Systemic and regional hemodynamic effects of dietary calcium supplementation in mineralocorticoid hypertension

This study was undertaken to determine the systemic and regional hemodynamic effects of long-term dietary calcium supplementation in mineralocorticoid (DOC)-salt hypertension. Systemic and regional hemodynamic measurements were determined by the radioactive microsphere technique in conscious and unrestrained rats (kidneys intact) with DOC-salt-induced hypertension that were pair-fed either a normal calcium (0.6% by weight, n=12) or a calcium-supplemented (high-calcium) diet (2.5% by weight, n=12). After 7 to 8 weeks, there were no differences in weight, heart rate, or cardiac output between the two groups. In contrast, the high-calcium rats had a significantly lower mean blood pressure (125±4 mm Hg, mean±SEM) than the normal calcium rats (143±5 mm Hg); this finding appeared to result predominantly from a reduction in total peripheral resistance. The high-calcium rats had a higher renal blood flow (7.8±0.5% vs. 6.2±0.4% cardiac output; p<0.05) and lower renal (14.3±1 vs. 19.3±2 mm Hg/min/ml/g tissue; p<0.05) and jejunal vascular resistance than did the normal calcium rats. Two additional identical groups of normal calcium- and high-calcium-DOC-salt rats (n=12 each) were also studied. In these rats, serum-ionized calcium decreased significantly (p<0.05) from baseline in both groups. Urinary sodium increased in both groups but did not differ significantly. In conclusion, dietary calcium supplementation attenuates the rise in peripheral vascular resistance that accompanies DOC-salt hypertension. This attenuated resistance appears to be relatively selective and is noted particularly in the renal vasculature.