The antiadrenergic effects of hypermagnesemia: an experimental study

ABSTRACT

The circulatory effects of norepinephrine (4 * g/kg) and phenylephrine (20 */kg) were determined in anesthetized dogs withnormal plasma magnesium and with induced hypermagnesemia. Norepinephrine caused a 24% increased in heart rate by 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 485 and 185 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 defferent (P<0.01), without and with the simultaneous administration of magnesium sulfate (plasma magnesium, 1.3ñ0.2mEq/l and 6.8ñ1.1 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