Oxytocin

Abstract: Preterm labor (PTL) is one of the main causes of fetal mortality and morbidity in obstetrical medicine. Current methods of treatment are not very effective and often have significant side effects. For this reason new methods of preventing PTL are currently being sought. In Western medicine the newest development is oxytocin antagonists. In Oriental medicine acupuncture and moxibustion are being utilized for the purpose of stopping PTL. The goals of this study were to determine if acupuncture in pregnant rats can suppress oxytocin induced uterine contractions and to compare these results with those inhibited by an oxytocin antagonist. Uterine contractions were induced by continuous infusion of exogenous oxytocin. The first fetus in one uterine horn near the ovarian end was removed and distilled water-filled catheter was inserted into that vacated amniotic sac to measure uterine contractions as intrauterine pressure changes. Two acupoints of Ho-Ku (LI-4) and San-Yin-Chiao (Sp-6) were selected for acupuncture and Kuan-Yuan (Co-4) was used for moxibustion. The oxytocin-induced uterine contractions were significantly suppressed by acupuncture on the LI-4 (p [is less than] 0.05), but not by Sp-6. Stimulation of Co-4 by moxibustion had no significant (p [is greater than] 0.05) tocolytic effect. The administration of oxytocin antagonist eliminated all the uterine contractions induced by oxytocin. The application of acupuncture to re-stimulate the activity that was suppressed by the oxytocin antagonist did not produce any positive results. However, prostaglandins did cause the uterus to contract. In conclusion, acupuncture on LI-4 was found to suppress uterine contractions induced by oxytocin in the pregnant rat. If acupuncture is similarly effective in counteracting the effects of oxytocin in women, then this may an alternative medical treatment for women in preterm labor.

Preterm labor and delivery is the number one problem in obstetrical medicine (Creasy, 1993). Despite a significant amount of money and scientific effort, a high number of babies are still born prematurely every year. It has been reported (National Academy of Sciences, 1985) that some $5 billion per year was spent on treating premature infants in the United States, mostly for high-tech neonatal care. Recent interest in oriental medicine to stop premature delivery has grown dramatically. Western medicine recently developed oxytocin antagonists such as atosiban (Goodwin et al., 1994) and TT-235 (Fejgin et al., 1994). Acupuncture and moxibustion are being utilized for that purpose in oriental medicine. Therefore the effects of acupuncture and moxibustion in reversing the uterine activity were investigated in this study.

Materials and Methods

Surgery was performed on six Sprague Dawley strain rats at day 21 of gestation (delivery = day 21 1/2 to 22 1/2). Animals (5 months old, weighing 428.33 [+ or -] 6.01 g) were anesthetized with urethane (750 mg/kg) and a midline laparotomy was performed. The fetus nearest the ovarian end of the uterus was removed leaving the placenta and membranes in place. One distilled water-filled cannula (PE50; Clay Adams, Parsippany, N.J.) was inserted into the vacated amniotic cavity to measure uterine contractions as intra-uterine pressure changes. The second cannula (PE50) was inserted into the left femoral vein for a continuous oxytocin infusion with a Harvard infusion pump. The third cannula (PE50) was inserted into the right femoral vein for bolus injections of oxytocin antagonist (10 [micro]g/kg) and [PGF.sub.2][Alpha] (10 [micro]g/ml). TT-235, from the Tokyo Tanabe Pharmaceutical Company (Tokyo, Japan) was used as the oxytocin antagonist.

Uterine contractions were initiated and maintained by continuous exogenous oxytocin infusion (50 mU/kg/min) through the left femoral vein. The cannula from the uterus was attached to a P23id Gould pressure transducer (Grass Instruments, Quincy, Mass) and this was connected to a polygraph (RM-7000, Nihon Kohden, Japan). Protocol for the study was to induce uterine contractions with oxytocin following 15 minutes of spontaneous contractions and after 30 minutes of activity the following treatments were given: (1) acupuncture for 2 minutes at Ho-Ku (LI-4) followed by rest period then another 2 minutes for San-Yin-Chiao (Sp-6); (2) rest then moxibustion at Kuan-Yuan (Co-4) was carried out 5 times; (3) rest again then TT-235 followed by LI-4, Sp-6 stimulation and PGF2[Alpha]. Each resting time was given long enough until the uterine activity subsided and returned to baseline. All the contractile data were expressed as contractile force (frequency x mean amplitude/5 minutes; Wilson et al., 1991) and they were an average of the 6 animals. The 5 minutes covered 2 minutes of stimulation with additional 3 minutes just before resting time began.

Data for the control were obtained by the sham stimulation on the same acupoints. Needles for acupuncture were 0.18 mm and 15 mm in diameter and length, respectively. Manually applied acupuncture followed the method of twisting and rotating the needle. Direct moxibustion was applied on the sheared acupoint until the moxa cone was burned about three-quarters. The contractile force data were analyzed by student t-test using SAS (1989). Significance was considered to be p [is less than] 0.05.

Two acupoints of LI-4 and Sp-6 were selected for acupuncture. The former is located between the first and second metacarpal bones while the latter is about 3 cun directly above the tip of the medial malleolus, on the posterior border of the tibia. For moxibustion, Co-4 was used and it is located on the midline of the abdomen, 3 cun below the umbilicus.

Results

All the integrated responses of rat uterine muscle were expressed as millimeters of mercury per minute for 10 minutes. When the acupuncture on LI-4 was administered, the oxytocin induced uterine contractions of the pregnant rat were significantly inhibited (p [is less than] 0.05) compared to the control (Figure 1). However, following acupuncture of Sp-6 uterine contractions were not significantly suppressed (p [is greater than] 0.05, Figure 1). After moxibustion was applied to Co-4, no inhibition of uterine contractions was noticed. But its inhibitory effect was shown in one rat (Figure 2).

[Figures 1-2 ILLUSTRATION OMITTED]

When a bolus injection of oxytocin antagonist, TT-235, was given during continuous oxytocin infusion uterine contractions were totally inhibited (p [is less than] 0.01, Figure 3). The oxytocin antagonist was potent enough to knock out all the myometrial activities and even acupuncture was not able to re-stimulate the relaxed uterus. However, prostaglandin F2[Alpha] did cause the uterus to contract significantly (Figure 4).

[Figures 3-4 ILLUSTRATION OMITTED]

Discussion

Preterm birth still remains as a major contributor to fetal morbidity. Thus, it is understandable that new treatments and approaches are being tested to inhibit preterm labor. In spite of side effects from those agents, they are only option to treat the premature labor due to the lack of the optimal one in perinatal medicine. This explains why oriental medicines including acupuncture are receiving much attention and are a source of alternative hope as a new treatment. However, the use of oriental medicine in treating the preterm labor has been very limited since there are few controlled studies evaluating its effectiveness. The present study is one of the first to show that acupuncture in the pregnant rat animal model can inhibit oxytocin induced uterine contractions. Our study confirmed the effectiveness of acupoint stimulation in suppressing the uterine contractions (Tsuei et al., 1977), implying the possible alternative medical treatment for women in labor. These studies also address the question of the potential mechanism of action of the acupuncture. Since spontaneous uterine contractions of labor in women are at least partially driven by oxytocin it is possible that acupuncture has an effect on the endocrine system, suppressing oxytocin release. However, in the present study, the uterine contractions were driven by exogenous oxytocin. Thus, any inhibition of uterine contractions would suggest a direct effect on the uterus and not on the endocrine system. The present study supports such an idea.

In contrast to the LI-4 acupoint inhibition of uterine contractions, moxibustion application on the abdomen did not show any significant effect. This lack of effect may be due to interference by the midline laparotomy with this technique. It should be repeated in the future by using noninvasive methods such as intravaginal cannulation into the uterine horn to measure the uterine pressure changes because it can be a meaningful approach based on the philosophy of oriental medicine.

Among several tocolytics, oxytocin antagonists were studied in rat (Wilson et al., 1990; Higby et al., 1993), guinea pig (Demarest et al., 1989), baboon (Wilson et al., 1991), rhesus monkey (Honnebeier et al., 1989) and human (Goodwin et al., 1994), resulting in reduction of spontaneous and oxytocin-induced uterine contractions. Unlike other tocolytic agents, oxytocin antagonist has minimal side effects. One such oxytocin antagonists, TT-235 was developed first by Wilson and Flouret (Wilson et al., 1990). The results from the present study confirm TT-235 has a potent effect by eliminating oxytocin-exerted uterine contractions (Wilson et al., 1991; Fejgin et al., 1994).

In reality, the acupuncture itself can be used both for inducing the labor (Kubista et al., 1975; Yip et al., 1976) and for inhibiting the labor (Tsuei et al., 1977). When the uterine contractions were inhibited by TT-235 injection, a different way of acupuncture to re-stimulate uterus was not successful. Substantial time of uterine relaxation by an oxytocin antagonist might be a concern to clinicians especially when a time comes to deliver the baby in an emergency situation. Prostaglandins were successfully used with other agents for induction of labor (Sanchez-Ramos et al., 1993). Our study confirmed this fact since PGF2[Alpha] was able to induce the uterine response which was not possible with either oxytocin or acupuncture. This finding with other study (Fejgin et al., 1994) suggests that oxytocin and prostaglandins have different mechanisms of action on the uterine myometrium.

In conclusion, acupuncture of LI-4 significantly suppressed the uterine contractions induced by oxytocin in the pregnant rat. This is an important observation because it implies that this method might be used to inhibit uterine contractions of women in preterm labor. A powerful oxytocin antagonist was confirmed in stopping the oxytocin-induced uterine activities, proving its usefulness in prenatal care. Another significant observation was that a very potent oxytocin antagonist does not affect the pregnant rat uterus response to prostaglandins which can be a crucial step for an immediate delivery.

Acknowledgment

The authors wish to thank Mitsubishi-Tokyo Pharmaceuticals, Inc. (Tokyo, Japan) for inviting SCP to carry out this study.

References

[1.] Creasy, R.K. Preterm birth prevention: where are we? Am. J. Obstet. Gynecol. 168: 1223-1230, 1993.

[2.] Demarest, K.T., Hahn, D.W., Ericson, E., Capetola, R.J., Fuchs, A.R., McGuire, J.L. Profile of an oxytocin antagonist, RWJ 22164 for the treatment of preterm labor in laboratory models of uterine contractility. Am. J. Perinatol. 6: 200-204, 1989.

[3.] Fejgin, M.D., Pak, S.C., Warnell, C., Flouret, G., Parsons, M.T., Wilson, L. Jr. Oxytocin antagonist inhibitory effect on the rat and baboon uterus may be overcome by prostaglandins. Am. J. Obstet. Gynecol. 171: 1076-1080, 1994.

[4.] Goodwin, T.M., Paul, R.H., Millar, L., Valenzuela, G., Silver, H., Chez, R., Spellacy, W., Parsons, M., Hayashi, R., Mauck, C., North, L., Merriman, R. The effect of the oxytocin antagonist Atosiban on preterm uterine activity in the human. Am. J. Obstet. Gynecol. 170: 474-478, 1994.

[5.] Higby, K., Xanakis, E.M., Pauerstein, C.J. Do tocolytic agents stop preterm labor? A critical and comprehensive review of efficacy and safety. Am. J. Obstet. Gynecol. 168: 1247-1256, 1993.

[6.] Honnebeier, M.B.O., Figueroa, J.P., Rivier, J., Vale, W., Nathanielsz, P. Studies in the role of oxytocin in late pregnancy in the rhesus monkey. J. Dev. Physiol. 12: 225 232, 1989.

[7.] Kubista, E., Kucera, H., Muller-Tyl, E. Initiating contractions of the gravid uterus through electro-acupuncture. Am. J. Chin. Med. 3:343-346, 1975.

[8.] Sanchez-Ramos, L., Kaunitz, A.M., Del Valle, G.O., Delke, I., Schroeder, P.A., Brions, D.K. Labor induction with prostaglandin E1 methyl analogue misoprostol versus oxytocin: a randomized trial. Obstet. Gynecol. 81: 332-336, 1993.

[9.] SAS. SAS/STAT User's Guide. Version 6. 4th edition. Cary. NC: Statistical Analysis Systems Institute, Inc.; 1989.

[10.] Tsuei, J.J., Lai, Y., Sharma, S.D. The influence of acupuncture stimulation during pregnancy: the induction and inhibition of labor. Obstet. Gynecol. 50: 479-488, 1977.

[11.] Wilson, L. Jr., Parsons, M.T., Flouret, G. Inhibition of oxytocin-induced uterine contraction by an oxytocin antagonist in the pregnant baboon. Am. J. Obstet. Gynecol. 165: 456-460, 1991.

[12.] Yip, S.K., Pang, J.C., Sung, M.L. Induction of labor by acupuncture electro-stimulation. Am. J. Chin. Med. 4: 257-265, 1976.

Sok Cheon Pak(1), Chang Su Na(1), Jeong Sang Kim(1), Woo Suk Chae(1), Seiji Kamiya(2), Daisuke Wakatsuki(2), Yasuhiro Morinaka(2) and Laird Wilson, Jr.(3)

(1) Department of Acupuncture and Anatomy, Dongshin University, Naju, South Korea 520-714

(2) Mitsubishi-Tokyo Pharmaceuticals, Inc., Tokyo 115, Japan

(3) Department of Obstetrics and Gynecology, University of Illinois at Chicago, Chicago, Illinois 60612, USA

(Accepted for publication September 13, 1999)

COPYRIGHT 2000 Institute for Advanced Research in Asian Science and Medicine
COPYRIGHT 2000 Gale Group