title: The antiadrenergic effects of hypermagnesemia: an experimental study.
abstract: The circulatory effects of norepinephrine (4 micrograms/kg), isoproterenol (10 micrograms/kg) and phenylephrine (20 micrograms/kg) were determined in anesthetized dogs with normal plasma magnesium and with induced hypermagnesemia. Norepinephrine caused a 24% increase in heart rate and a 103% increase in the systemic vascular resistance index in normomagnesemic dogs, while with hypermagnesemia the variations were of 13% and 1%, respectively. Isoproterenol increased heart rate by 48% and 18% in dogs with normo- and hypermagnesemia, respectively. Phenylephrine increased the systemic vascular resistance index (74%) only in the normomagnesemic state. The effects of all the drugs were significantly different (P less than 0.01), without and with the simultaneous administration of magnesium sulfate (plasma magnesium, 1.3 +/- 0.2 mEq/l and 6.8 +/- 1.1 mEq/l, respectively). We conclude that acute induced hypermagnesemia antagonizes the circulatory effects of adrenergic stimulation, a fact that may explain its antiarrhythmic and hemodynamic effects during acute myocardial ischemia.
authors.affiliation: Divisão de Experimentação, Faculdade de Medicina de São Paulo, Universidade de São Paulo, Brasil.
authors.forename: L F
authors.initials: LF
authors.lastname: Barros
authors.forename: F
authors.initials: F
authors.lastname: Pileggi
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D003327:Coronary Disease / Q000503:physiopathology; D004285:Dogs; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects*; D007545:Isoproterenol / Q000037:antagonists & inhibitors*; D008274:Magnesium / Q000097:blood* / Q000494:pharmacology; D009638:Norepinephrine / Q000037:antagonists & inhibitors*; D010656:Phenylephrine / Q000037:antagonists & inhibitors*; D014655:Vascular Resistance / Q000187:drug effects
chemical_list: D010656:Phenylephrine; D008274:Magnesium; D007545:Isoproterenol; D002118:Calcium; D009638:Norepinephrine