Calcium supplementation attenuates an enhanced platelet function in salt-loaded mildly hypertensive patients.

We designed this study to evaluate the effect of low versus high calcium intake on platelet function in salt-loaded patients with mild hypertension. After a 7-day period of dietary salt restriction, 19 patients were placed on a high salt (300 mmol/d), low calcium (6.25 mmol/d) diet for 7 days; 10 of these patients were given 54 mmol/d of supplementary calcium, and 9 patients were given placebo. At the end of the low and high salt regimens, we evaluated changes in blood pressure, platelet aggregation, and the platelet release reaction measured as plasma beta-thromboglobulin and platelet factor 4 levels. With high salt intake, significant increases in mean blood pressure (P < .02), red blood cell sodium (P < .01), and platelet aggregation induced by 3 mumol/L ADP (P < .01) and by 3.0 mg/L epinephrine (P < .05) were observed in the placebo-treated patients but not in the calcium-supplemented ones. Compared with the placebo-treated patients, calcium-supplemented patients had a smaller weight gain (P < .05) but excreted more sodium and calcium (P < .01) at the end of the high salt regimen. Calcium supplementation resulted in decreases in beta-thromboglobulin (P < .05), platelet factor 4 (P < .01), and plasma and urinary excretions of norepinephrine (P < .02) during the high salt, low calcium regimen. The decrease in plasma norepinephrine correlated positively with the decreases in beta-thromboglobulin (r = .72, P < .02) and platelet factor 4 (r = .85, P < .01).(ABSTRACT TRUNCATED AT 250 WORDS)