1. The effect of extracellular volume expansion (ECVE) on renal production of cyclic AMP was evaluated in 19 thyroparathyroidectomized dogs. ECVE was produced by the infusion of Ringer bicarbonate solution at a rate of 2 ml min−1 kg−1 body weight; cyclic AMP was measured in plasma obtained from the aorta and renal vein and in the urine.

2. During the natriuresis of ECVE urinary excretion of cyclic AMP, the clearance of cyclic AMP, net nephrogenous cyclic AMP added both to urine and to the renal vein and hence total nephrogenous cyclic AMP increased significantly.

3. This rise in net production of cyclic AMP and a significant natriuresis by the kidney persisted for 60–90 min after discontinuation of active ECVE and return of renal plasma flow to normal.

4. The results support the notion that an increase in the production of cyclic AMP by the kidney may play a role in the natriuresis of ECVE.

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