Plasma volumes, noradrenaline levels and renin activity during posture changes in end-stage renal failure

In nine normal subjects and nine patients with end-stage chronic renal failure (CRF) we studied the effect of prolonged (110 min) postural changes on the plasma volume, intrathoracic volume, plasma noradrenaline concentration, haemodynamic variables, and plasma renin activity (PRA). Upon standing, plasma volume decreased rapidly by about 11% in both groups as measured from the control volume and changes in haematocrit. This was accompanied by identical increments of plasma colloid osmotic pressure. The changes in intrathoracic volume (monitored by measurement of the electrical impedance of the thorax), as well as the alterations in plasma noradrenaline, blood pressure, and heart rate, were also comparable in the two groups. These similarities were in contrast with divergent responses of PRA. The increase in PRA on standing was significantly blunted in the CRF patients compared with the normal response (to 1.4 +/- 0.4 fold of the supine value in CRF v. 6.0 +/- 3.2 fold in the normals, P less than 0.0004). It is concluded that the attenuated increase in PRA upon standing in patients with CRF is not a consequence of diminished sympathetic stimulation or an altered response of the intravascular volume. Second, the unabated decrease in plasma volume upon standing pleads against a decrease of tissue compliance in CRF.