Stress-induced blood pressure responses in SHR: effect of dietary calcium.

To assess the influence of dietary calcium on stress-induced blood pressure responses, spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats were placed on low Ca2+ (0.1%) and Na+ (0.25%), intermediate Ca2+ (1.0%) and Na+ (0.45%), or high Ca2+ (2.0%) and Na+ (1.0%) diets for 13 wk prior to measuring blood pressure (BP) responses in an aversive classical conditioning paradigm. Forty-eight hours prior to testing, catheters were placed in a femoral artery under halothane anesthesia for recording direct pressure. On recovery the rats were classically conditioned to a 10-s tone followed by a brief electric shock using a discrimination paradigm. After 24 reinforced trials, SHRs on a low diet had significantly larger pressor responses to the conditioned tones than rats in the high diet condition. SHRs on the intermediate diet exhibited pressor responses midway between the low and high diet groups. In the WKY strain there was no significant dietary effect on conditioned BP response. In both strains the low diets resulted in significantly elevated base-line blood pressure levels. The data confirm earlier reports of elevated BP in SHRs and WKYs following dietary calcium restriction and provide suggestive evidence that the elevation in base-line BP may be related to diet-induced changes in BP reactivity in the SHR.