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

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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 less than 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 45Ca 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).(ABSTRACT TRUNCATED AT 250 WORDS)