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Effect of captopril on renal vascular tone in patients with essential hypertension
Insights
Captopril, an angiotensin-converting enzyme inhibitor, lowers blood pressure in hypertensive patients and increases renal plasma flow. It suggests angiotensin plays a role in maintaining renal vascular tone.
Area of Science:
- Nephrology
- Cardiovascular Medicine
- Pharmacology
Background:
- Essential hypertension is a common condition characterized by elevated blood pressure.
- The renin-angiotensin-aldosterone system plays a crucial role in blood pressure regulation.
- Angiotensin-converting enzyme (ACE) inhibitors are widely used to treat hypertension.
Purpose of the Study:
- To investigate the acute effects of captopril on renal hemodynamics and function in patients with essential hypertension.
- To explore the relationship between baseline plasma renin activity and the renal response to captopril.
Main Methods:
- Nine patients with essential hypertension were administered a single oral dose of captopril (50 mg).
- Measurements included arterial pressure, effective renal plasma flow (ERPF), glomerular filtration rate (GFR), filtration fraction (FF), and electrolyte excretion.
- Patients were on either unrestricted sodium intake or a low-sodium diet.
Main Results:
- Captopril caused a rapid and significant decrease in arterial pressure.
- Effective renal plasma flow (ERPF) increased, while glomerular filtration rate (GFR) remained unchanged, leading to a decreased filtration fraction (FF).
- Higher baseline plasma renin activity correlated positively with increased ERPF and negatively with decreased FF and renal resistance.
Conclusions:
- Acute ACE inhibition with captopril affects renal hemodynamics in essential hypertension.
- Angiotensin appears to actively maintain renal vascular tone at the efferent arteriolar level in these patients.
- The role of kinins in mediating these effects warrants further investigation.
Abstract:
1. The effect of acute inhibition of angiotensin-converting enzyme by captopril (50 mg) on renal haemodynamics and function was assessed in nine patients with essential hypertension on unrestricted sodium intake (n = 8) or low sodium diet (n = 1). 2. Captopril induced a rapid and significant decrease in arterial pressure, which was maximal within 60 min. 3. Effective renal plasma flow (ERPF) increased, glomerular filtration rate (GFR) did not change and filtration fraction (FF) decreased after captopril. No change in sodium excretion and a decrease in urinary potassium occurred. 4. In the patient on low sodium diet, captopril induced striking increases in GFR and ERPF (64 and 106% respectively). 5. The logarithm of baseline plasma renin activity was positvely correlated with the change in ERPF and negatively correlated with changes in FF and renal resistance. 6. The results indicate that in patients with essential hypertension angiotensin participates actively in the maintenance of renal vascular tone at the efferent arteriolar level. A possible influence of kinins remains to be defined.