AUGMENTED CENTRAL PRESSOR ACTION OF MAGNESIUM IN SHR

This study attempted to determine whether central magnesium (Mg) influ ences the regulation of blood pressure (BP). An intracerebroventricula r (icv) injection of a high Mg2+ solution (190.0 mEq/L, 10 muL), made by adding MgCl2 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 h ypertensive 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 respons e to Mg2+ given icv was dose-dependent in the range of Mg2+ concentrat ion between 47.5 and 190.0 mEq/L in SHR. A high Mg2+ solution (190.0 m Eq/L), made by adding MgSO4 given icv, also increased the mean BP in S HR (n = 7, p < 0.001) and WKY (n = 6, p < 0.01), whereas the high osmo larity solution (340 mOsm/kg H2O) 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 arg inine vasopressin antagonist (aAVP, (CH2)5Tyr(Me)AVP, 30 mug/kg iv). T he pressor response to the high Mg2+ solution was abolished by arginin e vasopressin antagonist both in SHR and WKY, although it was not canc eled by Hx. A high Mg2+ solution administered icv caused a 3.5-fold in crease in plasma arginine vasopressin concentration in SHR (n = 5, p < 0.001). These results suggest that central Mg influences the regulati on of BP through the modulation of vasopressin activity in SHR and WKY , though the effect of central Mg is greater in SHR.