Hyperresponsiveness to atrial natriuretic factor in adult Brattleboro rats

Renal and hemodynamic effects of an intravenous infusion of atrial natriuretic factor (ANF) (8 micrograms/h) were studied in homozygous Brattleboro rats, which lack endogenous vasopressin. Heterozygous rats were used as controls. ANF-induced increases in sodium, chloride and volume excretion were higher, whereas changes in potassium excretion were lower in homozygous, as compared to heterozygous rats. The initial decrease in arterial blood pressure after ANF infusion was greater in the homozygous group, whereas there were no differential effects on heart rate. Inulin clearance, as well as clearance and fractional excretion of lithium were not significantly different between groups. The results indicate that Brattleboro rats show an exaggerated diuretic as well as saluretic response to ANF. They suggest that these effects are localized in the distal nephron and may be due to the known anatomical abnormalities in juxtamedullary nephrons of Brattleboro rats.