What substance is primarily involved in the conversion of angiotensin I to angiotensin II?

The conversion of angiotensin I to angiotensin II is primarily facilitated by angiotensin-converting enzyme (ACE). Angiotensin I is an inactive precursor that is formed when renin converts angiotensinogen, a protein produced by the liver, into angiotensin I. Once angiotensin I enters the bloodstream, it is transported to the lungs and other tissues, where ACE catalyzes its conversion into angiotensin II, an active peptide with significant physiological effects.

Angiotensin II plays a crucial role in the body's regulation of blood pressure and fluid balance. It causes vasoconstriction, which increases blood pressure, and stimulates the secretion of aldosterone from the adrenal glands, leading to increased sodium and water reabsorption by the kidneys. This helps to maintain homeostasis in blood volume and pressure.

Understanding the role of ACE is key in pharmacology for the treatment of hypertension, as ACE inhibitors are commonly prescribed to lower blood pressure by preventing the formation of angiotensin II.