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Fuller W Bazer and William W Thatcher

It has been 38 years since a protein, now known as interferon tau (IFNT), was discovered in ovine conceptus-conditioned culture medium. After 1979, purification and testing of native IFNT revealed its unique antiluteolyic activity to prevent the regression of corpora lutea on ovaries of nonpregnant ewes. Antiviral, antiproliferative and immunomodulatory properties of native and recombinant IFNT were demonstrated later. In addition, progesterone and IFNT were found to act cooperatively to silence expression of classical interferon stimulated genes in a cell-specific manner in ovine uterine luminal and superficial glandular epithelia. But, IFNT signaling through a STAT1/STAT2-independent pathway stimulates expression of genes, such as those for transport of glucose and amino acids, which are required for growth and development of the conceptus. Further, undefined mechanisms of action of IFNT are key to a servomechanism that allows ovine placental lactogen and placental growth hormone to affect the development of uterine glands and their expression of genes throughout gestation. IFNT also acts systemically to induce the expression of interferon stimulated genes that influence secretion of progesterone by the corpus luteum. Finally, IFNT has great potential as a therapeutic agent due to its low cytotoxicity, anti-inflammatory properties and effects to mitigate diabetes, obesity-associated syndromes and various autoimmune diseases.

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R. M. Eley, W. W. Thatcher and F. W. Bazer

Summary. Conceptus (placental membranes, fetal fluids and fetus) development was characterized between Days 27 and 111 of gestation. Progestagens, oestrone, oestradiol, oestrone sulphate and prostaglandins (PG) F were measured in maternal plasma and allantoic and amniotic fluids. Protein concentrations are described for fetal fluids. The early increase in placental membrane weight from 1·12 g (27 days) to 58·45 g (50 days) was associated with oestrogen production presumably of conceptus origin. Oestrogens increased significantly in allantoic and amniotic fluids throughout the period studied with oestrone being the primary free oestrogen, rising from 2 pg/ml (Day 33) to 144 ng/ml by 111 days in allantoic fluid. Changes in plasma oestrogens of the maternal circulation were not detected until after Day 70 at which time oestrone concentration was greater than that of oestradiol. Fetal fluid concentrations of progestagens, oestrone sulphate and PGF were not related to maternal plasma levels and a sequestration of these hormones by the allantois is postulated.

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R. M. Eley, W. W. Thatcher and F. W. Bazer

Summary. The action of oestrone sulphate on luteal function was tested in cyclic beef heifers. Once daily injection of 28 or 56 mg oestrone sulphate in corn oil beginning on Day 10 of the cycle had a significant luteolytic effect as compared to corn oil-treated controls.

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C. Plante, W. W. Thatcher and P. J. Hansen

Summary. An experiment was conducted to (i) determine whether administration of recombinant bovine interferon-αI 1 (rBoIFN-α) attenuates oxytocin-induced release of prostaglandin F-2α and (ii) confirm previous observations that rBoIFN-α causes acute changes in body temperature and circulating concentrations of progesterone. Cows were treated twice a day from Day 14 to Day 17 after oestrus with a control regimen (bovine serum albumin (BSA), i.m. + BSA intrauterine (i.u.)), rBoIFN-α, i.u. + BSA, i.m. (rBoIFN-IU) or rBoIFN-α, i.m. + BSA, i.u. (rBoIFN-IM). On Day 17, plasma concentrations of 13,14-dihydro,15-keto-prostaglandin F-2α (PGFM) were measured after injection of oxytocin. Cows treated with rBoIFN-IU and rBoIFN-IM had longer oestrous cycles and luteal lifespans than control cows. A hyperthermic response and decline in plasma concentrations of progesterone was noticed after administration of rBoIFN-α on Day 14. On other days, the hyperthermic response was not present and the decline in progesterone was less pronounced. There was no significant effect of rBoIFN-α on circulating concentrations of oestradiol between Days 14 and 17. The release of PGFM induced by oxytocin was lower in cows treated with rBoIFN-α than in control cows. Oxytocin caused increased plasma concentrations of PGFM in four of five control cows, two of five rBoIFN-IU cows and two of five rBoIFN-IM cows. The peak PGF-2α response to oxytocin (peak value after injection minus mean concentration before injection) was 257·8 ± 60·3 pg/ml for control cows, 100·7 ± 40·8 pg/ml for rBoIFN-IU and 124·9 ± 40·4 pg/ml for rBoIFN-IM. It is concluded that rBoIFN-α can reduce oxytocin-induced PGFM release and may therefore extend the lifespan of the corpus luteum by interfering with events leading to luteolytic release of PGF from the uterus. Administration of rBoIFN-α can cause acute changes in body temperature and circulating concentrations of progesterone that become less severe after repeated exposure to rBoIFN-α.

Keywords: interferon; endometrium; prostaglandin F-2α; oestrous cycle; corpus luteum; cow

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D. J. Putney, T. S. Gross and W. W. Thatcher

Summary. Bilateral perifusion devices were utilized to measure prostaglandin F-2α (PGF) secretion by bovine endometrium in response to in-vitro heat stress. Tissues were collected at Day 17 after oestrus from cyclic (N = 4) and pregnant (N = 5) cows, placed into 3 perifusion devices, perifused (3 ml/10 min, Krebs–Ringer–bicarbonate [KRB]) for 5 h, and fractions were collected every 10 min. Endometrial tissues within each device were subjected to a different temperature and oxytocin (1 i.u./ml KRB) treatment sequence: (1) control–oxytocin: 1 h at 39°C; 2 h at 39°C, 0·5 h at 39°C with oxytocin, 0·5 h at 39°C and 1 h at 39°C; (2) heat–oxytocin: 1 h at 39°C, 2 h at 42°C, 0·5 h at 42°C with oxytocin, 0·5 h at 42°C and 1 h at 39°C; (3) heat–KRB: 1 h at 39°C, 2 h at 42°C, 0·5 h at 42°C, 0·5 h at 42°C and 1 h at 39°C. Regardless of reproductive status, heat stress induced a rapid increase (P < 0·01) in PGF secretion rates. Oxytocin induced an increase (P < 0·01) in PGF secretion for endometrium from cyclic cows regardless of temperature. Endometria from pregnant cows did not respond to oxytocin when perifused at 39°C. However, PGF secretion rates from endometrium of pregnant cows increased (P < 0·01) in response to oxytocin when perifused under heat stress conditions. Increased PGF secretion rates and responsiveness to oxytocin for endometria from pregnant cows in response to heat stress suggests that the ability of the conceptus to inhibit uterine PGF-2α synthesis may be compromised during early pregnancy when cattle are subjected to high ambient temperatures.

Keywords: endometrium; heat stress; prostaglandin; cattle; oxytocin

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S. D. Helmer, P. J. Hansen, W. W. Thatcher, J. W. Johnson and F. W. Bazer

Summary. Intrauterine infusion of enriched bovine trophoblast protein-1 complex (bTP-1) resulted in extension of interoestrous intervals and corpus luteum function in cyclic cattle. Conceptus proteins were obtained by culture of Day 17–18 conceptuses for 72 h. Media from the first (n = 28), second (n = 26) and third (n = 19) 24 h of conceptus incubations were utilized. A highly enriched preparation of bTP-1 was obtained by a combination of ammonium sulphate precipitation, ion-exchange chromatography, and h.p.l.c. gel filtration. Degree of purity of the final preparation was confirmed by gel electrophoresis and immunoblotting with antiserum to ovine trophoblast protein-1. Jersey cattle (3 per group) received intrauterine infusions, twice daily from Day 15·5 to 21·0, of bovine serum albumin, the entire array of bovine conceptus secretory proteins (bCSP) from the 3 days of conceptus culture, or bTP-1. Infusions were via a catheter into the uterine horn ipsilateral to the corpus luteum. Oestrous cycle length in bTP-1-treated cows 26·1 ± 1·3 days) was greater than for cows given BSA (19·5 ± 1·3 days) or bCSP (21·5 ± 1·3 days). Similarly, progesterone concentrations in serum remained elevated for a longer period of time for bTP-1-treated cows than for cows treated with BSA or bCSP. Residual variance associated with vena cava concentrations of PGF-2α at Days 19–21 after oestrus (which included the variance between 15-min periods within cows) was reduced in cows treated with bTP-1 as compared to other groups. Lack of a bCSP effect may have been due to low amounts of bTP-1 in conceptus-conditioned medium from cultures of >24 h. None the less, purified bTP-1 was effective in extending luteal function and appears to be the antiluteolytic agent of early pregnancy.

Keywords: cattle; trophoblast protein-1; oestrous cycle; intrauterine infusion; corpus luteum; prostaglandins; luteolysis

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T. S. Gross, D. J. Putney, F. W. Bazer and W. W. Thatcher

Summary. Endometrium from cyclic (N = 4) and pregnant (N = 4) gilts at Day 14 after oestrus was placed into three bilateral perifusion devices which allow separate perifusion of luminal and myometrial sides. Perifused endometrium was subjected to 39 or 42°C. Incorporation of [3H]leucine into secreted and tissue proteins by endometrial explants following incubation at 39 or 42°C was examined using trichloroacetic acid (TCA) precipitation and one-dimensional SDS polyacrylamide gel electrophoresis. Secretion of PGF was greater from the myometrial side for cyclic gilts (endocrine orientation), but greater from the luminal side for pregnant gilts (exocrine orientation). Regardless of reproductive status or endometrial side, heat stress induced a rapid increase (P < 0·01) in PGF secretion rates. However, PGF secretion in response to heat stress was greater (P < 0·01) from the myometrial side and greater (P < 0·01) for pregnant gilts. PGF secretion rates increased by 63% and 42% from the luminal side, and 40% and 156% from the myometrial side in response to heat stress for cyclic and pregnant gilts, respectively (status × treatment × side interaction; P < 0·01). Heat stress did not alter incorporation of [3H]leucine into secreted proteins regardless of reproductive status, while incorporation into tissue proteins was decreased (P < 0·05) by heat stress for pregnant gilts, but not altered for cyclic gilts. Heat stress, in vitro, redirects PGF secretion for endometria of pregnant gilts from an exocrine to an endocrine orientation where it would be available to effect luteolysis and compromise the establishment of pregnancy.

Keywords: pig; heat stress; endometrium; prostaglandins; perifusion; proteins

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J. L. Vallet, F. W. Bazer, M. F. V. Fliss and W. W. Thatcher

Summary. Conceptus secretory proteins (oCSP) were obtained from medium in which sheep conceptuses, collected on Day 16 of pregnancy, were cultured for 30 h. A portion of the culture medium (500 ml) was prepared for intrauterine infusion by concentrating the proteins by Amicon ultrafiltration (M r 500 cutoff). A second portion (500 ml medium) was used to purify sheep trophoblast protein one (oTP-1). Proteins remaining after oTP-1 purification were concentrated and then passed through an anti-oTP-1 sepharose CL-4B affinity column to remove any remaining oTP-1 (oCSP – oTP-1). Serum proteins (oSP) were collected from a Day-16 pregnant ewe and diluted for infusion. Catheters were placed in the uterus of cyclic (Day 10) ewes. The following combinations of proteins were infused: 0·75 mg oCSP + 0·75 mg oSP (5 ewes), 0·75 mg oCSP – oTP-1 + 0·75 mg oSP (4 ewes), 0·05 mg oTP-1 + 1·45 mg oSP (5 ewes) and 1·5 mg oSP only (5 ewes). Infusions were twice daily on Days 12 and 13 (08:00 and 17:00 h) and once on Day 14 (08:00 h). On Day 14, ewes were injected intravenously at 08:00 h with 0·5 mg oestradiol-17β. Blood sampling began 30 min before oestradiol injection and continued every 30 min for 10 h. On Day 15 ewes received 10 i.u. oxytocin intravenously (08:00 h). Blood samples were collected 10 min before oxytocin and every 10 min for 1 h after oxytocin injection. Concentrations of prostaglandin (PG) F, PGE-2/PGE-1 (PGE) and 13,14-dihydro-15-keto-PGF-2α (PGFM) were measured by specific radioimmunoassay. Ewes treated with oTP-1 and oCSP had longer (P < 0·05) interoestrous intervals (27 and 25 days, respectively) compared to ewes treated with oSP and oCSP – oTP-1 (19 and 19 days, respectively) (s.e.m. = 1·56 days). These results indicate that oTP-1 alone is as potent as total conceptus secretory proteins in extending luteal maintenance. Ewes treated with oTP-1 and oCSP had no increase in PGF after oestradiol injection while production of PGF did increase 6–10 h after oestradiol in ewes treated with oSP and oCSP – oTP-1. PGFM was correlated with PGF concentrations (r = 0·57, P < 0·01) although presence or absence of increases in production of PGFM for the treatment groups were not the same as those for PGF. No effects of treatment on PGE were detected. Ewes treated with oTP-1 had lower (P < 0·05) PGF and PGFM values after oxytocin injection than did ewes in the other 3 treatment groups (P < 0·05). PGFM and PGF values were correlated (r = 0·69, P < 0·01). No differences in PGE values were detected between the 4 treatment groups

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K. B. Finchert, F. W. Bazer, P. J. Hansen, W. W. Thatcher and R. M. Roberts

Summary. In Exp. I, 0·5 mg oestradiol or vehicle (0·5 ml absolute ethanol + 0·5 ml 0·9% NaCl) was injected i.v. at 08:00 h on Day 14 (onset of oestrus = Day 0). Blood samples were obtained via a jugular catheter at 30 and 1 min before oestradiol and every 30 min for 10 h afterwards. Plasma was obtained and assayed for 15-keto-13,14-dihydro-PGF-2α (PGFM) by radioimmunoassay. Before oestradiol, PGFM basal values were higher (P < 0·01) in pregnant (N = 10) than nonpregnant (N = 6) ewes (193 ± 30 vs 67 ± 8 pg/ml). However, at 4–10 h after oestradiol, pregnant ewes (N = 5) had less variable (P < 0·01) PGFM values than did nonpregnant ewes (N = 5). In Exp II, conceptus secretory proteins (CSP) were obtained by pooling medium from cultures of Day-16 sheep conceptuses (N = 40). Ewes received 750 μg CSP + 750 μg plasma protein (N = 6) or 1500 μg plasma protein (N = 6) per uterine horn at 08:00 h and 18:00 h on Days 12–14. All ewes received 0·5 mg oestradiol at 08:00 h on Day 14 and blood samples were collected as in Exp. I and assayed for PGFM. On Day 15, 3 ewes in each group received 10 i.u. oxytocin and 3 received saline i.v. at 08:00 h and blood samples were taken continuously from 10 min before to 60 min after treatment. Mean PGFM response to oestradiol was suppressed (P = 0·05) in CSP- vs plasma protein-treated ewes (371 ± 129 vs 1188 ± 139 pg/ml). Oxytocin induced a greater (P < 0·01) PGFM peak response in plasma protein-treated (3972 ± 2199 pg/ml) than CSP-treated (1669 ± 287 pg/ml) ewes. Uterine production of PGF in response to oestradiol was suppressed in pregnant and CSP-treated ewes and oxytocin-induced PGF production was also suppressed in CSP-treated ewes. These results are consistent with the theory that CSP act to prevent luteolysis by altering either the amount of PGF released by the uterus or the pattern of PGF release.

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F. W. Bazer, W. W. Thatcher, F. Martinat-Botte and M. Terqui

Summary. Body weight of Large White gilts was greater at birth, weaning, 5 months of age and at slaughter; however, Meishan gilts reached puberty at an earlier age (91 ± 2 vs 192 ± 3 days, P < 0·01), had longer periods of oestrus (60 ± 2 vs 49 ± 2 h, P < 0·01) and experienced more oestrous cycles (7 ± 0·4 vs 4 ± 0·4, P < 0·01) before slaughter. The interoestrous interval was longer (P < 0·01) for Large White gilts (19·8 ± 0·2 vs 19·1 ± 0·2 days). At slaughter, uterine length (P < 0·05), uterine weight, width of uterine horns, endometrial surface area, endometrial weight and percentage of uterine weight represented by endometrium was greater (P < 0·01) for Large White gilts. However, breed differences were not significant when slaughter weight was included in analyses as a covariate. This indicated that development of the reproductive tract was proportionate to body weight at slaughter for each breed. When body weight at slaughter was included as a covariate, effects of day of the oestrous cycle and pregnancy on uterine width, uterine weight, endometrial surface area and endometrial weight were detected (P < 0·01) and for uterine length there was a day-by-status interaction (P < 0·01). Total number of CL (P < 0·05) and total ovarian weight (P < 0·05) were also greater for Large White gilts independent of body weight at slaughter. There were more CL in left ovaries for Meishan (8·1 ± 0·4 vs 6·6 ± 0·4) and Large White (8·4 ± 0·4 vs 7·9 ± 0·5) gilts. These results indicate that the more prolific Meishan gilts: (1) reach puberty at an earlier age and at a lighter body weight; (2) express oestrus longer and have slightly shorter oestrous cycles; (3) have morphologically smaller uteri; and (4) have lower numbers of CL in ovaries that are smaller than those of Large White gilts.

Keywords: pig; uterus; ovary; development