AJP - Regulatory, Integrative and Comparative Physiology, Vol 253, Issue 3 501-R508, Copyright © 1987 by American Physiological Society
Analysis of BP response and Ca2+ metabolism using the saturation kinetics model
N. Karanja, J. A. Metz, L. P. Mercer and D. A. McCarron
The provision of supplemental dietary calcium (dCa) lowers blood pressure
(BP) in the spontaneously hypertensive rat (SHR). Whether calcium's
antihypertensive effects can be expressed in the presence of potentially
hypertensinogenic nutrients is not known. Furthermore, the amount of dCa
required to attenuate hypertension in the SHR remains undetermined. Along
with establishing the effects of dCa on BP under conditions of a high Na+
intake, we sought to define the lowest dose of dCa associated with the
greatest attenuation in arterial pressure in the young SHR. Thirty-five
6-wk-old SHR were fed one of five diets containing either 0.1, 0.25, 0.5,
1.0, or 2.0% dCa. All diets contained 1.0% Na+. The rates of change (delta)
in body weight, BP, and serum ionized calcium were determined between 6 and
20 wk of age. Bone density (BD) was measured only at 20 wk of age. The data
were analyzed using the saturation kinetics model. Results indicate that
the half-maximal dose (K50) of dCa needed to lower pressure is 0.67 +/-
0.18%, which is higher than the K50 for weight (0.23 +/- 0.18) and BD (0.36
+/- 0.22). It is concluded that supplemental dCa lowers BP despite a high
Na+ intake. Furthermore, a dose of approximately 1.5 dCa is sufficient to
attenuate the rate of hypertension in the young growing SHR.
