A system of metabolic interactions by products produced in the distal nephron of the kidney. These products include KALLIKREIN; kinins; KININASE I; KININASE II; and ENKEPHALINASE. This system participates in the control of renal functions. It interacts with the renin-ANGIOTENSIN-aldosterone SYSTEM to regulate blood pressure, generation of prostaglandins, release of vasopressins, and water-electrolyte balance.