title: Relaxant effects of metoclopramide and magnesium sulfate on isolated pregnant myometrium: an in vitro study.
abstract: BACKGROUND
  Metoclopramide and magnesium sulfate are extensively used agents in obstetrics. In this study, the relaxant properties of metoclopramide and magnesium sulfate on pregnant myometrium, together with the possible reversing influences of oxytocin and cabergoline (a dopamine D2 receptor agonist), were investigated.
  
  
  METHODS
  Myometrial strips from 24 parturients were randomly allocated to four groups: control (Group CON), magnesium sulfate and oxytocin (Group MSO), metoclopramide and oxytocin (Group MEO), and metoclopramide and cabergoline (Group MEC). Myometrial strips were mounted on a myograph bathed in Krebs buffer. Saline (Group CON) and five incremental doses of magnesium sulfate (Group MSO) or metoclopramide (Groups MEO and MEC) were sequentially microinjected into the bath. Subsequently, oxytocin (Groups CON, MSO and MEO) or cabergoline (Group MEC) was microinjected into the bath. The myometrial contractile characteristics after each drug injection, including contractile force, interval and duration, were analyzed.
  
  
  RESULTS
  Magnesium sulfate was more potent for prolonging myometrial contractile interval than reducing contractile force. Metoclopramide relaxed myometrial contractions by inhibiting contractile force and prolonging contractile interval in a concentration-dependent manner. Oxytocin reversed both the inhibited contractile force and the prolonged contractile interval caused by a high concentration of magnesium sulfate but accelerated the contractile interval and had no significant effect on the contractile force suppressed by metoclopramide. The relaxant effects of metoclopramide were completely reversed by cabergoline.
  
  
  CONCLUSIONS
  Both magnesium sulfate and metoclopramide relaxed myometrial contractions, and exhibited different responses to subsequent oxytocin treatment. The relaxant mechanism of metoclopramide may be via blockade of dopamine D2 receptor, which requires further investigation.
authors.affiliation: Department of Anesthesiology, West China Second Hospital, Sichuan University, Chengdu, Sichuan, China.
authors.forename: Y Y
authors.initials: YY
authors.lastname: Tang
authors.affiliation: Department of Anesthesiology, West China Second Hospital, Sichuan University, Chengdu, Sichuan, China.
authors.forename: Y
authors.initials: Y
authors.lastname: Du
authors.affiliation: Department of Anesthesiology, West China Second Hospital, Sichuan University, Chengdu, Sichuan, China.
authors.forename: J
authors.initials: J
authors.lastname: Ni
authors.affiliation: Department of Anesthesiology, West China Second Hospital, Sichuan University, Chengdu, Sichuan, China.
authors.forename: Y S
authors.initials: YS
authors.lastname: Ma
authors.affiliation: Department of Anesthesiology, West China Second Hospital, Sichuan University, Chengdu, Sichuan, China. Electronic address: hxfeymz@sohu.com.
authors.forename: X M
authors.initials: XM
authors.lastname: Lin
authors.affiliation: Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA.
authors.forename: J
authors.initials: J
authors.lastname: Zhou
mesh_terms: D000328:Adult; D000077465:Cabergoline; D018491:Dopamine Agonists / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000494:pharmacology*; D004873:Ergolines / Q000494:pharmacology; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008278:Magnesium Sulfate / Q000494:pharmacology*; D008787:Metoclopramide / Q000494:pharmacology*; D009126:Muscle Relaxation / Q000187:drug effects; D009215:Myometrium / Q000187:drug effects*; D010121:Oxytocin / Q000494:pharmacology; D011247:Pregnancy; D015149:Tocolytic Agents / Q000494:pharmacology*; D014590:Uterine Contraction / Q000187:drug effects*
chemical_list: D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D004873:Ergolines; D015149:Tocolytic Agents; D010121:Oxytocin; D008278:Magnesium Sulfate; D008787:Metoclopramide; D000077465:Cabergoline
keywords: Magnesium sulfate; Metoclopramide; Myometrial contractions; Oxytocin