Plasma catecholamine levels during water immersion in man.

In ten normal subjects thermoneutral neck-out water immersion produced a highly significant natriuresis and diuresis mediated via an induced central hypervolaemia. During immersion suppression of plasma noradrenaline and adrenaline was observed but no change occurred in plasma dopamine levels. No correlation was found between the suppression of noradrenaline and the diuresis and natriuresis. The reduction in plasma noradrenaline observed may reflect a widespread diminution of sympatho-adrenal activity during water immersion. This reduction could be a consequence of the cardiovascular changes of immersion and may not be directly involved in the mechanism of the renal response.