Magnesium-induced vasodilation in the dorsal hand vein.
OBJECTIVE
Magnesium affects blood pressure by modulating vascular tone and reactivity. In obstetric patients, magnesium is administered to prevent eclamptic seizures and as a tocolytic to treat preterm labour. Prior to studying vascular sensitivity in women with pre-eclampsia, we sought to determine the effect of magnesium on venous tone in healthy women of childbearing age.


METHODS
Dose-response study.


METHODS
Columbia-Presbyterian Medical Center, New York.


METHODS
Ten healthy non-pregnant women (age range 21-47 years).


METHODS
Vascular response to magnesium sulphate (MgSO4) was measured in a dorsal hand vein using the linear variable differential transformer (LVDT) technique. Complete dose-response curves to MgSO4 (0.0000275-0.088 mmol/min) were determined after 50% preconstriction of the vein with phenylephrine.


METHODS
The ED50 of MgSO4 (dose resulting in 50% of maximal effect, Emax) was determined. Blood samples from the contralateral upper extremity were obtained to assess total plasma magnesium levels at baseline and at the highest infused dose of magnesium. ED50 results are expressed as geometric mean (95% confidence interval, CI). Emax results and magnesium plasma concentrations are expressed as mean [SD].


RESULTS
The ED50 of MgSO4 was 0.000307 mmol/min (95% CI 0.138, 0.666) and Emax was 102% [20%].


CONCLUSIONS
Magnesium induces dose-dependent venodilation in healthy women in the absence of systemic haemodynamic effects. The dose resulting in vasodilation using the LVDT/hand vein model is two to three orders of magnitude less than the therapeutic doses of magnesium used for tocolysis or seizure prophylaxis. Studies of the effect of systemically administered therapeutic doses of magnesium on vascular reactivity in pre-eclampsia will be of interest.
Landau
Ruth
R
Department of Anesthesiology, Columbia University College of Physicians and Surgeons, New York, New York, USA.
Scott
Jason A
JA
Smiley
Richard M
RM
D000328:Adult; D001794:Blood Pressure / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005260:Female; D006225:Hand / Q000098:blood supply*; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D008274:Magnesium / Q000494:pharmacology*; D008875:Middle Aged; D010656:Phenylephrine / Q000494:pharmacology; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014664:Vasodilation; D014680:Veins / Q000187:drug effects / Q000502:physiology
D014662:Vasoconstrictor Agents; D010656:Phenylephrine; D008274:Magnesium