Effect of magnesium deficiency on autonomic circulatory regulation in conscious rats

A close relationship between magnesium and cardiovascular function has been reported; however, the effect of magnesium deficiency on autonomic cardiov ascular regulation has not been clarified. We investigated the effect of ma gnesium deficiency on the autonomic regulation of oscillations of the R-R i nterval, arterial blood pressure (BP), and renal sympathetic nerve activity (RSNA) by using the maximum entropy method in conscious rats. Its effect o n baroreflex control of RSNA and heart rate were also investigated with a l ogistic function curve. Mean BP in magnesium-deficient rats was higher than that in control rats (mean+/-SE, 114.0+/-4.3 versus 101.6+/-3.4 mmHg; P<0. 05), and urinary excretion of catecholamine was increased by 2.4-fold, The fraction of low-frequency oscillation of RSNA was reduced (31.7+/-0.9% vers us 36.2+/-1.5 %, P<0.05) and the correlation between low-frequency oscillat ions of BP and RSNA was weakened in magnesium-deficient rats. There was no difference in high-frequency oscillation of the R-R interval, which is rela ted to vagal tone, whereas sympathetic tone became dominant (square root of low-frequency/high-frequency ratio of R-R interval, 1.00+/-0.05 versus 0.6 7+/-0.05, P<0.0001) in magnesium-deficient rats. The maximal gain in the BP -RSNA relation tended to be reduced in magnesium-deficient rats (-7.7+/-1.1 % versus -12.2+/-1.9%/mm Hg, P=0.07); however, that in the BP-heart rate re lation was increased (-8.1+/-0.7 versus -4.5+/-0.5 bpm/mm Hg, P<0.01). Thes e results suggest that magnesium deficiency induces sympathetic excitation, which results in hypertension but attenuates the baroreflex-related respon se of sympathetic nerves, whereas magnesium deficiency enhances the sensiti vity of the sinus node to autonomic regulation.