[Effect of dialysis on Na+/K+-ATP-ase activity in uremic children]

The enzyme Na+/K(+)-ATPase plays a central role in the regulation of transmembrane ionic transports. According to previous reports its activity decreased in uremic state. The activity of Na+/K(+)-ATPase in detergent pretreated erythrocytes was studied in seven uremic children prior to and following the hemodialysis (HD) session. Additionally, the level of endogenous digoxin like factors in the plasma (EDLF) was determined. Before the HD session the Na+/K(+)-ATPase activity decreased compared to the control value (mean +/- SD: 2078 +/- 527 vs 3245 +/- 362 nmol P/ml RBC/h, p < 0.01). Following HD it became normal (3366 +/- 952 nmol P/ml RBC/h, n.s.). Prior to the HD the EDLF level was higher, while after the HD no difference was noted from the control value (0.29 +/- 0.04, p < 0.05; 0.24 +/- 0.04 n. s. vs control; 0.21 +/- 0.04 ng/ml). Before the HD blood pressure was significantly elevated compared to the control (117 +/- 20/92 +/- 18 vs 95 +/- 2/64 +/- 2 Hgmm, p < 0.05). By the end of the HD it became normal (100 +/- 14/79 +/- 11, n.s.). Although no correlation was found between the EDLF level and Na+/K(+)-ATPase activity, a positive significant correlation was found between the changes of enzyme activity and the changes in the systolic (r = 0.83, p < 0.05) and diastolic (r = 0.82, p < 0.05) blood pressure during the HD. Our results indicate, that in uremic children the Na+/K+ pump is inhibited by a dialysable, blood-pressure regulator substance and so the enzyme activity elevates following the HD session. However, decreased blood pressure activates counterregulatory mechanisms, which-to lower extent-inhibit the activity of the pump.