Effects of anesthetic agents on contractions of the pregnant rat myometrium in vivo and in vitro

Abstract

Background: Several anesthetic agents are used in cesarean sections for both regional and general anesthesia purposes. However, there are no data comparing the in vivo effects of propofol, sevoflurane, and dexmedetomidine on the contraction of the myometrium in pregnant rats. The aim of this study was to investigate the effect of these anesthetic agents on myometrial contraction and elucidate the underlying mechanisms.

Methods: Contraction force and frequency changes in response to propofol, dexmedetomidine, or sevoflurane were evaluated in vivo and in vitro. To test the effect of arachidonic acid on myometrial contraction enhanced by dexmedetomidine, changes in myometrial contraction with dexmedetomidine after administration of indomethacin were evaluated. The amount of phosphorylated myosin phosphatase target subunit 1 (MYPT1) in the membrane fraction was expressed as a percentage of the total fraction by Western blot analysis.

Results: This study demonstrated that dexmedetomidine enhances oxytocin-induced contraction in the myometrium of pregnant rats, whereas propofol and sevoflurane attenuate these contractions. The dexmedetomidine-induced enhancement of myometrial contraction force was abolished by the administration of indomethacin. Propofol did not affect oxytocin-induced MYPT1 phosphorylation, whereas sevoflurane attenuated oxytocin-induced MYPT1 phosphorylation.

Conclusions: Inhibition of myofilament calcium sensitivity may underlie the inhibition of myometrial contraction induced by sevoflurane. Arachidonic acid may play an important role in the enhancement of myometrial contraction induced by dexmedetomidine by increasing myofilament calcium sensitivity. Dexmedetomidine may be used as a sedative agent to promote uterine muscle contraction and suppress bleeding after fetal delivery.

Keywords: Dexmedetomidine; Myometrial contraction; Pregnant rat.

Fig. 1

(A) Photo of actual gestational uterine ring, (B) diagram of isolated organ bath system: Isolated organ bath system with an organ bath, heating circulator, force transducer and recording system. Uterine rings (2–3 mm) were sliced from the uterine horns and mounted vertically in an organ bath containing 10 mL Krebs solution bubbled with 95% O₂ and 5% CO₂. The temperature of the organ bath was maintained at 37 °C with a heating circulator. The amplitude and frequency of contraction force in the uterine rings were measured using an isometric force transducer (ULA-10GR) and recorded using a recording system (ML846 PowerLab 4/26)

Fig. 2

Protocol for in vitro myometrial contraction measurement (n = 10 per group). (A) Protocol for propofol, (B) Protocol for dexmedetomidine, (C) Protocol for sevoflurane. After equilibration, oxytocin (20 nM) was administered to the organ bath. Contraction-force and -frequency changes in response to propofol (10⁻⁷–10⁻⁵ M), dexmedetomidine (10⁻⁹–10⁻⁷ M), or sevoflurane (2.0, 3.5, 5.0%) were evaluated. In the sevoflurane group, sevoflurane was administered into the gas mix (95% O₂ and 5% CO₂). For each concentration of anaesthetic agent, recording was performed for 15 min. Force and frequency of myometrial contractions were measured from the last 10 min of the 15-min exposure

Fig. 3

Balloon developed to measure myometrial contractions using a catheter and rubber. The tip of the catheter was covered with rubber, and saline was poured inside. The balloon was then connected to the pressure transducer

Fig. 4

Protocol for in vivo myometrial contraction measurement (n = 8 per group). (A) Protocol for propofol, (B) Protocol for dexmedetomidine, (C) Protocol for sevoflurane. Pregnant rats were anesthetized with sevoflurane subjected to tracheostomy, after which vascular access was obtained and the balloon was inserted in the uterus to measure myometrial contractions. Contraction-force and -frequency changes in response to propofol (30, 150 mg/kg/h), dexmedetomidine (6, 30 μg/kg/h), or sevoflurane (2, 5%) were evaluated. For each concentration of each anesthetic agent, recording was performed for 15 min. Force and frequency of myometrial contractions were measured from the last 10 min of the 15-min exposure

Fig. 5

Typical traces of uterine contractions in the organ bath experiments with oxytocin (A) and after the addition of different concentrations of anesthetics (B: dexmedetomidine, C: propofol, D: sevoflurane). DEX: dexmedetomidine, PROP: propofol, SEVO: sevoflurane

Fig. 6

Effects of anesthetic agents on in vitro oxytocin-induced contractions in the myometrium of pregnant rats (n = 10). (A) Ratio of AUC (% of oxytocin [20 nM]); (B) Ratio of frequency (% of oxytocin [20 nM]). AUC: area under the curve, * P < 0.05

Fig. 7

Effects of anesthetics on in vivo oxytocin-induced contractions in the myometrium of pregnant rats (n = 8). (A) AUC: area under the curve; (B) Frequency of contractions. * P < 0.05

Fig. 8

Effect of indomethacin (5 mg/kg) on myometrial contraction enhanced by dexmedetomidine (n = 6). AUC: area under the curve, * P < 0.05

Fig. 9

Western blot analysis (n = 6). MYPT1: myosin phosphatase targeting subunit 1, p-MYPT1: phosphorylated MYPT 1, OXY: oxytocin (20 nM), PROP: propofol (10⁻⁵ M), SEVO: sevoflurane (5.0%), Y27632: Rho-kinase inhibitor (10⁻⁶ M), * P < 0.05