A decrease in blood pressure/volume stimulates the hypothalamus to release ADH (Anti-Diuretic Hormone) as well as JGA (Juxtaglomerular Apparatus) cells to release renin. Renin by the renin-angiotensin mechanism activates the adrenal cortex to release aldosterone. Atrial Natriuretic Factor (ANF) is produced by the atria of a heart during increased blood pressure/volume. It can cause vasodilation and thereby, decrease blood pressure.