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Prostacyclin versus thromboxane metabolite excretion: changes in pregnancy and labor
European Journal of Obstetrics & Gynecology and Reproductive Elsevier
B~ologv, 35 (1990) 15-21
15
EUROBS 00900
Prostacyclin versus thromboxane excretion: changes in pregnancy Willy Department
A. Noort
and Marc
J.N.C.
metabolite and labor
Keirse
of Obstetrics, Leiden University Hospital. Leiden, The Netherlands Accepted for publication 5 July 1989
Summary Urinary TXB, and 6-keto-PGF,, were measured by high pressure liquid chromatography combined with radioimmunoassay, in order to determine whether or and TXB, followed a same pattern in not urinary excretion of 6-keto-PGF,, pregnancy and labor. The excretion of 6-keto-PGF,, was higher than that of TXB, in both non-pregnant and pregnant women, but the ratio between them increased in pregnancy. The urinary excretion of both 6-keto-PGF,, and TXB, excretion was significantly increased (p < 0.001) in pregnancy. Labor was associated with a much wider inter-individual variation in the excretion of 6-keto-PGF,, and TXB, than observed in pregnancy and in non-pregnant women. Also, the ratio between the two compounds varied more in labor than in pregnancy. The data indicate that the urinary levels of these two compounds do not follow a single well-determined pattern in pregnancy and labor. Thromboxane;
Prostacyclin; Prostanoids; Pregnancy; Labor
Introduction Pregnancy and labor are associated with marked changes in prostanoid metabolism. The changes apply to all of the prostanoids derived from arachidonic acid, but not all of these changes occur at the same time. Levels of prostaglandins and their metabolites, for example, remain remarkably constant in amniotic fluid, plasma and urine throughout most of pregnancy. Significant increases in their concentration are observed only at the onset of and during labor (reviewed by Keirse [9]). The production of prostacyclin (PGI,) and thromboxane (TXA,) on the other hand
Correspondence: Prof. Dr. M.J.N.C. Keirse, Department of Obstetrics & Gynecology, Leiden University Hospital, P.O. Box 9600, 2300 RC Leiden. The Netherlands.
0028-2243/90/%03.50
0 1990 Elsevier Science Publishers B.V. (Biomedical Division)
16
appears to increase far earlier in gestation. Thus, Goodman et al. [7] Ylikorkala et al. [21] and Fitzgerald et al. [4] all reported a 445-fold increase in the excretion of a major urinary metabolite of PGI,, 2,3-dinor-6-keto-PGF,,, during human pregnancy as compared with non-pregnant women. Noort et al. [15] observed an increase of similar magnitude in the urinary excretion of 6-keto-PGF,,, the stable hydrolysis product of PGI,, during pregnancy. The urinary excretion of both TXB, [16] and 2,3-dinor-TXB, [S] were found to be also significantly higher in pregnancy than in non-pregnant women, although Ylikorkala et al. [21] found no statistically significant differences between pregnant and puerperal women. Currently, there has been increasing interest in the regulation of thromboxane and prostacyclin synthesis in pregnancy. This has been fueled by the apparent success of thromboxane synthetase inhibition in the treatment of pregnancy-induced hypertension [18] and by the promising results of randomized controlled trials of prophylactic aspirin treatment in pregnancy [1,19]. In view of the widely aroused interest in the potential value of such treatments [3,12] there is a great need for further information on PGI, and TXA, production in normal pregnancy. We have previously reported the development of methods for measurement of urinary excretion of the stable products of PGI, and TXA,, 6-keto-PGF,, [15] and TXB, [16] in pregnancy. Although these investigations were conducted in two different groups of women, they suggested that changes in PGI, and TXA, production in pregnancy follow a different time pattern in that an increase in TXA, production appeared to precede the increase in PGI, production. Such a pattern would be consistent with in vitro observations that the human placenta produces mainly TXA, in early gestation [lo] and has only a limited capacity for PGI, synthesis [ll]. Although it is unknown as to what extent placental production contributes to the urinary excretion of 6-keto-PGF,, .and TXB,, there was thus a case for examining whether there really is a difference between the time patterns of 6-keto-PGF,, and TXB, excretion in human pregnancy. In addition, we investigated the relative proportions of urinary 6-keto-PGF,, and TXB, in individual women to assess whether the ratio between the excretions of these two compounds would change during pregnancy and labor. Material and methods Early morning (first voided) urine samples were collected, one sample each, from 36 women at different stages of clinically normal gestation ranging from 6 to 38 weeks and from 12 non-pregnant women of similar age. Samples were further obtained from 12 women in early labor with a contraction frequency of less than 3 per 10 min and a cervical dilatation of 4 cm or less, and from 12 women in advanced first-stage labor. Some of these pregnant women with normal pregnancies had been included in our previous study on urinary 6-keto-PGF,, levels [15]. The clinical characteristics of the pregnant women are shown in Table I; all were normotensive with blood pressures below 140/90 mmHg. Urine samples were centrifuged at 4°C and stored at - 20°C until analysis. Samples of 4 ml were acidified with 1 M citric acid to pH 3 and extracted with 10 ml petroleum ether after addition of 3000 cpm 6-keto[3H]PGF,, and [‘HITXB,
17 TABLE
I
Clinical characteristics Characteristics Age (years) Parity Gestational age at delivery (weeks) Infant birthweight (g)
of pregnant women included in the study mean + SD 28 + 1.9+ 40 3256
5.6 1.4
+ 1.5 +448
(Amersham International, Amersham U.K.). The aqueous phase was then extracted twice with methyl tert-butyl ether and these organic phases were evaporated under nitrogen for further extraction on Seppak C-18 octadecylsilyl silica cartridges (Waters Ass., Milford, MA). The dry residue was dissolved in 2 ml citric acidacidified water for application to the cartridges, which were then washed first with 10 ml acidified ethanol/water (15 : 85, v/v) and subsequently with 10 ml petroleum ether: methyl tert-butyl ether (90: 10, v/v). TXB, and 6-keto-PGF,, were eluted together with 10 ml methyl tert-butyl ether. The methyl tert-butyl ether was evaporated under nitrogen, and the residue dissolved in 0.25 ml water/acetic acid (99.25 : 0.75, v/v) for high-pressure liquid chromatography (HPLC) as described previously [ 161. The prostanoids were eluted with an increasing gradient of acetonitrile from 27 to 100% (v/v) in water/acetic acid (99.25 : 0.75, v/v) at a flow rate of 2 ml per min. One-ml fractions were collected and combined into a 6-keto-PGF,, (fractions 15-17) and a TXB, (fractions 25-28) fraction. The samples were lyophilized after excess acetonitrile had been evaporated under nitrogen. Radioimmunoassays of TXB, and 6-keto-PGFia were as described by Noort et al. [15,16]. Levels of TXB, and 6-keto-PGF,,were expressed per gram urinary creatinine. Creatinine was determined by the calorimetric method described by Folin [6]. The Mann-Whitney test was used for statistical analysis. The confidence intervals (ci) reported refer to 95% confidence intervals. Results Levels of both 6-keto-PGF,, and TXB, were significantly higher in urine of pregnant women than in that of non-pregnant women (p < 0.001). The increase above non-pregnant levels appeared to occur only toward the end of the first trimester (Fig. 1). Before 10 weeks of gestation (n = lo), all 6-keto-PGF,, levels and 8 of 10 TXB, levels fell within the range of values observed in non-pregnant women. From 20 weeks onwards this was the case for none of the 6-keto-PGF,, levels and for only 3 of 19 TXB, levels. Although there thus was a trend for an increase in both 6-keto-PGF,, and TXB, levels with advancing gestational age, most of this trend can be attributed to the low levels obtained before 10 weeks of gestation and the much higher levels thereafter (Fig. I). 6-Keto-PGF,, levels showed a statistically significant increase between the period from 10 to 19 weeks of gestation and that from 20 to 29 weeks. Levels at 10
&keto-PGF,,
ngfg treat. 12.5
TX82
rig/g treat.
6-keto-PGFk
/TXB2
ratio
5.0
2.5
C
.O NONPREGNANT
SQ
lo-19
20-29 WEEKS
z30
EARLY LATE FIRST STAGE
Fig. 1. Concentrations (rig/g creatinine; means with 95% confidence intervals) of and ratio between 6-keto-PGF,, and TXB, in urine before and during pregnancy and labor.
19 weeks were lower than at 20 to 29 weeks or at 30 to 39 weeks (p I 0.002), but there were no statistically significant differences between the latter two groups. TXB, excretion increased also significantly between the period of 10 to 19 weeks of gestation and that of 20 to 29 weeks (p I 0.02) with no further statistically significant increase in the second half of pregnancy. With the onset of labor, as judged from levels obtained in early labor with a uterine contractility of less than three contractions per 10 min, the mean level of both TXB, and 6-keto-PGF,, was higher than, but not statistically significantly different from, the mean level obtained in late pregnancy before the onset of labor. For both TXB, and especially 6-keto-PGF,, the range of values was much wider in early labor than in pregnancy, and this trend for a widening of the range increased further in advanced labor (Fig. 1). Levels in advanced labor just reached a statistically significant difference at p < 0.05 with levels in late pregnancy. to
Excretion of 6-keto-PGF,, was higher than that of TXB, in both pregnant and non-pregnant women. In accordance with the levels themselves, there was no change in the ratio of 6-keto-PGF,, to TXB, between non-pregnant women (2.5 f 1.0, mean f SD; ci: 1.9-3.1) and women in the first 10 weeks of pregnancy (2.6 & 1.0; ci: 1.9-3.3). Thereafter, the proportionally much larger increase in 6-keto-PGF,, excretion led to a more than 2-fold increase in the ratio of 6-keto-PGF,,/TXB, up to 5.9 (k1.8; ci: 4.4-7.4) in the third trimester of pregnancy (Fig. 1). The wide and TXB, levels during both early and individual variation in 6-keto-PGF,, advanced labor was also reflected in a wide individual variation in the ratio of these two compounds: 5.2 f 3.9 (mean + SD; ci: 2.7-7.7) in early and 7.7 &-5.5 (ci: 4.2-11.2) in advanced labor. Discussion
This study confirms our previous data and those of others of an increased excretion of 6-keto-PGF,, [15,21] and TXB, [16] in pregnancy. The increase appears to occur only at or after the first quarter of pregnancy, but the increase is well established before the second half of pregnancy is reached. These changes therefore appear to coincide with some of the major physiological changes and adaptations in pregnancy [14]. Some of these physiological adaptations have been credited to a relative predominance of PGI, production over that of TXA, in pregnancy [20] and this would be consistent with the increase in the ratio between 6-keto-PGF,, and TXB, observed in our study. We cannot assume, however, that all of the 6-keto-PGF,. and TXB, measured in this study originates from the systemic circulation, since the kidney itself can produce both TXB, and 6-keto-PGF,, [8,17]. Irrespective of the origin of these compounds it is clear that there is a much larger increase in 6-keto-PGF,, than in TXB, excretion in pregnancy, since the ratio between these two compounds doubles in comparison with that observed in the non-pregnant state. It is also clear that the levels of TXB, and 6-keto-PGF,, do not follow each other: an increase in one is not necessarily accompanied by a proportional increase in the other. This was particular obvious in urine samples obtained during labor. Levels of both 6-keto-PGF,. and TXB, in labor showed a much larger individual variation than at any other time in pregnancy and so did the ratio between 6-keto-PGF,, and TXB,, suggesting that levels of both compounds are not regulated by the same mechanism(s). The increase in TXB, in pregnancy may be partly derived from the placenta, which is known to contain a large amount of thromboxane synthase (Erwich and Keirse, unpublished data). Fitzgerald and colleagues [5], on the other hand, have argued that the increase in TXB, production in pregnancy is mainly derived from blood platelets and represents a state of increased platelet activation throughout pregnancy. Neither of these two sources would contribute much to the increase in 6-keto-PGF,,, since the placenta has a relatively poor capacity for PGI, production [ll] and since aspirin-inhibition of platelet prostanoid biosynthesis has little effect on the excretion of PGI, metabolites. Apart from a possible renal contribution, 6-keto-PGF,, levels are more likely to originate not from the platelets or the placenta but from the expanded vascular bed in pregnancy and/or from the
20
myometrium. Myometrium has a high capacity for PGI, production [2] and both the size of the myometrium and its PGI, synthase concentration per unit of weight are known to increase markedly in pregnancy [13]. The current observations did not confirm our hypothesis [15] than an increase in TXB, excretion would precede that of 6-keto-PGF,*; both appeared to increase at or about the 10th week of pregnancy. This had not been obvious in our previous study on TXB, excretion in pregnancy, since most samples in the first trimester of pregnancy had been obtained between 9 and 13 weeks of gestation, Both 6-ketoPGF,, and TXB, also showed an increase in labor and a much wider individual variation than in late pregnancy. This wide individual variation in both the levels of 6-keto-PGF,, and TXB, and the ratio between them indicates that production and/or excretion of these compounds in pregnancy and labor are largely independent from each other. Acknowledgements We are grateful to Mr. F.A. de Zwart for technical assistance. The Hague. supported by grant 28-1118 from the Praeventiefonds,
The study
was
References 1 Beaufils M, Uzan S, Donsimoni R, Colau JC. Prevention of pre-eclampsia by early antiplatelet therapy. Lancet 1985;i:840-842. 2 Christensen NJ, Green K. Bioconversion of arachidonic acid in human pregnant reproductive tissues. Biochem Med 1983;30:162-180. 3 Collins R, Wallenburg HCS. Pharmacological prevention and management of hypertensive disorders in pregnancy. In: Chalmers I, Enkin M, Keirse MJNC, eds. Effective care in pregnancy and childbirth. Oxford: Oxford University Press, 1989, in press. 4 Fitzgerald DJ, Entman SS, Mulloy K, FitzGerald GA. Decreased prostacychn biosynthesis preceding the clinical manifestation of pregnancy-induced hypertension. Circulation 1987;75:956-963. 5 Fitzgerald DJ, Mayo G, Catella F, Entman SS. FitzGeraId GA. Increased thromboxane biosynthesis in normal pregnancy is mainly derived from platelets. Am J Obstet Gynecol 1987;157:325-330. 6 Folin 0. On the determination of creatinine and creatine in urine. J Biol Chem 1914;17:469-473. 7 Goodman RP, Killam AP, Brash AR, Branch RA. Prostacyclin production during pregnancy: comparison of production during normal pregnancy and pregnancy complicated by hypertension. Am J Obstet Gynecol 1982;142:817-822. 8 Hassid A, Dunn MJ. Microsomal prostaglandin biosynthesis of human kidney. J Biol Chem 1980;255:2472-2475. 9 Keirse MJNC. Endogenous prostaglandins in human parturition. In: Keirse MJNC, Anderson ABM, Bennebroek Gravenhorst J, eds. Human parturition. The Hague: Leiden University Press, 1979;101-142. 10 Keirse MJNC. Biosynthesis and metabolism of prostaglandins within the human uterus in early and late pregnancy. In: Wood C, ed. The role of prostaglandins in Iabour. Royal Society of Medicine London 1985;25-38. 11 Keirse MJNC, Erwich JJHM, KIok G. Does or can human placenta produce prostacyclin? Placenta 1986;7:37-42. 12 Lancet. Editorial: Aspirin and pre-eclampsia. Lancet 1986;1:18-20. 13 Moonen P, Klok G, Keirse MJNC. Increase in concentrations of prostaglandin endoperoxide synthase and prostacyclin synthase in human myometrium in late pregnancy. Prostaglandins 1984;28:309-322.
21 14 Morgan DLM, Hytten FE. Midtrimester pregnancy a time of tranguility or activity? Br J Obstet Gynaecol 1984;91:532-537. 15 Noort WA, De Zwart FA, Keirse MJNC. Changes in urinary 6-keto-PGF,, excretion during pregnancy and labor. Prostaglandins 1988;35:573-582. 16 Noort WA, De Zwart FA, Keirse MJNC. Increase in urinary thromboxane excretion during pregnancy and labor. Prostaglandins 1987;34:413-421. 17 Schlondorff D, Ardaillou R. Prostaglandins and other arachidonic acid metabolites in the kidney. Kidney Int 1986;29:108-119. 18 Van Asscbe FA, Spitz B, Vermylen J, Deckmijn H. Preliminary observations on treatment of pregnancy-induced hypertension with a thromboxane synthetase inhibitor. Am J Obstet Gynecol 1984;148:216-218. 19 Wallenburg HCS, Dekker GA, Makovitz JW, Rotmans P. Low-dose aspirin prevents pregnancy-induced hypertension and pre-eclampsia in angiotensin-sensitive primigravidae. Lancet 1986;i:l-3. 20 Ylikorkala 0, MHkila U-M, Viinnikka L. Amniotic fluid prostacychn and thromboxane in normal, pre-eclamptic and some other complicated pregnancies. Am J Obstet Gynecol 1981;141:487-490. 21 Ylikorkala 0, Pekonen F, Viinnikka L. Renal prostacychn and thromboxane in normotensive and pre-eclamptic pregnant women and their infants. J Clin Endocrinol Metab 1986;63:1307-1312.
B~ologv, 35 (1990) 15-21
15
EUROBS 00900
Prostacyclin versus thromboxane excretion: changes in pregnancy Willy Department
A. Noort
and Marc
J.N.C.
metabolite and labor
Keirse
of Obstetrics, Leiden University Hospital. Leiden, The Netherlands Accepted for publication 5 July 1989
Summary Urinary TXB, and 6-keto-PGF,, were measured by high pressure liquid chromatography combined with radioimmunoassay, in order to determine whether or and TXB, followed a same pattern in not urinary excretion of 6-keto-PGF,, pregnancy and labor. The excretion of 6-keto-PGF,, was higher than that of TXB, in both non-pregnant and pregnant women, but the ratio between them increased in pregnancy. The urinary excretion of both 6-keto-PGF,, and TXB, excretion was significantly increased (p < 0.001) in pregnancy. Labor was associated with a much wider inter-individual variation in the excretion of 6-keto-PGF,, and TXB, than observed in pregnancy and in non-pregnant women. Also, the ratio between the two compounds varied more in labor than in pregnancy. The data indicate that the urinary levels of these two compounds do not follow a single well-determined pattern in pregnancy and labor. Thromboxane;
Prostacyclin; Prostanoids; Pregnancy; Labor
Introduction Pregnancy and labor are associated with marked changes in prostanoid metabolism. The changes apply to all of the prostanoids derived from arachidonic acid, but not all of these changes occur at the same time. Levels of prostaglandins and their metabolites, for example, remain remarkably constant in amniotic fluid, plasma and urine throughout most of pregnancy. Significant increases in their concentration are observed only at the onset of and during labor (reviewed by Keirse [9]). The production of prostacyclin (PGI,) and thromboxane (TXA,) on the other hand
Correspondence: Prof. Dr. M.J.N.C. Keirse, Department of Obstetrics & Gynecology, Leiden University Hospital, P.O. Box 9600, 2300 RC Leiden. The Netherlands.
0028-2243/90/%03.50
0 1990 Elsevier Science Publishers B.V. (Biomedical Division)
16
appears to increase far earlier in gestation. Thus, Goodman et al. [7] Ylikorkala et al. [21] and Fitzgerald et al. [4] all reported a 445-fold increase in the excretion of a major urinary metabolite of PGI,, 2,3-dinor-6-keto-PGF,,, during human pregnancy as compared with non-pregnant women. Noort et al. [15] observed an increase of similar magnitude in the urinary excretion of 6-keto-PGF,,, the stable hydrolysis product of PGI,, during pregnancy. The urinary excretion of both TXB, [16] and 2,3-dinor-TXB, [S] were found to be also significantly higher in pregnancy than in non-pregnant women, although Ylikorkala et al. [21] found no statistically significant differences between pregnant and puerperal women. Currently, there has been increasing interest in the regulation of thromboxane and prostacyclin synthesis in pregnancy. This has been fueled by the apparent success of thromboxane synthetase inhibition in the treatment of pregnancy-induced hypertension [18] and by the promising results of randomized controlled trials of prophylactic aspirin treatment in pregnancy [1,19]. In view of the widely aroused interest in the potential value of such treatments [3,12] there is a great need for further information on PGI, and TXA, production in normal pregnancy. We have previously reported the development of methods for measurement of urinary excretion of the stable products of PGI, and TXA,, 6-keto-PGF,, [15] and TXB, [16] in pregnancy. Although these investigations were conducted in two different groups of women, they suggested that changes in PGI, and TXA, production in pregnancy follow a different time pattern in that an increase in TXA, production appeared to precede the increase in PGI, production. Such a pattern would be consistent with in vitro observations that the human placenta produces mainly TXA, in early gestation [lo] and has only a limited capacity for PGI, synthesis [ll]. Although it is unknown as to what extent placental production contributes to the urinary excretion of 6-keto-PGF,, .and TXB,, there was thus a case for examining whether there really is a difference between the time patterns of 6-keto-PGF,, and TXB, excretion in human pregnancy. In addition, we investigated the relative proportions of urinary 6-keto-PGF,, and TXB, in individual women to assess whether the ratio between the excretions of these two compounds would change during pregnancy and labor. Material and methods Early morning (first voided) urine samples were collected, one sample each, from 36 women at different stages of clinically normal gestation ranging from 6 to 38 weeks and from 12 non-pregnant women of similar age. Samples were further obtained from 12 women in early labor with a contraction frequency of less than 3 per 10 min and a cervical dilatation of 4 cm or less, and from 12 women in advanced first-stage labor. Some of these pregnant women with normal pregnancies had been included in our previous study on urinary 6-keto-PGF,, levels [15]. The clinical characteristics of the pregnant women are shown in Table I; all were normotensive with blood pressures below 140/90 mmHg. Urine samples were centrifuged at 4°C and stored at - 20°C until analysis. Samples of 4 ml were acidified with 1 M citric acid to pH 3 and extracted with 10 ml petroleum ether after addition of 3000 cpm 6-keto[3H]PGF,, and [‘HITXB,
17 TABLE
I
Clinical characteristics Characteristics Age (years) Parity Gestational age at delivery (weeks) Infant birthweight (g)
of pregnant women included in the study mean + SD 28 + 1.9+ 40 3256
5.6 1.4
+ 1.5 +448
(Amersham International, Amersham U.K.). The aqueous phase was then extracted twice with methyl tert-butyl ether and these organic phases were evaporated under nitrogen for further extraction on Seppak C-18 octadecylsilyl silica cartridges (Waters Ass., Milford, MA). The dry residue was dissolved in 2 ml citric acidacidified water for application to the cartridges, which were then washed first with 10 ml acidified ethanol/water (15 : 85, v/v) and subsequently with 10 ml petroleum ether: methyl tert-butyl ether (90: 10, v/v). TXB, and 6-keto-PGF,, were eluted together with 10 ml methyl tert-butyl ether. The methyl tert-butyl ether was evaporated under nitrogen, and the residue dissolved in 0.25 ml water/acetic acid (99.25 : 0.75, v/v) for high-pressure liquid chromatography (HPLC) as described previously [ 161. The prostanoids were eluted with an increasing gradient of acetonitrile from 27 to 100% (v/v) in water/acetic acid (99.25 : 0.75, v/v) at a flow rate of 2 ml per min. One-ml fractions were collected and combined into a 6-keto-PGF,, (fractions 15-17) and a TXB, (fractions 25-28) fraction. The samples were lyophilized after excess acetonitrile had been evaporated under nitrogen. Radioimmunoassays of TXB, and 6-keto-PGFia were as described by Noort et al. [15,16]. Levels of TXB, and 6-keto-PGF,,were expressed per gram urinary creatinine. Creatinine was determined by the calorimetric method described by Folin [6]. The Mann-Whitney test was used for statistical analysis. The confidence intervals (ci) reported refer to 95% confidence intervals. Results Levels of both 6-keto-PGF,, and TXB, were significantly higher in urine of pregnant women than in that of non-pregnant women (p < 0.001). The increase above non-pregnant levels appeared to occur only toward the end of the first trimester (Fig. 1). Before 10 weeks of gestation (n = lo), all 6-keto-PGF,, levels and 8 of 10 TXB, levels fell within the range of values observed in non-pregnant women. From 20 weeks onwards this was the case for none of the 6-keto-PGF,, levels and for only 3 of 19 TXB, levels. Although there thus was a trend for an increase in both 6-keto-PGF,, and TXB, levels with advancing gestational age, most of this trend can be attributed to the low levels obtained before 10 weeks of gestation and the much higher levels thereafter (Fig. I). 6-Keto-PGF,, levels showed a statistically significant increase between the period from 10 to 19 weeks of gestation and that from 20 to 29 weeks. Levels at 10
&keto-PGF,,
ngfg treat. 12.5
TX82
rig/g treat.
6-keto-PGFk
/TXB2
ratio
5.0
2.5
C
.O NONPREGNANT
SQ
lo-19
20-29 WEEKS
z30
EARLY LATE FIRST STAGE
Fig. 1. Concentrations (rig/g creatinine; means with 95% confidence intervals) of and ratio between 6-keto-PGF,, and TXB, in urine before and during pregnancy and labor.
19 weeks were lower than at 20 to 29 weeks or at 30 to 39 weeks (p I 0.002), but there were no statistically significant differences between the latter two groups. TXB, excretion increased also significantly between the period of 10 to 19 weeks of gestation and that of 20 to 29 weeks (p I 0.02) with no further statistically significant increase in the second half of pregnancy. With the onset of labor, as judged from levels obtained in early labor with a uterine contractility of less than three contractions per 10 min, the mean level of both TXB, and 6-keto-PGF,, was higher than, but not statistically significantly different from, the mean level obtained in late pregnancy before the onset of labor. For both TXB, and especially 6-keto-PGF,, the range of values was much wider in early labor than in pregnancy, and this trend for a widening of the range increased further in advanced labor (Fig. 1). Levels in advanced labor just reached a statistically significant difference at p < 0.05 with levels in late pregnancy. to
Excretion of 6-keto-PGF,, was higher than that of TXB, in both pregnant and non-pregnant women. In accordance with the levels themselves, there was no change in the ratio of 6-keto-PGF,, to TXB, between non-pregnant women (2.5 f 1.0, mean f SD; ci: 1.9-3.1) and women in the first 10 weeks of pregnancy (2.6 & 1.0; ci: 1.9-3.3). Thereafter, the proportionally much larger increase in 6-keto-PGF,, excretion led to a more than 2-fold increase in the ratio of 6-keto-PGF,,/TXB, up to 5.9 (k1.8; ci: 4.4-7.4) in the third trimester of pregnancy (Fig. 1). The wide and TXB, levels during both early and individual variation in 6-keto-PGF,, advanced labor was also reflected in a wide individual variation in the ratio of these two compounds: 5.2 f 3.9 (mean + SD; ci: 2.7-7.7) in early and 7.7 &-5.5 (ci: 4.2-11.2) in advanced labor. Discussion
This study confirms our previous data and those of others of an increased excretion of 6-keto-PGF,, [15,21] and TXB, [16] in pregnancy. The increase appears to occur only at or after the first quarter of pregnancy, but the increase is well established before the second half of pregnancy is reached. These changes therefore appear to coincide with some of the major physiological changes and adaptations in pregnancy [14]. Some of these physiological adaptations have been credited to a relative predominance of PGI, production over that of TXA, in pregnancy [20] and this would be consistent with the increase in the ratio between 6-keto-PGF,, and TXB, observed in our study. We cannot assume, however, that all of the 6-keto-PGF,. and TXB, measured in this study originates from the systemic circulation, since the kidney itself can produce both TXB, and 6-keto-PGF,, [8,17]. Irrespective of the origin of these compounds it is clear that there is a much larger increase in 6-keto-PGF,, than in TXB, excretion in pregnancy, since the ratio between these two compounds doubles in comparison with that observed in the non-pregnant state. It is also clear that the levels of TXB, and 6-keto-PGF,, do not follow each other: an increase in one is not necessarily accompanied by a proportional increase in the other. This was particular obvious in urine samples obtained during labor. Levels of both 6-keto-PGF,. and TXB, in labor showed a much larger individual variation than at any other time in pregnancy and so did the ratio between 6-keto-PGF,, and TXB,, suggesting that levels of both compounds are not regulated by the same mechanism(s). The increase in TXB, in pregnancy may be partly derived from the placenta, which is known to contain a large amount of thromboxane synthase (Erwich and Keirse, unpublished data). Fitzgerald and colleagues [5], on the other hand, have argued that the increase in TXB, production in pregnancy is mainly derived from blood platelets and represents a state of increased platelet activation throughout pregnancy. Neither of these two sources would contribute much to the increase in 6-keto-PGF,,, since the placenta has a relatively poor capacity for PGI, production [ll] and since aspirin-inhibition of platelet prostanoid biosynthesis has little effect on the excretion of PGI, metabolites. Apart from a possible renal contribution, 6-keto-PGF,, levels are more likely to originate not from the platelets or the placenta but from the expanded vascular bed in pregnancy and/or from the
20
myometrium. Myometrium has a high capacity for PGI, production [2] and both the size of the myometrium and its PGI, synthase concentration per unit of weight are known to increase markedly in pregnancy [13]. The current observations did not confirm our hypothesis [15] than an increase in TXB, excretion would precede that of 6-keto-PGF,*; both appeared to increase at or about the 10th week of pregnancy. This had not been obvious in our previous study on TXB, excretion in pregnancy, since most samples in the first trimester of pregnancy had been obtained between 9 and 13 weeks of gestation, Both 6-ketoPGF,, and TXB, also showed an increase in labor and a much wider individual variation than in late pregnancy. This wide individual variation in both the levels of 6-keto-PGF,, and TXB, and the ratio between them indicates that production and/or excretion of these compounds in pregnancy and labor are largely independent from each other. Acknowledgements We are grateful to Mr. F.A. de Zwart for technical assistance. The Hague. supported by grant 28-1118 from the Praeventiefonds,
The study
was
References 1 Beaufils M, Uzan S, Donsimoni R, Colau JC. Prevention of pre-eclampsia by early antiplatelet therapy. Lancet 1985;i:840-842. 2 Christensen NJ, Green K. Bioconversion of arachidonic acid in human pregnant reproductive tissues. Biochem Med 1983;30:162-180. 3 Collins R, Wallenburg HCS. Pharmacological prevention and management of hypertensive disorders in pregnancy. In: Chalmers I, Enkin M, Keirse MJNC, eds. Effective care in pregnancy and childbirth. Oxford: Oxford University Press, 1989, in press. 4 Fitzgerald DJ, Entman SS, Mulloy K, FitzGerald GA. Decreased prostacychn biosynthesis preceding the clinical manifestation of pregnancy-induced hypertension. Circulation 1987;75:956-963. 5 Fitzgerald DJ, Mayo G, Catella F, Entman SS. FitzGeraId GA. Increased thromboxane biosynthesis in normal pregnancy is mainly derived from platelets. Am J Obstet Gynecol 1987;157:325-330. 6 Folin 0. On the determination of creatinine and creatine in urine. J Biol Chem 1914;17:469-473. 7 Goodman RP, Killam AP, Brash AR, Branch RA. Prostacyclin production during pregnancy: comparison of production during normal pregnancy and pregnancy complicated by hypertension. Am J Obstet Gynecol 1982;142:817-822. 8 Hassid A, Dunn MJ. Microsomal prostaglandin biosynthesis of human kidney. J Biol Chem 1980;255:2472-2475. 9 Keirse MJNC. Endogenous prostaglandins in human parturition. In: Keirse MJNC, Anderson ABM, Bennebroek Gravenhorst J, eds. Human parturition. The Hague: Leiden University Press, 1979;101-142. 10 Keirse MJNC. Biosynthesis and metabolism of prostaglandins within the human uterus in early and late pregnancy. In: Wood C, ed. The role of prostaglandins in Iabour. Royal Society of Medicine London 1985;25-38. 11 Keirse MJNC, Erwich JJHM, KIok G. Does or can human placenta produce prostacyclin? Placenta 1986;7:37-42. 12 Lancet. Editorial: Aspirin and pre-eclampsia. Lancet 1986;1:18-20. 13 Moonen P, Klok G, Keirse MJNC. Increase in concentrations of prostaglandin endoperoxide synthase and prostacyclin synthase in human myometrium in late pregnancy. Prostaglandins 1984;28:309-322.
21 14 Morgan DLM, Hytten FE. Midtrimester pregnancy a time of tranguility or activity? Br J Obstet Gynaecol 1984;91:532-537. 15 Noort WA, De Zwart FA, Keirse MJNC. Changes in urinary 6-keto-PGF,, excretion during pregnancy and labor. Prostaglandins 1988;35:573-582. 16 Noort WA, De Zwart FA, Keirse MJNC. Increase in urinary thromboxane excretion during pregnancy and labor. Prostaglandins 1987;34:413-421. 17 Schlondorff D, Ardaillou R. Prostaglandins and other arachidonic acid metabolites in the kidney. Kidney Int 1986;29:108-119. 18 Van Asscbe FA, Spitz B, Vermylen J, Deckmijn H. Preliminary observations on treatment of pregnancy-induced hypertension with a thromboxane synthetase inhibitor. Am J Obstet Gynecol 1984;148:216-218. 19 Wallenburg HCS, Dekker GA, Makovitz JW, Rotmans P. Low-dose aspirin prevents pregnancy-induced hypertension and pre-eclampsia in angiotensin-sensitive primigravidae. Lancet 1986;i:l-3. 20 Ylikorkala 0, MHkila U-M, Viinnikka L. Amniotic fluid prostacychn and thromboxane in normal, pre-eclamptic and some other complicated pregnancies. Am J Obstet Gynecol 1981;141:487-490. 21 Ylikorkala 0, Pekonen F, Viinnikka L. Renal prostacychn and thromboxane in normotensive and pre-eclamptic pregnant women and their infants. J Clin Endocrinol Metab 1986;63:1307-1312.