Influence of ultrafiltration on plasma renin activity and adrenergic system.

The influence of efficient ultrafiltration without dialysis fluid was compared to the standard dialysis technique in two groups of 4 patients with chronic renal failure on maintenance haemodialysis. Supine plasma renin activity (PRA), plasma concentration of noradrenaline (NA), and adrenaline (A) and the Valsalva manoeuvre were determined before and after the period of ultrafiltration at the beginning and at the end of the experiment. The behaviour of these parameters was related to changes of blood pressure and body weight. The rapid weight loss was well tolerated during ultrafiltration only, with a significant increase of plasma catecholamines concentration; in contrast, patients treated with ultrafiltration and dialysis showed no significant increase of NA and A levels and they frequently became hypotensive. No relationship was observed between changes in PRA and those in body weight and blood pressure. Our data suggest that rapid removal of catecholamines during standard dialysis hinders the compensatory increase of the adrenergic activity and is responsible for hypotension.