Atrial natriuretic peptide (ANP) is an important regulator of sodium metabolism and indirectly of blood pressure. Evidence has accumulated that ANP regulates sodium metabolism through a cascade of steps involving an increase in the level of cGMP, activation of cGMP-dependent protein kinase (PKG), and inhibition of renal tubular Na[SUP+], K[SUP+] -ATPase activity. One of the major substrates for PKG is DARPP-32. In the present study we observed that ANP does not induce natriuresis in mice that lack DARPP32. In contrast, there was a 4-fold increase in urinary sodium excretion following ANP administration to wild type mice. ANP as well as Zaprinast, a selective inhibitor of cGMP phosophodiesterase, inhibited renal Na[SUP+], K[SUP+] -ATPase activity in wild type mice but had no such effect in mice lacking DARPP-32. Mean arterial blood pressure, measured in conscious animals, was significantly increased in DARPP-32 deficient mice as compared to wild type mice. The results confirm that DARPP-32 acts as a third messenger in the ANP signaling pathway in renal tissue and suggest an important role of DARPP-32 in the maintenance of normal blood pressure. [ABSTRACT FROM AUTHOR]