REN and Hypertension: Mechanistic causes of hypertension include the reduction of glomerular filtration rate or increased renal tubular reabsorption of salt and water, the excessive activation of renin-angiotensin-aldosterone and sympathetic nervous systems, increased formation of reactive oxygen species (ROS), the vasoconstrictor peptide endothelin and of inflammatory cytokines and decreased synthesis of endothelial nitric oxide.