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Do mares possess an intracellular endometrial inhibitor of prostaglandin synthesis during early pregnancy?
THERIOGENOLOGY
DO MARES POSSESS OF PROSTAGLANDIN
AN INTRACELLULAR SYNTHESIS DURING
ENDOMETRIAL INHIBITOR EARLY PREGNANCY?
E. D. Watson Section of Reproductive Studies School of Veterinary Medicine, University of Pennsylvania New Bolton Center Kennett Square, PA 19348 Received for publication: Accepted:
December 6, 1990 May 10, 2991
ABSTRACT Cytosol was prepared from endometrium collected from regnant or nonpregnant mares 14 d after ovulation and was a c!ded to a prostaglandin-generating system (bovine fetal cotyledonary microsomes). Addition of endometrial cytosol from pregnant mares suppressed microsomal synthesis of prostaglandin F, but addition of endometrial cytosol from nonpregnant mares increased microsomal synthesis of prostaglandin F. The results suggest that mares possess an intracellular inhibitor of prostaglandin F syntheses during early pregnancy. Key words:
prostaglandin
synthesis, pregnancy,
mares
INTRODUCTION There is strong circumstantial evidence that prostaglandin F-2d from the endometrium acts as the luteolysin in the mare. Concentrations of prostaglandin F in the uterine lumen (1) and uterine vein (2) and of the prostaglandin F metabolite, 13,14 dihydro-15-keto-prostaglandinF-2d (prostaglandm FM), in the peripheral circulation (3) increase at the time of luteolysis in the mare. In addition, administration of exogenous rostaglandin F-2ti to mares results in premature termination of luteal function P2). Concentrations of prostaglandin F in the uterine lumen (1) and uterine vein (2) and of prostaglandin FM in jugular blood (3) are significantly lower in early pregnant mares than in nonpregnant mares around the time of maternal recognmon of pregnancy. There is evidence from in vitro studies that the conceptus exerts a Acknowledgments The author thanks Ms. Heidi Zanecosky for technical assistance and Dr. Richard Bartholomew for obtaining bovine This study was lacentomes. supported by the Marion Dilley and David 8 eorge Jones Trust and by the Raker Research Fund. Dr. Watson’s current address is Department of Veterinary Clinical Studies, Royal (Dick) School of Veterinary Studies, Veterinary Field Station, nr Roslin, Midlothian EH25 9RG, Scotland, United Kingdom.
JULY 1991 VOL. 36 NO. 1
67
THERIOGENOLOGY
direct effect on the endometrium to inhibit prostaglandin F production (45). This factor has recently been found to have a molecular weight between 1000 and 6000 (6). Vernon and co-workers (7) and Watson and Sertich (5) found that, in the absence of the conceptus, endometrium from pregnant mares released as much prostaglandin F as endometrium from nonpregnant mares. This might suggest that there are no endogenous inhibitory factors within the pregnant endometrium itself. However, recent work has shown in vitro that endometrium from early pregnant mares does not show an increased release of prostaglandin F after oxytocin stimulation (8). This suggests that the corpus luteum of early pregnancy is maintained because of endogenous inhibition of prostaglandin F synthesis or an In cattle, an inability to respond to stimulators of prostaglandin F release. endogenous inhibitor of prostaglandin F synthesis has been detected in the high-speed supernatant of homogenized bovine endometrium and in caruncular tissue during mid- to late gestation (9,lO). Inhibition of prostaglandin F synthesis is much greater during early pregnancy than during the estrous cycle in cattle (lO,ll), and it has been proposed that this inhibition of prostaglandin F synthesis is induced in the maternal endometrium by conceptus secretory proteins, including bovine trophoblast protein-l (12,13). Because inclusion of exogenous arachidonic acid does not counteract the inhibitory activity, it appears that bovine endometrial cytosol inhibits the cyclooxygenase enzyme rather than the earlier steps of arachidonate metabolism (10). It is not known whether a mechanism exists for inhibition of prostaglandin F synthesis in the endometrium of the early pregnant mare at the time of maternal recognition of pregnancy. The present study used a preparation of bovine fetal cotyledonary tissue as a source of prosta landin F-generating microsomes and investigated whether endometrial cytosol Prom mares was capable of inhibiting synthesis of prostaglandin F by the mrcrosomes. MATERIALS Preparation
of Microsomes
AND METHODS
(Prostaglandin-Generating
System)
Bovine fetal cotyledonary tissue was collected within 1 h of calving and stored at -7OOC until further recessing. Microsomes were prepared by the procedure of Gross et al. (10). Brie+l y, tissue was homogenized, and the filtered supematant was centrifuged at 800 g for 15 min at 4’C to remove nuclei and mitochondria. The supernatants were then centrifuged at 100,000 g for 60 min at 4OC to pellet the mrcrosomes. The microsomes were resuspended in 0.1 M potassium phosphate (pH 7.5) and were stored in aliquots at -7O’C. Preparation
of Equine Endometrium
Endometrial biopsy samples were collected from pregnant (n = 7) and nonpregnant (n = 3) horse mares 14 d after ovulation. Minced fragments of tissue were placed in Medium 199 (Sigma Chemical Co., St. Louis, MO) and incubated for 20.5 h at 39OC in an humidified atmosphere of 5% CO : 95% air. The conditioned medium was harvested and used in another study and t l!e tissue was stored at -7O’C. Tissues from regnant and nonpregnant mares were treated as described under Because there was only a small amount of tissue preparation o! microsomes. available, the tissue of 5 of the pregnant mares was pooled. Tissues from other mares were processed separately. The high speed supernatant (cytosol) was stored in aliquots at -7OOC.
66
JULY 1991 VOL. 36 NO. 1
THERIOGENOLOGY
Assay for Inhibition
of Prostaglandin
Synthesis
The technique described by Gross et al. (10) was used. Microsomes (equivalent of 500 mg tissue) were incubated in 0.1 M otassium phosphate buffer (pH 7.5) with 100 ug arachidonic acid (Sigma Chemical e o., St. Louis, MO) and with and without the high s eed supernatant from the endometrium of pregnant or nonpregnant mares (25 B mg tissue equivalent) for 1 h at 39OC in a shakin waterbath (2.6 ml Indomethacin (100 ng; a prostaglandin-syn tf; esis inhibitor) was total volume). added to duplicate tubes as a positive control. The incubation was terminated by the addition of 0.25 ml ethanol. The tubes were centrifu ed at 1500 $for 29 mm at 4OC to pellet the precipitate and the supernatants were Brozen at -70 C unttl being assayed for prostaglandin F. Assay of Prostaglandin
F
Incubation medium and cytosols were assayed for prostaglandin F using a direct radioimmunoassay previous1 described by Watson and Sertich (5) with the exception that a different anti *4:ody was used (Sigma Chemical Co., St. Louis, MO). Cross-reactivity of the antiserum was < 0.1% with all prostaglandins tested except for prostaglandin F-a (60% cross-reactivity). Because of the high cross-reactivity of the antiserum with prostaglandin F-14, results are quoted as total immunoreactive prostaglandin F. Limit of detection of the assay was 0.1 rig/tube. Intra- and inter-assay coefficients of variation were 10.3 and 8.7%, respectively. Concentrations of prostaglandin F present in cytosol added to incubations were subtracted from concentrations present in incubation medium. Statistical Analysis Effect of treatment on concentrations of prostaglandin F synthesized microsomes was analyzed by a paired t-test. All means are quoted + SEM.
by
RESULTS Microsomes from bovine cotyledonary tissue synthesized large quantities of prostaglandin F. There were no significant differences in the cytosolic concentrations of prostaglandin F between the pregnant and nonpregnant endometrium. Figure 1 shows the concentrations of prostaglandin F generated by microsomes in the presence of endometrial cytosol from regnant and nonpregnant mares. The cytosol preparation from the endometrium o P pregnant mares abolished microsomal prostaglandin F synthesis. Concentrations measured were lower (32 + 21.1%) than those originally added in the cytosol, but this was not significant. Concentrations also tended to be lower than those of the indomethacin control. In the presence of endometrial cytosol from nonpregnant mares, amounts of prostaglandin F synthesized by microsomes were increased, but not significantly (120 + 14.2%), compared with that of the controls. Addition of indomethacin to microsomes significantly (P = 0.05) reduced synthesis of prostaglandin F. DISCUSSION Microsomes from bovine placental tissue synthesized prostaglandins and produced similar concentrations of prostaglandin F to those found in another study (10). In the present study, there was evidence of the presence of an intracellular prostaglandin F synthesis inhibitor in the endometrium of the pregnant mare. The degree of inhibition of prostaglandin F synthesis by endometrial cytosol of pregnant mares was greater than the degree of inhibition that occurred in the presence of
JULY 1991 VOL. 36 NO. 1
69
THERIOGENOLOGY
indomethacin. Because prostaglandin F synthesis was inhibited even in the presence of. exogenous arachidomc acid, the m vivo inhibitory effect was probably mediated vra the cyclooxygenase enzyme system rather than by interfering with It is not clear why cytosol from pregnant intracellular arachidonate mobilization. mare endometrium was apparently more effective at inhibiting synthesis of prostaglandin F than indomethacin. Preliminary studies had shown that 100 ug mdomethacin induced a higher degree of inhibition of prostaglandin F synthesis than other concentrations tested. There was endogenous prostaglandin F present in the cytosol from the endometrium of pregnant mares, and the mrcrosomes produced prostaglandin F during incubation. However, the post-incubation concentration of prostaglandin F measured in the medium was even lower than the pre-incubation concentration of prostaglandin F. It is possible that not only was production of prostaglandin F inhibited, but degradation of prostaglandin F also occurred. Prostaglandin is highly susceptible to enzymatic degradation at body temperature. Perhaps enzymes were present in the endometrial cytosol that metabolized the prostaglandin F during incubation. a.0 -
6.0 --
I
CONTROL
III
PREGNANT
CZ
NONPREGNANT
m
INDOMETHACIN
i
Figure 1. The effect of addition of endometrial cytosol from pregnant and nonpregnant mares on prostaglandin synthesis by microsomes. Cytosolic prostaglandin F concentrations were subtracted from prostaglandin F concentrations measured in incubation medium. Endometrial cytosol from nonpregnant mares tended to increase prostaglandin F synthesis by microsomes, which may help to explain the increased synthesis of prostaglandin F by the nonpregnant mare endometrmm at the time of luteolysis. By contrast, in cows exhibiting normal estrous cycles, some prostaglandin F inhibitory capacity was present even at the time of luteolysis (11). It is possible, therefore, that the reduced secretion of prostaglandin F during early pregnancy in the mare is due to the presence of endogenous prostaglandin synthesis inhibitors within the endometrmm. Release of prostaglandin by It IS possible, endometrium from pregnant and nonpregnant mares is similar. therefore, that these inhibitors may be acttvated in the presence of the developing conceptus and may explain the reduced secretion of prostaglandin F during co-incubation of conceptus and endometrial tissue (56).
70
JULY 1991 VOL. 36 NO. 1
THERIOGENOLOGY
REFERENCES 1. Zavy, M.T., Vernon, M.W., Asquith, R.L., Bazer, F.W. and Sharp, D.C. Effect of exogenous gonadal steroids and pre ancy on uterine luminal prostaglandin F in mares. Prostaglandins 22:311-320 $”1984). 2. Douglas, R-H. and Ginther, O.J. Concentration venous plasma of anesthetized mares during pregnancy. Prostaglandins U:251-260 (1976).
of prostaglandins F in uterine the estrous cycle and early
H., Knudsen, O., Madej, A. and Edqvist, LE. Progesterone, 3. Kindahl, prostaglandin F-2 , PMSG and oestrone sul hate during early pregnancy in the mare. J. Reprod. Fertil. QSuppl.):353-359 Q1982). 4. Berglund, LA., Sharp, D.C., Vernon, M.W. and Thatcher, W.W. Effect of pregnancy and collection techni ue on prostaglandin F in the uterine lumen of 4 pony mares. J. Reprod. Fertil. 3_(Suppl.):335-341(1982). 5. Watson, E.D. and Sertich, P.L. Prostaglandin production by horse embryos and the effect of co-culture of embryos with endometrium from pregnant mares. 5. Reprod. Fertil. 82:331-336 (1989). J. and Thatcher, 6. Sharp, D.C., McDowell, K.J., Weithenauer, continuum of events leading to maternal recognition of pregnancy Reprod. Fertil. ~(Suppl.):lOl-107 (1989).
W.W. The in mares. J.
F-2 7. Vernon, M-W., Zavy, M.T., Asquith, R.L. and Sharp, D.C. Prostaglandin in the equine endometrium: steroid modulation and production capacities during the estrous cycle and early pregnancy. Biol. Reprod. =581-589 (1981). 8. Franklin, K.J, Gross, T.S., Dubois, D.H. and Sharp, D.C. In vitro prostaglandin secretion from lummal and myometrial sides of endometrium from cyclic and Biol. Reprod. Abstr. @(Suppl. 1):199 pregnant mares at Day 14 post-estrus. Abstr. (1989). 9. Shemesh, M., Hansel, W. and Strauss, J.F. Modulation prosta landin s nthesis by an endogenous inhibitor. 115:14 8 l-1405 (1 %84).
of bovine placental Endocrinology
10. Gross, T.S., Thatcher, W.W., Hansen, P.J., Johnson, J.W. and Helmer. S.D. Presence of an intracellular endometrial inhibitor of rosta landin synthesis during early pregnancy in the cow. Prostaglandins a:35 g-378 81988). 11. Basu, S. and Kindahl, endometrium during 28:175-193 (1987).
H. Inhibitor of prostaglandin biosynthesis in the bovine Theriogenology estrous cycle and early pregnancy.
12. Helmer, S.D., Gross, T.S., Newton, G.R., Hanson, P.J. and Thatcher, W.W. Bovine trophoblast protein-l complex alters endometrial protein and prostaglandin secretion and induces an intracellular inhibitor of prostaglandin synthesis in vitro. J. Reprod. Fertil. 82:421-430 (1989). 13. Knickerbocker, J.J., Thatcher, W.W., Bazer, F.W., Drost, M., Barron, D.H., Fincher, K.D. and Roberts, R.M. Proteins secreted by Day-16 to -18 bovine J. Reprod. Fertil. conce tuses extend corpus luteum function in cows. n:3813-391(1986). JULY 1991 VOL. 36 NO. 1
71
DO MARES POSSESS OF PROSTAGLANDIN
AN INTRACELLULAR SYNTHESIS DURING
ENDOMETRIAL INHIBITOR EARLY PREGNANCY?
E. D. Watson Section of Reproductive Studies School of Veterinary Medicine, University of Pennsylvania New Bolton Center Kennett Square, PA 19348 Received for publication: Accepted:
December 6, 1990 May 10, 2991
ABSTRACT Cytosol was prepared from endometrium collected from regnant or nonpregnant mares 14 d after ovulation and was a c!ded to a prostaglandin-generating system (bovine fetal cotyledonary microsomes). Addition of endometrial cytosol from pregnant mares suppressed microsomal synthesis of prostaglandin F, but addition of endometrial cytosol from nonpregnant mares increased microsomal synthesis of prostaglandin F. The results suggest that mares possess an intracellular inhibitor of prostaglandin F syntheses during early pregnancy. Key words:
prostaglandin
synthesis, pregnancy,
mares
INTRODUCTION There is strong circumstantial evidence that prostaglandin F-2d from the endometrium acts as the luteolysin in the mare. Concentrations of prostaglandin F in the uterine lumen (1) and uterine vein (2) and of the prostaglandin F metabolite, 13,14 dihydro-15-keto-prostaglandinF-2d (prostaglandm FM), in the peripheral circulation (3) increase at the time of luteolysis in the mare. In addition, administration of exogenous rostaglandin F-2ti to mares results in premature termination of luteal function P2). Concentrations of prostaglandin F in the uterine lumen (1) and uterine vein (2) and of prostaglandin FM in jugular blood (3) are significantly lower in early pregnant mares than in nonpregnant mares around the time of maternal recognmon of pregnancy. There is evidence from in vitro studies that the conceptus exerts a Acknowledgments The author thanks Ms. Heidi Zanecosky for technical assistance and Dr. Richard Bartholomew for obtaining bovine This study was lacentomes. supported by the Marion Dilley and David 8 eorge Jones Trust and by the Raker Research Fund. Dr. Watson’s current address is Department of Veterinary Clinical Studies, Royal (Dick) School of Veterinary Studies, Veterinary Field Station, nr Roslin, Midlothian EH25 9RG, Scotland, United Kingdom.
JULY 1991 VOL. 36 NO. 1
67
THERIOGENOLOGY
direct effect on the endometrium to inhibit prostaglandin F production (45). This factor has recently been found to have a molecular weight between 1000 and 6000 (6). Vernon and co-workers (7) and Watson and Sertich (5) found that, in the absence of the conceptus, endometrium from pregnant mares released as much prostaglandin F as endometrium from nonpregnant mares. This might suggest that there are no endogenous inhibitory factors within the pregnant endometrium itself. However, recent work has shown in vitro that endometrium from early pregnant mares does not show an increased release of prostaglandin F after oxytocin stimulation (8). This suggests that the corpus luteum of early pregnancy is maintained because of endogenous inhibition of prostaglandin F synthesis or an In cattle, an inability to respond to stimulators of prostaglandin F release. endogenous inhibitor of prostaglandin F synthesis has been detected in the high-speed supernatant of homogenized bovine endometrium and in caruncular tissue during mid- to late gestation (9,lO). Inhibition of prostaglandin F synthesis is much greater during early pregnancy than during the estrous cycle in cattle (lO,ll), and it has been proposed that this inhibition of prostaglandin F synthesis is induced in the maternal endometrium by conceptus secretory proteins, including bovine trophoblast protein-l (12,13). Because inclusion of exogenous arachidonic acid does not counteract the inhibitory activity, it appears that bovine endometrial cytosol inhibits the cyclooxygenase enzyme rather than the earlier steps of arachidonate metabolism (10). It is not known whether a mechanism exists for inhibition of prostaglandin F synthesis in the endometrium of the early pregnant mare at the time of maternal recognition of pregnancy. The present study used a preparation of bovine fetal cotyledonary tissue as a source of prosta landin F-generating microsomes and investigated whether endometrial cytosol Prom mares was capable of inhibiting synthesis of prostaglandin F by the mrcrosomes. MATERIALS Preparation
of Microsomes
AND METHODS
(Prostaglandin-Generating
System)
Bovine fetal cotyledonary tissue was collected within 1 h of calving and stored at -7OOC until further recessing. Microsomes were prepared by the procedure of Gross et al. (10). Brie+l y, tissue was homogenized, and the filtered supematant was centrifuged at 800 g for 15 min at 4’C to remove nuclei and mitochondria. The supernatants were then centrifuged at 100,000 g for 60 min at 4OC to pellet the mrcrosomes. The microsomes were resuspended in 0.1 M potassium phosphate (pH 7.5) and were stored in aliquots at -7O’C. Preparation
of Equine Endometrium
Endometrial biopsy samples were collected from pregnant (n = 7) and nonpregnant (n = 3) horse mares 14 d after ovulation. Minced fragments of tissue were placed in Medium 199 (Sigma Chemical Co., St. Louis, MO) and incubated for 20.5 h at 39OC in an humidified atmosphere of 5% CO : 95% air. The conditioned medium was harvested and used in another study and t l!e tissue was stored at -7O’C. Tissues from regnant and nonpregnant mares were treated as described under Because there was only a small amount of tissue preparation o! microsomes. available, the tissue of 5 of the pregnant mares was pooled. Tissues from other mares were processed separately. The high speed supernatant (cytosol) was stored in aliquots at -7OOC.
66
JULY 1991 VOL. 36 NO. 1
THERIOGENOLOGY
Assay for Inhibition
of Prostaglandin
Synthesis
The technique described by Gross et al. (10) was used. Microsomes (equivalent of 500 mg tissue) were incubated in 0.1 M otassium phosphate buffer (pH 7.5) with 100 ug arachidonic acid (Sigma Chemical e o., St. Louis, MO) and with and without the high s eed supernatant from the endometrium of pregnant or nonpregnant mares (25 B mg tissue equivalent) for 1 h at 39OC in a shakin waterbath (2.6 ml Indomethacin (100 ng; a prostaglandin-syn tf; esis inhibitor) was total volume). added to duplicate tubes as a positive control. The incubation was terminated by the addition of 0.25 ml ethanol. The tubes were centrifu ed at 1500 $for 29 mm at 4OC to pellet the precipitate and the supernatants were Brozen at -70 C unttl being assayed for prostaglandin F. Assay of Prostaglandin
F
Incubation medium and cytosols were assayed for prostaglandin F using a direct radioimmunoassay previous1 described by Watson and Sertich (5) with the exception that a different anti *4:ody was used (Sigma Chemical Co., St. Louis, MO). Cross-reactivity of the antiserum was < 0.1% with all prostaglandins tested except for prostaglandin F-a (60% cross-reactivity). Because of the high cross-reactivity of the antiserum with prostaglandin F-14, results are quoted as total immunoreactive prostaglandin F. Limit of detection of the assay was 0.1 rig/tube. Intra- and inter-assay coefficients of variation were 10.3 and 8.7%, respectively. Concentrations of prostaglandin F present in cytosol added to incubations were subtracted from concentrations present in incubation medium. Statistical Analysis Effect of treatment on concentrations of prostaglandin F synthesized microsomes was analyzed by a paired t-test. All means are quoted + SEM.
by
RESULTS Microsomes from bovine cotyledonary tissue synthesized large quantities of prostaglandin F. There were no significant differences in the cytosolic concentrations of prostaglandin F between the pregnant and nonpregnant endometrium. Figure 1 shows the concentrations of prostaglandin F generated by microsomes in the presence of endometrial cytosol from regnant and nonpregnant mares. The cytosol preparation from the endometrium o P pregnant mares abolished microsomal prostaglandin F synthesis. Concentrations measured were lower (32 + 21.1%) than those originally added in the cytosol, but this was not significant. Concentrations also tended to be lower than those of the indomethacin control. In the presence of endometrial cytosol from nonpregnant mares, amounts of prostaglandin F synthesized by microsomes were increased, but not significantly (120 + 14.2%), compared with that of the controls. Addition of indomethacin to microsomes significantly (P = 0.05) reduced synthesis of prostaglandin F. DISCUSSION Microsomes from bovine placental tissue synthesized prostaglandins and produced similar concentrations of prostaglandin F to those found in another study (10). In the present study, there was evidence of the presence of an intracellular prostaglandin F synthesis inhibitor in the endometrium of the pregnant mare. The degree of inhibition of prostaglandin F synthesis by endometrial cytosol of pregnant mares was greater than the degree of inhibition that occurred in the presence of
JULY 1991 VOL. 36 NO. 1
69
THERIOGENOLOGY
indomethacin. Because prostaglandin F synthesis was inhibited even in the presence of. exogenous arachidomc acid, the m vivo inhibitory effect was probably mediated vra the cyclooxygenase enzyme system rather than by interfering with It is not clear why cytosol from pregnant intracellular arachidonate mobilization. mare endometrium was apparently more effective at inhibiting synthesis of prostaglandin F than indomethacin. Preliminary studies had shown that 100 ug mdomethacin induced a higher degree of inhibition of prostaglandin F synthesis than other concentrations tested. There was endogenous prostaglandin F present in the cytosol from the endometrium of pregnant mares, and the mrcrosomes produced prostaglandin F during incubation. However, the post-incubation concentration of prostaglandin F measured in the medium was even lower than the pre-incubation concentration of prostaglandin F. It is possible that not only was production of prostaglandin F inhibited, but degradation of prostaglandin F also occurred. Prostaglandin is highly susceptible to enzymatic degradation at body temperature. Perhaps enzymes were present in the endometrial cytosol that metabolized the prostaglandin F during incubation. a.0 -
6.0 --
I
CONTROL
III
PREGNANT
CZ
NONPREGNANT
m
INDOMETHACIN
i
Figure 1. The effect of addition of endometrial cytosol from pregnant and nonpregnant mares on prostaglandin synthesis by microsomes. Cytosolic prostaglandin F concentrations were subtracted from prostaglandin F concentrations measured in incubation medium. Endometrial cytosol from nonpregnant mares tended to increase prostaglandin F synthesis by microsomes, which may help to explain the increased synthesis of prostaglandin F by the nonpregnant mare endometrmm at the time of luteolysis. By contrast, in cows exhibiting normal estrous cycles, some prostaglandin F inhibitory capacity was present even at the time of luteolysis (11). It is possible, therefore, that the reduced secretion of prostaglandin F during early pregnancy in the mare is due to the presence of endogenous prostaglandin synthesis inhibitors within the endometrmm. Release of prostaglandin by It IS possible, endometrium from pregnant and nonpregnant mares is similar. therefore, that these inhibitors may be acttvated in the presence of the developing conceptus and may explain the reduced secretion of prostaglandin F during co-incubation of conceptus and endometrial tissue (56).
70
JULY 1991 VOL. 36 NO. 1
THERIOGENOLOGY
REFERENCES 1. Zavy, M.T., Vernon, M.W., Asquith, R.L., Bazer, F.W. and Sharp, D.C. Effect of exogenous gonadal steroids and pre ancy on uterine luminal prostaglandin F in mares. Prostaglandins 22:311-320 $”1984). 2. Douglas, R-H. and Ginther, O.J. Concentration venous plasma of anesthetized mares during pregnancy. Prostaglandins U:251-260 (1976).
of prostaglandins F in uterine the estrous cycle and early
H., Knudsen, O., Madej, A. and Edqvist, LE. Progesterone, 3. Kindahl, prostaglandin F-2 , PMSG and oestrone sul hate during early pregnancy in the mare. J. Reprod. Fertil. QSuppl.):353-359 Q1982). 4. Berglund, LA., Sharp, D.C., Vernon, M.W. and Thatcher, W.W. Effect of pregnancy and collection techni ue on prostaglandin F in the uterine lumen of 4 pony mares. J. Reprod. Fertil. 3_(Suppl.):335-341(1982). 5. Watson, E.D. and Sertich, P.L. Prostaglandin production by horse embryos and the effect of co-culture of embryos with endometrium from pregnant mares. 5. Reprod. Fertil. 82:331-336 (1989). J. and Thatcher, 6. Sharp, D.C., McDowell, K.J., Weithenauer, continuum of events leading to maternal recognition of pregnancy Reprod. Fertil. ~(Suppl.):lOl-107 (1989).
W.W. The in mares. J.
F-2 7. Vernon, M-W., Zavy, M.T., Asquith, R.L. and Sharp, D.C. Prostaglandin in the equine endometrium: steroid modulation and production capacities during the estrous cycle and early pregnancy. Biol. Reprod. =581-589 (1981). 8. Franklin, K.J, Gross, T.S., Dubois, D.H. and Sharp, D.C. In vitro prostaglandin secretion from lummal and myometrial sides of endometrium from cyclic and Biol. Reprod. Abstr. @(Suppl. 1):199 pregnant mares at Day 14 post-estrus. Abstr. (1989). 9. Shemesh, M., Hansel, W. and Strauss, J.F. Modulation prosta landin s nthesis by an endogenous inhibitor. 115:14 8 l-1405 (1 %84).
of bovine placental Endocrinology
10. Gross, T.S., Thatcher, W.W., Hansen, P.J., Johnson, J.W. and Helmer. S.D. Presence of an intracellular endometrial inhibitor of rosta landin synthesis during early pregnancy in the cow. Prostaglandins a:35 g-378 81988). 11. Basu, S. and Kindahl, endometrium during 28:175-193 (1987).
H. Inhibitor of prostaglandin biosynthesis in the bovine Theriogenology estrous cycle and early pregnancy.
12. Helmer, S.D., Gross, T.S., Newton, G.R., Hanson, P.J. and Thatcher, W.W. Bovine trophoblast protein-l complex alters endometrial protein and prostaglandin secretion and induces an intracellular inhibitor of prostaglandin synthesis in vitro. J. Reprod. Fertil. 82:421-430 (1989). 13. Knickerbocker, J.J., Thatcher, W.W., Bazer, F.W., Drost, M., Barron, D.H., Fincher, K.D. and Roberts, R.M. Proteins secreted by Day-16 to -18 bovine J. Reprod. Fertil. conce tuses extend corpus luteum function in cows. n:3813-391(1986). JULY 1991 VOL. 36 NO. 1
71