In vascular smooth muscle cells, relaxant actions of guanosine--3',5'-cyclic monophosphate (cGMP) are well recognized, but there is increasing evidence that cGMP also plays regulatory roles in vascular endothelium. However, the autacoid and endocrine mechanisms controlling cGMP production in endothelium are not well understood. The objective of these studies was to examine the mechanisms of cGMP accumulation in human umbilical vein endothelial cells (HUVEC) in response to natriuretic peptides. Expression in HUVEC of natriuretic peptide receptors, particulate guanylyl cyclases (GC)-A and GC-B, was confirmed by RT-PCR and Western blot analysis. In the presence of the phosphodiesterase inhibitor IBMX 500 microM, 3 h incubation of HUVEC with B-type natriuretic peptide (BNP) (preferential GC-A agonist) or C-type natriuretic peptide (CNP) (preferential GC-B agonist) stimulated concentration-dependent increases in cGMP production. At 10 and 100 nM, we observed two to three-fold greater potency of CNP compared to BNP. In the absence of IBMX, CNP-stimulated cGMP accumulation was significantly less than cGMP accumulation in response to sodium nitroprusside 1 mM. This greater sensitivity of GC-B-derived cGMP to phosphodiesterases suggests compartmentalization of two pools of cGMP from particulate and soluble guanylyl cyclases. Although CNP 100 nM and 1 microM was observed to increase nitrite + nitrate (stable metabolites of NO) production in HUVEC two-fold above basal level, the soluble guanylyl cyclase inhibitor ODQ 10 microM did not significantly modify CNP-stimulated cGMP accumulation suggesting that endothelial actions of CNP may be NO-independent. In conclusion, these studies indicate functional signaling by natriuretic peptides in endothelial cells, supporting possible roles of these mediators in regulating endothelial cell function.