Atrial natriuretic factor modulates nitric oxide production: an ANF-C receptor-mediated effect

To investigate the possible immunomodulatory and regulatory functions of atrial natriuretic factor (ANF) and the natriuretic peptide C (NPR-C) receptor in the control of cytokine-stimulated nitric oxide production in primary cultures of human proximal tubular cells.

Freshly prepared human proximal tubular cells were seeded on plastic plates and allowed to reach confluence. The confluent cells were then incubated with ANF or cyclic(4-23)ANF (c(4-23)ANF) alone, or preincubated with ANF or c(4-23)ANF before incubation with the nitric oxide-stimulating combination of cytokines interleukin-1 beta (10 u/ml), tumour necrosis factor-alpha (10 ng/ml) and interferon-gamma (100 u/ml).

In the present series of experiments we have found that incubation of primary cultures of human proximal tubular cells with ANF or c(4-23)ANF stimulates nitric oxide production dose-dependently. Paradoxically, ANF acting via the NPR-C receptor also inhibits cytokine activation of the enzyme-inducible nitric oxide synthase via a cyclic GMP-independent mechanism. Both of these effects were reproduced by the NPR-C receptor-specific ligand c(4-23)ANF.

These findings represent novel actions of ANF mediated via the NPR-C receptor. The results also provide a simple model system in which to study the subcellular mechanisms of NPR-C receptor activation.