Noise-induced hypertension and magnesium in rats: relationship to microcirculation and calcium

It has been demonstrated that audiogenic stress (AS) can induce elevation of arterial blood pressure (ABP) in animals and humans and that noise-induced hearing loss may be associated with alterations in Mg metabolism. Experiments were designed to determine whether 1) there is a causal relationship among environmental noise stress, serum and vascular tissue (aortas and portal veins) Mg contents, and development of hypertension and 2) such noise-induced hypertension has a microcirculatory basis and what the mechanism may be. Rats maintained on normal Mg-containing diets for 12 wk (plasma [Mg] = 0.96 +/- 0.02 mM) and subjected to AS (85 dB(A), 12 h/day for 8 wk; 95 dB(A), 16 h/day for 4 wk) demonstrated significant elevation in systolic and diastolic ABP; plasma [Mg] showed a 15% deficit, whereas aortic and portal vein muscle exhibited slight reductions in Mg content and elevation in Ca. Moderate and more severely Mg-deficient animals not subjected to AS also exhibited significant elevations in systolic and diastolic ABP; vascular tissue Mg content decreased, whereas Ca content rose. Animals subjected to combined Mg deficiency and AS for 12 wk exhibited the greatest deficits in plasma and vascular muscle Mg and the greatest elevations in systolic and diastolic ABP; vascular tissue Ca contents also showed the greatest increases. In situ measurements of mesenteric arterioles, venules, and precapillary sphincters in the various subgroups revealed that the lower the plasma [Mg], the more constricted the microvessels, and the higher the ABP, the lower the plasma [Mg]. Capillary blood flow velocities were decreased in relation to the degree of plasma Mg deficit.(ABSTRACT TRUNCATED AT 250 WORDS)