Dynamic renal function testing by compartmental analysis: assessment of renal functional reserve in essential hypertension

Background. In essential hypertension, acute haemodynamic changes due to dietary protein load cause patterns of acute changes in renal function that are fundamentally different from changes in normal controls. Methods. Renal clearances of sinistrin, an inulin-like polyfructosan, and p-aminohippurate were determined before and after protein ingestion. These tests were performed in healthy controls and in patients with essential hypertension (mean arterial pressure of 112 +/- 2 mmHg, age, 52 +/- 2 years; mean +/- SEM) within a washout period, and after long-term treatment with carvedilol and fosinopril, respectively. Results. In 15 healthy volunteers, protein ingestion increased glomerular filtration rate (GFR) from 110.3 +/- 3.6 to 120.6 +/- 4.4 ml/min (P = 0.0006; two-tailed pairwise t-test). In contrast, it led to an acute decrease in GFR in 16 hypertensive patients, from 111.8 +/- 2.9 to 103.6 +/- 3.3 ml/min (P = 0.0010). The eight patients who were randomized to receive carvedilol improved in their renal response to protein (GFR increased from 101.4 +/- 6.4 to 107.1 +/- 5.4 ml/min; P = 0.04), whereas the eight other patients randomized to receive fosinopril exhibited no change in GFR (final value 105 +/- 4.9 ml/min). In the patients, the acute shifts in renal plasma flows were not significant. Mean arterial blood pressure of the patients decreased from 112 +/- 2 to 100 +/- 3 mmHg (P = 0.0015). Conclusions. In essential hypertension an acute protein load induces a decrease in GFR that may normalize under antihypertensive treatment. The acute changes in GFR can be reliably monitored by the here-described compartmental analysis method of renal functional reserve.