The interactive effects of dietary sodium chloride and calcium on cardiovascular stress responses.

Blood pressure increases associated with salt loading in the spontaneously hypertensive rat (SHR) are attenuated with increased dietary calcium. To assess the cardiovascular effects of these nutrients during stress, blood pressure and sympathoadrenal responses to stress were compared in salt-sensitive SHRs fed diets containing normal (0.73%) or high (8.0%) NaCl combined with either low (0.2%) or high (2.0%) calcium. NaCl-loaded rats showed increased blood pressure and exaggerated plasma epinephrine changes during restraint stress. Elevated blood pressure responses to exogenous NE were also observed with high salt intake. Supplementary calcium reduced blood pressure and attenuated the hypertensive effect of NaCl during restraint stress. Animals fed the high calcium diets had lower plasma epinephrine levels while vascular reactivity was not affected. The results indicate that increased sympathoadrenal activity and vascular reactivity contribute to elevated blood pressure and exaggerated pressor responses produced by NaCl loading in the salt-sensitive SHR. However, the hypotensive effects of dietary calcium appear to be related to sympathoadrenal activity but not vascular reactivity.