Red blood cell calcium level is elevated in women: enhanced calcium influx by estrogens.

Red blood cell (RBC) calcium level had been found to be higher in women than in men. This study was designed to evaluate whether this is a general phenomenon and to elucidate a possible mechanism for a gender-related difference in RBC calcium levels. Differences in RBC calcium levels between women and men were examined in normal subjects, in patients with chronic renal failure (CRF) who were known to have elevated RBC calcium levels, and in female and male rats. RBC calcium level was higher in healthy women (6.1 +/- 0.5 mumol/L in women vs 4.4 +/- 0.3 mumol/L in men; p < 0.01), in women with CRF (45.8 +/- 11.8 mumol/L vs 15.4 +/- 1.1 mumol/L in men with CRF; p < 0.025) and women undergoing hemodialysis treatment (43.4 +/- 4.7 mumol/L vs 8.8 +/- 0.9 mumol/L in men undergoing hemodialysis p < 0.001). RBC calcium levels in female rats were also significantly higher than those in male rats. Ovariectomy reduced RBC calcium levels in female rats to those of male rats, whereas castration of male rats had no effect on RBC calcium levels. These in vivo findings suggest that the elevated RBC calcium level is associated with activity of female sex hormones. To investigate a possible mechanism, the in vitro effect of beta-estradiol on calcium 45 influx into RBCs and its effect on basal and calmodulin-stimulated Ca adenosine triphosphatase (CaATPase) activity in RBC membranes was determined. CaATPase activity was not affected by beta-estradiol at various concentrations and different incubation periods.(ABSTRACT TRUNCATED AT 250 WORDS)