rénine

Renin (French: rénine) is an aspartyl protease enzyme produced chiefly by the juxtaglomerular cells of the kidney. It catalyzes the rate-limiting step of the renin–angiotensin system, cleaving angiotensinogen to form angiotensin I, a decapeptide subsequently activated to angiotensin II by angiotensin-converting enzyme. Angiotensin II acts as a potent vasoconstrictor and stimulates aldosterone secretion, promoting sodium reabsorption and contributing to blood pressure regulation.

Renin is synthesized as prorenin, with a prosegment that is removed intracellularly to yield active renin. It is stored in secretory granules and released into the bloodstream in response to stimuli including decreased renal perfusion pressure, increased sympathetic activity (beta-1 adrenergic receptors), and reduced delivery of sodium chloride to the macula densa. The presence of angiotensin II provides negative feedback by inhibiting further renin release.

Structurally, renin is a secreted aspartyl protease of the pepsin family with a catalytic dyad of two aspartate residues at the active site. Its substrate recognition is specific for angiotensinogen, and it cleaves a defined peptide bond to release angiotensin I, the precursor to angiotensin II.

Physiological and clinical relevance centers on the renin–angiotensin system's role in blood pressure and fluid balance. Abnormal renin activity is linked to hypertension and cardiovascular disease. Pharmacological modulation includes direct renin inhibitors (for example, aliskiren) and agents targeting downstream components, such as ACE inhibitors and angiotensin receptor blockers, used to treat hypertension and heart failure.