Tubulo-glomerular feedback activation in humans before and after nephrectomy.

BACKGROUND/AIMS: Tubulo-glomerular feedback (TGF) is a key mechanism for controlling glomerular filtration. Nephrectomy for kidney donation provides a good opportunity for studying TGF status before and after a defined loss of renal function. METHODS: A total of 22 kidney donors were studied before and one year after nephrectomy. Effective renal plasma flow and glomerular filtration rate were measured by means of para-amino-hippurate and inulin plasma clearances before and after intravenous acetazolamide. RESULTS: TGF activation was not dependent on sex, age or familiality for hypertension either before or after nephrectomy, however, it increased the filtration fraction before, but not after nephrectomy. Nephrectomy did not affect TGF response, but elicited a correlation between TGF response and renal plasma flow, not present in the intact state. Donors with a more activated TGF before nephrectomy had a lower filtration fraction that increased after nephrectomy, while subjects with a less activated TGF before nephrectomy had a higher basal filtration fraction that showed a blunted increase after nephrectomy. CONCLUSION: TGF is a stable mechanism quantitatively unaltered by nephrectomy, age, sex, menopausal status or family history of hypertension. However, its degree of activation before nephrectomy determines different responses to the loss of a kidney.

Acute and long-term effects of ACE inhibition on renal haemodynamics in glomerular and interstitial nephropathies.

BACKGROUND: Angiotensin-converting enzyme (ACE) inhibitors are the drugs of choice for the treatment of hypertension in patients with non-diabetic nephropathies. However, not every trial has reported better results with ACE inhibitors (ACE-I) than with other drugs. This study investigates whether the acute and chronic effects of ACE inhibition on renal and glomerular haemodynamics are similar in glomerular and interstitial nephropathies. METHODS: We studied 20 hypertensive patients, on their usual diet, with mild-to-moderate chronic renal failure secondary to non-diabetic nephropathy. After a three-week wash out period, we determined plasma clearances of para-amino-hippurate and inulin before, and after acute oral administration of either enalapril or ramipril. This same test was carried out after one and two years of treatment with the same drug. RESULTS: Acute ACE inhibition causes a decrease of renal perfusion, glomerular filtration and pressure with an increase of afferent resistances. Long-term ACE inhibition is associated only with a decrease in renal perfusion, with a non-significant tendency to higher filtration fraction and lower afferent resistances. All the renal haemodynamic modifications mentioned above are present only in patients with glomerular diseases. CONCLUSIONS: Renal and glomerular haemodynamic responses are not similar after acute and chronic ACE inhibition. Only patients with glomerular diseases show acute or long-term responses to ACE inhibition.