Dietary calcium alters blood pressure reactivity in spontaneously hypertensive rats.

Plasma catecholamines and blood pressure reactivity were investigated in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats maintained on three levels of dietary calcium: low (0.1%), intermediate (1.0%), or high (2.0%). In the SHR, restricted dietary calcium resulted in elevations of mean arterial pressure that were most pronounced during handling and restraint stress (p less than 0.05). There was no difference between SHR on intermediate and high calcium diets and no dietary effects in the WKY rats. Resting and stressed levels of circulating catecholamines did not differ across diet conditions in either strain. The SHR on low calcium diets had significantly larger pressor responses to infused norepinephrine (p less than 0.05). There were no differences between the rats on intermediate and high calcium diets. The results indicate that differences observed in blood pressure reactivity across diets in this study may have been a consequence of altered postsynaptic sensitivity rather than an increase in norepinephrine release.