- Email: [email protected]
Do catechol estrogens participate in the initiation of labor?
October 1991 Am J Obstet Gynecol
Satin, Hankins, and Yeomans
spective comparison of hourly and quarter hourly oxytocin dose increase intervals for the induction of labor at term. Obstet Gynecol 1990;75:757-61. 15. Seitchik], Amico ], Robinson A, Castillo M. Oxytocin augmentation of dysfunctional labor. IV. Oxytocin pharmacokinetics. AM] OBSTET GYNECOL 1984;150:225-8.
16. Tuppy H. The influence of enzymes on neuro-hypophyseal hormones and similar peptides. Hand Exp Pharmacol 1968;23:67-129. 17. Ryden K, Sjoholm 1. Half-life of oxytocin in blood of pregnant and nonpregnant women. Acta Endocrinol (Copenh) 1969;61:425-31.
Do catechol estrogens participate in the initiation of labor? Anjan Biswas, PhD, Anjan Chaudhury, MD, Sati C. Chattoraj, PhD, and Sidney L. Dale, PhD Boston, Massachusetts To assess the role of catechol estrogens in the initiation of labor, we compared the levels in amniotic fluid during the second and third trimesters and from women undergoing cesarean section at term not in labor and those with spontaneous labor at term. Catechol estrogen concentrations in amniotic fluid increased significantly with the progress of pregnancy. Further, concentrations (mean ± SE) were significantly higher in spontaneous labor at term (468.6 ± 29.5 pg/ml) compared with those obtained during cesarean section (242.6 ± 22.3 pg/ml) at term not in labor. We suggest that catechol estrogens, through their stimulating effects on prostaglandin synthesis, participate in the initiation of labor. (AM J OBSTET GYNECOL 1991 ;165:984-7.)
Key words: Catechol estrogens, amniotic fluid, labor, gestational age, prostaglandin The mechanism of the onset of labor in humans still remains incompletely understood. As opposed to ruminants, human parturition is not preceded by dramatic changes in the concentration of progesterone or estrogens in maternal circulation or changes in cortisol levels in the fetal circulation. 1 In spite of the differences in the biochemical events occurring before labor among species, the central role of prostaglandins in the normal onset and progression oflabor in all mammalian species studied so far has become evident in recent years. 2 Whereas the factors initiating and regulating prostaglandin synthesis in the fetal membrane and the uterine wall remain to be elucidated, catechol estrogens, major metabolites of estrone and estradiol in both laboratory animals and humans,'· 4 can be a significant factor in this regard. Recent studies have shown that catechol estrogens increase the production of prostaglandins even more than does the parent compound in rat From the Department of Obstetrics and Gynecology and the Division of Perinatology, Boston University School of Mecicine. Supported in part by grant CA-39381 from the National Cancer 1nstitute. Presented at the Eleventh Annual Meeting of the Society of Perinatal Obstetricians, San Francisco, California, January 28-February 2,
1991.
Reprint requests: Sati C. Chattoraj, PhD, Department of Obstetrics and Gynecology, Boston Univesity School of Medicine, 80 East Concord St., No. 801, Boston, MA 02118. 6/6/30946
and human uterus,5 intrauterine tissues at parturition,6 and rabbit blastocysts and endometrium. 7 As potent competitive inhibitors of catechol-O-methyltransferase, catechol estrogens potentiate the lipolytic effect of epinephrine in releasing arachidonic acid from phospholipids. 8 It is interesting to note that catechol-O-methyltransferase, which is the enzyme of prime importance in the metabolism of catechol estrogens and the catecholamines, has been found to be very high in human decidua vera tissue during pregnancy, reaching maximum levels at term.9 The conversion of estrogens to catechol estrogens in human uterus lO and placental! and in a host of other tissues including the fetal brain and pituitary' make catechol estrogens an important factor to be considered in the mechanism of parturition. We have previously shown that umbilical venous and arterial levels of catechol estrogens are significantly higher at vaginal delivery than at abdominal delivery, without any significant difference in the maternal peripheral plasma content between the two modes of delivery.12 We have also reported recently that urinary catechol estrogens excretion in rats increases during pregnancy, reaching maximum levels before labor. 13 In view of these considerations, our investigation was undertaken to evaluate further the status of catechol estrogens in amniotic fluid during pregnancy and at different modes of delivery. Results show that levels of catechol estrogens increase with the progress of preg-
Catechol estrogens in parturition
Volume 165 Number 4, Part 1
nancy and are significantly higher at vaginal delivery in comparison with those obtained at abdominal delivery not in labor. Material and methods
Fifty-four healthy women who gave informed consent (21 to 36 years old) were included in our study, which was approved by the institutional review board. Amniocentesis was performed as a part of clinical care. Amniotic fluid was collected during the second trimester (17.1 ± 1.2 weeks) of pregnancy for fetal karyotyping (n = 7) and from third-trimester patients (36.1 ± 0.9 weeks) for determination of fetal lung maturity (n = 9). Samples of amniotic fluid (38.8 ± 1.5 weeks) were obtained during cesarean section (not in labor) by needle aspiration through the intact membrane after the uterine wall was opened (n = 18) and from women in active labor (39.9 ± 1.3 weeks) from a pressure catheter introduced at the time of amniotomy (n = 20). Patients in the study group were free of medical and obstetric complications. Oxytocin, narcotics, anesthetic agents, and antibiotics were not used before delivery. Continuous epidural analgesia was provided for both modes of delivery. The fluid was collected in sterile containers containing 0.5 ml of 5% aqueous ascorbic acid to ensure the stability of catechol estrogens and stored at - 20° C until analyzed. Radioactive and inert 2-hydroxyestrone was synthesized, purified, and stored as described by us.' Organic solvents were purchased (glass distilled) from Burdick and Jackson Labs, Inc. (Muskegon, Mich.). The phosphate-saline solution buffer (0.1 mollL, pH 7.2; 0.9% sodium chloride, 0.1 % sodium azide, and 0.1 % globulin fraction II) used in the radioimmunoassay contained 0.05% ascorbic acid for the protection of the catechol estrogens. 4 Dextran-coated charcoal was prepared by adding 0.5 gm dextran T-70 (Pharmacia Fine Chemicals, Piscataway, N.J.) to 5 gm Norit A (Fisher Scientific Company, Pittsburgh) in 40 ml buffer and was diluted to 10 mg charcoall0.2 ml before use. Radioactivity was counted in 10 ml Liquiscint (National Diagnostics, Somerville, N.J.). Radioimmunoassay was performed as previously described by us4 . 12 with minor changes. Samples of 1 ml aliquots were extracted with 10 ml methylene chloride that was washed with 2 ml bicarbonate buffer and 10% acetic acid. The organic extract was evaporated to dryness under a stream of nitrogen. Catechol estrogen was then quantitated with a 5 % aliquot of the extract, in duplicate, by radioimmunoassay. Water blanks and control samples were also included in each assay. Blank values were subtracted before final computation. Recovery of added radioactive 2-hydroxyestrone was 72.3% ± 7.3% (mean ± SD). Water blanks were 3.4 ± 1.9 pg (mean ± SD). Sensitivity, defined as the mean of the blank value plus 2 SD, is 7.2 pg per tube.
985
Table I. Parallelism tests for catechol estrogen analysis in amniotic fluid (picograms per milliliter)* Dilution
Observed value
Expected value (% difference)
o
375 200 108
375 188 (+6) 125 (- 13.6)
1 :2 1: 3
*Data yielded a correlation coefficient of ,.
=
0.99.
The specificity of measurements of catechol estrogens has been reported in our previous publications." 12 For this study samples were further subjected to parallelism tests by assaying undiluted and diluted samples (Table I) . The correlation coefficient (0.99) of parallelism tests indicates that the relative rankings of the two data sets involved are nearly perfect. The intraassay and interassay coefficients of variation were 5.8% and 6.7%, respectively. In our study no chromatographic separation was performed before radioimmunoassay; thus the results include 2-hydroxyestrone and 2-hydroxyestradiol because both cross react 100% with the antisera.' Statistical comparison of the mean level of catechol estrogens across the four study groups was made through analysis of variance . Subsequent pairwise comparisons of groups were made through the Tukey multiple comparison procedure. Results
Levels of catechol estrogens in amniotic fluid during pregnancy and in amniotic fluid obtained during both modes of delivery are depicted in Fig. I. The gestational age between two modes of delivery was not statistically different. Levels of catechol estrogens differ significantly (p < 0.001) across the four study groups. Multiple comparisons show that levels of catechol estrogens (mean ± SE) increase significantly (p < 0.001) in the third trimester (208.5 ± 22.4 pg/ml) compared with the levels observed in the second trimester (65.0 ± 9.5 pg/ml). A sharp rise in the level of catechol estrogens was observed (p < 0.001 pg/ml) during spontaneous labor at term (468.6 ± 29.5 pg/ml) compared with that of the third trimester and at cesarean section (242.6 ± 22.3 pgi ml). There was no significant difference in levels observed between the third trimester and cesarean section at term. Comment
Concentrations of catechol estrogens in ammo tic fluid increase significantly with the progress of pregnancy, reaching maximum at term. There is no significant difference between the levels in the third trimester and those obtained at cesarean section at term. How-
986
Biswas et al.
October 1991 Am J Obstet C yoccol
00'
70.
E
a.
§
'00
o
Q.
c CII
o
so.
CII 0
!::
W
'0 ~
0 CII
iii
(.)
'" 0 100
0 0
t
lOO
10'
t A
(n=7)
0 0
§ 0
€l
*
A 2nd trimester B 3rd trimester C C-section at term not in labor o Spontaneous labor at term
fo o (3
o o
0
(3 0 0
B
C
o
(n=9)
(n=18)
(n=20)
Fig. 1. Catechol estrogen concentrations (picograms per milliliter) during pregnancy and at different modes of delivery. Mean indicated by horizontal bar. A versus B, p < 0.001 ; B versus D, p < 0.001; B versus C, NS; C versus D, p < 0.001.
ever, a dramatic increase in concentration of catechol estrogens is observed in amniotic fluid collected at vaginal delivery (Fig. 1). Our data corroborate our previous findings of a significantly elevated concentration of catechol estrogens in cord blood at vaginal delivery. 12 Significantly higher levels in both cord blood and amniotic fluid at vaginal delivery in comparison with those obtained at abdominal delivery would suggest that before or at the onset of labor there is an increase in production of catechol estrogens. Furthermore, since there is no significant difference in maternal peripheral plasma levels of catechol estrogens between the two modes of delivery,12 the increased production is perhaps localized to the fetoplacental complex, including fetal membranes. We have previously suggested that because of the high metabolic clearance rate, catechol estrogens in the peripheral circulation are not able to playa significant role in the reproductive processes. 14 If there is any intrinsic role for catechol estrogens, then it is through their formation in the tissues in which they act. 14. 15 Indeed, the absence of perceptible changes in progesterone and estrogen concentrations in the maternal peripheral plasma, either at term or in association with preterm labor,'6. 17 prompted investigators to study the formation of steroids within the intrauterine tissues and consequent paracrine regulation of prostaglandin production.'·' 19 Fetal membranes and decidua are capable of producing estrone and estradiol, and the activity of the enzyme estrone sulfatase in decidua and chorion increases substantially with the onset of labor.20 Thus the supply of unconjugated estrone may result in increased formation of catechol estrogens in the fetal membranes. Alternatively, the increased accumulation of catechol estrogens in amniotic fluid
may be due to fetal urinary excretion. It is possible that as the fetus matures there is increased excretion of catechol estrogens into the amniotic fluid, reaching a maximum before the onset oflabor. Catechol estrogens in turn, by transmembrane diffusion, directly or indirectly augment the synthesis of prostaglandin in the fetomaternal lining, leading to the initiation of labor and delivery. The report on the existence in fetal urine of a stimulatory substance of small molecular weight for prostaglandin synthesis 2' strengthens such a proposition. Catechol estrogens may also indirectly stimulate prostaglandin formation. Catecholamines are present in amniotic fluid in increasing concentration during late pregnancy.22 They may stimulate adenylate cyclase and influence prostaglandin production through l3-adrenergic receptors present in the amnion tissue." Because catechol estrogens are potent competitive inhibitors of catechol-O-methyltransferase, they can protect catecholamines from inactivation, thereby potentiating and prolonging the action of these substances. The existence of protein-stimulating and protein-inhibitory substances in amniotic fluid for prostaglandin synthesis has been reported. I S Wilson et aU4 have recently described the isolation and purification of a protein from amniotic fluid that inhibits release of arachidonic acid from human decidual cells. The functional relationship of catechol estrogens with this and other inhibitory substances in amniotic fluid is not known. We thank Dr. David Acker for his continued support and interest, Dr. Tim Haren for statistical analysis, Dr. Aleksander Gajewski for his technical assistance, and Ms. Dallas Slawter for her assistance with manuscript preparation.
Catechol estrogens in parturition
Volume 165 Number 4, Part 1
REFERENCES 1. Thorburn GD, Challis ]RG. Endocrine control of parturition. Physiol Rev 1979;59:863-918. 2. Casey ML, MacDonald PC. The initiation of labor in women: regulations of phospholipid and arachidonic acid metabolism and of prostaglandin production. Semin PerinatoI1986;10:270-5. 3. Ball P, Knuppen R. Catecholoestrogens: chemistry, biogenesis, metabolism, occurrence and physiological significance. Acta Endocrinol (Copenh) 1980;232(suppl): 1-128. 4. Chattoraj SC, Fanous AS, Cecchini D], Lowe EW. A radioimmunoassay method for urinary catechol estrogens. Steroids 1978;31 :375-91. 5. Kelly RW, Abel MH. A comparison of the effects of 4catechol oestrogens and 2-pyrogallol oestrogens on prostaglandin synthesis by the rat and human uterus . .I Steroid Biochem 1981;14:787-91. 6. Olson DM, Skinner K, Challis ]RG. Estradiol-I 713 and 2hydroxyestradiol-1713-induced differential production of prostaglandins by cells dispersed from human intrauterine tissues at parturition. Prostaglandins 1983;25:639-51. 7. Pakrasi PL, Dey SK. Catechol estrogens stimulate synthesis of prostaglandins in the pre-implantation rabbit blastocyst and endometrium. Bioi Reprod 1983;29:347-54. 8. Ackerman GE, Johnston ]M, Mendelson CR. The potentiation of epinephrine induced lipolysis by the catechol estrogens and their methoxy derivatives [Abstract 724]. In: Proceedings of the sixty-second annual meeting of the Endocrine Society, Washington, DC, June 18-20, 1980. Washington, DC: Endocrine Society, 1980:255. 9. Linette CM, MacDonald Pc. Characterization of catecholO-methyltransferase activity in human uterine decidua vera tissues. AM] OBSTET GYNECOL 1983; 145:453-7. 10. Reddy VVR, Hanjani P, Rajan R. Synthesis of catecholestrogens by human uterus and leiomyoma. Steroids 1981 ;37: 195-203. 11. Fishman], Dixon D. 2- Hydroxylation of estradiol by human placental microsomes. Biochemistry 1967;6:1683-7. 12. Gross GL, Chattoraj SC, Schinfield ]S, Mastico R, Brennan TF, Edelin KC. Catechol estrogen concentration in maternal and umbilical circulation at different modes of delivery. AM] OBSTET GYNECOL 1988;158:1196-1200. 13. Biswas A, Dale SL, Gajewski A, Nuzzo P, Chattoraj SC. Temporal relationships among the excretory patterns of
14.
15. 16.
17.
18. 19.
20.
21.
22.
23.
24.
987
2-hydroxyestrone, estrone, estradiol, progesterone during pregnancy in the rat. Steroids 1991;56:136-41. Cecchini D], Chattoraj SC, Fanous AS, Panda SK, Brennan TF, Edelin KC. Radioimmunoassay of 2-hydroxyestrone in plasma during the estrous cycle of the rat; interrelationships with estriol, progesterone, and the gonadotropins. Endocrinology 1983; 112: 1122-6. Fishman]. Aromatic hydroxylation of estrogens. Ann Rev PhysioI1983;45:61-72. Block BSB, Liggins GC, Creasy RK. Preterm delivery is not predicted by serial plasma estradiol or progesterone concentration measurements. AM ] OBSTET GYNECOL 1984; 150:716-22. Smit DA, Essed GGM, de Haan]. Predictive value ofuterine contractility and the serum levels of progesterone and oestrogens with regard to preterm labour. Gynecol Obstet Invest 1984; 18:252-63. Challis JRG. In: Creasy R, Resnick R, eds. Maternal-fetal medicine: principles and practice. 2nd ed. Philadelphia: WB Saunders, 1989:463-76. Romero R, Scoccia B, Mazor M, Wu YK, Benveniste R. Evidence for a local change in the progesterone/estrogen ratio in human parturition in term. AM] OBSTET GYNECOL 1988;159:657-60. Chibbar R, Hobkirk R, Mitchell B. Sulfohydrolase activity for estrone sulfate and dehydroepiandrosterone sulfate in human fetal membranes and decidua around the time of parturition. ] Clin Endocrinol Metab 1986;62:90-4. Strickland DM, Saeed SA, Casey ML, Mitchell MD. Stimulation of prostaglandin biosynthesis by urine of human fetus may serve as a trigger for parturition. Science 1983;220:521-2. Divers WA, Wilkes MM, Babknia A, Yen SSC. An increase in catecholamines and metabolites in the amniotic fluid compartment from middle to late gestation. AM] OBSTET GYNECOL 1981;139:483-6. DiRenzo GC, Venincasa MD, Bleasdale ]E. The identification and characterization of l3-adrenergic receptors in human amnion tissue. AM ] OBSTET GYNECOL 1984; 148:398-405. Wilson T, Liggins GC, Joe L. Purification and characterization of a uterine phospholipase inhibitor that loses activity after labor onset in women. AM] OBSTET GYNECOL 1989;160:602-6.
Satin, Hankins, and Yeomans
spective comparison of hourly and quarter hourly oxytocin dose increase intervals for the induction of labor at term. Obstet Gynecol 1990;75:757-61. 15. Seitchik], Amico ], Robinson A, Castillo M. Oxytocin augmentation of dysfunctional labor. IV. Oxytocin pharmacokinetics. AM] OBSTET GYNECOL 1984;150:225-8.
16. Tuppy H. The influence of enzymes on neuro-hypophyseal hormones and similar peptides. Hand Exp Pharmacol 1968;23:67-129. 17. Ryden K, Sjoholm 1. Half-life of oxytocin in blood of pregnant and nonpregnant women. Acta Endocrinol (Copenh) 1969;61:425-31.
Do catechol estrogens participate in the initiation of labor? Anjan Biswas, PhD, Anjan Chaudhury, MD, Sati C. Chattoraj, PhD, and Sidney L. Dale, PhD Boston, Massachusetts To assess the role of catechol estrogens in the initiation of labor, we compared the levels in amniotic fluid during the second and third trimesters and from women undergoing cesarean section at term not in labor and those with spontaneous labor at term. Catechol estrogen concentrations in amniotic fluid increased significantly with the progress of pregnancy. Further, concentrations (mean ± SE) were significantly higher in spontaneous labor at term (468.6 ± 29.5 pg/ml) compared with those obtained during cesarean section (242.6 ± 22.3 pg/ml) at term not in labor. We suggest that catechol estrogens, through their stimulating effects on prostaglandin synthesis, participate in the initiation of labor. (AM J OBSTET GYNECOL 1991 ;165:984-7.)
Key words: Catechol estrogens, amniotic fluid, labor, gestational age, prostaglandin The mechanism of the onset of labor in humans still remains incompletely understood. As opposed to ruminants, human parturition is not preceded by dramatic changes in the concentration of progesterone or estrogens in maternal circulation or changes in cortisol levels in the fetal circulation. 1 In spite of the differences in the biochemical events occurring before labor among species, the central role of prostaglandins in the normal onset and progression oflabor in all mammalian species studied so far has become evident in recent years. 2 Whereas the factors initiating and regulating prostaglandin synthesis in the fetal membrane and the uterine wall remain to be elucidated, catechol estrogens, major metabolites of estrone and estradiol in both laboratory animals and humans,'· 4 can be a significant factor in this regard. Recent studies have shown that catechol estrogens increase the production of prostaglandins even more than does the parent compound in rat From the Department of Obstetrics and Gynecology and the Division of Perinatology, Boston University School of Mecicine. Supported in part by grant CA-39381 from the National Cancer 1nstitute. Presented at the Eleventh Annual Meeting of the Society of Perinatal Obstetricians, San Francisco, California, January 28-February 2,
1991.
Reprint requests: Sati C. Chattoraj, PhD, Department of Obstetrics and Gynecology, Boston Univesity School of Medicine, 80 East Concord St., No. 801, Boston, MA 02118. 6/6/30946
and human uterus,5 intrauterine tissues at parturition,6 and rabbit blastocysts and endometrium. 7 As potent competitive inhibitors of catechol-O-methyltransferase, catechol estrogens potentiate the lipolytic effect of epinephrine in releasing arachidonic acid from phospholipids. 8 It is interesting to note that catechol-O-methyltransferase, which is the enzyme of prime importance in the metabolism of catechol estrogens and the catecholamines, has been found to be very high in human decidua vera tissue during pregnancy, reaching maximum levels at term.9 The conversion of estrogens to catechol estrogens in human uterus lO and placental! and in a host of other tissues including the fetal brain and pituitary' make catechol estrogens an important factor to be considered in the mechanism of parturition. We have previously shown that umbilical venous and arterial levels of catechol estrogens are significantly higher at vaginal delivery than at abdominal delivery, without any significant difference in the maternal peripheral plasma content between the two modes of delivery.12 We have also reported recently that urinary catechol estrogens excretion in rats increases during pregnancy, reaching maximum levels before labor. 13 In view of these considerations, our investigation was undertaken to evaluate further the status of catechol estrogens in amniotic fluid during pregnancy and at different modes of delivery. Results show that levels of catechol estrogens increase with the progress of preg-
Catechol estrogens in parturition
Volume 165 Number 4, Part 1
nancy and are significantly higher at vaginal delivery in comparison with those obtained at abdominal delivery not in labor. Material and methods
Fifty-four healthy women who gave informed consent (21 to 36 years old) were included in our study, which was approved by the institutional review board. Amniocentesis was performed as a part of clinical care. Amniotic fluid was collected during the second trimester (17.1 ± 1.2 weeks) of pregnancy for fetal karyotyping (n = 7) and from third-trimester patients (36.1 ± 0.9 weeks) for determination of fetal lung maturity (n = 9). Samples of amniotic fluid (38.8 ± 1.5 weeks) were obtained during cesarean section (not in labor) by needle aspiration through the intact membrane after the uterine wall was opened (n = 18) and from women in active labor (39.9 ± 1.3 weeks) from a pressure catheter introduced at the time of amniotomy (n = 20). Patients in the study group were free of medical and obstetric complications. Oxytocin, narcotics, anesthetic agents, and antibiotics were not used before delivery. Continuous epidural analgesia was provided for both modes of delivery. The fluid was collected in sterile containers containing 0.5 ml of 5% aqueous ascorbic acid to ensure the stability of catechol estrogens and stored at - 20° C until analyzed. Radioactive and inert 2-hydroxyestrone was synthesized, purified, and stored as described by us.' Organic solvents were purchased (glass distilled) from Burdick and Jackson Labs, Inc. (Muskegon, Mich.). The phosphate-saline solution buffer (0.1 mollL, pH 7.2; 0.9% sodium chloride, 0.1 % sodium azide, and 0.1 % globulin fraction II) used in the radioimmunoassay contained 0.05% ascorbic acid for the protection of the catechol estrogens. 4 Dextran-coated charcoal was prepared by adding 0.5 gm dextran T-70 (Pharmacia Fine Chemicals, Piscataway, N.J.) to 5 gm Norit A (Fisher Scientific Company, Pittsburgh) in 40 ml buffer and was diluted to 10 mg charcoall0.2 ml before use. Radioactivity was counted in 10 ml Liquiscint (National Diagnostics, Somerville, N.J.). Radioimmunoassay was performed as previously described by us4 . 12 with minor changes. Samples of 1 ml aliquots were extracted with 10 ml methylene chloride that was washed with 2 ml bicarbonate buffer and 10% acetic acid. The organic extract was evaporated to dryness under a stream of nitrogen. Catechol estrogen was then quantitated with a 5 % aliquot of the extract, in duplicate, by radioimmunoassay. Water blanks and control samples were also included in each assay. Blank values were subtracted before final computation. Recovery of added radioactive 2-hydroxyestrone was 72.3% ± 7.3% (mean ± SD). Water blanks were 3.4 ± 1.9 pg (mean ± SD). Sensitivity, defined as the mean of the blank value plus 2 SD, is 7.2 pg per tube.
985
Table I. Parallelism tests for catechol estrogen analysis in amniotic fluid (picograms per milliliter)* Dilution
Observed value
Expected value (% difference)
o
375 200 108
375 188 (+6) 125 (- 13.6)
1 :2 1: 3
*Data yielded a correlation coefficient of ,.
=
0.99.
The specificity of measurements of catechol estrogens has been reported in our previous publications." 12 For this study samples were further subjected to parallelism tests by assaying undiluted and diluted samples (Table I) . The correlation coefficient (0.99) of parallelism tests indicates that the relative rankings of the two data sets involved are nearly perfect. The intraassay and interassay coefficients of variation were 5.8% and 6.7%, respectively. In our study no chromatographic separation was performed before radioimmunoassay; thus the results include 2-hydroxyestrone and 2-hydroxyestradiol because both cross react 100% with the antisera.' Statistical comparison of the mean level of catechol estrogens across the four study groups was made through analysis of variance . Subsequent pairwise comparisons of groups were made through the Tukey multiple comparison procedure. Results
Levels of catechol estrogens in amniotic fluid during pregnancy and in amniotic fluid obtained during both modes of delivery are depicted in Fig. I. The gestational age between two modes of delivery was not statistically different. Levels of catechol estrogens differ significantly (p < 0.001) across the four study groups. Multiple comparisons show that levels of catechol estrogens (mean ± SE) increase significantly (p < 0.001) in the third trimester (208.5 ± 22.4 pg/ml) compared with the levels observed in the second trimester (65.0 ± 9.5 pg/ml). A sharp rise in the level of catechol estrogens was observed (p < 0.001 pg/ml) during spontaneous labor at term (468.6 ± 29.5 pg/ml) compared with that of the third trimester and at cesarean section (242.6 ± 22.3 pgi ml). There was no significant difference in levels observed between the third trimester and cesarean section at term. Comment
Concentrations of catechol estrogens in ammo tic fluid increase significantly with the progress of pregnancy, reaching maximum at term. There is no significant difference between the levels in the third trimester and those obtained at cesarean section at term. How-
986
Biswas et al.
October 1991 Am J Obstet C yoccol
00'
70.
E
a.
§
'00
o
Q.
c CII
o
so.
CII 0
!::
W
'0 ~
0 CII
iii
(.)
'" 0 100
0 0
t
lOO
10'
t A
(n=7)
0 0
§ 0
€l
*
A 2nd trimester B 3rd trimester C C-section at term not in labor o Spontaneous labor at term
fo o (3
o o
0
(3 0 0
B
C
o
(n=9)
(n=18)
(n=20)
Fig. 1. Catechol estrogen concentrations (picograms per milliliter) during pregnancy and at different modes of delivery. Mean indicated by horizontal bar. A versus B, p < 0.001 ; B versus D, p < 0.001; B versus C, NS; C versus D, p < 0.001.
ever, a dramatic increase in concentration of catechol estrogens is observed in amniotic fluid collected at vaginal delivery (Fig. 1). Our data corroborate our previous findings of a significantly elevated concentration of catechol estrogens in cord blood at vaginal delivery. 12 Significantly higher levels in both cord blood and amniotic fluid at vaginal delivery in comparison with those obtained at abdominal delivery would suggest that before or at the onset of labor there is an increase in production of catechol estrogens. Furthermore, since there is no significant difference in maternal peripheral plasma levels of catechol estrogens between the two modes of delivery,12 the increased production is perhaps localized to the fetoplacental complex, including fetal membranes. We have previously suggested that because of the high metabolic clearance rate, catechol estrogens in the peripheral circulation are not able to playa significant role in the reproductive processes. 14 If there is any intrinsic role for catechol estrogens, then it is through their formation in the tissues in which they act. 14. 15 Indeed, the absence of perceptible changes in progesterone and estrogen concentrations in the maternal peripheral plasma, either at term or in association with preterm labor,'6. 17 prompted investigators to study the formation of steroids within the intrauterine tissues and consequent paracrine regulation of prostaglandin production.'·' 19 Fetal membranes and decidua are capable of producing estrone and estradiol, and the activity of the enzyme estrone sulfatase in decidua and chorion increases substantially with the onset of labor.20 Thus the supply of unconjugated estrone may result in increased formation of catechol estrogens in the fetal membranes. Alternatively, the increased accumulation of catechol estrogens in amniotic fluid
may be due to fetal urinary excretion. It is possible that as the fetus matures there is increased excretion of catechol estrogens into the amniotic fluid, reaching a maximum before the onset oflabor. Catechol estrogens in turn, by transmembrane diffusion, directly or indirectly augment the synthesis of prostaglandin in the fetomaternal lining, leading to the initiation of labor and delivery. The report on the existence in fetal urine of a stimulatory substance of small molecular weight for prostaglandin synthesis 2' strengthens such a proposition. Catechol estrogens may also indirectly stimulate prostaglandin formation. Catecholamines are present in amniotic fluid in increasing concentration during late pregnancy.22 They may stimulate adenylate cyclase and influence prostaglandin production through l3-adrenergic receptors present in the amnion tissue." Because catechol estrogens are potent competitive inhibitors of catechol-O-methyltransferase, they can protect catecholamines from inactivation, thereby potentiating and prolonging the action of these substances. The existence of protein-stimulating and protein-inhibitory substances in amniotic fluid for prostaglandin synthesis has been reported. I S Wilson et aU4 have recently described the isolation and purification of a protein from amniotic fluid that inhibits release of arachidonic acid from human decidual cells. The functional relationship of catechol estrogens with this and other inhibitory substances in amniotic fluid is not known. We thank Dr. David Acker for his continued support and interest, Dr. Tim Haren for statistical analysis, Dr. Aleksander Gajewski for his technical assistance, and Ms. Dallas Slawter for her assistance with manuscript preparation.
Catechol estrogens in parturition
Volume 165 Number 4, Part 1
REFERENCES 1. Thorburn GD, Challis ]RG. Endocrine control of parturition. Physiol Rev 1979;59:863-918. 2. Casey ML, MacDonald PC. The initiation of labor in women: regulations of phospholipid and arachidonic acid metabolism and of prostaglandin production. Semin PerinatoI1986;10:270-5. 3. Ball P, Knuppen R. Catecholoestrogens: chemistry, biogenesis, metabolism, occurrence and physiological significance. Acta Endocrinol (Copenh) 1980;232(suppl): 1-128. 4. Chattoraj SC, Fanous AS, Cecchini D], Lowe EW. A radioimmunoassay method for urinary catechol estrogens. Steroids 1978;31 :375-91. 5. Kelly RW, Abel MH. A comparison of the effects of 4catechol oestrogens and 2-pyrogallol oestrogens on prostaglandin synthesis by the rat and human uterus . .I Steroid Biochem 1981;14:787-91. 6. Olson DM, Skinner K, Challis ]RG. Estradiol-I 713 and 2hydroxyestradiol-1713-induced differential production of prostaglandins by cells dispersed from human intrauterine tissues at parturition. Prostaglandins 1983;25:639-51. 7. Pakrasi PL, Dey SK. Catechol estrogens stimulate synthesis of prostaglandins in the pre-implantation rabbit blastocyst and endometrium. Bioi Reprod 1983;29:347-54. 8. Ackerman GE, Johnston ]M, Mendelson CR. The potentiation of epinephrine induced lipolysis by the catechol estrogens and their methoxy derivatives [Abstract 724]. In: Proceedings of the sixty-second annual meeting of the Endocrine Society, Washington, DC, June 18-20, 1980. Washington, DC: Endocrine Society, 1980:255. 9. Linette CM, MacDonald Pc. Characterization of catecholO-methyltransferase activity in human uterine decidua vera tissues. AM] OBSTET GYNECOL 1983; 145:453-7. 10. Reddy VVR, Hanjani P, Rajan R. Synthesis of catecholestrogens by human uterus and leiomyoma. Steroids 1981 ;37: 195-203. 11. Fishman], Dixon D. 2- Hydroxylation of estradiol by human placental microsomes. Biochemistry 1967;6:1683-7. 12. Gross GL, Chattoraj SC, Schinfield ]S, Mastico R, Brennan TF, Edelin KC. Catechol estrogen concentration in maternal and umbilical circulation at different modes of delivery. AM] OBSTET GYNECOL 1988;158:1196-1200. 13. Biswas A, Dale SL, Gajewski A, Nuzzo P, Chattoraj SC. Temporal relationships among the excretory patterns of
14.
15. 16.
17.
18. 19.
20.
21.
22.
23.
24.
987
2-hydroxyestrone, estrone, estradiol, progesterone during pregnancy in the rat. Steroids 1991;56:136-41. Cecchini D], Chattoraj SC, Fanous AS, Panda SK, Brennan TF, Edelin KC. Radioimmunoassay of 2-hydroxyestrone in plasma during the estrous cycle of the rat; interrelationships with estriol, progesterone, and the gonadotropins. Endocrinology 1983; 112: 1122-6. Fishman]. Aromatic hydroxylation of estrogens. Ann Rev PhysioI1983;45:61-72. Block BSB, Liggins GC, Creasy RK. Preterm delivery is not predicted by serial plasma estradiol or progesterone concentration measurements. AM ] OBSTET GYNECOL 1984; 150:716-22. Smit DA, Essed GGM, de Haan]. Predictive value ofuterine contractility and the serum levels of progesterone and oestrogens with regard to preterm labour. Gynecol Obstet Invest 1984; 18:252-63. Challis JRG. In: Creasy R, Resnick R, eds. Maternal-fetal medicine: principles and practice. 2nd ed. Philadelphia: WB Saunders, 1989:463-76. Romero R, Scoccia B, Mazor M, Wu YK, Benveniste R. Evidence for a local change in the progesterone/estrogen ratio in human parturition in term. AM] OBSTET GYNECOL 1988;159:657-60. Chibbar R, Hobkirk R, Mitchell B. Sulfohydrolase activity for estrone sulfate and dehydroepiandrosterone sulfate in human fetal membranes and decidua around the time of parturition. ] Clin Endocrinol Metab 1986;62:90-4. Strickland DM, Saeed SA, Casey ML, Mitchell MD. Stimulation of prostaglandin biosynthesis by urine of human fetus may serve as a trigger for parturition. Science 1983;220:521-2. Divers WA, Wilkes MM, Babknia A, Yen SSC. An increase in catecholamines and metabolites in the amniotic fluid compartment from middle to late gestation. AM] OBSTET GYNECOL 1981;139:483-6. DiRenzo GC, Venincasa MD, Bleasdale ]E. The identification and characterization of l3-adrenergic receptors in human amnion tissue. AM ] OBSTET GYNECOL 1984; 148:398-405. Wilson T, Liggins GC, Joe L. Purification and characterization of a uterine phospholipase inhibitor that loses activity after labor onset in women. AM] OBSTET GYNECOL 1989;160:602-6.