1. After a run-in period, six healthy, recumbent, water-loaded male subjects breathed through an inspiratory threshold load for 90 min. To correct for prolonged recumbency, a similar protocol was followed on a separate control day, but without an inspiratory load.
2. A negative intrathoracic pressure of at least 30 cmH2O was required to overcome the threshold load.
3. Urine was collected every 30 min and analysed for sodium concentration.
4. Plasma samples were collected every 30 min and analysed for atrial natriuretic peptide concentration.
5. The inspiratory load had no effect on urine volume, urinary sodium excretion or plasma atrial natriuretic peptide levels.