Prostaglandin Biosynthesis by Human Decidual Cells: Effects of Inflammatory Mediators M. D. Mitchell, S. Edwin and R. J. Romero* Department of Obstetrics and Gynecology, University of Utah Medical Center, 50 North Medical Drive, Salt Lake City, Utah 84132 and *Department of Obstetrics and Gynecology, Yale University, P.O. Box 3333 339 FMB, New Haven, Connecticut 06510-8063, USA (Reprint requests to MDM) ABSTRACT. There is substantial evidence that decidual activation, in association with infection, is lied with the onset of both preterm and term labor. We therefore undertook the present study to evaluate prostaghmdin production and its potential regulation by inflammatory mediators in human decidual cells in primary monolayer culture. Upon attaining confluence, the cells were incubated with endotoh, interleukin la (ILlol), interieukin 18 (ILlp); or tumor necrosis factor (TNF). Production of pros&&andin (PG) E2 and and these cytokines aiI ioduced PGFzc, was determined using specific radioimmunoassa ys. Endototi significant concentrationdependent increases in PGEz and PGFh production. Our rest&s suggest that term human decidual cells are responsive to endotoxin and cytokines and that generation of these sub&ances in the decidua or nearby (eg. in response to infection) will lead to increased prostaglandin production and uterine conlractions.
INTRODUCTION
taglandin production by amnion cells (6, 7, 8). The actions of these substances on decidua are unknown. Whether they are generated in the fetal membranes or within the decidua itself, any action on prostaglandin production would be of significance due to direct access to the myometrium. Hence, we have evaluated the effects of endotoxin and cytokines dn decidual prostaglandin production.
Infection in pregnancy frequently is associated with preterm labor (1). The mechanism whereby infection may cause preterm labor remains uncertain. It has been specuIated that infection leads to an increased generation of prostaglandins by intrauterine tissues and that this causes preterm labor as seems to be the case for term labor. Several mechanisms have been suggested for this action. Firstly, bacteria have been shown to contain phospholipase AZ activity (2) and this enzyme could act to increase substrate availability for prostaglandin biosynthesis. Secondly, certain bacteria have been demonstrated to act directly on amnion and stimulate prostaglandin biosynthesis (3, 4). Additionally, we have proposed (5) that the host reaction to infection, particularly recruitment of macrophages and their secretion of cytokines, is an important part of the mechanism of infection-driven preterm labor. In support of this proposal, we have provided evidence that endotoxin, interleukin 1 (ILla and ILl@ and tumor necrosis factor (TNF) will all enhance pros-
METHODS Placentae were obtained at elective cesarean section at term before the onset of labor. Decidua was *craped from the maternal face of the chorion and cells prepared by the method of Devlin et al. (9). Briefly, tissue is digested using a collagenase/DNAse solution. The cells and debris are passed through a discontinuous Percoll gradient (16% to 50%) and band 3 is plated in 24 well culture dishes (Pig. 1). We found, as shown previouSly (9), that these cells consistently produce prolactin, whereas this is not the case for cells from band 2 or 4. Incubations were conducted in quadruplicate on confluent cells from nine individual women for 16 hours with the following substances: - endotoxin
Date received 26 February 1990 Date accepted 21 April 1990 35
36
Prostaglandins Leukotrienes
and Essential Fatty Acids
biscdPercd&adent’
Fig. 1 Diagrammatic representation
-
of the Percoll gradient used for separation cells.
(E coli lipopolysaccharide, Sigma, St. Louis, MO.), interleukin 19 (ILlar) and interleukin 16 (IL18) (Dr. C. Dinarello, Tufts University, Boston), and tumor necrosis factor, TNF (Dr. A. Cerami, Rockefeller University, New York). The concentrations used were based on those found physiologically and pathophysiologically e.g. in the amniotic fluid of women with infections (8, 10). Prostaglandins were assayed directly in the culture media by specific radioimmunoassay techniques (11, 12, 13) using antisera purchased from Advanced Magnetics Inc., Cambridge, MA. Cellular protein was determined using the method of Lowry et al. (14). Statistical differences were assessed using Fisher’s Least Significance Difference Test.
El
Fig. 2
F24
WA Fla
RI
Ml
Prostaglandin production by cells from decidua.
RESULTS The rates of prostaglandin production under basal conditions were determined for cells from 4 individual patients. The results of a representative experiment are depicted in Figure 2. Additionally, we have computed the mean percentages of total production for each of these prostaglandins using data from all 4 experiments; this is based only on the prostaglandins measured. The mean percentage productions were prostaglandin Ez (PGEa 36%), prostaglandin Fza: (PGFz,, 29%), 13,14-dihydro-15 keto-PG& (PGFM, 12%), 6-keto-prostaglandin F,, (6-keto-PGFr,, 12%) and 11-deoxy-13,14-dihydro15keto-11,16-bicycle-PGE2 (PGEMII, 11%). On the basis of these results we chose to assay both PGEz and PGF*, in future experiments.
Fig. 3 The effects of bacterial endotoxin on prostaglandin production (mean k SEM, n = 4) by cells from decidua. Control vs endotoxin: PGE, p < 0.01; PGF,, p < 0.04
Prostaglandin Biosynthesis by Human Decidual Cells
31
The effects of interleukin lo and interleukin on (a) prostaglandin Er and^ (b) production_(mean ^_ -prostaglandin . __.^Fti --^^^ ---+ __ 18~__ SEM, n = 4) by cells from decidua. Control vs ILla: PGE, p < 0.03; PGF, p < 0.05 Control vs ILlp: POE, p < U.tMJ8; PUY,, (ILla, Sng/ml) p < 0.01
Fig. 5 The effects of tumor necrosis factor on prostaglandin production (mean f SEM, n = 4) by cells from decidua. Control vs TNF: PGE, p < 0.04; PGF, (TNF, 10 and 100 r&ml) p C 0.05
Endotoxin caused a significant concentration-related increase in the rate of both PGb and PGF2, production (Fig. 3). Both ILlm and ILll3 induced a massive stimulation of prostaglandin production by decidual cells (Fig. 4). We could not distinguish a significant difference between the dose-responses to those two cytokines. Addition of TNF to the incubation media likewise ‘enhanced both PGl& and PGF2, production (Fig. 5).
DISCUSSION
Our results indicate that decidual prostaglandin production may be a part of the mechanism of the onset of labor in response to infection. The response of decidual cells, in terms of prostaglandin
output, to IL1 and TNF is quite dramatic and consistent with responses of other cell types (15-18) including amnion (19, 20). The concentrations of these cytokines needed to cause this stimulating action are consistent both with those required in other cell types and, importantly, to those found in amniotic fluid during infection (21). The role of the decidua in the labor process has often focused on labor associated with pathologic conditions. For instance, decidual activation was first noted in association with abortion induced by extra-amniotic administration of saline (22). A similar sequence of events was suggested as a possibility in the initiation of spontaneous labor at term and indeed increased concentrations of prostaglandins have been found in decidua obtained after labor at term (23). Nevertheless, most subsequent studies have been unable to demonstrate any increase, with spontaneous labor at term, in prostaglandin production by decidual tissue or cells (e.g. 24-26). We believe that decidua may play a role in the mechanism of infection-driven preterm labor. It is believed (21) that the pathway for ascending infection involves a stage during which there is decidual invasion by microorganisms. Decidua contains cells that can respond to this challenge by secreting cytokines (27, 28). We have now shown that cytokines so formed can stimulate prostaglandin production by decidual cells and these prostaglandins may act on the adjacent myometrium to induce contractions and thence delivery. Acknowledgements We thank Susan Krantx for expert editorial assistance. We are grateful to Dr. C. A. Dinarello, Tufts University, Boston, and Dr. A. Cerami, Rockefeller University, New York for the gifts of recombinant ILlar, ILlS and TNF. These studies were supported in part by NIH Grants HD2U779 and HDCKV28.
38
Prostaglandins Leukotrienes
and Essential Fatty Acids
References 1. Garite T J, Freeman R K. Chorioamnionitis in the preterm gestation. Obstet Gynecol 59: 539-45, 1982. 2. Bejar R, Cube10 V, Davis C, Gluck L. Premature labor: Bacterial sources of phospholipase. Obstet Gynecol57: 479-82, 1981. 3. Lamont R F, Rose M, Elder M G. Effects of bacterial products on prostaglandin E production by amnion cells. Lancet 2: 1131-3, 1985. 4. Bennett P R, Rose M P, Myatt L. Preterm labor: Stimulation of arachidonic acid metabolism in human amnion by bacterial products. Am J Obstet Gynecoll56: 649-55,1987. 5. Romero R, Durum S, Dinarello C, Hobbins J C, Mitchell M D. Cellular and biochemical mechanisms for the onset of labor in intraamniotic infections. Proceedings of the Annual Meeting of the Society of Perinatal Obstetricians, San Antonio 37: Abstract 101, 1986. 6. Romero R, Hobbins J C, Mitchell M D. Endotoxin stimulates prostaglandin E, release from human amnion. Obstet Gynecol 71: 227-8, 1988. 7. Romero R, Dun& S, Dinarello C A, Hobbins J C, Mitchell M D. Interleukin-1 stimulates prostaglandin biosynthesis by human amnion. Prostaglandins 37: 13-22,1989. 8. Romero R, Manogue K, Mitchell M D, Wu Y K, Hobbins J C. Cerami A. Cachectin/tumor necrosis factor in the’amniotic fluid of women with intraamniotic infection and preterm labor. Am J Obstet Gynecol 161: 336-41, 1989. 9 Devlin E E, Arabian A, Glorieux F, Mamer 0. In Vitro Metabolism of 25-Hydroxycholecalciferol by Isolated Cells from Human Decidua. J Clin Endocrinol Metab 60(5): 880-5, 1985. 10 Romero R, Brody DT, Oyarzun E, Mazor M, Wu Y K. Hobbins J. Durum S K. Infection and labor. III. Interleukin-1: A signal for the onset of parturition. Am J Obstet Gynecol 160: 1117-23, 1989. 11. Mitchell M D, Flint A P F. Prostaglandin production by intrauterine tissues from periparturient sheep: use of a superfusion technique. J Endocrinol76: 11-21, 1978. 12. Strickland D M, Brennecke S P, Mitchell M D. Measurement of 13,14-dihydro-15-keto-prostaglandin F, and 6-keto-prostaglandin F,, in plasma by radioimmunoassay without prior extraction and chromatography. Prostaglandins Leukotrienes Med 9: 491-3,1982. 13. Mitchell M D, Ebenhack K, Kramer D L, Cox K, Cutrer S, Strickland D M. A sensitive radioimmunoassay for 1l-deoxy-13,14-dihydro-15-keto-ll,16-cyclo-prostagland in E, biosynthesis during human pregnancy and parturition. Prostaglandins Leukotrienes Medicine 9: 549-57,1982. 14. Lowry 0 H, Rosebrough N J, Farr A L, Randall R J. Protein measurement with the Folin phenol reagent. J Biol Chem 193: 265-75, 1951. 15. Mizel S B, Dayer J M, Krane S M, Mergenhagen
S E. Stimulation of rheumatoid synovial cell collagenase and prostaglandin production by partially purified lymphocyte-activating factor (interleukin-1). Proc Nat1 Acad Sci USA 78: 2474-2477,198l. 16. Baracos V, Rodemann H P, Dinarello C A, Goldberg A L. Stimulation of muscle protein degradation and prostaglandin E, release by leukocytic pyrogen (interleukin-1). A mechanism for the increased degradation of muscle proteins during fever. N Engi J Med 308: 553-558, 1983. 17. Rossi V R. Breviario F. Ghezzi P. Deiana E. Mantovani A. Prostacyclin synthesis induced in vascular cells by interleukin-1 , Science 229: 174-176,1985. 18. Xiao D, Levine L. Stimulation of arachidonic acid metabolism: Differences in potencies of recombinant human interleukin-1 on two cell types. Prostaglandins 32: 709-718, 1986. 19. Romero R, Durum S, Dinarello C A, Oyarzun E, Hobbins J C, Mitchell M D. Interleukin-1 stimulates prostaglandin biosynthesis by human amnion. Prostaalandins 37: 13-22, 1989. 20 Romero R, Manogue K R, Mitchell M D, Wu Y K. Ovarzun E. Hobbins J C. Cerami A. Infectiou and labor: cachectin-tumor necrosis factor in the amniotic fluid of women with intraamniotic infection and preterm labor. Am J Obstet Gynecol 161: 336-341. 21. Romero R, Mazor M, Wu Y K, Sirtori M, Oyarzun E, Mitchell M D, Hobbins J C. Infection in the pathogenesis of pretenn labor. Seminars in Perinatology 12: 262-279, 1988. 22. Gustavii B. Human decidua and uterine contractilitv. Q 343 in The Fetus and Birth. (J Knight, M-O’Connor eds) Elsevier, Amsterdam, 1977. 23. Willman E A, Collins W P. Distribution of prostaglandins E, and F,, within the foetoplacental unit throughout human pregnancy. J Endocr 69: 413-419,1976. 24. Mitchell M D, Bibby J, Hicks B R, TumbuIl A C. Specific production of prostaglandin E by human amnion in vitro. Prostaglandins 15: 377-382, 1978. 25. Okazaki T, Casey M L, Okita J R, MacDonald P C, Johnston J M. Initiation of human parturition XII. Biosynthesis and metabolism of prostaglandins in human fetal membranes and uterine decidua. Am J Obstet Gynecol 139: 373-381, 1981. 26. Olson D M, Skinner K, Challis J R G. Prostaglandin output in relation to parturition by cells dispersed from human intrauterine tissues. J Clin Endocrinol Metab 57: 694-699, 1983. 27. Kauma S W. The expression and localization of interleukin-18 (IL-18) mRNA in fetal membranes and placenta, with and without chorioamnionitis. Proceedings of the Annual Meeting of the Society for Gynecologic Investigation, San Diego, Abstract 550, 1989. 28. Romero R, Wu Y K, Brody D T, Oyarzun E, Duff G W, Durum S K. Human decidua: a source of interleukin-1. Obstet Gynecol73: 31-34, 1989.
INTRODUCTION
taglandin production by amnion cells (6, 7, 8). The actions of these substances on decidua are unknown. Whether they are generated in the fetal membranes or within the decidua itself, any action on prostaglandin production would be of significance due to direct access to the myometrium. Hence, we have evaluated the effects of endotoxin and cytokines dn decidual prostaglandin production.
Infection in pregnancy frequently is associated with preterm labor (1). The mechanism whereby infection may cause preterm labor remains uncertain. It has been specuIated that infection leads to an increased generation of prostaglandins by intrauterine tissues and that this causes preterm labor as seems to be the case for term labor. Several mechanisms have been suggested for this action. Firstly, bacteria have been shown to contain phospholipase AZ activity (2) and this enzyme could act to increase substrate availability for prostaglandin biosynthesis. Secondly, certain bacteria have been demonstrated to act directly on amnion and stimulate prostaglandin biosynthesis (3, 4). Additionally, we have proposed (5) that the host reaction to infection, particularly recruitment of macrophages and their secretion of cytokines, is an important part of the mechanism of infection-driven preterm labor. In support of this proposal, we have provided evidence that endotoxin, interleukin 1 (ILla and ILl@ and tumor necrosis factor (TNF) will all enhance pros-
METHODS Placentae were obtained at elective cesarean section at term before the onset of labor. Decidua was *craped from the maternal face of the chorion and cells prepared by the method of Devlin et al. (9). Briefly, tissue is digested using a collagenase/DNAse solution. The cells and debris are passed through a discontinuous Percoll gradient (16% to 50%) and band 3 is plated in 24 well culture dishes (Pig. 1). We found, as shown previouSly (9), that these cells consistently produce prolactin, whereas this is not the case for cells from band 2 or 4. Incubations were conducted in quadruplicate on confluent cells from nine individual women for 16 hours with the following substances: - endotoxin
Date received 26 February 1990 Date accepted 21 April 1990 35
36
Prostaglandins Leukotrienes
and Essential Fatty Acids
biscdPercd&adent’
Fig. 1 Diagrammatic representation
-
of the Percoll gradient used for separation cells.
(E coli lipopolysaccharide, Sigma, St. Louis, MO.), interleukin 19 (ILlar) and interleukin 16 (IL18) (Dr. C. Dinarello, Tufts University, Boston), and tumor necrosis factor, TNF (Dr. A. Cerami, Rockefeller University, New York). The concentrations used were based on those found physiologically and pathophysiologically e.g. in the amniotic fluid of women with infections (8, 10). Prostaglandins were assayed directly in the culture media by specific radioimmunoassay techniques (11, 12, 13) using antisera purchased from Advanced Magnetics Inc., Cambridge, MA. Cellular protein was determined using the method of Lowry et al. (14). Statistical differences were assessed using Fisher’s Least Significance Difference Test.
El
Fig. 2
F24
WA Fla
RI
Ml
Prostaglandin production by cells from decidua.
RESULTS The rates of prostaglandin production under basal conditions were determined for cells from 4 individual patients. The results of a representative experiment are depicted in Figure 2. Additionally, we have computed the mean percentages of total production for each of these prostaglandins using data from all 4 experiments; this is based only on the prostaglandins measured. The mean percentage productions were prostaglandin Ez (PGEa 36%), prostaglandin Fza: (PGFz,, 29%), 13,14-dihydro-15 keto-PG& (PGFM, 12%), 6-keto-prostaglandin F,, (6-keto-PGFr,, 12%) and 11-deoxy-13,14-dihydro15keto-11,16-bicycle-PGE2 (PGEMII, 11%). On the basis of these results we chose to assay both PGEz and PGF*, in future experiments.
Fig. 3 The effects of bacterial endotoxin on prostaglandin production (mean k SEM, n = 4) by cells from decidua. Control vs endotoxin: PGE, p < 0.01; PGF,, p < 0.04
Prostaglandin Biosynthesis by Human Decidual Cells
31
The effects of interleukin lo and interleukin on (a) prostaglandin Er and^ (b) production_(mean ^_ -prostaglandin . __.^Fti --^^^ ---+ __ 18~__ SEM, n = 4) by cells from decidua. Control vs ILla: PGE, p < 0.03; PGF, p < 0.05 Control vs ILlp: POE, p < U.tMJ8; PUY,, (ILla, Sng/ml) p < 0.01
Fig. 5 The effects of tumor necrosis factor on prostaglandin production (mean f SEM, n = 4) by cells from decidua. Control vs TNF: PGE, p < 0.04; PGF, (TNF, 10 and 100 r&ml) p C 0.05
Endotoxin caused a significant concentration-related increase in the rate of both PGb and PGF2, production (Fig. 3). Both ILlm and ILll3 induced a massive stimulation of prostaglandin production by decidual cells (Fig. 4). We could not distinguish a significant difference between the dose-responses to those two cytokines. Addition of TNF to the incubation media likewise ‘enhanced both PGl& and PGF2, production (Fig. 5).
DISCUSSION
Our results indicate that decidual prostaglandin production may be a part of the mechanism of the onset of labor in response to infection. The response of decidual cells, in terms of prostaglandin
output, to IL1 and TNF is quite dramatic and consistent with responses of other cell types (15-18) including amnion (19, 20). The concentrations of these cytokines needed to cause this stimulating action are consistent both with those required in other cell types and, importantly, to those found in amniotic fluid during infection (21). The role of the decidua in the labor process has often focused on labor associated with pathologic conditions. For instance, decidual activation was first noted in association with abortion induced by extra-amniotic administration of saline (22). A similar sequence of events was suggested as a possibility in the initiation of spontaneous labor at term and indeed increased concentrations of prostaglandins have been found in decidua obtained after labor at term (23). Nevertheless, most subsequent studies have been unable to demonstrate any increase, with spontaneous labor at term, in prostaglandin production by decidual tissue or cells (e.g. 24-26). We believe that decidua may play a role in the mechanism of infection-driven preterm labor. It is believed (21) that the pathway for ascending infection involves a stage during which there is decidual invasion by microorganisms. Decidua contains cells that can respond to this challenge by secreting cytokines (27, 28). We have now shown that cytokines so formed can stimulate prostaglandin production by decidual cells and these prostaglandins may act on the adjacent myometrium to induce contractions and thence delivery. Acknowledgements We thank Susan Krantx for expert editorial assistance. We are grateful to Dr. C. A. Dinarello, Tufts University, Boston, and Dr. A. Cerami, Rockefeller University, New York for the gifts of recombinant ILlar, ILlS and TNF. These studies were supported in part by NIH Grants HD2U779 and HDCKV28.
38
Prostaglandins Leukotrienes
and Essential Fatty Acids
References 1. Garite T J, Freeman R K. Chorioamnionitis in the preterm gestation. Obstet Gynecol 59: 539-45, 1982. 2. Bejar R, Cube10 V, Davis C, Gluck L. Premature labor: Bacterial sources of phospholipase. Obstet Gynecol57: 479-82, 1981. 3. Lamont R F, Rose M, Elder M G. Effects of bacterial products on prostaglandin E production by amnion cells. Lancet 2: 1131-3, 1985. 4. Bennett P R, Rose M P, Myatt L. Preterm labor: Stimulation of arachidonic acid metabolism in human amnion by bacterial products. Am J Obstet Gynecoll56: 649-55,1987. 5. Romero R, Durum S, Dinarello C, Hobbins J C, Mitchell M D. Cellular and biochemical mechanisms for the onset of labor in intraamniotic infections. Proceedings of the Annual Meeting of the Society of Perinatal Obstetricians, San Antonio 37: Abstract 101, 1986. 6. Romero R, Hobbins J C, Mitchell M D. Endotoxin stimulates prostaglandin E, release from human amnion. Obstet Gynecol 71: 227-8, 1988. 7. Romero R, Dun& S, Dinarello C A, Hobbins J C, Mitchell M D. Interleukin-1 stimulates prostaglandin biosynthesis by human amnion. Prostaglandins 37: 13-22,1989. 8. Romero R, Manogue K, Mitchell M D, Wu Y K, Hobbins J C. Cerami A. Cachectin/tumor necrosis factor in the’amniotic fluid of women with intraamniotic infection and preterm labor. Am J Obstet Gynecol 161: 336-41, 1989. 9 Devlin E E, Arabian A, Glorieux F, Mamer 0. In Vitro Metabolism of 25-Hydroxycholecalciferol by Isolated Cells from Human Decidua. J Clin Endocrinol Metab 60(5): 880-5, 1985. 10 Romero R, Brody DT, Oyarzun E, Mazor M, Wu Y K. Hobbins J. Durum S K. Infection and labor. III. Interleukin-1: A signal for the onset of parturition. Am J Obstet Gynecol 160: 1117-23, 1989. 11. Mitchell M D, Flint A P F. Prostaglandin production by intrauterine tissues from periparturient sheep: use of a superfusion technique. J Endocrinol76: 11-21, 1978. 12. Strickland D M, Brennecke S P, Mitchell M D. Measurement of 13,14-dihydro-15-keto-prostaglandin F, and 6-keto-prostaglandin F,, in plasma by radioimmunoassay without prior extraction and chromatography. Prostaglandins Leukotrienes Med 9: 491-3,1982. 13. Mitchell M D, Ebenhack K, Kramer D L, Cox K, Cutrer S, Strickland D M. A sensitive radioimmunoassay for 1l-deoxy-13,14-dihydro-15-keto-ll,16-cyclo-prostagland in E, biosynthesis during human pregnancy and parturition. Prostaglandins Leukotrienes Medicine 9: 549-57,1982. 14. Lowry 0 H, Rosebrough N J, Farr A L, Randall R J. Protein measurement with the Folin phenol reagent. J Biol Chem 193: 265-75, 1951. 15. Mizel S B, Dayer J M, Krane S M, Mergenhagen
S E. Stimulation of rheumatoid synovial cell collagenase and prostaglandin production by partially purified lymphocyte-activating factor (interleukin-1). Proc Nat1 Acad Sci USA 78: 2474-2477,198l. 16. Baracos V, Rodemann H P, Dinarello C A, Goldberg A L. Stimulation of muscle protein degradation and prostaglandin E, release by leukocytic pyrogen (interleukin-1). A mechanism for the increased degradation of muscle proteins during fever. N Engi J Med 308: 553-558, 1983. 17. Rossi V R. Breviario F. Ghezzi P. Deiana E. Mantovani A. Prostacyclin synthesis induced in vascular cells by interleukin-1 , Science 229: 174-176,1985. 18. Xiao D, Levine L. Stimulation of arachidonic acid metabolism: Differences in potencies of recombinant human interleukin-1 on two cell types. Prostaglandins 32: 709-718, 1986. 19. Romero R, Durum S, Dinarello C A, Oyarzun E, Hobbins J C, Mitchell M D. Interleukin-1 stimulates prostaglandin biosynthesis by human amnion. Prostaalandins 37: 13-22, 1989. 20 Romero R, Manogue K R, Mitchell M D, Wu Y K. Ovarzun E. Hobbins J C. Cerami A. Infectiou and labor: cachectin-tumor necrosis factor in the amniotic fluid of women with intraamniotic infection and preterm labor. Am J Obstet Gynecol 161: 336-341. 21. Romero R, Mazor M, Wu Y K, Sirtori M, Oyarzun E, Mitchell M D, Hobbins J C. Infection in the pathogenesis of pretenn labor. Seminars in Perinatology 12: 262-279, 1988. 22. Gustavii B. Human decidua and uterine contractilitv. Q 343 in The Fetus and Birth. (J Knight, M-O’Connor eds) Elsevier, Amsterdam, 1977. 23. Willman E A, Collins W P. Distribution of prostaglandins E, and F,, within the foetoplacental unit throughout human pregnancy. J Endocr 69: 413-419,1976. 24. Mitchell M D, Bibby J, Hicks B R, TumbuIl A C. Specific production of prostaglandin E by human amnion in vitro. Prostaglandins 15: 377-382, 1978. 25. Okazaki T, Casey M L, Okita J R, MacDonald P C, Johnston J M. Initiation of human parturition XII. Biosynthesis and metabolism of prostaglandins in human fetal membranes and uterine decidua. Am J Obstet Gynecol 139: 373-381, 1981. 26. Olson D M, Skinner K, Challis J R G. Prostaglandin output in relation to parturition by cells dispersed from human intrauterine tissues. J Clin Endocrinol Metab 57: 694-699, 1983. 27. Kauma S W. The expression and localization of interleukin-18 (IL-18) mRNA in fetal membranes and placenta, with and without chorioamnionitis. Proceedings of the Annual Meeting of the Society for Gynecologic Investigation, San Diego, Abstract 550, 1989. 28. Romero R, Wu Y K, Brody D T, Oyarzun E, Duff G W, Durum S K. Human decidua: a source of interleukin-1. Obstet Gynecol73: 31-34, 1989.
