SIEP publications are protected by copyright and all rights are reserved.  SIEP publications may not be reproduced in any form or by any means without written permission from the copyright owner. This includes the posting of electronic files on the Internet, transferring electronic files to other persons, distributing printed output, and photocopying. Requests for authorization to make photocopies should be directed to:   SIEP, 1697 Lark Lane, Cherry Hill, NJ 08003-3157 Tel: (856) 429 2699, Fax:  (856) 429 7414, Email: barnea@earlypregnancy.org

EARLY PREGNANCY: Biology and Medicine Editor-in-Chief: Eytan R. Barnea MD, FACOG

April 2001
Volume V, Number 2
ISSN: 1537-6583
Pages: 113-120

Comparison Of Periovulatory And Early Pregnancy Blood Levels Of Oxytocinase (CAP₁) And Isooxytocinase (CAP₂)*

Marek Dziechciowski, Rudolf Klimek

Chair and Department of Endocrinology and Fertility, Jagiellonian University, Kopernika 23, Cracow, Poland, Tel./fax. (48-12) 42 13 666

Key words: oxytocinase (CAP₁), isooxytocinase (CAP₂), early pregnancy

*Paper presented at Fourth World Conference on Early Pregnancy, Pecs, Hungary, 2000

Abstract

The previous studies on oxytocinase concentrated on its practical usability in monitoring advanced pregnancies, both normal and abnormal. However in early pregnancy the enzymatic values are within the norm for non-pregnant women and because of that they were not interesting for medicine, which makes use only of enzymatic values beyond the range of the norm.

The aim of our study was to compare serum levels of oxytocinase (CAP₁) and isooxytocinase (CAP₂) in the first trimester of pregnancy between women who had miscarriage and those who delivered healthy babies. The study involved 234 pregnant women after infertility treatment. Serum oxytocinase and isosoxytocinase levels were evaluated in 157 women who delivered and in 77 women who had spontaneous miscarriage. Oxytocinase was assessed by means of H. Tuppy and H. Nesvadba's method modified by R. Klimek.

For the first time it has been shown, that oxytocinase and isooxytocinase may play some role in proper development of early pregnancy, because the level of both isoenzymes at the beginning of pregnancy is statistically significantly higher in pregnancies ending in labor. Also about 3 weeks later and only in those successful pregnancies both enzymes undergo statistically significant further increase. Enzymatic changes correspond to hCG measurements.

Introduction

Under the influence of gestatational enlargement of the uterine cavity, the mother’s hypothalamus produces an increasing amount of hormones including oxytocin, which in turn induces an increasing oxytocinase synthesis in the placenta in order to prevent the hormone in the blood reaching the level, which could bring about uterine contractions. Also, the growing fetus additionally induces the production of oxytocinase by releasing its own hormones. At the end of pregnancy, the production of oxytocin is the highest and sufficient for stimulation of labor activity of the uterus. However, if earlier there was any decline in the synthesis of the enzyme, which decomposes it, it does not require an additional production of the hormone, which is adequate, but inactivated in physiological conditions.

In the existing studies on oxytocinase a particular emphasis was placed on its practical usability in monitoring pregnancies both physiological, and during treatment of their complications (1). However, after discovery of the role of oxytocinase in regulation of production and action of neurohormones, researchers put themselves out to find its possible effect on maturation of the Graafian follicle and development of early pregnancy (2-7). In both cases, the blood-levels of the enzyme fall within the norm for non-pregnant women and therefore they have not drawn clinical interest, which principally pertains to the predictive and diagnostic significance of enzymatic values beyond the range of the norm.

Those enzymes belong to the most stabile in the blood and decide about the speed of degradation of hypothalamic neurohormones, which during pregnancy are additionally produced in the placenta. Research into behaviour of those enzymes in early pregnancy may allow for new evaluation of induction of their synthesis, especially in early pregnancy and not only under the influence of oxytocin.

In this study, oxytocinase blood-levels in women in the first trimester of pregnancy were compared depending on its miscarriage or carrying to term, to evaluate the possibility of their prognostic value.

Material and Methods

The study involved 234 pregnant women after infertility treatment, of which 157 (67.1%) pregnancies ended in labor (group I) and 77 (32.9%) pregnancies ended in spontaneous miscarriage (group II). The results of enzymatic assessment were also compared to periovulatory levels in 362 women treated for infertility which – when the treatment was successful - were observed from the beginning of pregnancy.

Oxytocinase was assessed by means of H. Tuppy and H. Nesvadba's method modified by R. Klimek (5), taking into account only the first and second assessments of oxytocinase (CAP₁) and isooxytocinase (CAP₂) observed in pregnancy. The duration of gestation was calculated from the first day of the last menstrual period verified by a clinical examination and ultrasound scan, as well as results of hCG assessment in a direct latex test (Rapi Tex hCG-Dade Behring).

Having checked the normal distribution of data by means of W-test (Shapiro and Wilk). The t-Student test was applied to compare the differences between parametric data. In case of non-parametric data chi-square test was used; p-value£ 0.05 was considered significant.

Results

Table 1 presents the characteristics of both studied groups of the pregnant women: age (in years), duration of gestation (in days) at the time of hCG, CAP₁ and CAP₂ assessments, and their results. The comparison of data shows that those groups did not differ in age of women and duration of pregnancy at the time of laboratory assessments. As expected, the hCG concentration appeared more than four times (4.6) statistically significantly lower (p<0.001) when pregnancy ended in miscarriage (Fig. 1). Also, in those cases the oxytocinase and isooxytocinase levels appeared to be statistically significantly lower (p<0.01 and p<0.05, respectively), than in group I with successful pregnancy (Fig. 2 and 3). Notably, in the first pregnancy examinations, cytohormonal assessment of smears from the posterior fornix of vagina differed only in the statistically significantly four times more frequent estrogenic reaction, which occurred in 11.9% of threatened pregnancies (Table 2).

Enzymatic assessments made on an average 3 weeks later showed further statistically significant increase of both enzymes (p<0.001; p<0.003) only in the successfully ended pregnancies (CAP₁ by 21%, CAP₂ by 10.6%), remaining on the same level in the case of miscarriage (Table 3).

Table 4, in turn, compares the first results of enzymatic assessments to periovulatory values CAP₁ and CAP₂. There was found statistically significant increase in both enzymes, CAP₁ by 27.5% and 10.1% and CAP₂ by 14.3% and 6.8% respectively. The half as high increase in isooxytocinase (i.e. tissular enzyme, CAP₂) compared to the placental isoenzyme CAP₁ corresponds to the analogous lower increase in threatened pregnancy.

Conclusions

For the first time it has been shown, that oxytocinase and isooxytocinase may play some role in proper development of early pregnancy. Determination of those enzymes seem to be a clinically useful tool in regard to prediction of early pregnancy fate, when only the increase of both isoenzymes (CAP₁ and CAP₂) provides a positive gestatational prognosis.

The mean values of those enzymes found in the periovulatory period of non-pregnant women double in successful pregnancies only at the beginning of the II trimester (2,4). In this paper it has been shown that at the first examination of those enzymes during pregnancy statistically significant increase of mean values is found already at the beginning of pregnancy, but it remains within the range observed in non-pregnant women. This explains the lack of interest of measuring oxytocinase for clinical purposes so far.

The aim of our study has been the attempt to show whether, apart from many well-known factors deciding about successful development of early pregnancy , there is a characteristic behaviour of aminopeptidases (CAP₁ and CAP₂) in the serum of pregnant women depending on the future course of pregnancy. In our paper we have shown that already at the second examination of women with miscarriage there is no statistically significant increase of both enzymes, differently from successful pregnancies. Closer explanations of that fact in future papers will allow to show the role of both enzymes in the early pregnancy, similarly like the description of enzymatic block in 1967 explained the role of oxytocine-oxytocinase system in the development of late pregnancy and the initiation of delivery (8). In those days structures of hypothalamic neurohormones, which are also active in the development of the pregnancy and undergo degradation by the examined enzymes, were unknown.

For personal use. Only reproduce with permission from SIEP.

References

1. Klimek R., Fraczek A., Klimek M., Karolik A. (1998). Oxytocinase aided monitoring of fetal well being. Pre-Neonatal Med., 3, 168

2. Klimek R. (1999). Enzymes as the most important obstetrical markers. In Klimek R., Breborowicz G. (eds) Seminars in Perinatal Medicine - Evaluation of selected enzymes in pregnancy monitoring, Poznan, II, 55-59

3. Klimek R., Janeczko J., Kukulski T., Rzepecka A., Wójcik R. (1999). Periovulatory serum oxitocinase levels in women. In Klimek R., Breborowicz G. (eds) Seminars in Perinatal Medicine - Evaluation of selected enzymes in pregnancy monitoring, Poznan, II, 55-59

4. Klimek R. (2000). Enzymes: the most important markers of pregnancy development. Early Pregnancy: Biology and Medicine, vol. IV, 4, 219-229

5. Klimek R., Pietrzycka M. (1961). Biochemische Methode zur Bestimmung der Oxytocinase und Klinische Bewertung (Biochemical method for the determination of oxytocinase and its clinical value). Clin Chim Acta, 6, 326

6. Klimek M. (1996). Medical prognosis versus statistical prediction of birth term. In Klimek R. et al., (ed) A Time to Be Born, DREAM Publ. Comp. Inc, Cracow, 9-32

7. Klimek R. (1994). Monitoring of Pregnancy and Prediction of Birth-date. London, Casterton, New York: Parthenon Publ. Group

8. Klimek R. (1967). Relative duration of human pregnancy and oxytocin therapy. Part I and II. Gynecologia, Switzerland, 163, 48 –54

Table 1
Characteristic of material: maternal age, isooxytocinases blood levels in the first examination and hCG urine level in studied groups

Table 2
Comparison of Pap smears in studied groups

Table 3
Assessment of oxytocinase (CAP₁) and isooxytocinase (CAP₂) blood levels in studied groups

Table 4
Comparison of oxytocinase (CAP₁) and isooxytocinase (CAP₂) blood levels in pregnancies ended by labor
(Group I) and miscarriage (Group II) with preovulatory blood levels of CAP₁ and CAP₂

1p< 0,001; ²p< 0,02; ³p<0,05

Figure 1
Comparison of urine hCG levels in group I and II

 Figure 2
Comparison of serum oxytocinase (CAP₁) levels in group I and II

Figure 3
Comparison of serum isooxytocinase (CAP₂) levels in group I and II