Racial differences in platelet cytosolic calcium and calcitropic hormones in normotensive subjects.

Elevated levels of serum parathyroid hormone (PTH) and platelet cytosolic free calcium ([Ca2+]i) have been reported in subjects with essential hypertension. In addition, there is a positive correlation between serum PTH and platelet [Ca2+]i in white subjects with essential hypertension. Black normotensive subjects have relatively higher levels of serum PTH when compared to white normotensive subjects. To investigate the possibility that elevated serum PTH levels in black normotensives may contribute to elevated platelet [Ca2+]i, calcitropic hormone profiles and platelet [Ca2+]i were determined in 31 black normotensive subjects and 34 age-matched white normotensive subjects. There was no difference between the two groups in total serum calcium, plasma ionized calcium, or creatinine clearance. However, serum PTH was significantly elevated (P < .02) in the black normotensive group. Serum 1,25(OH)2 vitamin D levels were similar between the two groups whereas serum 25(OH) vitamin D levels were significantly lower (P < .001) in the blacks. The 24 h urinary excretion of Ca was also lower (P < .05) in the black normotensive group. Basal platelet [Ca2+]i was significantly lower (P < .05) in black normotensive than in white normotensive subjects. Serum PTH levels did not correlate with platelet [Ca2+]i in either group, or in the groups combined. These results demonstrate that the higher serum PTH concentrations in black normotensives is not associated with higher platelet [Ca2+]i, as is the case in white hypertensive patients.