Li et al. / J Zhejiang Univ SCIENCE B 2006 7(9):757-762
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Journal of Zhejiang University SCIENCE B ISSN 1673-1581 (Print); ISSN 1862-1783 (Online) www.zju.edu.cn/jzus; www.springerlink.com E-mail: jzus@zju.edu.cn
Effects of levobupivacaine and bupivacaine on rat myometrium*
LI Zi-gang1, ZHOU Liang1, TANG Hui-fang2
(1Department of Anesthesiology, Women's Hospital, School of Medicine, Zhejiang University, Hangzhou 310003, China) (2Zhejiang Respiratory Drugs Research Laboratory of State Food & Drugs Administration of China, School of Medicine, Zhejiang University, Hangzhou 310031, China)
E-mail: tanghuifang@zju.edu.cn
Received Apr. 25, 2006; revision accepted July 20, 2006
Abstract: Objective: To study the effect of levobupivacaine and bupivacaine on the contractility of isolated uterine muscle strips from pregnant and non-pregnant female rats. Methods: Full-thick myometrial strips were prepared from 18- to 21-day pregnant (n=8) and non-pregnant rats (n=7). After contractions became regular, strips were exposed to cumulative concentrations of the two drugs from 108 to 104 mol/L, amplitude and frequency of the uterine contraction was recorded. Results: Two local anesthetics caused a concentration dependent inhibition on contractility of myometrial strips from pregnant and non-pregnant rats. In the myometrium from non-pregnant rats, logIC50 of levobupivacaine and bupivacaine were 4.85 and 4.25 respectively. In the myometrium from pregnant rats, similar concentrations of levobupivacaine and bupivacaine were observed, logIC50 were 2.7 and 2.9 respectively. Levobupivacaine produced an increase in amplitude of contractions, while bupivacaine showed an increased trend in frequency. Conclusion: These results demonstrate that levobupivacaine and bupivacaine may inhibit myometrium contractility. The inhibitory effect of levobupivacaine or bupivacaine is not enhanced by gestation in rat. Levobupivacaine may have more positive influence than bupivacaine in pregnant myometrium. Key words: Levobupivacaine, Bupivacaine, Myometrium, Rat doi:10.1631/jzus.2006.B0757 Document code: A CLC number: R719; R96
INTRODUCTION Bupivacaine as a racemic mixture of its enantiomers, dextrobupivacaine and levobupivacaine, has been the most widely used local anaesthetic for years. Both in vitro and in vivo studies showed that dextrobupivacaine has more inherent central nervous system (CNS) and cardiovascular toxicity than levobupivacaine. So, levobupivacaine as a new long-acting amide local anaesthetic, the pure S-enantiomer of racemic bupivacaine, has been developed. Pharmacological studies demonstrated that levobupivacaine has equal local anaesthetic potency with reduced potential for cardiac and CNS toxicity compared to bupivacaine (Bremerich and Zwissler, 2004). Regional anesthesia and analgesia have come
*
into widespread use for women in gynecological procedures. Local anesthetic agents are often used for obstetric analgesia and anesthesia. Previous studies reported that bupivacaine inhibited spontaneous contractions of isolated gravid rat myometrium (Arici et al., 2004; Karsli et al., 2003; Santos et al., 1995). But there is no report on the effect of levobupivacaine in pregnant or non-pregnant myometrium in vitro. In this study, we compared the effects of bupivacaine and levobupivacaine on contractions of myometrium isolated from pregnant or non-pregnant rats, then discuss its role in obstetric analgesia and anaesthesia.
MATERIALS AND METHODS Animals Pregnant female Sprague-Dawley (SD) rats at 18 ~21 d and non-pregnant female SD rats were used. Non-pregnant female SD rats weighing (200±20) g
Corresponding author Project (No. 2005038281) supported by the Postdoctor Foundation of China
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Li et al. / J Zhejiang Univ SCIENCE B 2006 7(9):757-762
were pretreated with 40 g diethylstilbestrol subcutaneously for 2 d to induce oestrus and improve the response to drug. The study procedures were approved by the Medical Faculty Ethic Committee of Zhejiang University. Experiments procedures Pregnant and non-pregnant rats were anesthetized with urethane (25%, 4 ml/kg) intravenously, then killed by cervical subluxation for the study. The preparation of myometrial strip followed the method of Karsli et al.(2003). The uterine horns were rapidly excised and carefully cleaned of surrounding connective tissue and opened longitudinally along the mesenteric border. Fetuses of the late-stage pregnant rats were removed and non-uterine tissues were dissected and discarded. We obtained longitudinal full-thickness myometrial muscle strips (measuring 4 mm×10 mm) from each animal. The uterine tissues of non-pregnant SD rats were rapidly isolated and carefully cleaned of surrounding connective tissue, then two uterine strips from one uterus were prepared. The strips were mounted vertically, one end of the strip was connected to the lower hook of the bath and the other end of the strip was connected to a force rod. The strips were incubated in the 10 ml tissue bath containing De-Jalon's solution (composition in mmol/L: NaCl 153.9, KCl 5.6, glucose 2.7, NaHCO3 5.9, and CaCl2 0.27), which were aerated continuously with 95% oxygen and 5% carbon dioxide. The pH was kept at 7.4 and the temperature was maintained at (32±0.5) °C. The solution was constituted daily for each experiment. Myometrial strips of pregnant rats were allowed to equilibrate at 1 g tension for 20 min before the contractions became regular. The characteristics of the contraction frequency and amplitude were recorded by a force displacement transducer (JZ100, Xinhang Machine and Equipment, Gaobeidian, China) coupled to MedLab Biological Signal Collection System (Medease Science and Technology, Nanjing, China). When the contractions of the strips became regular, the contraction frequency and amplitude were recorded as baseline activity, then levobupivacaine (Suka, Jiangsu Hengrui Medicine Co. Ltd., Shanghai, China) or bupivacaine (Shanghai Harvest Pharmaceutical Co. Ltd., Shanghai, China) was added at cumulative concentrations, duration of each concentration was 20 min. At the end of the drug exposure, the muscle
strips were washed out 3 times. Drug-containing solutions were prepared immediately before the experiment. The non-pregnant myometrial strips were allowed to equilibrate at 2 g tension for 40 min after the preparation was induced by appropriate concentration of oxytocin (0.05 U/10 ml). When the contractions became regular, the contractions frequency and amplitude were recorded as baseline activity, then the experimental drugs were added and recorded as above described. Each concentration duration was 15 min, washed out at the end of the experiment, wash interval was 5 min for 3 times. Each strip was exposed to only one anesthetic agent. Data analysis All data were expressed as mean±SD and intergroup and intragroup differences analyzed by unpaired t-test and one-way ANOVA using SPSS software (version 11.0 for Windows, SPSS Inc.). P<0.05 was considered to be statistically significant. RESULTS Effects of bupivacaine and levobupivacaine on non-pregnant rat myometrium The exposure to bupivacaine and levobupivacaine with cumulative concentrations from 108 mol/L to 104 mol/L significantly decreased the contractile activity, both on the amplitude and on frequency in dose-dependent manner (Figs.1 and 2). Meanwhile levobupivacaine was stronger than bupivacaine (P<0.05). The logIC50 of bupivacaine and levobupivacaine on contraction amplitude were 4.25 and 4.85, respectively. In two groups, the baseline values of the contractile forces were (3.11±0.59) g (bupivacaine), (3.31±0.48) g (levobupivacaine), respectively, and the baseline values of the frequency were (8.14±2.27)/(15 min) (bupivacaine) or (8.08± 2.20)/(15 min) (levobupivacaine), respectively. There was no significant difference between the two groups. Effects of bupivacaine and levobupivacaine on pregnant rat myometrium Bupivacaine and levobupivacaine at cumulative concentrations did not show significant decrease in contractile amplitude and frequency of myometrial strips isolated from pregnant rat. Furthermore
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levobupivacaine produced significant increase in the amplitude of contractions from 3×107 mol/L to 3×106 mol/L. However, bupivacaine did not. Higher concentration of bupivacaine and levobupivacaine both produced significant reduction in amplitude (Figs.3 and 4). logIC50 of bupivacaine and levobupivacaine on contraction amplitude were very close, 2.9 and 2.7, respectively. Bupivacaine produced an increase in the frequency in concentration dependent manner (Fig.3b),
150 120 Contraction (%) 90 60 30 0 8 7 6 5 logC 4.5
#* ## #
and reaching statistical significance at a concentration of 3×105 mol/L; however, levobupivacaine had no similar action. But at higher concentration, 104 mol/L of the two drugs showed slight inhibitory effects without statistical significance. The baseline values of the contractile amplitude were (3.01±0.31) g (bupivacaine) and (2.94±0.45) g (levobupivacaine), respectively. The baseline values of contraction frequency were (8.33±0.58)/(20 min) (bupivacaine) and (7.94±0.52)/(20 min) (levobupivacaine), respectively.
120
#
Frequency (%)
90 60 30 0
#
# #
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4
8
7
6 5 logC
4.5
4
(a)
(b)
Fig.1 The effects of levobupivacaine (■) and bupivacaine (□) on the amplitude (a) and frequency (b) of contractions of myometrial strips isolated from non-pregnant rats Data (mean±SD) expressed relative to baseline; n=7; *P<0.05 levobupivacaine vs bupivacaine; #P<0.05, ##P<0.01 vs baseline; C: Concentration (mol/L)
Fig.2 Respresentative trace showing the effect of bupivacaine (a) and levobupivacaine (b) on contraction of isolated non-pregnant rat myomerium at cumulative concentrations (108~104 mol/L)
210 180 Contraction (%) Frequency (%) 150 120 90 60 30 0 8 7.5 7 6.5 6 5.5 5 logC 4.5 4
# # # # #
140 120 100 80 60 40 20 0 8 7.5 7 6.5 6 5.5 5 logC
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(b) (a) Fig.3 The effects of levobupivacaine (■) and bupivacaine (□) on the amplitude (a) and frequency (b) of contractions of myometrial strips isolated from pregnant rats Data (mean±SD) expressed relative to baseline; n=8; #P<0.05, ##Pbupivacaine, but in pregnant rats was bupivacaine≈levobupivacaine. However, the reduced toxic potential of levobupivacaine supports the clinical use to decrease the risk of systemic toxicity related to either overdosing or unwanted intravascular injection, such as during epidural or peripheral nerve blocks. Meanwhile, the slightly different action of levobupivacaine on contraction amplitude of pregnant uterus and frequency of non-pregnant uterine muscles may provide positive influence in operations during pregnancy. This result may provide evidence for clinical implication, but further studies are required to verify its efficacy in pregnant women. References
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