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

flow; essential hypertension; glomerular filtration rate; renal functional reserve 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 Introduction controls. Methods. Renal clearances of sinistrin, an inulin-like Sensitive clinical methods for detecting early changes polyfructosan, and p-aminohippurate were determined in renal vascular reactivity of patients with essential before and after protein ingestion. These tests were hypertension have been lacking to date [1]. Because performed in healthy controls and in patients with of possible hyperfiltration [2], single clearance measessential hypertension (mean arterial pressure of urements cannot detect vascular changes, which may 112±2 mmHg, age, 52±2 years; mean±SEM ) within be induced by hypertension or reversed by antihypera washout period, and after long-term treatment with tensive treatment. Therefore, dynamic renal function carvedilol and fosinopril, respectively. tests, which consist of two consecutive kinetic clearance Results. In 15 healthy volunteers, protein ingestion measurements before and after a dietary protein load, increased glomerular filtration rate (GFR) from have been tried previously in patients at risk for 110.3±3.6 to 120.6±4.4 ml/min (P=0.0006; two- hypertensive renal damage in order to assess the extent tailed pairwise t-test). In contrast, it led to an acute of renal vascular impairment [3]. In healthy subjects, decrease in GFR in 16 hypertensive patients, from increases in glomerular filtration rate (GFR) after 111.8±2.9 to 103.6±3.3 ml/min (P=0.0010). The protein ingestion have been uniformly observed [4], eight patients who were randomized to receive carvedi- but in patients with essential hypertension most lol improved in their renal response to protein (GFR authors have found ‘blunted increases’ in GFR after increased from 101.4±6.4 to 107.1±5.4 ml/min; P= dietary stresses [5]. This so-called ‘blunted increase’ in 0.04), whereas the eight other patients randomized to GFR was originally thought to be due to an increase receive fosinopril exhibited no change in GFR (final in intraglomerular pressure. However, the alleged value 105±4.9 ml/min). In the patients, the acute shifts increase in GFR in response to protein ingestion was in renal plasma flows were not significant. Mean arter- not accompanied by a change in albumin excretion, ial blood pressure of the patients decreased from and there was lack of dynamic GFR response after 112±2 to 100±3 mmHg (P=0.0015). administration of ACE inhibitors. Conclusions. In essential hypertension an acute protein These contradictory results suggest that the earlier load induces a decrease in GFR that may normalize dynamic test methods that described qualitatively under antihypertensive treatment. The acute changes normal increases in GFR after amino acid stimulation in GFR can be reliably monitored by the here- were probably not sensitive enough. Stationary creatindescribed compartmental analysis method of renal ine levels cannot reveal short-term changes in clearfunctional reserve. ance. Traditional steady-state methods of GFR determination [6 ] are inappropriate for acute evalu