HORMONAL INTERACTIONS AND RENAL-FUNCTION DURING MECHANICAL VENTILATION AND ANF INFUSION IN HUMANS

To investigate the influence of atrial natriuretic factor (ANF) on renal function during mechanical ventilation (MV), we examined the renal and hormonal responses to synthetic human ANF infusion in eight patients during MV with zero (ZEEP) or 10 cmH2O positive end-expiratory pressure (PEEP). Compared with ZEEP, MV with PEEP was associated with a reduction in diuresis (V) from 208 +/- 51 to 68 +/- 11 ml/h (P < 0.02), in natriuresis (U(Na)) from 12.4 +/- 3.3 to 6.2 +/- 2.1 mmol/h (P < 0.02), and in fractional excretion of sodium (FE(Na)) from 1.07 +/- 0.21 to 0.67 +/- 0.17% (P < 0.02) and with an increase in plasma renin activity (PRA) from 4.83 +/- 1.53 to 7.85 +/- 3.02 ng.ml-1.h-1 (P < 0.05). Plasma ANF levels markedly decreased during PEEP in four patients but showed only minor changes in the other four patients, and mean plasma ANF levels did not change (163 +/- 33 pg/ml during ZEEP and 126 +/- 30 pg/ml during PEEP). Glomerular filtration rate and renal plasma flow were unchanged. Infusion of ANF (5 ng.kg-1.min-1) during PEEP markedly increased V and U(Na) by 110 +/- 61 and 107 +/- 26%, respectively, whereas PRA decreased from 7.85 +/- 3.02 to 4.40 +/- 1.5 ng.ml-1.min-1 (P < 0.05). In response to a 10 ng.kg-1.min-1 ANF infusion, V increased to 338 +/- 79 ml/h during ZEEP but only to 134 +/- 45 ml/h during PEEP (P < 0.02), whereas U(Na) increased, respectively, to 23.8 +/- 5.3 and 11.3 +/- 3.3 mmol/h (P < 0.02). The results indicate that a decrease in ANF secretion is not a prerequisite for PEEP-induced antidiuresis. Infusion of ANF opposed the effects of PEEP on renal function and renin release, also suggesting that ANF may serve as a counterregulatory mechanism against the renal effects of PEEP.