NPPB and hydrops fetalis: Several mechanisms have been proposed to explain the hyporesponsiveness to BNP in HF [103,104], including an increase in the proximal tubule sodium reabsorption with a resultant decrease of sodium delivery to the distal nephron where the BNP receptor is located, increased activity of peptidases that degrade and inactivate these peptides and/or decreased activity of peptidases that activate the peptides.