[Diurnal alteration of platelet-free Ca2+ in subjects with normal renal function and patients undergoing CAPD]

We examined the relation of diurnal alteration of platelet-free Ca2+ to blood pressure and plasma vasoactive substances in 6 subjects with normal renal function (N group) (with both normal GFR and normal urine concentration, and with the renal biopsy finding of minor glomerular change) and 7 patients undergoing CAPD (CAPD group), then evaluated the pathophysiological difference in diurnal variations between both groups and the effect of native kidney function. Diurnal values of platelet basal-free Ca2+ concentration in N showed a positive correlation with the corresponding PRA levels. On the other hand, in CAPD they showed a positive correlation with the corresponding levels of plasma AVP. The larger increases in platelet-free Ca2+ concentration due to thrombin stimulation were observed in the daytime and the smaller increases in the nighttime in the N groups. The thrombin-induced changes showed a positive correlation with the diurnal levels of mean blood pressure in N (p < 0.004). However, in contrast, in CAPD the increase in platelet-free Ca2+ due to thrombin tended to be larger in the nighttime and showed a negative correlation with the daily mean blood pressure levels (p < 0.004). These findings suggest that there might be differences in the regulation of intracellular-free Ca2+ dynamics and the diurnal variation between subjects with normal renal function and patients undergoing CAPD. Those differences could affect the progression of vascular disturbance in CAPD patients.