Sodium-Lithium countertransport in red cells

To the Editor : Woods et al. provide evidence for a decrease in the rate of sodium-lithium countertransport in red cells after hemodialysis, and suggest that this effect is related to the removal of a plasma factor. They did not observe a difference in ouabain-dependent sodium efflux during hemodialysis, but this conclusion is based on data in only two patients. This latter observation disagrees with previous date, which demonstrated a decrease in the sodium-potassium pump activity in patients with chronic renal failure. We have studied the sodium exchange in red cells of 11 patients receiving hemodialysis. These date suggest that the modifications in the rate of ouabain-sensitive sodium efflux observed after hemodialysis may be related to a volume-dependent plasma factor and not only to a decrease in th concentration of a dialyzable factor; this factor may be similar to the "natriuretic digoxin-like factor" postulated by de Wardener and MacGregor as playing a part in primary hypertension. It is also possible that the effect observed by Woods et al. on sodium-lithium countertransport is linked to improvement of the sodium-pump activity.