title: Effect of magnesium sulfate on contractile force and intracellular calcium concentration in pregnant human myometrium.
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.
  
  
  METHODS
  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 Ca(2+)-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 micromol/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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Obstetrics and Gynecology, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Victor P
authors.initials: VP
authors.lastname: Fomin
authors.forename: Shawn G
authors.initials: SG
authors.lastname: Gibbs
authors.forename: Ram
authors.initials: R
authors.lastname: Vanam
authors.forename: Akira
authors.initials: A
authors.lastname: Morimiya
authors.forename: William W
authors.initials: WW
authors.lastname: Hurd
mesh_terms: D002118:Calcium / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism*; D008278:Magnesium Sulfate / Q000008:administration & dosage / Q000494:pharmacology*; D009215:Myometrium / Q000378:metabolism / Q000502:physiology*; D009994:Osmolar Concentration; D011247:Pregnancy; D013997:Time Factors; D015149:Tocolytic Agents / Q000008:administration & dosage / Q000494:pharmacology*; D014590:Uterine Contraction / Q000187:drug effects*
chemical_list: D015149:Tocolytic Agents; D008278:Magnesium Sulfate; D002118:Calcium