THE RELATIONSHIP BETWEEN LOW-CALCIUM-INDUCED INCREASE IN SYSTOLIC BLOOD-PRESSURE AND VITAMIN-B6

Objective: To investigate the relationship between the increase in sys tolic blood pressure caused by a low-calcium (0.1%) diet and the vitam in B-6 status in the rat. Methods: Male Sprague-Dawley rats fed a vita min B-6-deficient diet did not show any change in systolic blood press ure (SEP) for the first 4 weeks (prehypertensive phase), but from week 5 there was an increase in SEP lasting until week 10 (hypertensive ph ase). SEP declined to below normal levels in most rats from week 12 on the vitamin B-6-deficient diet (posthypertensive phase). The effect o f altering the level of calcium in the diet at different phases of vit amin B-6 deficiency was studied. In another experiment the effect on t he change in blood pressure induced by the low-calcium diet of increas ing the dietary vitamin B-6 level to 2.5-, 5- or 10-fold the normal in take was studied. Results: Lowering dietary calcium caused a significa nt increase in SEP in rats on the vitamin B-6-sufficient diet. This oc curred during weeks 3 and 4 on the low-calcium diet. Low levels of cal cium in the diet potentiated the hypertension induced by the vitamin B -6-deficient diet when both deficiencies were present from the beginni ng of the experiment. Feeding a low-calcium diet during the hypertensi ve or posthypertensive phase failed to raise the SEP in these rats. No rmalizing the vitamin B-6 status Of posthypertensive vitamin B-6-defic ient rats restored the ability of low dietary calcium to increase SEP in these rats. Increasing dietary levels of vitamin B-6 by itself redu ced SEP in normal rats, and attenuated the increase in SEP induced by the low-calcium diet. Conclusions: Dietary vitamin B-6 deficiency and low calcium in the diet seem to share the mechanisms increasing SEP.