DIETARY CALCIUM AND MAGNESIUM IN THE DEVELOPMENT AND TREATMENT OF HYPERTENSION IN THE SPONTANEOUSLY HYPERTENSIVE RAT
Abstract
To determine the therapeutic effectiveness of dietary magnesium in the treatment of established hypertension, 21 male spontaneously hypertensive rats (SHR) were fed altered levels of magnesium oxide from 17 to 29 weeks of age. The rats were divided into three groups of similar mean baseline systolic blood pressures (205, 208, 214 mm Hg) and fed AIN 76A semipurified diets containing magnesium at 0.01% (low), 0.05% (normal), and 0.40% (high) levels. Weekly mean systolic blood pressures were not significantly different among treatment groups. Total and ultrafilterable serum magnesium concentrations reflected magnesium intake. Total and ultrafilterable serum calcium levels were significantly higher (p < 0-.05) in the low magnesium-fed SHR. Histopathologic alterations did not differ among treatment groups. Therefore, in spite of altered serum mineral status, blood pressure and histopathology were not affected by dietary magnesium. The role of dietary calcium and magnesium in the development of hypertension was studied in nine groups of nine SHR ages 8 to 31 weeks. The animals were fed AIN 76A semipurified diets altered in calcium (0.075%, 0.5%, and 2.5%) and magnesium (0.01%, 0.05%, and 0.75%) using a 3 x 3 factorial design. An inverse relationship between dietary calcium and systolic blood pressure as determined by the photoelectric tail cuff method became significant (p < 0.05) after 12 weeks. Repeated measures analysis of variance indicated that dietary magnesium had no effect on systolic blood pressure; no calcium x magnesium interaction was observed. Total and ultrafilterable serum calcium had a significant inverse correlation with blood pressure (r = -0.46, p = .001 and r = -0.57, p = .001, respectively). Bone, kidney, and total and ultrafilterable serum magnesium generally reflected dietary magnesium concentration. Magnesium deficiency signs, deposition of calcium in kidneys, and histological lesions were observed in high calcium fed groups receiving normal and low levels of magnesium. Thus, a lowering of blood pressure by calcium supplementation without concomitant magnesium supplementation was accompanied by biochemical and histologic abnormalities in this animal model. Thus: (1) magnesium supplementation had no significant effect on systolic blood pressure to SHR; (2) the antihypertensive role of dietary calcium was confirmed; and (3) high calcium:magnesium ratios affected magnesium status and precipitated magnesium deficiency.
Degree
Ph.D.
Subject Area
Nutrition
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