The effects of bupivacaine, ropivacaine and mepivacaine on the contractility of rat myometrium

Analgesia during Parturition in Domestic Animals: Perspectives and Controversies on Its Use

This article analyzes the physiological role of pain during parturition in domestic animals, discusses the controversies surrounding the use of opioids, non-steroidal anti-inflammatory drugs (NSAIDs), and local analgesics as treatments during labor, and presents the advantages and disadvantages for mother and offspring. Labor is a potentially stressful and painful event, due to the contractions that promote expulsion of the fetus. During labor, neurotransmitters such as the prostaglandins contribute to the sensitization of oxytocin receptors in the myometrium and the activation of nociceptive fibers, thus supporting the physiological role of pain. Endogenously, the body secretes opioid peptides that modulate harmful stimuli and, at the same time, can inhibit oxytocin's action in the myometrium. Treating pain during the different stages of parturition is an option that can help prevent such consequences as tachycardia, changes in breathing patterns, and respiratory acidosis, all of which can harm the wellbeing of offspring. However, studies have found that some analgesics can promote myometrial contractility, increase expulsion time, affect fetal circulation, and alter mother-offspring recognition due to hypnotic effects. Other data, however, indicate that reducing the number of uterine contractions with analgesics increases their potency, thus improving maternal performance. Managing pain during labor requires understanding the tocolytic properties of analgesics and their advantages in preventing the consequences of pain.

Parturition in Mammals: Animal Models, Pain and Distress

Parturition is a complex physiological process and involves many hormonal, morphological, physiological, and behavioural changes. Labour is a crucial moment for numerous species and is usually the most painful experience in females. Contrary to the extensive research in humans, there are limited pain studies associated with the birth process in domestic animals. Nonetheless, awareness of parturition has increased among the public, owners, and the scientific community during recent years. Dystocia is a significant factor that increases the level of parturition pain. It is considered less common in polytocous species because newborns' number and small size might lead to the belief that the parturition process is less painful than in monotocous animal species and humans. This review aims to provide elements of the current knowledge about human labour pain (monotocous species), the relevant contribution of the rat model to human labour pain, and the current clinical and experimental knowledge of parturition pain mechanisms in domestic animals that support the fact that domestic polytocous species also experience pain. Moreover, both for women and domestic animal species, parturition's pain represents a potential welfare concern, and information on pain indicators and the appropriate analgesic therapy are discussed.

Uterine contractility changes in a perfused swine uterus model induced by local anesthetics procaine, lidocaine, and ropivacaine

Background

Local anesthetics (LAs) are increasingly used as therapeutics due to their multiple molecular effects. They may be potential agents also in gynecology and reproductive medicine. The objective of this study was to investigate the contractility response of the perfused swine uterus to different concentrations of the LAs procaine, lidocaine, and ropivacaine.

Methods and findings

In an extracorporeal perfusion model with fresh swine uteri, effects of administered boli of these three LAs in concentrations of 0.1 mg/mL, 0.5 mg/mL and 1.0 mg/mL on uterine contractility and peristalsis were assessed using an intrauterine double-chip micro-catheter. A dose-dependent increase in intrauterine pressure (IUP) in the isthmus and corpus uteri was observed after the administration of the ester-LA procaine 0.1, 0.5, and 1.0%, which was not seen with lower concentrations, or buffer solution. An increase-decrease curve was found after increasing concentrations of the amide-LA lidocaine and ropivacaine, with an IUP plateau with 0.1 and 0.5%, and a decrease with 1% (p<0.01). All reactions were seen in both the isthmus and corpus uteri. The difference of the contractility pattern between ester- and amide-LA at 1% concentration was significant.

Conclusion

LAs dose-dependently modulate contractility in non-pregnant swine uteri. The amid-LAs lidocaine and ropivacaine reduce contractility in higher concentrations and may be used as therapeutics in disorders with increased uterine contractility, as dysmenorrhoea, endometriosis, and infertility. The multiple molecular effects of LAs may explain these effects. This in-vitro pilot study in vitro provides initial data for designing further studies to transfer the results onto humans.

Effects of Ropivacaine in Patient-Controlled Epidural Analgesia on Uterine Electromyographic Activities during Labor

Epidural analgesia is effective in relieving pain during labor. However, concerns as to compromised labor progress and outcomes arise. This study aimed to assess the effect of patient-controlled epidural analgesia (PCEA) with ropivacaine on uterine electromyography (EMG) activities and outcomes in labor. A total of 213 pregnant women were divided into three groups: the PCEA with ropivacaine group (n = 78), the PCEA with levobupivacaine group (n = 66), and a control group that did not receive PCEA (n = 69). Uterine EMG activities were recorded during the first stage of labor. Maternal and fetal outcomes also were assessed. The primary outcomes of this study were EMG activities. No significant differences were observed in patient demographics or neonatal weight among the three groups. Compared to the PCEA with levobupivacaine group, the control and PCEA with ropivacaine groups had lower rates of oxytocin administration (P < 0.05) and shorter durations of the first stage of labor (P < 0.05). For the EMG activities, the PCEA with ropivacaine group showed a higher power (P < 0.01) and higher peak frequency (P < 0.05) than the PCEA with levobupivacaine group. With ropivacaine, the EMG activities remained stable 30–120 min. Compared with levobupivacaine, the use of ropivacaine in PCEA has no suppressive effect on uterine EMG activities during the first stage of labor. In addition, ropivacaine leads to labor progress and delivery outcomes similar to those in the control group, as well as similar and favorable analgesic satisfaction with the use of levobupivacaine.

Lignocaine augments the in-vitro uterine contractions involving NO-guanylyl cyclase dependent mechanisms

AIMS

Lignocaine is used during intrapartum and postpartum period but there are conflicting reports regarding the effect of lignocaine on uterine contractility. Therefore, this study was undertaken to delineate the effect of lignocaine on uterine contractility and the underlying mechanisms.

MAIN METHODS

The in vitro contractions were recorded from the uterine segments obtained from adult rats (in estrous phase) and also from human myometrial tissue. Effect of lignocaine on spontaneous uterine contractions was recorded in the absence or presence of antagonists. Effect of sodium nitroprusside (SNP, NO donor) on uterine contractility was assessed. The NO₂^- was assayed (indicator of NO activity) from the supernatant after exposing the myometrial tissue to lignocaine in the absence or the presence of L-NAME or hemoglobin.

KEY FINDINGS

Lignocaine (100μM) increased the amplitude of uterine contractions by 75% with no alterations in frequency. Similar magnitude of increase was seen with human myometrial tissue also. The spontaneous activities were absent in Ca²⁺-free or in nifedipine (10μM) containing medium. Heparin (IP₃ blocker, 10IU/ml), but not the indomethacin (10μM) blocked the lignocaine-induced augmentation. L-NAME (NOS inhibitor, 10μM) or methylene blue (guanylyl cyclase inhibitor, 100μM) partially blocked the lignocaine-induced augmentation. SNP (30μM) increased the amplitude of spontaneous uterine contractions. Lignocaine increased the NO₂^- content (indicator of NO activity) of uterine tissue and the increase was blocked by L-NAME or hemoglobin.

SIGNIFICANCE

Present observations indicate that lignocaine augments the amplitude of uterine contractions via Ca²⁺-dependent mechanisms involving NO-G cyclase-dependent mechanisms.

Dexmedetomidine modifies uterine contractions in pregnancy terms of rats

OBJECTIVES

The present study was aimed at determining the effective doses of Dexmedetomidine (Dex) involved in amplitude of contraction-force and frequency of uterine rings in pregnancy terms of rats. All experiments involving animal subjects were carried out with the approval of animal care and use Ethical Committee of Cukurova University. Experiments were performed on female Albino-Wistar rats (200-260 g; n = 40).

MATERIALS AND METHODS

Uterine rings from pregnant rats were placed in organ bath with Krebs and calcium ion (Ca(2+))-free solutions to record and exposed to serially increasing log10 concentrations of Dex.

RESULTS

In Krebs solution, while Dex caused an increase in the spontaneous contraction-forces in all pregnancy terms of rats in a significant dose-dependent manner, it led to a decrease in contraction-frequency in late-pregnancy term of rats. In Ca(2+)-free, the spontaneous contraction-force decreased in late-pregnancy term and increased in early and middle-pregnancy terms. In addition, while Dex increased the contraction-frequency in early and middle-pregnancy terms, it decreased in late-pregnancy term in a dose-dependent manner.

STATISTICAL ANALYSIS USED

The data were subjected to one-way analysis of variance. Repeated measures were employed for comparison of several group means through the Tukey post-hoc test (SPSS 10.00 Inc., Chicago, Ill, USA). P < 0.05 was considered statistically significant.

CONCLUSIONS

This study suggested that Dex might differently alter the spontaneous contraction-forces and contraction-frequencies of uterine rings in all pregnancy terms of rats in Krebs and Ca(2+)-free solutions.

In vivo comparison of the effects of bupivacaine and levobupivacaine on the pregnant rat myometrium using electrohysterogram

BACKGROUND AND AIMS

The effect of local anesthetics on myometrial contractility during labor analgesia is debatable. We aimed to compare the effects of bupivacaine and levobupivacaine on rat uterine contractility in an in vivo setting.

METHODS

Electrical activities of 40 pregnant rat uteruses were recorded on electrohysterogram after dividing the rats into bupivacaine and levobupivacaine groups. Uterine contraction frequencies were recorded at each 5-min interval. The first 5-min recording was considered the control, which was immediately followed by intramyometrial administration of either bupivacaine or levobupivacaine. The recordings were continued for 30 min. The changes in frequencies at each time interval of the groups were compared with each other and the control recording.

RESULTS

The frequencies from both groups at each interval were lower than the control values, but not different between the groups. The frequencies of the bupivacaine group during the 5-10 min and 10-15 min intervals were lower than the control time interval, but no significant differences were present between the control and the other time intervals. However, no significant differences were found at any time interval for the levobupivacaine group.

CONCLUSION

Levobupivacaine led to less muscle relaxation compared to bupivacaine and may be a better option for labor analgesia and anesthesia considering uterine contractility.

A comparison of the inhibitory effects of bupivacaine and levobupivacaine on isolated human pregnant myometrium contractility

BACKGROUND

Epidural analgesia with levobupivacaine and bupivacaine is a common and effective method of labor pain relief. However, its use is associated with an increased instrumental delivery rate. One of the mechanisms postulated to account for this unwanted effect is the direct effect of local anesthetics on myometrial contractility. We determined the effects of bupivacaine and levobupivacaine on the amplitude and frequency of contractions of human term myometrium.

METHODS

Uterine specimens were obtained from nonlaboring parturients scheduled for elective lower-segment cesarean delivery at term. Longitudinal muscle strips were prepared and mounted vertically in tissue chambers, and changes in the amplitude (peak force) and the frequency of contractions were recorded. Spontaneous contractions commenced after a period of application of 1 g (9.81 mN) of tension to the myometrial strips. No uterotonic drugs were used. The muscle strips were then exposed to cumulative concentrations of bupivacaine and levobupivacaine and dose-response curves were generated.

RESULTS

Both bupivacaine and levobupivacaine decreased the amplitude of contractions in human myometrium in a concentration-dependent manner, reaching significance at 1x10(-4) M for both bupivacaine and levobupivacaine compared with the internal control amplitude. With both drugs, the decrease in amplitude was accompanied by an increase in the frequency of contractions reaching significance at 3x10(-5) M for both bupivacaine and levobupivacaine compared with the internal control frequency.

CONCLUSIONS

The concentrations required for the effects on amplitude are much higher (33 fold) than the clinically relevant plasma concentrations of these drugs after epidural administration, and are unlikely to be significant in the setting of low-dose epidural analgesia in labor.

Effects of levobupivacaine and bupivacaine on rat myometrium

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 10(-8) to 10(-4) 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, -logIC(50) 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, -logIC(50) 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.

The effects of dexmedetomidine on spontaneous contractions of isolated gravid rat myometrium

The direct effects of dexmedetomidine on isolated gravid rat myometrium were investigated in this in vitro study; such effects may have clinical repercussions in the administration of anesthesia to obstetric patients. Samples of myometrium were taken from 12 gravid rats. Myometrial strips were dissected microscopically and mounted on the myograph at a resting tension of 1 g in bath that contained Krebs solution. After spontaneous contractions of the myometrium had been steadily established, increasing concentrations of dexmedetomidine were added to baths via micropipette, and the effects of these additions were recorded via myograph. Dexmedetomidine in vitro caused a significant increase in the amplitude, frequency, and area under the curve of myometrial contractions in a dose-dependent manner. Results of this study demonstrate that dexmedetomidine increases spontaneous contractions in rat myometrium; however, further investigation is needed to clarify the usefulness of dexmedetomidine in the administration of obstetric anesthesia.

The in vitro effects of clonidine and dexmedetomidine on human myometrium

BACKGROUND

alpha(2)-adrenergic agonists have been used extensively in the field of anaesthesia. Their direct effect on the human myometrium was investigated in this in vitro study, as this may have clinical repercussions in obstetric anaesthesia.

METHOD

Strips of pregnant human myometrium obtained from six individuals at elective caesarean section were mounted on the Mulvany myograph in Krebs solution to which increasing concentrations of clonidine and dexmedetomidine (1x10(-11) to 1x10(-6) g/mL) were added.

RESULTS

Dexmedetomidine increased uterine contractility at simulated clinical plasma concentrations (1x10(-9) g/mL). These effects were seen with clonidine only at much higher tissue bath concentrations (1x10(-7) g/mL).

CONCLUSION

The effect of dexmedetomidine on human myometrium has profound implications in obstetric anaesthesia and needs further clinical investigation.