Captopril is a blood pressure lowering drug, but how does it work?
Captopril Tablets - Clinical Pharmacology
Mechanism of Action:
The mechanism of action of captopril has not yet been fully elucidated. Its beneficial effects in hypertension and heart failure appear to result primarily from suppression of the renin-angiotensin-aldosterone system. However, there is no consistent correlation between renin levels and response to the drug. Renin, an enzyme synthesized by the kidneys, is released into the circulation where it acts on a plasma globulin substrate to produce angiotensin I, a relatively inactive decapeptide. Angiotensin I is then converted by angiotensin converting enzyme (ACE) to angiotensin II, a potent endogenous vasoconstrictor substance. Angiotensin II also stimulates aldosterone secretion from the adrenal cortex, thereby contributing to sodium and fluid retention.
Captopril prevents the conversion of angiotensin I to angiotensin II by inhibition of ACE, a peptidyldipeptide carboxy hydrolase. This inhibition has been demonstrated in both healthy human subjects and in animals by showing that the elevation of blood pressure caused by exogenously administered angiotensin I was attenuated or abolished by captopril. In animal studies, captopril did not alter the pressor responses to a number of other agents, including angiotensin II and norepinephrine, indicating specificity of action.
ACE is identical to “bradykininase”, and captopril may also interfere with the degradation of the vasodepressor peptide, bradykinin. Increased concentrations of bradykinin or prostaglandin E2 may also have a role in the therapeutic effect of captopril.
Inhibition of ACE results in decreased plasma angiotensin II and increased plasma renin activity (PRA), the latter resulting from loss of negative feedback on renin release caused by reduction in angiotensin II. The reduction of angiotensin II leads to decreased aldosterone secretion, and, as a result, small increases in serum potassium may occur along with sodium and fluid loss. The antihypertensive effects persist for a longer period of time than does demonstrable inhibition of circulating ACE. It is not known whether the ACE present in vascular endothelium is inhibited longer than the ACE in circulating blood.
To make it more simple, it helps open the blood vessels wider so the pressure inside the vessels is decreased. Think about a garden hose for a minute, say you have a skinny one and a fat one hooked up to the same kind of fauset and you turn on the faucets to the same amount of water coming out into the hose. Which hose will have the most forceful pressure coming out? The skinny one right? So this drug relaxes the constriction of the blood vessels making them fatter and decreasing the pressure within.
- Captopril Information for Consumers
- Captopril Information for Healthcare Professionals (includes dosage details)
- Side Effects of Captopril (detailed)
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