Dialysance of adrenocorticoids during continuous ambulatory peritoneal dialysis

We postulated that significant quantities of both protein-bound and unbound adrenocorticoids are lost during continuous ambulatory peritoneal dialysis (CAPD). To test this hypothesis we measured the dialysate removal rates (DRR) of adrenocorticoids in six CAPD patients. The distribution of the adrenocorticoids among unbound, albumin-bound, and transcortin-bound fractions in dialysate effluent was determined. The distribution of cortisol among unbound, albumin-bound, and transcortin-bound fractions in plasma was determined in six other CAPD patients. The mean DRR of cortisol was 193.8 +/- 20.3 (+/- SE) nmol/day. Smaller quantities of 11-deoxycorticosterone, corticosterone, aldosterone, 18-hydroxy-11-deoxycorticosterone, and 18-hydroxycorticosterone were removed during CAPD. The mean DRR values for total protein, albumin, and transcortin were 11.2 +/- 2.1, 6.0 +/- 2.2, and 0.087 +/- 0.018 g/day, respectively. The distribution of cortisol among unbound, albumin-bound, and transcortin-bound fractions was normal in plasma from CAPD patients. Plasma transcortin had a normal affinity (2 x 10(7) mol/L-1) and a normal binding capacity (559 nmol/L) for cortisol. In contrast, dialysate transcortin had a low affinity (1.4 x 10(7) mol/L-1) for cortisol and a low cortisol-binding capacity (11.5 nmol/L). The fractional occupancy rates of high affinity cortisol-binding sites on transcortin were 52.0 +/- 3.3% and 3.3 +/- 0.6% in plasma and dialysate effluent, respectively (P less than 0.001). The transcortin to cortisol molar concentration ratio in dialysate (6.3 +/- 0.6) was significantly higher than that in plasma (1.6 +/- 0.2; P less than 0.001). These results demonstrate that cortisol is the major adrenocorticoid lost during CAPD. However, the amount of cortisol removed in the dialysate is less than 1% of the normal daily secretion rate. Significant quantities of other adrenocorticoids are also lost during CAPD. The adrenocorticoids present in dialysate effluent are principally unbound, in contrast to their state in plasma. However, small fractions of the respective steroids are bound to transcortin and albumin.