Effects of posture and positive airway pressure on plasma atrial natriuretic peptide and renal urodilatin excretion

Aims: To determine whether a coupling of plasma atrial natriuretic peptide (ANP) and renal excretion of urodilatin (UUROV)-recently observed during su praphysiological concentrations of ANP-may also be detected during moderate changes in ANP levels, i.e. if ANP is increased by supine positioning and decreased by applying continuous positive airway pressure (CPAP). Material and methods: We investigated 10 healthy male volunteers, orally hydrated wi th 200 ml water/h, in a randomized crossover study for periods of 1 hour fo llowing 2 protocols. Protocol 1: sitting and supine position. Protocol 2: s itting with and without a CPAP of 8 cm H2O. Results: ANP increased ongoing from the sitting to the supine position (SIT-1: 13.2 +/-4.7; SUP: 27.9 +/- 21.9 pg x ml(-1); p<0.01) during protocol 1 and decreased after the onset o f CPAP in seated subjects (SIT-2: 16.9<plus/minus>7.9; SIT-CPAP: 13.9 +/-6. 5 pg x ml(-1); p<0.05) during protocol 2. UUROV decreased slightly, but not significantly, during protocol 1 (SIT-1: 63.9<plus/minus>21.7; SUP: 49.9 /- 13.2 fmol x min(-1)) and remained unchanged after institution of CPAP in the sitting position (SIT-2: 68.5 +/- 25.2; SIT-CPAP: 68.5 +/- 50.2 fmol x min(-1)). Correlation analysis revealed no relationship between plasma ANP and UUROV Conclusions: Moderate variations in the levels of ANP in water-l oaded volunteers do not induce parallel changes in the urinary excretion of urodilatin.