Sympathetic nervous system overactivity in hypertensive patients with chronic renal failure - Role of upright body position

Objective: The renal functional consequences of an activated sympathetic ne rvous system and plasma atrial natriuretic hormone (ANP) in various renal d iseases are not well described. We hypothesize that norepinephrine. (NE) an d ANP have antagonizing effects on renal hemodynamics in diseased kidneys. Material and Methods: Plasma NE, ANP, glomerular filtration rate (GFR), eff ective renal plasma flow (ERPF) and mean arterial pressure (IMA-P) were mea sured in the upright position in healthy controls (n = 9) and hypertensive patients with reduced GFR (n = 11). The same parameters were compared betwe en healthy controls (n = 6) and hypertensive patients with reduced GFR (n = 6) in upright and supine positions. Results: Upright plasma NE and ANP were significantly elevated in the patie nts compared with the controls (4.4 +/- 0.4 vs 2.1 +/- 0.2 nmol/l (p < 0.00 1) and 13.5 +/- 2.1 vs 6.9 +/- 1.0 nmol/l (p < 0.01) respectively). With ch ange from upright to supine position plasma NE decreased in the controls (2 .2 +/- 0.3 vs 1.7 +/- 0.3 nmol/l) (p < 0.01) and patients (3.8 +/- 0.4 vs 2 .6 +/- 0.4) (p < 0.01). Supine ANP increased in controls (5.5 +/- 1.0 vs 8. 3 +/- 1.1) (p < 0.01) but not in patients (14.3 +/- 3.8 vs 16.1 +/- 3.8 nmo l/l) (p > 0.10). Plasma NE correlated positively with MAP (p < 0.001) and n egatively with GFR (p < 0.01) in the upright but not supine position. A pos itive correlation between NE and ANP was observed in upright (p < 0.001) bu t not in supine position. ANP correlated negatively with GFR in the upright < 0.01) but not supine position. No position dependent changes were seen i n GFR and ERPF, but supine filtration fraction (FF) increased insignificant ly in the patient group (0.23 +/- 0.02 vs 0.24 +/- 0.02) (p < 0.05). Conclusion: Hypertensive patients with reduced GFR have elevated levels of plasma NE and ANP in the upright body position. When the upright and supine positions are compared, plasma NE declines in the supine position in contr ols and hypertensive renal failure patients, and plasma ANP levels are elev ated only in the upright position in hypertensive renal failure patients wh ere the sympathetic nervous system is activated. A significant positive rel ationship between plasma NE and ANP was observed only in the upright positi on. The upright body position seems superior to recumbency in the character ization of these hormonal changes in hypertensive chronic renal failure pat ients.