Synthetic atrial natriuretic peptide (carperitide) and B-type natriuretic peptide (BNP; nesiritide) are used to treat congestive heart failure. However, despite beneficial cardiac unloading properties, reductions in renal perfusion pressures limit their clinical effectiveness. Recently, CD-NP, a chimeric peptide composed of C-type natriuretic peptide (CNP) fused to the C-terminal tail of Dendroaspis natriuretic peptide (DNP), was shown to be more glomerular filtration rate-enhancing than BNP in dogs. However, the molecular basis for the increased responsiveness was not determined. Here, we show that the DNP tail has a striking effect on CNP, converting it from a nonagonist to a partial agonist of natriuretic peptide receptor (NPR)-A while maintaining the ability to activate NPR-B. This effect is specific for human receptors because CD-NP was only a slightly better activator of rat NPR-A due to the promiscuous nature of CNP in this species. Interesting, the DNP tail alone had no effect on any NPR even though it is effective in vivo. To further increase the potency of CD-NP for NPR-A, we converted two different triplet sequences within the CNP ring to their corresponding residues in BNP. Both variants demonstrated increased affinity and full agonist activity for NPR-A, whereas one was as potent as any NPR-A activator known. In contrast to a previous report, we found that DNP binds the natriuretic peptide clearance receptor (NPR-C). However, none of the chimeric peptides bound NPR-C with significantly higher affinity than endogenous ligands. We suggest that bifunctional chimeric peptides represent a new generation of natriuretic peptide therapeutics.The human natriuretic peptide system consists of atrial natriuretic peptide (ANP), 2 B-type natriuretic peptide (BNP), C-type natriuretic peptide (CNP), and an N-terminally extended renal form of ANP called urodilatin (1). ANP, BNP, and urodilatin bind natriuretic peptide receptor (NPR)-A, whereas CNP binds NPR-B. Both receptors are transmembrane guanylyl cyclases, which when activated catalyze the synthesis of cGMP. The natriuretic peptide clearance receptor (NPR-C) lacks guanylyl cyclase activity and functions primarily to clear natriuretic peptides from the circulation. However, a signaling function has been proposed for this receptor as well (2).Both ANP and BNP reduce blood pressure by increasing natriuresis, diuresis, vasodilation, and endothelial permeability. They also prevent cardiac hypertrophy and suppress the reninangiotensin-aldosterone systems. In 2001, BNP was approved by the United States Food and Drug Administration for the treatment of acutely decompensated heart failure. However, recent reports have suggested impaired renal function, which may be related to excessive hypotension (3, 4).CD-NP represents a new class of natriuretic peptide drug that may circumvent the hypotensive nature of BNP and preserve or augment renal function in the congestive heart failure setting. CD-NP contains the full-length 22-amino acid human CNP fused to the 15-amino acid C...