The relationship between low-calcium-induced increase in systolic blood pressure and vitamin B6.

OBJECTIVE

To investigate the relationship between the increase in systolic blood pressure caused by a low-calcium (0.1%) diet and the vitamin B6 status in the rat.

METHODS

Male Sprague-Dawley rats fed a vitamin B6-deficient diet did not show any change in systolic blood pressure (SBP) for the first 4 weeks (prehypertensive phase), but from week 5 there was an increase in SBP lasting until week 10 (hypertensive phase). SBP declined to below normal levels in most rats from week 12 on the vitamin B6-deficient diet (posthypertensive phase). The effect of altering the level of calcium in the diet at different phases of vitamin B6 deficiency was studied. In another experiment the effect on the change in blood pressure induced by the low-calcium diet of increasing the dietary vitamin B6 level to 2.5-, 5- or 10-fold the normal intake was studied.

RESULTS

Lowering dietary calcium caused a significant increase in SBP in rats on the vitamin B6-sufficient diet. This occurred during weeks 3 and 4 on the low-calcium diet. Low levels of calcium on the diet potentiated the hypertension induced by the vitamin B6-deficient diet when both deficiencies were present from the beginning of the experiment. Feeding a low-calcium diet during the hypertensive or posthypertensive phase failed to raise the SBP in these rats. Normalizing the vitamin B6 status of posthypertensive vitamin B6-deficient rats restored the ability of low dietary calcium to increase SBP in these rats. Increasing dietary levels of vitamin B6 by itself reduced SBP in normal rats, and attenuated the increase in SBP induced by the low-calcium diet.

CONCLUSIONS

Dietary vitamin B6 deficiency and low calcium in the diet seem to share the mechanisms increasing SBP.