Atrial natriuretic factor inhibits vasotocin-induced water reabsorption in the toad urinary bladder

Peptides recently isolated from atrial extracts possess potent natriuretic and diuretic activities, which are thought to be due to hemodynamic actions, such as increased glomerular filtration or altered medullary blood flow. A direct tubular site of action cannot be ruled out; therefore we have examined the effect of one of these peptides, atriopeptin III on vasotocin-induced water absorption in the toad urinary bladder. Our results indicate that equimolar doses (10(-12) to 10(-11) M) of atriopeptin III can significantly inhibit vasotocin-induced water reabsorption in vitro and suggest a physiologic role for the cardiac peptides to alter water reabsorption directly at the level of the tubules or collecting ducts, independent of any hemodynamic effects they might also exert in vivo.