Neuronal nitric oxide synthase knockout mice (nNOS^-/-) are unable to increase their plasma renin concentration (PRC) during sodium restriction, suggesting a pivotal role for locally produced nitric oxide (NO) by nNOS at the macula densa in the control of renin secretion. An increase in cytosolic cAMP in the juxtaglomerular cells will acutely increase renin exocytosis. In the present study, we investigated whether NO increases renin secretion by production of cGMP that inhibits phosphodiesterase 3 (PDE3) in the juxtaglomerular cells using nNOS^-/- and their wild-type controls in a crossover study protocol. Animals were given a low sodium diet for ten days, whereupon either the PDE3 inhibitor milrinone (0.5 mg/kg bw) or vehicle were given as an i.p. injection. After 15–20 minutes, a blood sample was taken for PRC determination. Animals were then returned to normal sodium diet for two weeks whereby they once again were given low sodium diet for ten days. The experiment was repeated, but animals that had been given milrinone, was instead given vehicle, and vice versa, allowing us to calculate the effects of milrinone on PRC in every subject. Blood pressure was measured in a separate group of conscious mice using telemetry. The basal PRC levels were reduced in nNOS^-/- compared to the wild-types. Administration of milrinone increased PRC in both genotypes. The increase was higher in nNOS^-/- resulting in normalized renin levels. The blood pressure was similar in both genotypes and the chosen milrinone dose did not affect blood pressure compared to vehicle administration. These findings add evidence to the hypothesis that nNOS derived NO increases PRC during sodium restriction by PDE3 inhibition.