NPPA and hydrops fetalis: However, as HF progresses, the potency of the NP system may diminish due in part to reduced levels of the pro-ANP convertase corin, impaired pro-ANP/pro-BNP cleavage, downregulation of renal NPs receptors and/or degradation of ANP by NEP [5,16,24,25,26,46,47,48,49].