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

Background. In essential hypertension, acute haemodynamic changes due to di etary protein load cause patterns of acute changes in renal function that a re 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 t ests were performed in healthy controls and in patients with essential hype rtension (mean arterial pressure of 112 +/- 2 mmHg, age, 52 +/- 2 years; me an +/- SEM) within a washout period, and after long-term treatment with car vedilol and fosinopril, respectively. Results. In 15 healthy volunteers, protein ingestion increased glomerular f iltration 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 ra ndomized 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 we re 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 decr ease in GFR that may normalize under antihypertensive treatment. The acute changes in GFR can be reliably monitored by the here-described compartmenta l analysis method of renal functional reserve.