AJP - Heart and Circulatory Physiology, Vol 246, Issue 3 324-H331, Copyright © 1984 by American Physiological Society
Evidence for the role of PO4 deficiency in antihypertensive action of a high-Ca diet
K. Lau, S. Chen and B. Eby
Previous studies indicated a salutary effect of a high-Ca diet on high
blood pressure (BP). The mechanism, however, is obscure. With balance and
clearance techniques, the role of parathyroid hormone (PTH), volume
contraction, hypercalcemia, and PO4 deficiency was evaluated in female
spontaneous hypertensive rats (SHR). The antihypertensive effects of a high
(4.3%) Ca diet in intact animals (groups I and II) could be reproduced in
both 9- and 22-wk-old chronic stable parathyroidectomized (PTX) rats
(groups III and IV), when compared with a low (0.22%) or normal (1.2%) CA
diet. In both short (7 days) and long (12 wk) term exposure to the high-Ca
diet, evidence for volume contraction could not be documented despite
hypercalcemia sustained through the 12th wk (10.8 vs. 9.7 mg/100 ml, group
I control, P less than 0.02). When produced by ip injections, chronic
hypercalcemia of similar magnitudes as oral Ca supplements failed to reduce
BP in either intact (group VI) or PTX (group IV) rats. Rats in group IV fed
the high-Ca diet displayed marked hypophosphatemia (3.2 vs. 6.9 mg/100 ml),
hypophosphaturia (0.15 vs. 15 mg/day), hypermagnesiuria (11 vs. 7.7
mg/day), and drastically reduced net intestinal PO4 absorption (13.3 +/-
7.5 vs. 66.8 +/- 7.5 mg/day) compared with rats fed 1.2% Ca diet. To test
the PO4-deficiency hypothesis, additional SHR (group V) were fed either
1.2% Ca diet and injected ip with NaCl or fed 4.3% Ca diet, with half of
these animals injected with neutral NaPO4 and half with NaCl.(ABSTRACT
TRUNCATED AT 250 WORDS)
