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Role of progesterone in regulating uteroovarian venous concentrations of PGF2 α and PGE2 during the estrous cycle and early pregnancy in ewes
PROSTAGLANDINS
ROLE OF PROGESTERONE IN REGULATING UTBROOVARIAR VENOUS CORCRRTRATIORS OF PGF a AND PGE DURIRG THE ESTROOS CYC2R Am RARZY PRRGRARCY IR EWES D.L. VINCENT and E.K. INSKEEP Division of Animal and Veterinary Sciences West Virginia University Horgantown, West Virginia 26506-6108 ABSTRACT The role of progesterone in regulation of uteroovarian venous concentrations of prostaglandins F2e(PGF2a) 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 ovariectomixed on day12 and of these, 7 mated and 5 unmated ewes were given10 mgprogesterone 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 PGE in the uteroovarian vein than in unmated ewes. Ovarieczomy 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 PGF2a or the patterns of the natural logarithm (In) of the variance of PGF20. Ovariectomy resulted in higher mean concentrations and In variances of PGF2a on day 13 and lower mean concentrations and In variances of PGF2a on days 15 and 16. Replacement with progesterone prevented these changes in patterns of mean concentrations and In variances of PGF2a following ovariectomy. It is concluded that progesterone regulates the release of PGF2a from the uterus, maintaining high concentrations while also preventing the occurrence of the final peaks of PGF2a 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.
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Prostaglandin P2a (PGF2a) is the major naturally occurring luteolysin in the ewe (1,2). Luteal regression results from uterine secretion of PGF2= beginning on d 11 to 13 postestrus (3,4). Progesterone appears to play a role in the regulation of uterine secretion of PGF a from the uterus. In ovariectomixed ewes, treatmen % with progesterone for several days increased uterine release (5) or caruncular endometrial concentrations (6) of PGF2a. A period of progestational influence has been proposed to regulate the timing of initial peaks of secretion of PGF2a may (4r7). Ottobre et al. (8) reported that progesterone be required only through d 9 of the cycle for increased secretion of PGF2a from the uterus to begin by day 12. The effects of the uterine luteolysin must be negated for pregnancy to be established successfully in the ewe. The mechanism by which the embryo prevents luteal regression is not clear. It has been suggested by many that uterine secretion of PGF 2cis suppressed by action of the embryo (3,9-11). The absence, in early pregnant ewes of very high concentrations of PGF a in plasma associated with the follicular phase (day 1 5 to 17) in nonpregnant ewes has been taken as evidence for embryonic suppression of uterine secretion of PGF2a. Yet this secretion of PGF occurs as progesterone concentrations are decreasing an8 luteal regression is nearing completion. Others have found that the pattern of secretion of PGF2aby the uterus in the early pregnant ewe is not different from that observed in nonpregnant ewes on comparable days postestrus, particularly nearer to the onset of luteolysis (12-18). Since concentrations of PGF a in blood leaving the uterus of pregnant and non-pregnan$ ewes do not differ at the time of onset of luteal regression, the actions of PGF2a must be prevented by some antiluteolytic factor(s). The antiluteolytic effect of the embryo is expressed locally (19,20) and is mediated by some blood borne factor(s) which passes from the uterine vein to the ovarian artery (20,21). One might expect this factor(s) to be lipid soluble and to have chemical properties similar to the luteolysin, PGF2a. Although initial studies by Wilson et al. (12) and Lewis et al. (22) did not detect increased concentrations of prostaglandin E2 ( PGE2) in the uteroovarian vein of pregnant ewes, more recent work (16-18) has shown that concentrations of PGE2 in the uteroovarian vein of pregnant ewes increase at the time of the critical period for maternal recognition of pregnancy, days 12 to 13 postestrus (23). Prostaglandins of the E series have been shown
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to lessen the effects of PGF a when given concomitantly Spontaneous lutea ? regression or that induced (24-26). by estradiol or intrauterine devices have been delayed by uterine luminal infusion of PGEl or PGE2 (27-31). In order to exert this effect, PGE or PGE must be infused into the uterine horn or broad + igamen ? adjacent to the ovary bearing the corpus luteum (29-32). Secretion of progesterone by bovine luteal tissue (33-35) or dispersed ovine large luteal cells (36,371 tiyi&o was stimulated by PGE1 and PGE2. The morphological changes and reduced viability seen following incubation of dispersed large ovine luteal cells with PGF2a were prevented if PGE2 was added to the medium (37). The purpose of this experiment was to examine the role of progesterone in regulating uterine secretion of PGF2a and PGE2 during the estrous cycle and early pregnancy in the ewe. MRTEODSARD HATBRIALS
Animals and Surgical
Procedures
Mature ewes of mixed breeding were pastured with brisket-painted, vasectomized rams and checked for standing estrus twice daily. Ewes with at least one previous estrous cycle of 15.5 to 19 days were selected randomly for either fertile or no mating. Ewes assigned to fertile mating were penned with a brisket-painted, intact ram at first detection of standing estrus (day 0). Ewes assigned to no mating remained in the main flock. On day 12 after estrus, each ewe was anesthetized with sodium pentobarbital and the reproductive tract was exposed through a midventral abdominal incision. A siliconized, polyvinyl catheter was placed into a uteroovarian vein contralateral to the corpus luteum as described by Ottobre et al. (8) and Silvia et al. (18). Ewes in the intact control group received no further treatment (n = 7 unmated and 6 mated). Uteroovarian venous concentrations of PGF2a and PGE2 were compared among these ewes and those in two other experimental groups: bilateral ovariectomy on day 12 postestrus (n = 7 unmated and 8 mated) and bilateral ovariectomy on day 12 postestrus plus immediate replacement with progesterone (n = 6 unmated and 7 mated). Replacement therapy with progesterone consisted of a subcutaneous injection of 10 mg of progesterone and the placement of an intravaginal sponge containing 30 mg of progesterone. Blood was collected from the indwelling catheters, daily at 15 min intervals during 3-h periods beginning between 0600 and 1100 on day 13 after estrus. Sampling was continued, when possible, through day 16 postestrus.
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Samples were processed as described by Pexton et al. (38) and the plasma was stored at -20 C until assayed for prostaglandins. To maintain catheter patency all ewes received a constant infusion of 200 ml/day of sterile saline containing 200 IU sodium heparin and 20000 IU potassium penicillin G’per ml into the indwelling uteroovarian venous catheters via Buchler infusion pumps. Heparin infusion was interrupted during the 3-h sampling period. During that time each day, catheters were flushed with 2 to 3 ml of sterile saline containing 200 IU/ml sodium heparin after each blood sample. On day 17 or at loss of catheter patency, ewes were sacrificed with an overdose of sodium pentobarbital. Their uteri were excised and flushed for the presence of blastocysts to confirm pregnancy. Assays
for
PGF2a and PGE2
by radioimmuConcentrations of PGF a were quantified noassay, as described by $ exton et al. (38) and Lewis et al. (22). Sensitivity of the assay was 30 pg/tube and volumes gfplasmaassayed ranged from 50to 200 ul. Recovery of H-PGF2a after extraction and column chromatoEach sample was graphy was measured in each assay. adjusted for procedural losses and external recoveries averaged 48.7 +_ 1.2% for 110 assays. Within and between assay coefficients of variation were 11.2% and 22.6%, respectively. Concentrations of PGE in the uteroovarian venous described plasma were quantified by t?1e radioimmunoassay by Lewis et al. (22) and Silvia et al. (18). Procedural losses were estimated in each assay by measuring the recovery of 3H-PGE2 after extraction and column chromatoEach sample was adjusted for procedural losses graphy. and external recoveries averaged 59.5 +- 1.2% over 110 assays. Within and between assay coefficients of variation were 8.8% and 17.4%, respectively. Sensitivity of the assay was 2.5 pg/tube and volumes assayed ranged from 50 to 200 ul. Statistical
Analyses
Treatments were arranged in a 2 x 3 factorial design with pregnancy status and ovarian status as main effects. Patterns of mean concentrations of PGFp and PGE2 within sampling period were compared among groups using analysis of variance for a completely randomized split-plot design with treatment as the main plot and day as the subplot. Because differences in patterns of secretion of PGFpand PGE2 may be missed by examination of only means within period and because differences in amplitudes of peaks might occur as a result of treatment, patterns of fluctua-
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tions in concentrations of PGF2a and PGE2 among groups were compared. This was done by determining the variances for the thirteen samples collected within each sampling period from each ewe (18). To reduce the large range of these variances, they were transformed to their natural logarithms. Patterns of natural logarithms of variances (In variance) of concentrations of PGF2a and PGE2 within sampling period were then compared among groups using analysis of variance for a split-plot design. Patterns of mean concentrations and In variance of PGF2a and PGE2 were compared using preplanned orthogonal contrasts. RESULTS
Blastocysts were found in 7 of 8 mated ewes that were intact and 6 of 8 mated ewes treated with progesterone after ovariectomy. Only ewes having confirmed pregnancies in these groups were included in the data analysis. Blastocysts were not found in any (0 of 8) mated ewes Because it was ovariectomized on day 12 postestrus. impossible to confirm pregnancy prior to ovariectomy in these ewes and because of a combined pregnancy rate of 81% in the other mated ewes, it was assumed that most of the ewes mated to fertile rams and ovariectomized were pregnant prior to ovariectomy. Therefore, all ewes from this group were included in the analysis of the data. Mated and unmated ewes did not differ in patterns of mean concentrations or In variances of PGF2a on days 13 through 16 postestrus. Ovariectomy resulted in higher mean concentrations of PGF a on day 13 (P(.Ol) and lower mean concentrations of PGa2a on days 15 and 16 (P&OS). Replacement of progesterone prevented the increase on day 13 and the decrease on days 15 and 16. Thus ovariectomized ewes had a pattern of mean concentrations of PGFpdifferent from both intact ewes and ovariectomized ewes treated with progesterone (P&001, figure 1) on days 13 through 16. Patterns of In variance of PGF2a of ovariectomized ewes also differed from those in intact ewes and progesterone-treated ovariectomized ewes (P&001, figure 2). Neither mean concentrations within day, patterns of mean concentrations, In variances within day nor patterns of In variance of PGF2a were different intact ewes between and progesterone-treated ovariectomized ewes. Mated and unmated ewes differed in their patterns of mean concentrations of PGE2 on days 13 through 16 (P&OS; figure 3). Ovariectomy had no effect in unmated ewes (P&l, figure 3, panel A) but prevented the rise in PGE2 observed on days 13 to 16 in mated ewes (P&OS, figure 3, panel B). Replacement of progesterone after ovariectomy restored the increase in PGE2 in mated ewes but had no effect in unmated ewes (figure 3). The In variance of PGE2 increased linearly with day in mated ewes which were
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The effects of ovariectomy and progesterone replacement on mean daily concentrations of PGF2a in uteroovarian venous blood. Legend: (. .) intact ewes, IA-----A ovariectomized ewes and h -3 ovariectomized ewes treated with progesterone. The pattern for ovariectomized ewes differs (P1.001) from those for intact ewes and progesteronetreated, ovariectomized ewes.
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The effects of ovariectomy and progesterone replacement on patterns of In variance of PGF2a within day within ewes. Legend: (&____d intact ewes, ovariectomized ewes and (, .I, ovariectomlzed ewes treated with progesterone. Patterns for ovariectomized ewes are different (P(.OOl) from those for intact ewes and progesteronetreated, ovariectomized ewes.
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The effect of ovariectomy and progesterone replacement on mean daily concentrations of PGE2 in uteroovarian venous blood in unmated ewes (panel A) and mated ewes (panel B). Legend: * 0 intact ewes, (A----& ovariectomlzed ewes and (B_____I) ovariectomized treated with progesterone. Patterns for unmated ewes do not differ with treatment (P2.1, panel A). Among mated ewes, patterns for ovariectomized ewes differ (P1.05, panel B) from those for intact ewes and progesteronetreated, ovar iectomized ewes.
APRIL 1986 VOL. 31 NO. 4
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intact or treated with progesterone after ovariectomy (PI.001)but did not change with day among unmated ewes or ovariectomixed, mated ewes (figure 4). DISCUSSION Progesterone is required for the timing of the onset of the initial peaks of secretion of PGF a which usually occur on day 12 of the estrous cycle (4,5 ,8). Removal of ovaries on day 12 resulted in different patterns of mean daily concentrations of PGF2a than those seen in intact ewes on day 13 through 16 postestrus. Concentrations of PGF2a in the uteroovarian veins of ovariectomixed ewes rose rapidly on day 13, in a manner similar to the large final peaks of PGF2,x observed at the end of the estrous cycle, with luteal regression (3-5,7). By days 15 and 16, concentrations of PGF2ain ovariectomixed ewes had declined to lower levels than in the intact ewes. Replacement of progesterone in ovariectomixed ewes restored patterns of mean daily concentrations of PGF2a to values not different from those seen in intact ewes. Thus progesterone therapy prevented large increases in PGF2a observed after ovariectomy while also maintaining the high concentrations of PGF2a which eventually cause complete luteal regression in the intact ewe. In contrast, Ottobre et al. (8) reported that progesterone was not necessary to sustain normal patterns of secretion of PGF2a on days 15 and 16 in ewes ovariectomixed on day 14. No treatment differences in uteroovarian venous concentrations of PGFzQ were observed among groups in which progesterone was removed, with or without estrogen replacement, when compared to intact control ewes. However, the intact ewes were all undergoing natural luteolysis, so the rapid rise and fall in PGF2a in response to ovariectomy may have coincided with the same changes in response to the falling concentrations of progesterone in intact ewes. Removal of progesterone on day 14 by removal of either ovaries or corpora lutea, resulted in an initial increase in uteroovarian venous concentrations of PGF a followed by a gradual decline (8). A similar pattern oS secretion of PGF2a was observed in ewes ovariectomixed on day 12 in the present experiment. Removal of progesterone has been shown to increase concentrations of PGF2a in the uterus of other species. In the pregnant rat near term, Wilson and Stanisic (39) observed that following ovariectomy on day 19, concentrations of PGF2a in the uterus increased over intact controls. Progesterone replacement in ovariectomixed rats lowered uterine concentrations of PGF ato levels not different from intact control rats (39P. Incubation ti yitro of uteri from ovariectomixed rats with high concentrations of progesterone resulted in a large increase in release of PGF2q into the medium following removal of progesterone (40). Progesterone may
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The effects of ovariectomy and progesterone replacement on patterns of In variance of PGE within day ewes in unmated ewes (panel A) an !I mated ewes (panel B). Legend: Cc_--_.@ intt,ci ewes, CA-----4 ovariectomlzed ewes (I_____.) ovariectomized ewes treatd with progesterone. Patterns for unmated do not differ with treatment (PZ.1, panel A). Patterns for mated ewes increase linearly (PL.05, panel B) from intact ewes and progesterone-treated, ovariectomized ewes.
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regulate secretion of PGF2a in two ways; first, by timing the initial peaks of secretion early in the estrous cycle by modulating secretion of PGF2a until luteal and second, Then the uterus is released from regression is complete. the inhibition of progesterone and the large final peaks of secretion of PGFza are observed with falling concentrations of progesterone. increased uterine release and (or) Estradiol-l7g caruncular or endometrial concentrations of PGF2a if given after several days of exogenous (5,6,41) or endogenous (9,411 progesterone. Higher concentrations of estradiol in plasma have been associated temporally with the release This has been of PGF a in several species (1,4,42,43). true for the maximal uteroovarian concentraparticu 3 arly tions of PGF a during luteal regression in the ewe have led some researchers Resu 3 ts such as these (4r5r7). to suggest that endogenous estrogen stimulates production of PGF2a by the uterus after a period of prior progestational influence in the nonpregnant ewe (1). However, Baird et al. (7) and Ottobre et al. (4) found no relationship of the initial increases in PGF2a to increases in estradiol-178 during the mid-luteal phase. Recently, Ottobre et al. (9) observed that exogenous estradiol did not increase uteroovarian venous plasma concentrations of PGF a in ewes ovariectomixed on day 14 postestrus. It mus E be recognized that estrogen may have a role in luteolysis that does not involve uterine secretion of PGF a. Evidence for such an action lies in the observations t at was more effective the combination of PGF2a and estradiol in causing luteolysis in hysterectomixed ewes (44) or in heifers (45) than treatments with either PGF2a or estrogen alone. Such an action may account for the delay in completion of luteolysis in ewes following destruction of ovarian follicles (46, 47) or following inhibition of FSH by injection of follicular fluid (48). Given that secretion of PGF during days 12 through 16 is very similar in pregnan ? and nonpregnant ewes present study) the action of PGF2a must be (2,17,18, prevented if the corpus luteum is to be maintained and pregnancy is to be established successfully. Given further that injections of PGF2a were less effective in inducing luteal regression in pregnant than in nonpregnant ewes (21, 27, 49-511, the action of PGF2a must be prevented by some antiluteolytic factor(s). That the embryo produces and (or) controls production of this factor(s) is supported by the recent report by Silvia and Niswender (50) that more PGF was required to cause luteolysis in ewes with two em2D” ryos than in those with a single embryo. The nature of the antiluteolysin is not clear. Blastocysts at the critical time for maternal recognition
2
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of pregnancy produce both prostaglandins (17,52,53) and proteins (54-57). Ovine trophoblast protein 1 (oTP-l), the major protein secreted from day 13 to 21 blastocysts, binds to the endometrium (56) and extends luteal function when infused into the uterine lumen of nonpregnant ewes (57). Endometrial and (or) uteroovarian venous concentrations of PGE2 are increased during the same period (1618,52, present study) in pregnant ewes. PGEl and PGE have been shown to counteract the luteolytic action o3 (25-32) and hn PGF2a to varying degrees, both ti ykQ tif;rQ (36,371. Since the antiluteolytic effect of the blastocyst was shown to occur locally (201, via blood borne factors (21,231, one can speculate that the lipid soluble PGE2 may be a stronger candidate for the antiluteolytic agent at the ovarian level than oTP-1. However, oTP-1 or some other conceptus-derived protein could represent the primary signal from the free, floating blastocyst to the endometrium to stimulate endometrial production of PGE2, or the two substances (oTP-1 and PGE2) could act additively, synergistically or sequentially to maintain corpora lutea of pregnancy. From these data and previous literature discussed above and reviewed earlier by Ottobre et al. (81, one can propose an explanation for the regulation of uterine secretion of prostaglandins by steroids. At estrus, receptors for progesterone in the endometrium are induced by increased concentrations of estradiol-17B (see 8 for review). Early in the estrous cycle or pregnancy (days 4 to 9 postestrus), progesterone establishes the capacity of the endometrium to secrete prostaglandins and times the occurrence of the initial peaks of secretion of PGF2a. During days 12 to 16 postestrus, progesterone modulates by preventing the occurrence of the secretion of PGF final peaks of Pz?2a while maintaining secretion of PGF2a In the absence of a blastocyst, from the uterus. increased PGF2a brings about luteal regression and concentrations of progesterone begin decreasing on days 16 and 17, resulting in the large, final peaks of PGF a. At the same time, increasing concentrations of estra& 101-178 may further sensitize the corpus luteum to the luteolytic In the presence of a blastocyst, effects of PGF2a. progesterone permits a rise in and continued secretion of PGE2 from the endometrium, perhaps in response to secretion of oTP-1 from the blastocyst. Increased secretion of PGE2 reduces the sensitivity of the corpus luteum to the effects of PGF2a and secretion of progesterone is maintained. Continued secretion of progesterone from the corpus luteum maintains uterine quiescence and provides and the optimal environment for embryo survival establishment of the pregnancy.
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ACKNOWLEDGHENTS
Published with the approval of the Director of the west Virginia Agricultural and Forestry Experiment Station as Scientific Paper No. 1980. Supported by Hatch Project 224 (NE-72). DLV was supported by NIH Postdoctoral Training Grant AM0 7321-04 T32. The authors are indebted to Dr. John Pike, The Upjohn Co., Kalamazoo, MI, for generous supplies of authentic PGF a and PGE standards, to Dr. Lawrence Levine, % randeis &ft:r-",Y",",Y Waltham, MA for the highly specific antiserum to PGF2a (RA 546-Cl51 and to Dr. Norman Mason, The Lilly Research Labs, Indianapolis, IN, for the highly specific antiserum to PGE (No. 3-1-4-75). We gratefully acknowledge the tee%nical assistance of Phyllis Jenkins. REFERENCES 1.
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Mapletoft, R.J., D.R. Lapin and O.J. Ginther. The ovarian artery as the final component of the local pathway between a gravid uterine horn and ovary in ewes. Biol. Reprod. LI:414. 1976.
22.
R.L. Fogwell and E.K. Lewis, G.S., P.E. Jenkins, Inskeep. Concentrations of prostaglandins E2 and F2a and their relationship to luteal function in Sci. early pregnant ewes. J. Anim. ez:1314. 1978.
23.
Moor, R.M. and L.E.A. Effect of the sheep: on luteal function. 1966.
24.
and D.T. Baird. Henderson, K.M., R.J. Scaramuxxi Simultaneous infusion of prostaglandin E2 antagonizes the luteolytic action of prostaglandin F2a LB y&m. J. Endocrinol. =:379. 1977.
25.
Mapletoft, R.J., K.F. Miller and O.J. Ginther. Effects of PGF2a and PGE2 on corpora lutea in J. Anim. Sci. 41 (Suppl 1):185. 1977. ewes.
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Rowson. The corpus of the removal of J. Endocrinol.
luteum embryos 243233.
729
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26.
Reynolds, L.P., J. Stigler, G.L. Eoyer, R.R. Magness, J.M. Huie, T.P. Huecksteadt, G.L. Whysong, H.R. Behrman and C.W. Weems. Effect of PGEl or PGE2 on PGF u-induced luteolysis in 1981. nonbred ewes. Prostag% andins a:957.
27.
Pratt, B.R., R.L. Butcher and E.K. Inskeep. Antiluteolytic effect of the conceptus and of PGE2 in ewes. J. Anim. Sci. 46~784. 1977.
28.
Huecksteadt, T.P. and C.W. Weems. Effect of PGE on normal luteolysis and PGEl or PGE2 in IUDinduced luteolysis in ewes. Pharmacologist 2Q:233. 1978.
29.
M. Huie, G. Whysong and C. Hoyer, G., R. Magness, Weems. Effects of prostaglandin El (PGEl) on estradiol-176 induced luteolysis in the nonpregnant ewe. Prostagland. Leuk. Med. LL:137. 1985.
30.
Weems, C., G. Hoyer, R. Magness, G. Whysong and M. Huie. Effect of prostaglandin E2 (PGE2) on estradiol-17f3-induced luteolysis in the nonpregnant ewe. Prostaglandins a:233. 1985.
31.
Huie, J.M., R.R. Magness, L.P. Reynolds, G.L. Hoyer, T.P. Huecksteadt, M.L. Colcord, B. Stalcup, G.L. Whysong and C.W. Weems. Effect of chronic ipsilateral and contralateral intrauterine infusion of prostaglandin El (PGEl) on luteal function of unilaterally ovariectomized ewes. Prostaglandins 21:945. 1981.
32.
Magness, R.R., J.M. Huie, G.L. Hoyer, T.P. Huecksteadt, L.P. Reynolds, G.J. Seperich, G. Whysong and C.W. Weems. Effect of chronic ipsilateral or contralateral intrauterine infusion of prostaglandin E2 (PGE2) on luteal function of unilaterally ovariectomized ewes. Prostagland. Med. h:389. 1981.
33.
Speroff, L. and P. Ramwell. Prostaglandin stimulation of in ~&IO_ progesterone synthesis. J. Clin. Endocrinol. Metab. 3,Q:345. 1970.
34.
Marsh, J. The effect of prostaglandins on the adenyl cyclase of the bovine corpus luteum. Ann. N.Y. Acad. Sci. l&Q:416. 1971.
35.
Godkin, J., D. Black and R. Duby. Stimulation of cyclic AMP and progesterone synthesis by LB, PGE3 and isoproterenol in the bovine CL in y&m. Biol. Reprod. LL:514. 1977.
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1986 VOL. 31 NO. 4
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36.
Fitz, T.A., P.B. Hoyer and G.D. Niswender. Interactions of prostaglandins subpopulations of ovine luteal cells. I. Stimulatorv effects of prostaglandins El, E2 and 12. Prostaglandins a&:119. 1984.
37.
Fitz, T.A., E.J. Mock, M.H. Mayan and G.D. Niswender. Interactions of prostaglandins with subpopulations of ovine luteal cells. II. Inhibitory effects of PGF a and protection by PGE2. Prostaglandins 28:123. 1984.
38.
Pexton, J.E., S.P. Ford, L. Wilson, Jr., R.L. Butcher and E.K. Inskeep. Prostaglandins F in uterine tissue and venous plasma of ewes with intrauterine devices. J. Anim. Sci. &:144. 1975.
39.
Wilson, L., progesterone PGE, TxB2 and rat uterus. 1981.
40.
Gimeno, A.L., A.M. Franchi, E.T. Gonzalez and M.F. Gimeno. Progesterone and the output of prostaglandin F from the uterus of ovariectomized rats. Priming or withdrawal. Prostagland. Leuk. Med. L&:289. 1984.
41.
Ford, S.P., C.W. Weems, R.E. Pitts, J.E. Pexton, R.L. Butcher and E.K. Inskeep. Effects of estradiol-178 and progesterone on prostaglandin F in sheep uteri. Anim. Sci. g&1407.
42.
Shaik, Steroids
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Effect of Jr. and D. Stanisic. and estradiol-178 on uterine PGF, 6-keto-PGFla levels in the pregnant Biol. Reprod. 24 (Suppl. 1):159A.
K. the ovarian
S.K. Saksena. plasma and F
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Gengenbach, D.R., J.E. Hixon and W. Hansel. A luteolytic interaction between estradiol and prostaglandin F2a in hysterectomized ewes. Biol. Reprod. S&:571. 1977.
45.
Hixon, J.E., C.A. Pimentel, P.G. Weston, E.P. Chafetz, R.D. Shanks and W. Hansel. A luteolytic interaction between estradiol benzoate and prostaglandin F2a in cattle. J. Anim. Sci. lh:1190. 1983.
46.
Karsch, F.J., J.W. Noveroske, J.F. Roche, H.W. Norton and A.V. Nalbandov. Maintenance of ovine corpora lutea in the absence of ovarian follicles. Endocrinology U:1228. 1970.
47.
Ginther, O.J. Response of corpora lutea to cauterization of follicles in sheep. Am. J. Vet. Res. 22:59. 1971.
48.
Larson, G.H., P.E. Lewis, R.A. Dailey and E.K. Inskeep. Effects of stage of the estrous cycle on FSH pattern and subsequent luteal function in response to bovine follicular fluid. J. Anim. Sci. hl (Suppl. 1): submitted. 1985.
49.
Inskeep, E.K., W.J. Smutney, R.L. Butcher and J.E. Pexton. Effects of intrafollicular injections of prostaglandins in non-pregnant and pregnant ewes. J. Anim. Sci. 41:1098. 1975.
50.
Silvia, W.J. and G.D. Niswender. Maintenance of the corpus luteum of early pregnancy in the ewe. III. Differences between pregnant and nonpregnant ewes in responsiveness to prostaglandin F2a. J. Anim. Sci. 52:746. 1984.
51.
Silvia, W.J., T.A. Fitz, M.H. Mayan and G.D. Niswender. Cellular and molecular mechanisms involved in luteolysis and maternal recognition of pregnancy in the ewe. Anim. Reprod. Sci. 2:57. 1904.
52.
Marcus, G.J. Prostaglandin formation by the sheep embryo and endometrium as an indication of maternal recognition of pregnancy. Biol. Reprod. 21:56. 1981.
53.
Hyland, J.H., J-G. Manns and W.D. Humphrey. Prostaglandin production by ovine endometrium & ti!XQ. J. Reprod. Fertil. hs:299. 1982.
732
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PROSTAGLANDINS
54.
Martal, J., M.C. LaCroix, C. Loundes, M. Saunier and S. Wintenberger-Torres. Trophoblastin, an antiluteolytic protein present in early pregnancy in sheep. J. Reprod. Fertil. Z&63. 1979.
55.
Godkin, J.D., F.W. Baxer, J. Moffatt, F. Sessions and R.M. Roberts. Purification and properties of a major, low molecular weight protein released by the trophobast of sheep blastocysts at day 13-21. J. Reprod. Fertil. hl:141. 1982.
56.
Godkin, J.D., F.W. Baxer and R.M. Roberts. Ovine Trophoblatin Protein 1, an early secreted blastocyst protein, binds specifically to uterine and affects protein synthesis. Endocrinology LL4:120. 1984.
57.
Godkin, J.D., F.W. Baxer, W.W. Thatcher and R.M. Roberts. Proteins released by cultured day 15-16 conceptuses prolong luteal maintenance when introduced into uterine lumen of cyclic ewes. J. Reprod. Fertil. U:57. 1984.
Editor: H. Behrman
APRIL 1986VOL. 3 1 NO. 4
Received: 9-3-85
Accepted: 3-13-86
733
ROLE OF PROGESTERONE IN REGULATING UTBROOVARIAR VENOUS CORCRRTRATIORS OF PGF a AND PGE DURIRG THE ESTROOS CYC2R Am RARZY PRRGRARCY IR EWES D.L. VINCENT and E.K. INSKEEP Division of Animal and Veterinary Sciences West Virginia University Horgantown, West Virginia 26506-6108 ABSTRACT The role of progesterone in regulation of uteroovarian venous concentrations of prostaglandins F2e(PGF2a) 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 ovariectomixed on day12 and of these, 7 mated and 5 unmated ewes were given10 mgprogesterone 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 PGE in the uteroovarian vein than in unmated ewes. Ovarieczomy 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 PGF2a or the patterns of the natural logarithm (In) of the variance of PGF20. Ovariectomy resulted in higher mean concentrations and In variances of PGF2a on day 13 and lower mean concentrations and In variances of PGF2a on days 15 and 16. Replacement with progesterone prevented these changes in patterns of mean concentrations and In variances of PGF2a following ovariectomy. It is concluded that progesterone regulates the release of PGF2a from the uterus, maintaining high concentrations while also preventing the occurrence of the final peaks of PGF2a 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.
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IN'J!RODDCTIOl'd
Prostaglandin P2a (PGF2a) is the major naturally occurring luteolysin in the ewe (1,2). Luteal regression results from uterine secretion of PGF2= beginning on d 11 to 13 postestrus (3,4). Progesterone appears to play a role in the regulation of uterine secretion of PGF a from the uterus. In ovariectomixed ewes, treatmen % with progesterone for several days increased uterine release (5) or caruncular endometrial concentrations (6) of PGF2a. A period of progestational influence has been proposed to regulate the timing of initial peaks of secretion of PGF2a may (4r7). Ottobre et al. (8) reported that progesterone be required only through d 9 of the cycle for increased secretion of PGF2a from the uterus to begin by day 12. The effects of the uterine luteolysin must be negated for pregnancy to be established successfully in the ewe. The mechanism by which the embryo prevents luteal regression is not clear. It has been suggested by many that uterine secretion of PGF 2cis suppressed by action of the embryo (3,9-11). The absence, in early pregnant ewes of very high concentrations of PGF a in plasma associated with the follicular phase (day 1 5 to 17) in nonpregnant ewes has been taken as evidence for embryonic suppression of uterine secretion of PGF2a. Yet this secretion of PGF occurs as progesterone concentrations are decreasing an8 luteal regression is nearing completion. Others have found that the pattern of secretion of PGF2aby the uterus in the early pregnant ewe is not different from that observed in nonpregnant ewes on comparable days postestrus, particularly nearer to the onset of luteolysis (12-18). Since concentrations of PGF a in blood leaving the uterus of pregnant and non-pregnan$ ewes do not differ at the time of onset of luteal regression, the actions of PGF2a must be prevented by some antiluteolytic factor(s). The antiluteolytic effect of the embryo is expressed locally (19,20) and is mediated by some blood borne factor(s) which passes from the uterine vein to the ovarian artery (20,21). One might expect this factor(s) to be lipid soluble and to have chemical properties similar to the luteolysin, PGF2a. Although initial studies by Wilson et al. (12) and Lewis et al. (22) did not detect increased concentrations of prostaglandin E2 ( PGE2) in the uteroovarian vein of pregnant ewes, more recent work (16-18) has shown that concentrations of PGE2 in the uteroovarian vein of pregnant ewes increase at the time of the critical period for maternal recognition of pregnancy, days 12 to 13 postestrus (23). Prostaglandins of the E series have been shown
716
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PROSTAGLANDINS
to lessen the effects of PGF a when given concomitantly Spontaneous lutea ? regression or that induced (24-26). by estradiol or intrauterine devices have been delayed by uterine luminal infusion of PGEl or PGE2 (27-31). In order to exert this effect, PGE or PGE must be infused into the uterine horn or broad + igamen ? adjacent to the ovary bearing the corpus luteum (29-32). Secretion of progesterone by bovine luteal tissue (33-35) or dispersed ovine large luteal cells (36,371 tiyi&o was stimulated by PGE1 and PGE2. The morphological changes and reduced viability seen following incubation of dispersed large ovine luteal cells with PGF2a were prevented if PGE2 was added to the medium (37). The purpose of this experiment was to examine the role of progesterone in regulating uterine secretion of PGF2a and PGE2 during the estrous cycle and early pregnancy in the ewe. MRTEODSARD HATBRIALS
Animals and Surgical
Procedures
Mature ewes of mixed breeding were pastured with brisket-painted, vasectomized rams and checked for standing estrus twice daily. Ewes with at least one previous estrous cycle of 15.5 to 19 days were selected randomly for either fertile or no mating. Ewes assigned to fertile mating were penned with a brisket-painted, intact ram at first detection of standing estrus (day 0). Ewes assigned to no mating remained in the main flock. On day 12 after estrus, each ewe was anesthetized with sodium pentobarbital and the reproductive tract was exposed through a midventral abdominal incision. A siliconized, polyvinyl catheter was placed into a uteroovarian vein contralateral to the corpus luteum as described by Ottobre et al. (8) and Silvia et al. (18). Ewes in the intact control group received no further treatment (n = 7 unmated and 6 mated). Uteroovarian venous concentrations of PGF2a and PGE2 were compared among these ewes and those in two other experimental groups: bilateral ovariectomy on day 12 postestrus (n = 7 unmated and 8 mated) and bilateral ovariectomy on day 12 postestrus plus immediate replacement with progesterone (n = 6 unmated and 7 mated). Replacement therapy with progesterone consisted of a subcutaneous injection of 10 mg of progesterone and the placement of an intravaginal sponge containing 30 mg of progesterone. Blood was collected from the indwelling catheters, daily at 15 min intervals during 3-h periods beginning between 0600 and 1100 on day 13 after estrus. Sampling was continued, when possible, through day 16 postestrus.
AFWL 1986VOL. 31 NO. 4
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PROSTAGLANDINS
Samples were processed as described by Pexton et al. (38) and the plasma was stored at -20 C until assayed for prostaglandins. To maintain catheter patency all ewes received a constant infusion of 200 ml/day of sterile saline containing 200 IU sodium heparin and 20000 IU potassium penicillin G’per ml into the indwelling uteroovarian venous catheters via Buchler infusion pumps. Heparin infusion was interrupted during the 3-h sampling period. During that time each day, catheters were flushed with 2 to 3 ml of sterile saline containing 200 IU/ml sodium heparin after each blood sample. On day 17 or at loss of catheter patency, ewes were sacrificed with an overdose of sodium pentobarbital. Their uteri were excised and flushed for the presence of blastocysts to confirm pregnancy. Assays
for
PGF2a and PGE2
by radioimmuConcentrations of PGF a were quantified noassay, as described by $ exton et al. (38) and Lewis et al. (22). Sensitivity of the assay was 30 pg/tube and volumes gfplasmaassayed ranged from 50to 200 ul. Recovery of H-PGF2a after extraction and column chromatoEach sample was graphy was measured in each assay. adjusted for procedural losses and external recoveries averaged 48.7 +_ 1.2% for 110 assays. Within and between assay coefficients of variation were 11.2% and 22.6%, respectively. Concentrations of PGE in the uteroovarian venous described plasma were quantified by t?1e radioimmunoassay by Lewis et al. (22) and Silvia et al. (18). Procedural losses were estimated in each assay by measuring the recovery of 3H-PGE2 after extraction and column chromatoEach sample was adjusted for procedural losses graphy. and external recoveries averaged 59.5 +- 1.2% over 110 assays. Within and between assay coefficients of variation were 8.8% and 17.4%, respectively. Sensitivity of the assay was 2.5 pg/tube and volumes assayed ranged from 50 to 200 ul. Statistical
Analyses
Treatments were arranged in a 2 x 3 factorial design with pregnancy status and ovarian status as main effects. Patterns of mean concentrations of PGFp and PGE2 within sampling period were compared among groups using analysis of variance for a completely randomized split-plot design with treatment as the main plot and day as the subplot. Because differences in patterns of secretion of PGFpand PGE2 may be missed by examination of only means within period and because differences in amplitudes of peaks might occur as a result of treatment, patterns of fluctua-
718
APRIL 1986 VOL. 3 1 NO. 4
PROSTAGLANDINS
tions in concentrations of PGF2a and PGE2 among groups were compared. This was done by determining the variances for the thirteen samples collected within each sampling period from each ewe (18). To reduce the large range of these variances, they were transformed to their natural logarithms. Patterns of natural logarithms of variances (In variance) of concentrations of PGF2a and PGE2 within sampling period were then compared among groups using analysis of variance for a split-plot design. Patterns of mean concentrations and In variance of PGF2a and PGE2 were compared using preplanned orthogonal contrasts. RESULTS
Blastocysts were found in 7 of 8 mated ewes that were intact and 6 of 8 mated ewes treated with progesterone after ovariectomy. Only ewes having confirmed pregnancies in these groups were included in the data analysis. Blastocysts were not found in any (0 of 8) mated ewes Because it was ovariectomized on day 12 postestrus. impossible to confirm pregnancy prior to ovariectomy in these ewes and because of a combined pregnancy rate of 81% in the other mated ewes, it was assumed that most of the ewes mated to fertile rams and ovariectomized were pregnant prior to ovariectomy. Therefore, all ewes from this group were included in the analysis of the data. Mated and unmated ewes did not differ in patterns of mean concentrations or In variances of PGF2a on days 13 through 16 postestrus. Ovariectomy resulted in higher mean concentrations of PGF a on day 13 (P(.Ol) and lower mean concentrations of PGa2a on days 15 and 16 (P&OS). Replacement of progesterone prevented the increase on day 13 and the decrease on days 15 and 16. Thus ovariectomized ewes had a pattern of mean concentrations of PGFpdifferent from both intact ewes and ovariectomized ewes treated with progesterone (P&001, figure 1) on days 13 through 16. Patterns of In variance of PGF2a of ovariectomized ewes also differed from those in intact ewes and progesterone-treated ovariectomized ewes (P&001, figure 2). Neither mean concentrations within day, patterns of mean concentrations, In variances within day nor patterns of In variance of PGF2a were different intact ewes between and progesterone-treated ovariectomized ewes. Mated and unmated ewes differed in their patterns of mean concentrations of PGE2 on days 13 through 16 (P&OS; figure 3). Ovariectomy had no effect in unmated ewes (P&l, figure 3, panel A) but prevented the rise in PGE2 observed on days 13 to 16 in mated ewes (P&OS, figure 3, panel B). Replacement of progesterone after ovariectomy restored the increase in PGE2 in mated ewes but had no effect in unmated ewes (figure 3). The In variance of PGE2 increased linearly with day in mated ewes which were
APRIL 1986 VOL. 31 NO. 4
719
PROSTAGLANDINS
2.0
-\ \
I
\ \ \
1.5
\
1.0
0.5
m
F
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DAYS
720
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Fig. 1.
\
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14
15
AFTER
ESTRUS
16
The effects of ovariectomy and progesterone replacement on mean daily concentrations of PGF2a in uteroovarian venous blood. Legend: (. .) intact ewes, IA-----A ovariectomized ewes and h -3 ovariectomized ewes treated with progesterone. The pattern for ovariectomized ewes differs (P1.001) from those for intact ewes and progesteronetreated, ovariectomized ewes.
APRIL
1986 VOL. 31 NO. 4
PROSTAGLANDINS
.
.
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12
\
12
\
.
.
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DAYS AFTER ESTRUS
Fig. 2.
The effects of ovariectomy and progesterone replacement on patterns of In variance of PGF2a within day within ewes. Legend: (&____d intact ewes, ovariectomized ewes and (, .I, ovariectomlzed ewes treated with progesterone. Patterns for ovariectomized ewes are different (P(.OOl) from those for intact ewes and progesteronetreated, ovariectomized ewes.
APRIL1986VOL. 31N0.4
721
PROSTAGLANDINS
v
.
.
.
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Fig.
722
3.
14 AFTER
15 10 ESTRUS
The effect of ovariectomy and progesterone replacement on mean daily concentrations of PGE2 in uteroovarian venous blood in unmated ewes (panel A) and mated ewes (panel B). Legend: * 0 intact ewes, (A----& ovariectomlzed ewes and (B_____I) ovariectomized treated with progesterone. Patterns for unmated ewes do not differ with treatment (P2.1, panel A). Among mated ewes, patterns for ovariectomized ewes differ (P1.05, panel B) from those for intact ewes and progesteronetreated, ovar iectomized ewes.
APRIL 1986 VOL. 31 NO. 4
PROSTAGLANDINS
intact or treated with progesterone after ovariectomy (PI.001)but did not change with day among unmated ewes or ovariectomixed, mated ewes (figure 4). DISCUSSION Progesterone is required for the timing of the onset of the initial peaks of secretion of PGF a which usually occur on day 12 of the estrous cycle (4,5 ,8). Removal of ovaries on day 12 resulted in different patterns of mean daily concentrations of PGF2a than those seen in intact ewes on day 13 through 16 postestrus. Concentrations of PGF2a in the uteroovarian veins of ovariectomixed ewes rose rapidly on day 13, in a manner similar to the large final peaks of PGF2,x observed at the end of the estrous cycle, with luteal regression (3-5,7). By days 15 and 16, concentrations of PGF2ain ovariectomixed ewes had declined to lower levels than in the intact ewes. Replacement of progesterone in ovariectomixed ewes restored patterns of mean daily concentrations of PGF2a to values not different from those seen in intact ewes. Thus progesterone therapy prevented large increases in PGF2a observed after ovariectomy while also maintaining the high concentrations of PGF2a which eventually cause complete luteal regression in the intact ewe. In contrast, Ottobre et al. (8) reported that progesterone was not necessary to sustain normal patterns of secretion of PGF2a on days 15 and 16 in ewes ovariectomixed on day 14. No treatment differences in uteroovarian venous concentrations of PGFzQ were observed among groups in which progesterone was removed, with or without estrogen replacement, when compared to intact control ewes. However, the intact ewes were all undergoing natural luteolysis, so the rapid rise and fall in PGF2a in response to ovariectomy may have coincided with the same changes in response to the falling concentrations of progesterone in intact ewes. Removal of progesterone on day 14 by removal of either ovaries or corpora lutea, resulted in an initial increase in uteroovarian venous concentrations of PGF a followed by a gradual decline (8). A similar pattern oS secretion of PGF2a was observed in ewes ovariectomixed on day 12 in the present experiment. Removal of progesterone has been shown to increase concentrations of PGF2a in the uterus of other species. In the pregnant rat near term, Wilson and Stanisic (39) observed that following ovariectomy on day 19, concentrations of PGF2a in the uterus increased over intact controls. Progesterone replacement in ovariectomixed rats lowered uterine concentrations of PGF ato levels not different from intact control rats (39P. Incubation ti yitro of uteri from ovariectomixed rats with high concentrations of progesterone resulted in a large increase in release of PGF2q into the medium following removal of progesterone (40). Progesterone may
APRIL 1986VOL.31N0.4
723
PROSTAGLANDINS
9 :
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.
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14 DAYS
Fig. 4.
724
AFTER
15
16
ESTRUS
The effects of ovariectomy and progesterone replacement on patterns of In variance of PGE within day ewes in unmated ewes (panel A) an !I mated ewes (panel B). Legend: Cc_--_.@ intt,ci ewes, CA-----4 ovariectomlzed ewes (I_____.) ovariectomized ewes treatd with progesterone. Patterns for unmated do not differ with treatment (PZ.1, panel A). Patterns for mated ewes increase linearly (PL.05, panel B) from intact ewes and progesterone-treated, ovariectomized ewes.
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regulate secretion of PGF2a in two ways; first, by timing the initial peaks of secretion early in the estrous cycle by modulating secretion of PGF2a until luteal and second, Then the uterus is released from regression is complete. the inhibition of progesterone and the large final peaks of secretion of PGFza are observed with falling concentrations of progesterone. increased uterine release and (or) Estradiol-l7g caruncular or endometrial concentrations of PGF2a if given after several days of exogenous (5,6,41) or endogenous (9,411 progesterone. Higher concentrations of estradiol in plasma have been associated temporally with the release This has been of PGF a in several species (1,4,42,43). true for the maximal uteroovarian concentraparticu 3 arly tions of PGF a during luteal regression in the ewe have led some researchers Resu 3 ts such as these (4r5r7). to suggest that endogenous estrogen stimulates production of PGF2a by the uterus after a period of prior progestational influence in the nonpregnant ewe (1). However, Baird et al. (7) and Ottobre et al. (4) found no relationship of the initial increases in PGF2a to increases in estradiol-178 during the mid-luteal phase. Recently, Ottobre et al. (9) observed that exogenous estradiol did not increase uteroovarian venous plasma concentrations of PGF a in ewes ovariectomixed on day 14 postestrus. It mus E be recognized that estrogen may have a role in luteolysis that does not involve uterine secretion of PGF a. Evidence for such an action lies in the observations t at was more effective the combination of PGF2a and estradiol in causing luteolysis in hysterectomixed ewes (44) or in heifers (45) than treatments with either PGF2a or estrogen alone. Such an action may account for the delay in completion of luteolysis in ewes following destruction of ovarian follicles (46, 47) or following inhibition of FSH by injection of follicular fluid (48). Given that secretion of PGF during days 12 through 16 is very similar in pregnan ? and nonpregnant ewes present study) the action of PGF2a must be (2,17,18, prevented if the corpus luteum is to be maintained and pregnancy is to be established successfully. Given further that injections of PGF2a were less effective in inducing luteal regression in pregnant than in nonpregnant ewes (21, 27, 49-511, the action of PGF2a must be prevented by some antiluteolytic factor(s). That the embryo produces and (or) controls production of this factor(s) is supported by the recent report by Silvia and Niswender (50) that more PGF was required to cause luteolysis in ewes with two em2D” ryos than in those with a single embryo. The nature of the antiluteolysin is not clear. Blastocysts at the critical time for maternal recognition
2
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of pregnancy produce both prostaglandins (17,52,53) and proteins (54-57). Ovine trophoblast protein 1 (oTP-l), the major protein secreted from day 13 to 21 blastocysts, binds to the endometrium (56) and extends luteal function when infused into the uterine lumen of nonpregnant ewes (57). Endometrial and (or) uteroovarian venous concentrations of PGE2 are increased during the same period (1618,52, present study) in pregnant ewes. PGEl and PGE have been shown to counteract the luteolytic action o3 (25-32) and hn PGF2a to varying degrees, both ti ykQ tif;rQ (36,371. Since the antiluteolytic effect of the blastocyst was shown to occur locally (201, via blood borne factors (21,231, one can speculate that the lipid soluble PGE2 may be a stronger candidate for the antiluteolytic agent at the ovarian level than oTP-1. However, oTP-1 or some other conceptus-derived protein could represent the primary signal from the free, floating blastocyst to the endometrium to stimulate endometrial production of PGE2, or the two substances (oTP-1 and PGE2) could act additively, synergistically or sequentially to maintain corpora lutea of pregnancy. From these data and previous literature discussed above and reviewed earlier by Ottobre et al. (81, one can propose an explanation for the regulation of uterine secretion of prostaglandins by steroids. At estrus, receptors for progesterone in the endometrium are induced by increased concentrations of estradiol-17B (see 8 for review). Early in the estrous cycle or pregnancy (days 4 to 9 postestrus), progesterone establishes the capacity of the endometrium to secrete prostaglandins and times the occurrence of the initial peaks of secretion of PGF2a. During days 12 to 16 postestrus, progesterone modulates by preventing the occurrence of the secretion of PGF final peaks of Pz?2a while maintaining secretion of PGF2a In the absence of a blastocyst, from the uterus. increased PGF2a brings about luteal regression and concentrations of progesterone begin decreasing on days 16 and 17, resulting in the large, final peaks of PGF a. At the same time, increasing concentrations of estra& 101-178 may further sensitize the corpus luteum to the luteolytic In the presence of a blastocyst, effects of PGF2a. progesterone permits a rise in and continued secretion of PGE2 from the endometrium, perhaps in response to secretion of oTP-1 from the blastocyst. Increased secretion of PGE2 reduces the sensitivity of the corpus luteum to the effects of PGF2a and secretion of progesterone is maintained. Continued secretion of progesterone from the corpus luteum maintains uterine quiescence and provides and the optimal environment for embryo survival establishment of the pregnancy.
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ACKNOWLEDGHENTS
Published with the approval of the Director of the west Virginia Agricultural and Forestry Experiment Station as Scientific Paper No. 1980. Supported by Hatch Project 224 (NE-72). DLV was supported by NIH Postdoctoral Training Grant AM0 7321-04 T32. The authors are indebted to Dr. John Pike, The Upjohn Co., Kalamazoo, MI, for generous supplies of authentic PGF a and PGE standards, to Dr. Lawrence Levine, % randeis &ft:r-",Y",",Y Waltham, MA for the highly specific antiserum to PGF2a (RA 546-Cl51 and to Dr. Norman Mason, The Lilly Research Labs, Indianapolis, IN, for the highly specific antiserum to PGE (No. 3-1-4-75). We gratefully acknowledge the tee%nical assistance of Phyllis Jenkins. REFERENCES 1.
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Editor: H. Behrman
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Received: 9-3-85
Accepted: 3-13-86
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