Effect of magnesium sulfate on contractile force and intracellular calcium concentration in pregnant human myometrium

Victor P. Fomin, Shawn G. Gibbs, Ram Vanam, Akira Morimiya, William W. Hurd

Research output: Contribution to journalArticlepeer-review

30 Scopus citations

Abstract

Objective: This study was undertaken to evaluate the effects of magnesium sulfate (MgSO4) on contractile force and increases in free intracellular calcium concentration ([Ca2+]i) in human myometrial strips from pregnant women. Study design: Simultaneous measurements of isometric tension and [Ca2+]i were measured in myometrial strips obtained at the time of cesarean delivery from pregnant nonlaboring women at term with the use of a fluorescence spectrometer equipped with a displacement force transducer. Changes in [Ca2+]i were measured with fura-2, a Ca2+-sensitive fluorescent probe. Myometrial strips were exposed to MgSO4 (5 or 10 mmol/L) for 5, 10, 20, and 30 minutes and observed for spontaneous contractions or stimulated with either oxytocin (OT; 0.1 μmol/L) or potassium chloride (KCl; 90 mmol/L). Results: MgSO4 reduced spontaneous, OT, and KCl-evoked contractions and increases in [Ca2+]i in a time and concentration-dependent manner. After 20 minutes exposure to 5 mmol/L MgSO4, the OT-elicited changes in contractile response and [Ca2+]i were significantly decreased. MgSO4 did not change [Ca2+]i/force relationship of the responses to OT or KCl, or during spontaneous activity. Conclusion: At a pharmacologic concentration (5 mmol/L), MgSO4 inhibits contractile response and [Ca2+]i in pregnant human myometrial strips by a pattern that is consistent with both extra- and intracellular mechanisms. At a suprapharmacologic concentration (10 mmol/L), the more immediate effect of MgSO4 is consistent with an extracellular mechanism. MgSO4 does not appear to interfere at the level of the calcium-calmodulin interface, since the [Ca2+]i/force relationship was not changed.

Original languageEnglish (US)
Pages (from-to)1384-1390
Number of pages7
JournalAmerican Journal of Obstetrics and Gynecology
Volume194
Issue number5
DOIs
StatePublished - May 2006

Keywords

  • Calcium
  • Magnesium sulfate
  • Myometrium
  • Oxytocin
  • Pregnancy
  • Premature labor
  • Uterus

ASJC Scopus subject areas

  • Obstetrics and Gynecology

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