Blood pressure and calcium balance in the Wistar-Kyoto rat

Recent investigations in human and experimental hypertension have characterized previously unrecognized abnormalities of calcium homeostasis. Data from human and animal studies have indicated that adequate dietary calcium intake may be an important determinant for the development of high blood pressure. Since dietary calcium supplementation has been shown to attenuate the hypertension of the spontaneously hypertensive rat (SHR), the present study was undertaken to assess the effect of dietary calcium intake on the blood pressure of the Wistar-Kyoto rat (WKY), the normotensive genetic control for the SHR. One of three levels of dietary calcium was fed to 36 WKYs beginning at eight to 10 weeks of age (WOA) through 34 WOA. Throughout the period of observation, the WKYs stratified inversely with their level os dietary calcium (p less than .001), i.e. rats fed the lowest level of calcium had the highest blood pressure. WKYs on the high calcium diet experienced an attenuation of their blood pressure with increasing age and dietary calcium intake. These salutary blood pressure effects of dietary calcium were independent of growth and urinary sodium excretion of the rats. Serum ionized calcium (Ca++) increased in the high calcium diet WKYs and appeared to be associated with the blood pressure reduction. The results suggest that calcium intake must be assessed in experimental models of hypertension and that the state of calcium balance is a possibly important determinant of blood pressure regulation.