Renin is a central hormone in the control of blood pressure and various other physiological functions. It is produced in the kidney and stimulates aldosterone as part of the renin-angiotensin-aldosterone (RAAS) system. Renin normally falls in the presence of adequate sodium levels in the blood and increases when there is not enough. Normally, renin and aldosterone rise and fall roughly in parallel. In primary aldosteronism, aldosterone remains high even though renin is low (or suppressed) due to high sodium levels.