P less than .05) PGF2 alpha (9.0 +/- 4.1) and 6-keto-PGF1 alpha (15.9 +/- 2.7) than PGE2 (0.9 +/- 0.2) or PGFM (0.5 +/- 0.08). Day 14 and 16 endometrial slices released (ng/mg tissue) more (P less than .05) PGFM (3.0 +/- 0.2) and 6-keto-PGF1 alpha (4.0 +/- 0.4) than PGF2 alpha (0.5 +/- 0.08) or PGE2 (0.05 +/- 0.02). In experiment 3, conceptuses were recovered on days 16, 20 and 24 of pregnancy and incubated with [3H] AA to determine the effects of indomethacin on [3H] AA metabolism. In general, indomethacin (Id; 4 X 10(-4) M) reduced (P less than .05) the percentage of total dpm recovered as prostaglandins, but Id increased the release of chromatographic region I. Experiment 4 was conducted with day 16, 20 and 24 conceptuses to evaluate the time course of metabolism of [3H] AA, and the appearance of region I and of prostaglandins. In general, the percentage of total dpm in region I increased as the percentage of dpm as [3H] AA decreased. The percentage of dpm as prostaglandins increased as the percentage of dpm in region I decreased. Prostaglandins, probably essential for embryonal survival and development, were synthesized in vitro by ovine conceptuses.

Formation of cyclic adenosine monophosphate (cAMP) in the preovulatory rabbit follicle: role of prostaglandins and steroids

The preovulatory increase in follicular prostaglandins (PG) stimulated by luteinizing hormone (LH) is dependent upon 3'-5'-cyclic adenosine monophosphate (cAMP) and is essential for ovulation. It has been proposed that follicular PG stimulate a second rise in cAMP, independent of LH. This study examined the temporal relationships among PGE2, PGF2 alpha 6-keto-PGF1 alpha, estradiol-17 beta, progesterone, testosterone, androstenedione and the biphasic increases of cAMP in follicles of rabbits. Does received indomethacin (IN, 20 mg/kg, i.v.; n = 30) or phosphate buffer (C; n = 30), 0.5 h before 50 ug of LH. At laparotomy at 0, 0.5, 1, 2, 4 or 8 h after LH, blood was collected from each ovarian vein and two follicles per ovary were aspirated of fluid and excised. Plasma and follicular tissue and fluid were assayed for PG and steroids. Tissue and fluid were assayed for cAMP. In C does, cAMP (pmol/follicle) in tissue increased from 11.3 at 0 h to 14.2 at 0.5 h, decreased at 1 h (5.4) and increased linearly through 8 h to 14.5. In IN-treated does, cAMP remained high from 0.5 (13.2) to 2 h (16.3), decreased at 4 h (7.9) then increased again by 8 h (15.5). Indomethacin decreased all PG in follicular tissue but 6-keto-PGF1 alpha rose after 2 h, whereas PGE2 and PGF2 alpha did not. Estradiol-17 beta, progesterone, and androstenedione did not vary with treatment; testosterone was increased (P less than .05) by IN. PGE2 or PGF2 alpha may terminate the first phase of cAMP production, rather than initiate the second phase.

Luteal function in cows following destruction of ovarian follicles at midcycle

Luteal function was studied in the absence of non-ovulatory ovarian follicles to determine if these follicles are involved in luteal regression in cattle. After at least one estrous cycle, cows were assigned randomly to treatment (n=5) or control (n=5). All cows were laparotomized on day 10 postestrus (Estrus = day 0). During laparotomy of treated cows, all visible follicles on both ovaries were destroyed by electrocautery, and follicular growth was prevented by ovarian x-irradiation. In controls, laparotomy and ovarian manipulation were as in treated cows but follicles were not destroyed and ovaries were not irradiated. On day 22 postestrus, ovaries of 4 treated cows contained no visible follicles and concentrations of estradiol-17beta in jugular plasma (0.4 +/- 0.1 pg/ml) were less (P<0.05) than in controls (3.2 +/- 0.4 pg/ml). Daily mean concentrations of LH from surgery to day 22 postestrus in treated cows did not differ from controls. On day 22 postestrus, progesterone in jugular plasma and weights of corpora lutea in treated cows were greater (P<0.05) than in controls. Between days 12 and 18 postestrus, concentrations of estradiol-17beta and PGF(2)alpha in utero-ovarian venous plasma of controls increased prior to detectable declines in concentrations of progesterone. Therefore, non-ovulatory ovarian follicles present during mid to late diestrus are necessary for luteal regression in non-pregnant cattle.

Discriminating analysis of "in vitro" prostaglandin release by myometrial and luminal sides of the ewe endometrium

An original perifusion device which allows a discrimination between the 30 mn releases of prostaglandins F2 alpha and E2 by the luminal and the myometrial faces of sheep endometrium is described. Tissue was sampled on day 4, 14, 16 or 17 of the cycle and on day 14 or 17 of pregnancy. Total prostaglandin (PG) release measured with this device was in good agreement with PG's concentrations in media of in vitro endometrium incubations already described. Discrimination analysis of the PGs release by each side of the endometrial tissue during the 30 mn perifusion time revealed that PGF2 alpha concentrations of the perifusion medium issued from the lumen compartment were higher than those of the myometrial compartment in all physiological status where corpus luteum is active (including early pregnancy). Therefore in the ewe, it seems that luteal structure maintenance during early pregnancy is not due, as in the gilt, to a shift in PGF2 alpha secretion towards the uterine lumen.

Metabolism of arachidonic acid in vitro by porcine blastocysts and endometrium

Metabolism of radiolabeled arachidonic acid (*AA) by blastocysts and endometrial slices recovered from five gilts 16 days after detection of estrus was studied in vitro. Blastocysts from each gilt were divided into four 216 +/- 18 mg portions, and each portion was placed into a separate petri dish containing 15 ml modified minimum essential medium (MEM). The incubates from each gilt received either 25, 50, 100 or 200 micrograms radioinert arachidonic acid (AA). Endometrium was dissected from each uterine horn, sliced and duplicate 509 +/- 3 mg portions from each gilt were placed into petri dishes containing 15 ml MEM and 200 micrograms AA. All incubates received 5 microCi of *AA (either [14C]-arachidonic acid or [3H]-arachidonic acid). The incubates were rocked at 37 degrees C for 24 h in an atmosphere of 50% N2:45% O2:5% CO2. After incubation, tissues and MEM were separated by centrifugation. Metabolism of *AA was assessed in extracts of MEM and tissue homogenates by separating *AA and its metabolites on columns of Sephadex LH-20. Blastocysts produced compounds that migrated with [3H]-13,14-dihydro-15-keto-PGF2 alpha (*PGFM), [3H]-PGE2 (*PGE2) and [3H]-PGF2 alpha (*PGF2 alpha). The greatest (P less than .05) proportion (35.7 +/- 1.8%) of the radioactivity in blastocyst MEM was recovered as PGE2. In blastocyst homogenates, most (66.2 +/- 3.3%; P less than .05) of the radioactivity was in a nonpolar peak assumed to be arachidonate esters. The concentration of AA in MEM did not alter metabolism of *AA by blastocysts. Endometrial slices produced *PGFM and *PGE2 but only in small amounts, and they were capable of producing nonpolar, probably esterified, forms of *AA. It was concluded that porcine blastocysts produce and metabolize prostaglandins in vitro and that they make a contribution to the uterine milieu during early pregnancy.

Reduction by human chorionic gonadotropin of the luteolytic effect of prostaglandin F2 alpha in ewes

The ability of human chorionic gonadotropin (HCG) to reduce the luteolytic effect of prostaglandin (PGF2 alpha) was demonstrated in cycling ewes. As expected, treatment with 10 mg of PGF2 alpha alone on Day 10 of the estrous cycle exerted a potent negative effect on the function and structure of corpus luteum (CL) as indicated by reduced plasma progesterone, CL progesterone, and CL weight. However, the identical PGF2 alpha treatment failed to significantly reduce either luteal function or luteal weight when administered to ewes that were also treated with HCG on Days 9 and 10 of the estrous cycle. Treatment with HCG alone had a positive effect on CL as indicated by increased plasma progesterone, CL progesterone, and CL weight. Treatment with HCG did not render the CL totally insensitive to the negative effects of PGF2 alpha because plasma progesterone was reduced when the dose of PGF2 alpha was doubled. Whether CL regressed or continued to function after treatment with both HCG and PGF2 alpha appeared to depend upon a balance between the positive and negative effects of the two hormones.

Uterine prostaglandin F2 alpha & E2 production and content during the second half of the oestrous cycle of the sheep - possible local control of the uterus by the ovary

The amount of prostaglandin F2 alpha (PGF2 alpha) and prostaglandin E2 (PGE2) in the endometrial tissue of sheep and the ability of this tissue to synthesize these prostaglandins have been monitored daily during the latter part of 12 oestrous cycles in seven ewes. Plasma concentrations of PGF2 alpha and progesterne were measured simultaneously during ten of these cycles. No difference could be found between the content of or the synthesizing ability for PGF2 alpha or PGE2 of caruncular and non-caruncular endometrial tissue, although the myometrium contained and produced significantly less PGF2 alpha than either of these tissues. There was no relationship between PGF2 alpha content, secretion and synthesizing ability of endometrial tissue although changes in the uterine content of PGE2 and PGF2 alpha were directly related. Changes in the ability of the uterine endometrium to synthesize PGF2 alpha varied with the presence or absence of the neighbouring ovary. When the adjacent ovary was present there was a statistically significant increase in the ability of the endometrium to synthesize PGF2 alpha 3 and 2 days before the onset of oestrus. In the absence of the ovary this increase did not occur. The data suggests that the ovary has a local controlling influence over the ability of the endometrium to synthesize PGF2 alpha.

Prostaglandins F in uterine and ovarian compartments and in plasma from the uterine vein, ovarian artery and vein, and abdominal aorta of pseudopregnant rats with and without deciduomata

Prostaglandins F were measured in uterine and ovarian compartments and in uterine venous, ovarian arterial and venous and abdominal aorta plasma and the uptake of 3H-PGF2 alpha by ovarian compartments of 240 pseudopregnant rats with or without bilateral deciduomata in five experiments. Concentrations of PGF in deciduomal tissue, uterine venous plasma, ovarian arterial and venous plasma, corpora lutea, and remainder of the ovary and 3H-PGF2 alpha in the ovary were consistently as high or higher in pseudopregnant rats with deciduomata as in the endometrium, ovarian compartments, or samples of plasma from the same blood vessels of pseudopregnant rats without deciduomata. Levels of PGF were consistently 3 to 7 fold higher in uterine venous than in plasma from the abdominal aorta. It is concluded that extended luteal maintenance by deciduomal tissue is by some mechanism other than an inhibition of PGF synthesis by the uterus, transfer of PGF locally to the ovary, or uptake of PGF by the ovarian compartments.

Effects of PGE1 or PGE2 on luteal function in pseudopregnant rats

Effects of PGE1 or PGE2 on luteal function were studied in 163 pseudopregnant rats. PGE1 (10, 100, or 300 micrograms) given intrauterine every 6 hr did not shorten pseudopregnancy (P greater than 0.05), however, the same doses of PGE2 given intrauterine every 6 hr advanced luteolysis (P less than 0.05). PGE1 (100 or 300 micrograms) given every 4 hr intramuscular maintained levels of progesterone in peripheral blood above controls (P less than 0.05) while 100 or 300 micrograms of PGE2 hastened the decline in progesterone (P less than 0.05). The antiluteolytic effect of PGE1 was not via an inhibition of PGF secretion (P greater than 0.05) by the uterus or by induction of ovulation in treated animals. Moreover, PGE1 (100, 200, or 500 micrograms) given intramuscular every 4 hr from day 4 of pseudopregnancy until the next proestrus delayed luteal regression around 3 days (P less than 0.05). PGE2 at doses of 100, 200, or 500 micrograms every 4 hr given intramuscular consistently shortened pseudopregnancy (P less than 0.05). Lower doses were without effect (P greater than 0.05). Based on the above data it is concluded that PGE2 is consistently luteolytic whereas PGE1 is not luteolytic in pseudopregnant rats and that PGE1 may be an antiluteolysin.

The effect of a progesterone-releasing intrauterine contraceptive device on uterine secretion of prostaglandin F2alpha and life-span of corpora lutea in the ewe

Two studies were conducted to investigate the effect of a progesterone-releasing intrauterine contraceptive device (IUD) on uterine secretion of prostaglandin (PG) F2alpha associated with IUD-induced luteolysis in sheep. In bilaterally ovulating ewes receiving an IUD on day 3 (estrus = day 0) intrauterine release of progesterone (90 microgram per day) by the device did not prevent premature luteolysis or the increased concentration of PGF2alpha in uterine venous plasma on day 5 caused by conventional IUD's. In the second study a progesterone-releasing IUD (645 microgram per day) inserted adjacent to the intact ovary at unilateral ovariectomy on day 14 inhibited early luteolysis in the subsequent estrous cycle and reduced the uterine secretion of PGF2alpha on day 5, without affecting concentrations of progesterone in the peripheral circulation at the intervening estrus. It is suggested that locally delivered intrauterine progesterone can inhibit IUD-induced luteolysis in the ewe by suppressing the uterine secretion of PGF2alpha.