Reniin

Reniin is a term used in some languages to refer to the enzyme renin, a protease that initiates the renin-angiotensin system.

In humans, renin is produced by the juxtaglomerular cells of the kidney and acts on its substrate, angiotensinogen, to generate angiotensin I. Renin is produced as prorenin, an inactive precursor; proteolytic removal of the prosegment activates it.

Physiological role: The renin-angiotensin-aldosterone system (RAAS) regulates blood pressure, electrolyte balance, and fluid homeostasis. Angiotensin II, produced downstream, leads to vasoconstriction and aldosterone release, which promotes sodium and water retention. There is a negative feedback mechanism in which high levels of angiotensin II reduce further renin release.

Regulation: Renin release is stimulated by low renal perfusion pressure, increased sympathetic activity, and decreased NaCl delivery to the macula densa. It is inhibited by high blood pressure and by angiotensin II via negative feedback.

Clinical relevance: Abnormal renin activity is associated with hypertension and kidney disease. Measurements include plasma renin activity or direct renin concentration. Therapies that affect the RAAS include ACE inhibitors, angiotensin II receptor blockers, and direct renin inhibitors such as aliskiren, used in certain clinical contexts.

See also: Renin-angiotensin-aldosterone system; Prorenin; Renin receptor.