Digoxin-like immunoreactivity increases with intravenous infusion of saline in rats

1. The effects of sodium-loading on releases of endogenous digitalis-like substance were investigated by measuring digoxin-like immunoreactivity (DLI) during intravenous infusions of isotonic (0.15 mol/L) and hypertonic (1 mol/L) saline in anaesthetized rats. Plasma DLI was measured after death by a digoxin-radioimmunoassay. 2. The infusion of isotonic saline and hypertonic saline elevated the central venous pressure to similar levels. The plasma DLI concentration in both the infused groups rose significantly compared with that in the control rat not receiving the intravenous infusion. 3. The difference in the hypothalamic concentrations of DLI was not significant among the three groups, however, there was a significant inverse relationship between the plasma and hypothalamic concentrations of DLI. 4. Results indicate that the central venous pressure, but not sodium concentration, is essentially involved in the release of DLI, possibly from the hypothalamus.