Renin-Angiotensin-Aldosterone System in Blood Pressure Regulation

Renin-Angiotensin-Aldosterone System

• Regulates blood pressure and electrolyte metabolism

Renin

• Proteolytic enzyme produced in juxtaglomerular cells of the kidney
• Secretion stimulated by:
  • Decrease in fluid volume (dehydration, loss of fluid, or blood)
  • Decrease in NaCl concentration

Angiotensinogen

• Large inactive α2-globulin protein produced by the liver
• Substrate for renin, converted into angiotensin I (inactive peptide hormone with 10 amino acids)

Angiotensin-Converting Enzyme

• Glycoprotein enzyme found in lung, endothelial cells, and plasma
• Converts angiotensin I into angiotensin II (active peptide hormone with 8 amino acids)
• Angiotensin II increases blood pressure by:
  • Causing vasoconstriction of arterioles
  • Stimulating aldosterone production, resulting in Na+ and water retention

Angiotensin-Converting Enzyme Inhibitors

• Competitive inhibitors of angiotensin-converting enzyme, used to treat renin-dependent hypertension
• Angiotensin II inhibits renin release from juxtaglomerular cells

Angiotensin II and Angiotensin III

• Angiotensin II is converted into angiotensin III (active peptide hormone with 7 amino acids) by aminopeptidase enzyme
• Angiotensin III is an equally potent stimulator of aldosterone production
• Plasma level of angiotensin II is four times greater than that of angiotensin III, so most effects are exerted by angiotensin II
• Both angiotensin II and angiotensin III are rapidly inactivated by angiotensinases enzymes