Morphine inhibits nocturnal oxytocin secretion and uterine contractions in the pregnant baboon

Clinical Experiences and Mechanism of Action with the Use of Oxytocin Injection at Parturition in Domestic Animals: Effect on the Myometrium and Fetuses

Oxytocin is a key hormone for parturition and maternal traits in animals. During the peripartum period, the levels of endogenous oxytocin dictate physiological events such as myometrial contractions, prostaglandin production with the subsequent increase in oxytocin receptors, and the promotion of lactation when administered immediately after birth. While this hormone has some benefits regarding these aspects, the exogenous administration of oxytocin has been shown to have detrimental effects on the fetus, such as asphyxia, meconium staining, ruptured umbilical cords, and more dystocia cases in females. This review aims to analyze the main effects of oxytocin on myometrial activity during parturition, and its potential favorable and negative administration effects reflected in the fetus health of domestic animals. In conclusion, it is convenient to know oxytocin's different effects as well as the adequate doses and the proper moment to administrate it, as it can reduce labor duration, but it can also increase dystocia.

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.

μ and κ opioid receptor distribution in the monogamous titi monkey (Callicebus cupreus): implications for social behavior and endocrine functioning

The opioid system is involved in infant-mother bonds and adult-adult bonds in many species. We have previously shown that μ opioid receptors (MORs) and κ opioid receptors (KORs) are involved in regulating the adult attachment of the monogamous titi monkey. The present study sought to determine the distribution of MOR and KOR in the titi monkey brain using receptor autoradiography. We used [(3)H][D-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin (DAMGO) to label MORs and [(3)H]U69,593 to label KORs. MOR binding was heterogeneous throughout the titi monkey brain. Specifically, MOR binding was observed in the cingulate gyrus (CG), striatum, septal regions, diagonal band, amygdala, hypothalamus, hippocampus, and thalamus. Binding was particularly dense in the septum, medial amygdala, paraventricular nucleus of the hypothalamus, mediodorsal thalamus with moderate binding in the nucleus accumbens. Consistent with other primate species, MOR were also observed in "neurochemically unique domains of the accumbens and putamen" (NUDAPs). In general KOR binding was more homogenous. KORs were primarily found in the CG, striatum, amygdala and hippocampus. Dense KOR binding was observed in the claustrum. Relative MOR and KOR binding in the titi monkey striatum was similar to other humans and primates, but was much lower compared to rodents. Relative MOR binding in the titi monkey hypothalamus was much greater than that found in rodents. This study was the first to examine MOR and KOR binding in a monogamous primate. The location of these receptors gives insight into where ligands may be acting to regulate social behavior and endocrine function.

The effect of continuous morphine administration on maternal plasma oxytocin concentration and uterine contractions after open fetal surgery

OBJECTIVE

A major complication of open fetal surgery is prematurity. We propose that fetal and maternal stress/pain after surgery may affect the concentration of circulating oxytocin and the frequency of uterine contractions, thus increasing the risk of preterm delivery. The objective of this study was to test whether continuous morphine sulfate administration after open fetal surgery has an effect on maternal plasma oxytocin concentration and the frequency of uterine contractions.

METHODS

An established time-pregnant primate model for open fetal surgery was used. From the time of surgery until the end of the three-day study period, three animals received prophylactic antibiotics, a bolus of indomethacin, and a bolus of morphine sulfate (group I). Three other animals received the same prophylactic antibiotics and an i.v. bolus of indomethacin, as well as a continuous i.v. infusion of morphine sulfate throughout the entire study period (group II). Maternal blood samples were collected to determine oxytocin plasma concentrations. Oxytocin was measured by radioimmunoassay. Uterine activity was continuously recorded through an amniotic fluid catheter and quantified as number of contractions (10 mmHg increase from base line in intrauterine pressure) per hour (UCs/h).

RESULTS

The mean maternal plasma oxytocin concentration was higher (p < 0.01) and the number of uterine contractions more frequent (p < 0.05) in the group of animals with intermittent doses of morphine than in the group that received morphine continuously.

CONCLUSIONS

These data suggest that maternal plasma oxytocin concentration and uterine activity after open fetal surgery may be related to inadequate maternal/fetal analgesia/sedation.

The risk of cesarean delivery with neuraxial analgesia given early versus late in labor

BACKGROUND

Epidural analgesia initiated early in labor (when the cervix is less than 4.0 cm dilated) has been associated with an increased risk of cesarean delivery. It is unclear, however, whether this increase in risk is due to the analgesia or is attributable to other factors.

METHODS

We conducted a randomized trial of 750 nulliparous women at term who were in spontaneous labor or had spontaneous rupture of the membranes and who had a cervical dilatation of less than 4.0 cm. Women were randomly assigned to receive intrathecal fentanyl or systemic hydromorphone at the first request for analgesia. Epidural analgesia was initiated in the intrathecal group at the second request for analgesia and in the systemic group at a cervical dilatation of 4.0 cm or greater or at the third request for analgesia. The primary outcome was the rate of cesarean delivery.

RESULTS

The rate of cesarean delivery was not significantly different between the groups (17.8 percent after intrathecal analgesia vs. 20.7 percent after systemic analgesia; 95 percent confidence interval for the difference, -9.0 to 3.0 percentage points; P=0.31). The median time from the initiation of analgesia to complete dilatation was significantly shorter after intrathecal analgesia than after systemic analgesia (295 minutes vs. 385 minutes, P<0.001), as was the time to vaginal delivery (398 minutes vs. 479 minutes, P<0.001). Pain scores after the first intervention were significantly lower after intrathecal analgesia than after systemic analgesia (2 vs. 6 on a 0-to-10 scale, P<0.001). The incidence of one-minute Apgar scores below 7 was significantly higher after systemic analgesia (24.0 percent vs. 16.7 percent, P=0.01).

CONCLUSIONS

Neuraxial analgesia in early labor did not increase the rate of cesarean delivery, and it provided better analgesia and resulted in a shorter duration of labor than systemic analgesia.

Endogenous opiates: 1998

This paper is the twenty-first installment of our annual review of research concerning the opiate system. It summarizes papers published during 1998 that studied the behavioral effects of the opiate peptides and antagonists, excluding the purely analgesic effects, although stress-induced analgesia is included. The specific topics covered this year include stress; tolerance and dependence; eating and drinking; alcohol; gastrointestinal, renal, and hepatic function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurologic disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunologic responses; and other behaviors.

Level of postoperative analgesia is a critical factor in regulation of myometrial contractility after laparotomy in the pregnant baboon: implications for human fetal surgery

OBJECTIVES

We used 2 dosage levels of postoperative opioid administration to determine whether the degree of postoperative analgesia after laparotomy during the last third of baboon pregnancy alters maternal pituitary-adrenal function, androgen secretion, and placental estrogen production. We also determined the relationship of estrogen production to surgery-induced increase in myometrial contraction activity.

STUDY DESIGN

After laparotomy under halothane general anesthesia at 0.75 gestation, 10 pregnant baboons were administered intra-arterially either a normal dose or a double dose of the opioid analgesic buprenorphine for 48 hours. Maternal plasma samples for steroid hormone and oxytocin analyses were obtained at circadian time 1000 hours and at circadian time 1800 hours, 4 hours before and 4 hours after the lights went off, respectively. Myometrial electromyographic contraction activity was quantified for the 6 hours from circadian time 1100 hours to circadian time 1700 hours.

RESULTS

Maternal plasma cortisol and dehydroepiandrosterone sulfate concentrations were lower in the dark period (at circadian time 1800 hours) than during daylight (at circadian time 1000 hours) in the double-dose group but not the normal dose group. In contrast, maternal plasma estradiol level was higher at circadian time 1800 hours than at circadian time 1000 hours in the normal dose group but not in the double-dose group. Maternal plasma estrogen level was higher during the hours of darkness in the normal dose group than in the double-dose group. Furthermore the number of myometrial contractions around the onset of darkness was greater in the normal dose group than in the double-dose group.

CONCLUSIONS

The double dose of analgesia results in lower maternal nighttime plasma estradiol concentrations and significantly less nocturnal contraction activity. These observations further confirm an association between increased maternal plasma estrogen concentrations and increased myometrial contractility in the nonhuman primate. In addition, they suggest that adjustment of the level of postoperative analgesia may be of importance in preventing premature labor after chuman intrauterine fetal surgery.