Mechanisms of action of atrial natriuretic factor: clinical consequences

Atrial natriuretic factor (ANF) acts through specific receptors at its target tissues. Receptor-occupancy by ANF induces activation of particulate guanylate cyclase, increased cyclic GMP formation and also inhibition of adenylate cyclase which results in a decrease of cyclic AMP formation. These second messenger systems appear to mediate the effects of ANF in target tissues. Following receptor-mediated activation of particulate guanylate cyclase, cyclic GMP is extruded from the cells, which leads to elevated cyclic GMP levels in plasma and urine in man, whereas cyclic AMP levels remain unchanged. Since cyclic GMP has a much longer half-life than ANF, it is more sensitive as a marker for ANF release than ANF itself, which has a half-life of just a few minutes. Since cyclic GMP is excreted into urine, determinations of urine cyclic GMP can also allow conclusions about the ANF system when blood sampling is impractical. Thus, cyclic GMP and not cyclic AMP is a sensitive biological marker for ANF.