The effect of prostaglandin F2 alpha on relaxin release differs in the cyclic and pregnant sow.
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Animals↗
Biomedical subjects
G S Lewis
Publications and source records attributed to G S Lewis.
Bovine placental prostaglandin synthesis in vitro as it relates to placental separation.
Bovine placentomes were collected during late gestation, prepartum and immediately postpartum. Postpartum tissues were collected prior to fetal membrane separation. Maternal and fetal placentomal components each were examined for their ability to synthesize prostaglandins (PG's) from arachidonic acid (AA) and metabolize PGF2 alpha and PGE2 in vitro. Maternal placental PG synthesis was lower (P less than .05) than that for fetal placental tissue and was primarily PGF's. Fetal placental PG synthesis increased (P less than .05) prepartum and was primarily PGE's. Fetal placental PGE production predominated (P less than .05) postpartum if the fetal membranes were retained, while PGF production predominated (P less than .05) if the membranes were released. Maternal and fetal placental tissues were unable to convert PGE2 to PGF2 alpha (P greater than .05). Postpartum fetal placental tissue was able to convert PGF2 alpha to PGE2 (P less than .05) if the fetal membranes were retained but not if the membranes were released (P greater than .05). These results indicate that fetal placental synthesis of PGF's may be related to placental membrane separation. The shift in fetal placental PG production from PGE's to PGF's may be due to a cessation of the ability of released fetal tissue to convert PGF2 alpha to PGE2.
Animals↗
Effects of suckling, progestogen-impregnated pessaries or hysterectomy on ovarian function in autumn-lambing postpartum ewes.
In three experiments, we examined the effects of suckling, progestogen treatment, hysterectomy or exogenous gonadotropin releasing hormone (GnRH) on ovarian function in autumn-lambing, postpartum ewes. In each experiment, GnRH was injected on approximately d 25 postpartum. Suckling reduced (P less than .01) GnRH-induced release of luteinizing hormone (LH) but not of follicle stimulating hormone (FSH), and reduced (P less than .05) the proportion of ewes that developed corpora lutea in response to GnRH. Suckling had no effect on duration (8.8 d) of GnRH-induced luteal phases. Progestogen prior to GnRH increased (P less than .01) the duration of the first luteal phase (10.1 vs 7.6 d; progestogen-treated ewes vs control ewes), but progestogen did not affect the release of LH or FSH. Progestogen treatment did not alter the interval from parturition to the first detected estrus (42.6 d). The concentration of 13,14-dihydro-15-keto-PGF2 alpha (PGFM) just after lambing was greater than 400 pg/ml of jugular plasma, but concentrations of PGFM declined thereafter. Hysterectomy the day after lambing hastened (P less than .001) the decline in concentrations of PGFM, indicating that prostaglandins from the postpartum uterus probably caused the high concentrations of PGFM in jugular plasma. Hysterectomy reduced (P less than .05) the interval from parturition to detectable luteal function (19.6 vs 25.3 d) and enhanced (P less than .001) luteal production of progesterone. This study of autumn-lambing ewes indicates that the uterus has a negative effect on ovarian function and that suckling and progestogen affect ovarian response to GnRH.
Animals↗
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.
Animals↗
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.
Animals↗
Endocrine profiles associated with life span of induced corpora lutea in postpartum beef cows.
Two experiments were designed to examine whether hormonal profiles were related to luteal life span in pluriparous postpartum anestrous beef cows. Cows (Exp. 1, n = 34; Exp. 2, n = 23) received norgestomet (N) for 9 d or served as controls (C). Each cow received 1,000 IU human chorionic gonadotropin (hCG) 48 h after removal of N (d 0). Blood samples collected every 15 min for 8 h on d -5, 3 and 5 (Exp. 1) or on d -10 and -1 (Exp. 2) were assayed for luteinizing hormone (LH) and follicle stimulating hormone (FSH). Cortisol was determined in hourly samples collected on d -5 and in samples collected every 2 min during suckling on the same day (Exp. 1). Concentrations of 15-keto-13,14-dihydro-PGF2 alpha (PGFM) were determined in samples collected at 15-min intervals for 2 h on d -5, 3, 5 and 10 (Exp. 1). Estradiol-17 beta was measured in samples collected on d -5 (Exp. 1) or on d -10 and -1 (Exp. 2). Life span of induced corpora lutea was longer (P less than .05) in N than C cows. Percentages of N cows in which corpora lutea, formed in response to hCG, exhibited a normal life span were 83% on farm 1 and 25% on farm 2 (Exp. 1), and 90% (Exp. 2), compared with 0% in C cows. Concentrations of FSH were not affected by N but were lower (P less than .05) on d -5 in cows on farm 2 (.6 +/- .1 ng/ml) than in cows on farm 1 (.8 +/- .1 ng/ml). On d -5, a treatment X farm interaction (P less than .05) for mean LH was observed and frequency of pulses of LH was higher (P less than .01) in N than C cows (2.7 +/- .4 vs. .8 +/- .8 pulses/8 h). Neither cortisol nor PGFM was affected by N. Estradiol was increased in d -1 (6.1 +/- .5 vs 2.6 +/- .8 pg/ml; P less than .01) by N. It is suggested that pre-treatment with N enhanced life span of induced corpora lutea, in part, by influencing secretion of LH and development of follicles, but a threshold concentration of FSH was required for N to exert this effect.
Anestrus↗
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.
Animals↗
Uterine involution and postpartum ovarian activity in Nili-Ravi buffaloes.
Uterine involution and postpartum ovarian activity were studied in 53 Nili-Ravi buffaloes. Mean intervals to uterine involution (26 days), regression of the corpus albicans of pregnancy (22 days), resumption of follicular activity (21 days) and first postpartum estrus (56 days) were not affected by the month of calving or age. Mean interval to formation of first corpus luteum (CL) after calving as indicated by progesterone in plasma (>/= 1.5 ng/ml) was 23.8 +/- 1.7 days, but only 52% of these CL were palpable. The number of CL formed before first postpartum estrus ranged from zero to five per buffalo; mean values based upon progesterone and palpation were 1.6 +/- 1.3 and 0.8 +/- 0.2, respectively. Based upon either progesterone or palpation, length of first postpartum luteal phase (7.9 or 6.6 days) was shorter than the luteal phase immediately preceeding the first estrus (12.1 or 8.9 days). Intervals from regular cyclic ovarian activity was not established until first estrus and intervals from the end of one luteal phase to the onset of the next were as long as three weeks. High concentrations of progesterone (>/= 1.5 ng/ml) on the day of behavioral estrus were seen in 23% of the buffaloes studied.
Journal Article↗
Characterization of proteins produced in vitro by periattachment bovine conceptuses.
Bovine conceptuses from Days 16 (n = 4), 19 (n = 6), 22 (n = 3), and 24 (n = 4), and chorion from Day 69 (estrus/mating = Day 0) were cultured for 24 h in modified minimum essential medium (MEM) in the presence of radioactive L-leucine [( 3H] leucine) to characterize de novo synthesis and release of proteins. Proteins released into MEM were identified by two-dimensional polyacrylamide gel electrophoresis, fluorography, and gel and ion exchange chromatography. Major polypeptides identified in MEM were different from those identified in conceptus and chorionic tissues. Both uptake of [3H] leucine and quality of polypeptides produced de novo and released into MEM were related to stage of conceptus development. Percent retention of [3H] leucine in MEM was lowest (P less than 0.01) in Day 16 cultures (1.2 +/- 4.1%), increased in Days 19 (16.8 +/- 3.7%) and 22 cultures (20.9 +/- 5.8%), and decreased (P less than 0.07) in Day 24 cultures (6.9 +/- 4.1%). Complexity of polypeptides increased after Day 16. Days 16, 19, 22 and 24 conceptus culture MEM was enriched in low-Mr, acidic polypeptides (Mr/isoelectric point ranges: 22K-26K/6.5-5.6, 20K-26K/5.5-5.4, and 16K-20K/5.0-4.5), which were not prominent products of Day 29 and 69 tissues. A high-Mr (Mr +/- SEM; 735K +/- 22K) glycoprotein was produced by all conceptus and chorionic tissues. The transient nature of production of low-Mr polypeptides suggests that they may be required during the periattachment period.
Amino Acids↗
Effects of heat stress during pregnancy on postpartum reproductive changes in Holstein cows.
Effects of heat stress during the last third of gestation on reproductive changes postpartum were studied in Holstein cows. Cows and heifers 160 to 190 d of gestation were assigned in June 1978 to shade (n = seven cows and two heifers) or no shade (n = eight cows and two heifers) management treatments. After parturition, all cows (n = 19) were moved to the milking herd and managed uniformly. On the day of calving and on each Monday, Wednesday and Friday thereafter until d 50 postpartum, jugular blood samples were collected. Beginning approximately 7 d postpartum, the reproductive tract of each cow was examined rectally after collection of blood samples. Estrus was monitored twice daily and cows were inseminated after d 45 postpartum. Prepartum heat stress increased 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) concentrations postpartum and increased the rate of uterine involution. Regardless of prepartum treatment, progesterone concentrations indicated that luteal phases had begun by d 12.4 +/- 1.3 postpartum, which was about 3 d before PGFM was basal. The first luteal phase lasted only 10.7 +/- .9 d. First estrus was not detected until d 32.3 +/- 4.8 postpartum. The previously gravid uterine horn had a negative effect on ovarian volume, diameter of the largest follicle and percentage of ovaries with a corpus luteum. However, prepartum heat stress attenuated this effect. This study indicates that heat stress prepartum had residual effects on postpartum reproductive changes, and that the previously gravid uterine horn exerted some control, which was attenuated by heat stress, over ovarian recrudescense. Even though heat stress prepartum affected sensitive measures of postpartum reproductive function, it did not alter days to first estrus, days open (102.3 +/- 13.1) or services/conception (2.5 +/- .3).
Animals↗
Changes throughout estrous cycles of variables that might indicate estrus in dairy cows.
Two experiments examined physiological changes throughout estrous cycles of Holstein cows. In experiment one, changes were characterized for physical activity, vaginal pH, vaginal temperature, milk yield, heart rate, and concentration in blood plasma of progesterone and 13,14-dihydro-15-keto-prostaglandin F2 alpha. Variables were measured daily in 11 cows through a total of 28 estrous cycles. Cows in estrus at least once postpartum were used. Observations for estrus were at least twice daily. Variables changed significantly with day of estrous cycle. Changes of progesterone, physical activity, and 13,14-dihydro-15-keto-prostaglandin F2 alpha were more marked around estrus than were changes of the other variables. Peaks of physical activity coincided with estrus in 75% of the cases. Experiment two was to determine if increased physical activity, measured with pedometers, coincided with estrus in commercial dairy herds. Cows on 14 farms in New York were fitted with mechanical pedometers, and the pedometers were read at each milking. Readings from 3 days before until 3 days after estrus were used from 55 estrous periods identified by the producers. Physical activity was maximal on day of estrus in 73% of the estrous periods. Increased physical activity of commercial dairy cows agreed well with the producers' diagnoses of estrus. Pedometers could be a valuable component of an estrous detection program.
Animals↗
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.
Animals↗
Effects of endometrium on metabolism of arachidonic acid by bovine blastocysts in vitro.
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Animals↗
Plasma 13,14-dihydro-15-keto-PGF alpha (PGFM) in pregnant and nonpregnant heifers prior to and during surgery and following intrauterine injection of PGF2 alpha.
On day 17 postestrus or postmating, heifers were given intrauterine injections of saline (2 pregnant, 2 non-pregnant) or 200 micrograms PGF2 alpha (7 pregnant, 6 nonpregnant) through cannulae installed surgically into the uterine horn ipsilateral to the corpus luteum bearing ovary. Jugular blood samples were collected prior to the laparotomy at which the cannulae were installed during surgery, and for 90 min following the intrauterine injection. Plasma was assayed for progesterone and 13,14-dihydro-15-keto-PGF2 alpha (PGFM). Laparotomies were reopened to confirm proper cannula placement and to determine if blastocysts were present in mated heifers. Concentrations of PGFM were higher in pregnant compared to nonpregnant heifers during the presurgery (68 +/- 26 vs 24 +/- 26 pg/ml; P less than .025) and surgery (186 +/- 47 vs 65 +/- 17 pg/ml; P less than .05) periods. Pregnancy status did not alter the mean concentrations of PGFM (pregnant, 554 +/- 70 pg/ml; nonpregnant, 422 +/- 81 pg/ml) or the half-life of its decline in concentration (18 min) following intrauterine injection of PGF2 alpha. Pregnancy at 17 days in cattle does not appear to influence PGF2 alpha transport from the uterine lumen or its metabolism in the uterus or elsewhere in response to an acute intrauterine injection.
Animals↗
Pituitary and ovarian responses to gonadotropin releasing hormone, calf removal and progestogen in anestrous beef cows.
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Anestrus↗
Effect of suckling on postpartum changes in 13,14-dihydro-15-keto-PGF2 alpha and progesterone and induced release of gonadotropins in autumn-lambing ewes.
Postpartum changes in concentrations of 13, 14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) and progesterone and gonadotropin-releasing hormone (GnRH) induced release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were studied in two experiments on suckled and nonsuckled autumn-lambing ewes. In both experiments, one group of ewes had lambs weaned on d 3 +/- .5 postpartum and was compared with a second group of ewes that suckled one lamb each. In Exp. 1, jugular blood samples were collected daily from the day after lambing until d 50 postpartum for assay of PGFM and progesterone. On d 21 +/- .5 postpartum, ewes (eight suckled and eight nonsuckled) received GnRH (100 micrograms), and LH and FSH were measured in blood samples collected over a 340 min period. In Exp. 2, jugular blood samples were collected from the day of lambing until d 22 +/- .6 postpartum for assay of PGFM and progesterone. Ewes (six suckled and seven nonsuckled) received GnRH (100 micrograms) on d 22 +/- .6 postpartum, and LH and FSH were quantified in blood samples taken over a 185 min period. The pituitary was removed from each ewe 190 min after GnRH for LH and FSH determinations. Postpartum changes in concentrations of PGFM and progesterone did not differ with suckling in either experiment. In both experiments PGFM concentrations were high on d 1 postpartum, but declined to basal values by d 11. The release of LH after GnRH in Exp. 1 was greater (P less than .001) in suckled than in nonsuckled ewes. In Exp. 2, LH release after GnRH was not affected by suckling, but in both experiments suckled ewes had a greater (P less than .01) release of FSH than did nonsuckled ewes. Pituitaries from suckled ewes contained more FSH (P less than .01) than pituitaries from nonsuckled ewes. The resumption of ovarian cyclicity in well-fed autumn-lambing ewes appeared to be neither altered by suckling nor limited by the ability of the pituitary to respond to GnRH.
Animals↗
Metabolism of arachidonic acid in vitro by bovine blastocysts and endometrium.
Metabolism of arachidonic acid and prostaglandin F2 alpha by bovine blastocysts and endometrial slices recovered on Days 16 and 19 postmating was studied in vitro. In Experiment 1, arachidonic acid (10 microCi tritiated and 200 micrograms radioinert) was added to blastocysts and endometrial slices prior to incubation for 24 h. [3H]arachidonic acid ([3H]AA) and metabolites in extracts of culture medium and tissue homogenates were separated on columns of Sephadex LH-20. Elution profiles of [3H]AA and metabolites in extracts of culture medium revealed that 13, 14-dihydro-15-keto-PGF2 alpha (PGFM), Pge2, PGF2 alpha, and at least four unidentified compounds were produced by Day 16 and Day 19 blastocysts. Endometrial slices from both days of pregnancy produced 3H-prostaglandins. Experiment 2 was conducted to quantify PGE2, PGF2 alpha and PGFM in aliquots of culture medium from Day 16 and Day 19 blastocyst and endometrial incubates. These tissues were incubated with 200 micrograms of radioinert arachidonic acid. Day 16 blastocysts produced less (microgram/blastocyst; P less than 0.01) of each prostaglandin than Day 19 blastocysts (PGE2, 0.7 +/- 0.4 vs. 4.2 +/- 1.0; PGF2 alpha, 2.1 +/- 0.7 vs. 22.8 +/- 4.1; PGFM, 0.03 +/- 0.01 vs. 0.5 +/- 0.2). Endometrial slices produced PGE2, PGF2 alpha and PGFM, but quantities were not affected by day postmating or uterine horncorpus luteum relationships. The third experiment was conducted to determine directly if Day 19 blastocysts and endometrial slices metabolized [3H]PGF2 alpha to [3H]PGFM. Blastocysts and endometrial slices produced [3H]PGFM. Endometrial slices metabolized 34.3 +/- 1.5% of the [3H]PGF2 alpha to [3H]PGFM, while blastocysts metabolized 7.5 +/- 1.6% of the [3H]PGF2 alpha to [3H]PGFM. Results of this study indicate that bovine blastocysts and endometrial slices can metabolize [3H]AA in vitro. It is postulated that prostaglandins of blastocyst and endometrial orgin have a role in maintenance of early pregnancy in cattle.
Animals↗
Synthesis and release of polypeptides by pig conceptuses during the period of blastocyst elongation and attachment.
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Animals↗