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(Circulation Research. 1995;77:973.)
© 1995 American Heart Association, Inc.

Articles

Differential Regulation of Circulating Mg²⁺ in the Rat by ß₁- and ß₂-Adrenergic Receptor Stimulation

D. Keenan, A. Romani, A. Scarpa

From the Departments of Physiology and Biophysics (D.K., A.R., A.S.) and Surgery (D.K.), Case Western Reserve University, School of Medicine, Cleveland, Ohio.

Abstract Extracellular Mg²⁺ homeostasis was studied in vivo in the anesthetized rat. Animals were infused with isoproterenol (ISO) for 10 minutes, and serum Mg²⁺ was measured after the infusion and then 10 and 20 minutes later. A dose-dependent increase in circulating Mg²⁺ was observed in animals infused with ISO at a rate of 0.1 µg · kg^-1 · min^-1 or higher. The time course of the effect demonstrated that circulating Mg²⁺ continued to increase 20 minutes after the end of the ISO infusion. A predicted maximal increase in serum Mg²⁺ concentration of 19.3% was derived with a predicted EC₅₀ of 0.08 µg · kg^-1 · min^-1. The maximal percent increase corresponded to a net increase of 6.7 µmol/300 g body wt. Because infusion of ISO resulted in changes in hemodynamic parameters, most notably a drop in blood pressure, a group of animals was infused with nitroprusside to mimic the hypotensive response via a nonadrenergic mechanism. Under these conditions, there was a transient increase in circulating Mg²⁺ that was largely inhibited by propranolol, indicating that hypotension per se was not responsible for the mobilization of Mg²⁺. Infusion of salbutamol, but not prenalterol, also induced an increase in circulating Mg²⁺. Pretreatment with butoxamine, ICI-118551, or propranolol prevented the ISO-induced increase in serum Mg²⁺. Pretreatment with atenolol minimally affected the ISO-induced changes in circulating Mg²⁺. Pretreatment with CGP-20271A actually enhanced the ISO-induced increase in circulating Mg²⁺. This evidence demonstrates the existence of a pool of Mg²⁺ that is mobilized into the circulation in response to selective ß₂-adrenergic stimulation.

Key Words: Mg²⁺ • circulation • ß-adrenergic stimulation • rats

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