RENAL HYPER-RESPONSIVENESS TO BLOOD VOLUME EXPANSION IN BRATTLEBORO RATS IS NOT RELATED TO PLASMA ANF IMMUNOREACTIVITY

1. Anaesthetized homozygous Brattleboro (DI) rats were used to study the renal response to iso-oncotic blood volume expansion. 2. With the same degree of hypervolaemia DI rats had exaggerated diuresis, natriuresis, and chloriuresis, but not kaliuresis, compared with heterozygous control rats. This increased excretion resulted in negative water balance by the end of the experiment in DI rats, whereas the controls showed restoration of normal balance. The control rats retained significant amounts of sodium and chloride, the Brattleboro rats, however, did not. 3. The lithium clearance method was used to localize the defect in sodium reabsorption. As judged from this method, there was a significantly lower sodium reabsorption in the proximal tubules as well as in the distal parts of the nephron of DI rats. 4. Plasma immunoreactivity of atrial natriuretic factor (ANF) was not different between groups before volume expansion. ANF levels rose and fell similarly in both groups during and after the iso-oncotic infusion. 5. Our results demonstrate that DI rats respond to acute hypervolaemia with an exaggerated diuresis and saluresis. The mechanism of the increased salt excretion may involve inhibition of sodium transport in the proximal tubules as well as in the distal parts of the nephron. These transport defects are not dependent on differing plasma ANF levels.