1. Natriuresis was studied during water immersion in eight normal subjects either in the absence or in the presence of dopamine blockade by domperidone.

2. Creatinine clearance showed no significant changes; urine flow remained significantly above control values during water immersion, implying persistent suppression of antidiuretic hormone.

3. The marked natriuresis seen during water immersion alone was significantly blunted (P < 0.05) but not abolished during water immersion plus domperidone.

4. Suppression of the renin–aldosterone system by water immersion alone was not significantly different from that obtained during water immersion plus dopamine blockade.

5. On the contrary, plasma prolactin levels, previously suppressed during water immersion alone, were significantly stimulated during water immersion plus domperidone, thus indirectly suggesting a role of dopamine in mediating the blunted natriuresis seen during water immersion.

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