Natriuretic activity of digoxin-like immunoreactive substance extracted from cord blood

It was examined whether the digoxin-like immunoreactive substance (DLIS) extracted from cord blood has a natriuretic activity. The DLIS was prepared from cord blood of healthy fullterm infants by acetone-HCl extraction and a gel filtration column. A solution (solution A) containing 1.0 ng/ml of DLIS or another solution (solution B) consisting of solution A from which the DLIS had been completely absorbed by rat brain synaptosome, a crude digoxin receptor, were infused directly into the renal arteries of rats. Serum and urine were serially sampled. The excretion of sodium into the urine increased gradually after the initiation of infusion and reached a level two or three times higher than that before infusion (p less than 0.05). The infusion of a buffer solution or of the extract from which the DLIS had been absorbed by rat brain synaptosome did not significantly increase the urinary excretion of sodium. Statistical analysis showed a clear difference in the natriuretic activity between solutions A and B (p less than 0.01, p less than 0.05). Well-known natriuretic substances such as atrial natriuretic hormone, prostaglandin E2, F2 alpha, bradykinin and oxytocin dopamine were not detected enough to contribute to natriuresis in the extracts. From this data, we speculated that the DLIS in cord blood has a natriuretic activity and that it plays a role in water and sodium homeostasis in perinatal life.