Augmented central pressor action of magnesium in SHR.

This study attempted to determine whether central magnesium (Mg) influences the regulation of blood pressure (BP). An intracerebroventricular (icv) injection of a high Mg2 + solution (190.0 mEq/L, 10 μL), made by adding MgC12 to artificial cerebrospinal fluid, increased the mean BP in both conscious spontaneously hypertensive rats (SHR; n = 17, p < 0.001) and Wistar Kyoto rats (WKY; n = 8, p < 0.005). Spontaneously hypertensive rats showed a greater pressor response than WKY (+ 11.7 ± 0.9 mm Hg versus + 3.5 ± 1.1 mm Hg, p < 0.001). This pressor response to Mg2 + given icv was dose-dependent in the range of Mg2 + concentration between 47.5 and 190.0 mEq/L in SHR. A high Mg2 + solution (190.0 mEq/L), made by adding MgS04 given icv, also increased the mean BP in SHR (n = 7, p < 0.001) and WKY (n = 6, p < 0.01), whereas the high osmolarity solution (340 mOsm/kg H20) given icv did not change the mean BP in either SHR or WKY. Also administered was a high Mg2 + solution icv after either hexamethonium bromide (Hx; 50 mg/kg intravenously) or arginine vasopressin antagonist (aAVP, (CH2)5Tyr(Me)AVP, 30 μg/kg iv). The pressor response to the high Mg2 + solution was abolished by arginine vasopressin antagonist both in SHR and WKY, although it was not canceled by Hx. A high Mg2 + solution administered icv caused a 3.5-fold increase in plasma arginine vasopressin concentration in SHR (n = 5, p < 0.001). These results suggest that central Mg influences the regulation of BP through the modulation of vasopressin activity in SHR and WKY, though the effect of central Mg is greater in SHR.