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Dietary calcium and iron: effects on blood pressure and hematocrit in young spontaneously hypertensive rats
D Hatton1, M Muntzel, J Absalon
1Department of Medical Psychology, Oregon Health Sciences University, Portland 97201.
Insights
Supplemental calcium intake in spontaneously hypertensive rats (SHRs) lowered blood pressure and hematocrit. However, iron-modified diets showed blood pressure changes were independent of hematocrit, suggesting calcium
Area of Science:
- Cardiovascular Physiology
- Nutritional Science
- Hypertension Research
Background:
- Supplemental dietary calcium can decrease blood pressure and hematocrit in spontaneously hypertensive rats (SHRs).
- A simultaneous fall in hematocrit and blood pressure suggests potential links via blood viscosity.
Purpose of the Study:
- To investigate whether the blood pressure-lowering effects of calcium are mediated by changes in hematocrit.
- To determine the independent effects of calcium and iron on blood pressure and hematocrit in SHRs.
Main Methods:
- Spontaneously hypertensive rats (SHRs) were fed diets varying in iron content.
- Hematocrit and blood pressure were measured after dietary interventions.
- The ratio of calcium and iron in diets was manipulated to assess independent effects.
Main Results:
- Iron-induced variations in hematocrit were observed (P < 0.001) without affecting blood pressure.
- Manipulating calcium and iron ratios resulted in hematocrit variations independent of blood pressure alterations.
- Calcium's effects on blood pressure were not solely a consequence of hematocrit reduction.
Conclusions:
- Calcium's impact on blood pressure in SHRs is largely independent of its effects on hematocrit.
- Dietary iron influences hematocrit but not blood pressure in this model.
- The study dissociates the mechanisms of calcium's effects on blood pressure from its hematocrit-modulating properties.
Abstract:
Supplemental dietary calcium in spontaneously hypertensive rats (SHRs) aged 21-28 d produces a decrease in blood pressure and hematocrit. The simultaneous fall in hematocrit and blood pressure suggests that the changes in blood pressure may be, in part, a consequence of the decrease in hematocrit and reduction in viscosity. To examine this possibility, SHRs aged 21 d were placed on one of four diets varying in iron content. At age 28, the animals showed iron-induced variations in hematocrit (P less than 0.001) but no difference in blood pressure. Subsequent manipulation of the ratio of calcium and iron in the diets of additional groups of animals resulted in variations in hematocrit that were independent of the calcium-induced alterations in blood pressure. We conclude that the effects of calcium on blood pressure are relatively independent of its effects on hematocrit.
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