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Abnormal glomerular and tubular function during angiotensin converting enzyme inhibition in renovascular hypertension
E B Pedersen1, S S Sørensen, A Amdisen
1Department of Medicine C, Aarhus Kommunehospital, Denmark.
Insights
Captopril significantly reduced kidney function in renovascular hypertension (RVH) by decreasing glomerular filtration rate (GFR) and tubular reabsorption. Essential hypertension (EH) patients showed minimal changes, indicating RVH-specific effects of angiotensin converting enzyme inhibition.
Area of Science:
- Nephrology
- Cardiovascular Medicine
- Pharmacology
Background:
- Renovascular hypertension (RVH) involves kidney artery narrowing, leading to hypertension.
- Essential hypertension (EH) is high blood pressure without a known secondary cause.
- Angiotensin converting enzyme (ACE) inhibitors like captopril are used to treat hypertension.
Purpose of the Study:
- To investigate the effects of captopril on glomerular filtration rate (GFR) and tubular function in patients with RVH and EH.
- To compare the renal response to ACE inhibition between RVH and EH.
Main Methods:
- 14 patients with RVH and 8 with EH received oral captopril (25 mg).
- GFR and tubular function were assessed using the lithium clearance technique before and after captopril.
- Plasma levels of angiotensin II, aldosterone, atrial natriuretic peptide, and urinary prostaglandin E2 were measured.
Main Results:
- In RVH, captopril significantly reduced GFR (51-Cr-EDTA clearance), proximal fluid reabsorption, and distal sodium reabsorption (P < 0.01).
- Proximal fractional reabsorption slightly increased in RVH (P < 0.02).
- EH patients showed minimal changes in these renal parameters after captopril. Blood pressure decreased in both groups, more significantly in RVH.
Conclusions:
- ACE inhibition with captopril markedly reduces absolute tubular reabsorption in RVH, primarily due to a fall in GFR.
- The renal response to captopril differs significantly between RVH and EH.
- Increased proximal fractional reabsorption in RVH may be linked to reduced peritubular hydrostatic pressure.
Abstract:
Glomerular filtration rate (GFR) and tubular function were measured by means of the lithium clearance technique in 14 patients with renovascular hypertension (RVH) and eight patients with essential hypertension (EH) before and after oral administration of captopril 25 mg. In RVH captopril reduced 51-Cr-EDTA clearance (67.3 (median) to 47.5 ml min-1, P less than 0.01), proximal absolute reabsorption of fluid (53.9 to 41.5 ml min-1, P less than 0.01) and distal absolute reabsorption of sodium (2195 to 1402 mumol min-1, P less than 0.01), whereas proximal fractional reabsorption increased slightly (77.5 to 80.2%, P less than 0.02). In EH, however, these parameters were practically unaffected by captopril. In both RVH and EH plasma concentrations of angiotensin II and aldosterone were reduced after captopril, but atrial natriuretic peptide in plasma and urinary excretion rate of prostaglandin E2 were unchanged. Blood pressure decreased after captopril in both groups, but the maximum fall in systolic BP was more pronounced in RVH (22%) than EH (13%). It is concluded that angiotensin converting enzyme inhibition markedly reduced absolute reabsorption in both the proximal and distal tubules in RVH, in contrast to EH, predominantly due to fall in the GFR, and that the slight increase in proximal fractional reabsorption may be attributed to a reduction in the hydrostatic pressure in the peritubular vessels.
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