Effects of high calcium intake on blood pressure and calcium metabolism in young SHR

Naftali Stern, David B.N. Lee, Vincent Silis, Frances W.J. Beck, Leonard Deftos, Stavros C. Manolagas, James R. Sowers*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

108 Scopus citations

Abstract

Increased dietary calcium intake in the adult spontaneously hypertensive rat (SHR) has been reported to correct low serum ionized calcium concentration ([Ca++]) and to result in a significant amelioration of the prevailing hypertension. In the present study we examined several parameters of calcium metabolism in young (6-week-old) SHR and compared them with those observed in normotensive Wistar-Kyoto (WKY) rats fed equal amounts of a diet containing normal quantities of calcium (0.4%, wt/wt) for 4 weeks. A separate group of SHR was placed on an equal amount of a high calcium (2.8%, wt/wt) but otherwise identical diet. In SHR and WKY eating a normal calcium diet, serum total calcium concentration was not different, but [Ca+ +] was lower in SHR (1.58 ± 0.06 vs 1.91 ± 0.07 mmol/liter, p < 0.01). Serum immunoreactive parathyroid hormone (PTH) was increased in some, but not all, SHR. No difference was noted between the two groups in the following parameters: calcium intake, serum 1,25 dihydroxycholecalciferol (1,25(OH)2D3), urinary calcium excretion, fractional stool calcium content ([stool calcium/calcium intake] x 100), and in vitro 4SCa uptake by everted gut sacs constructed from segments of duodenum, mid-jejunum, ileum, and proximal colon. A high calcium diet corrected the abnormal serum [Ca+ +] and PTH but did not alter the progression or severity of the hypertension in SHR. A lower net weight gain was observed in SHR on a high calcium diet when compared to SHR eating normal calcium diet (9.1 ± 1.8 vs 27.0 ± 2.0 g). This was attributed, at least in part, to a consistently higher urinary sodium loss in the former group of rats (p < 0.05-0.001 throughout the study period). The progression of hypertension, even in the face of normalized serum [Ca+ + ] in young SHR, suggests that low [Ca+ + ] and hypertension do not have a cause-and-effect relationship. Sustained natriuresis caused by the augmented dietary calcium intake and increased urinary calcium excretion may contribute to the blood-pressure-lowering effect reported in adult SHR.

Original languageEnglish
Pages (from-to)639-646
Number of pages8
JournalHypertension
Volume6
Issue number5
DOIs
StatePublished - 1984
Externally publishedYes

Keywords

  • 1
  • 25(OH)2D
  • Calcium
  • Sodium
  • Spontaneously hypertensive rat

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