Plasma endogenous digitalis-like factors in healthy individuals and in dialysis-dependent and kidney transplant patients.

Plasma digitalis-like factors (DLF), dehydroepiandrosterone sulfate (DHEAS) and cortisol were assayed in 20 healthy subjects, 22 dialysis dependent subjects and 30 patients with kidney transplants. DLF were assayed on plasma extracts by digoxin radioimmunoassay (RIA), and by Na,K-ATPase inhibition and [3H]-ouabain displacement using hogbrain Na,K-ATPase. Values for the 3 methods strongly intercorrelated (r = 0.99, p less than .001). Mean values for plasma DLF, assayed by all three methods, were significantly greater in dialysis dependent subjects, than in healthy subjects (p less than .0001). Mean plasma DLF values measured by digoxin RIA in renal transplant recipients, were significantly lower than in dialysis dependent subjects (p less than 0.0001) and higher than in healthy subjects. Plasma DLF values correlated inversely with creatinine clearance (p less than 0.01). Plasma DHEAS levels were significantly lower and contributed substantially less to digoxin antibody reactivity and ouabain displacement in dialysis subjects and in renal transplants compared with healthy subjects. There was no change in plasma immunoreactive DLF, DHEAS or cortisol measured before and after dialysis. DHEAS is a major digoxin like immunoreactive DLF and a minor Na,K-ATPase inhibitor in healthy subjects but makes only a minor contribution to DLF in dialysis and transplant subjects. We found the assays involving Na,K-ATPase inhibition and [3H]-ouabain displacement from Na,K-ATPase to be more sensitive for plasma DLF than the digoxin RIA, but because of the strong correlation between the methods, we suggest the RIA on plasma extracts can be used as a screening procedure.