AJP - Regulatory, Integrative and Comparative Physiology, Vol 261, Issue 5 1070-R1074, Copyright © 1991 by American Physiological Society
Antihypertensive effect of dietary calcium loading in angiotensin II-salt rats
K. Ando, Y. Sato, A. Ono, K. Takahashi, T. Shimosawa, E. Ogata and T. Fujita
Fourth Department of Internal Medicine, University of Tokyo School of Medicine, Japan.
To clarify the hypotensive effect of high dietary Ca intake on
salt-sensitive hypertension, 7-wk-old Sprague-Dawley rats, 3.15% Na and/or
4.07% Ca diet loaded, were administered 125 ng/ml of angiotensin II (ANG
II) intraperitoneally for 12 days. Compared with control rats (mean blood
pressure 108 +/- 2 mmHg), ANG II administration caused hypertension (131
+/- 4 mmHg, P less than 0.05). Na loading enhanced the hypertensive effect
of ANG II (161 +/- 4 mmHg, P less than 0.01). Dietary Ca loading did not
significantly inhibit the pressor effect of ANG II alone (119 +/- 4 mmHg).
However, Ca loading suppressed hypertension in ANG II-salt rats (126 +/- 4
mmHg, P less than 0.01). Plasma total catecholamine (norepinephrine +
epinephrine) was increased in ANG II-salt rats (176 +/- 14 vs. 290 +/- 23
pg/ml, P less than 0.05), but Ca loading decreased plasma catecholamine
(182 +/- 13 pg/ml, P less than 0.05). In contrast, plasma catecholamine was
not significantly different between ANG II-treated rats with and without Ca
loading. Ca loading increased serum Ca in ANG II rats (10.9 +/- 0.1 vs.
11.7 +/- 0.1 mg/dl, P less than 0.05) but did not do so significantly in
ANG II-salt rats (10.8 +/- 0.2 vs. 10.9 +/- 0.1 mg/dl). Thus Ca loading
exclusively ameliorated salt-sensitive hypertension, which was induced with
ANG II administration and Na loading in rats, probably through suppression
of the increased sympathetic activity. In addition, these effects of Ca
loading were not mediated through an increased blood level of Ca.
