Atrial natriuretic peptide and exercise-induced fluid retention in man

Abstract

Previous studies have shown that day-long hill walking exercise results in significant sodium and water retention, followed during a recovery/rest period by natriuresis and diuresis. The purpose of this study was to assess the role of atrial natriuretic peptide (ANP) during the post-exercise natriuretic phase.

Five subjects ate a fixed diet for 13 days. A period of 4 rest days preceded 5 days of strenuous hill walking, followed by a 4-day recovery period. Daily measurement of aldosterone, ANP and haematocrit, and sodium and water balances were performed. Exercise was associated with sodium retention and a positive cumulative balance, mean 268 mmol (SD 17) after 5 days. There was a mean cumulative positive water balance of 700 ml (sd 34). Haematocrit was reduced from 44.6% to 39.3%, indicating an increase in plasma volume of 22%. Plasma aldosterone concentration during exercise was elevated. Plasma ANP concentrations were raised significantly throughout the exercise period (mean 20.3 pmol I⁻¹ [sd 6.4], control 9.4 pmol I⁻¹ [sd 5.4], P < 0.001). There was a fall (non-significant) during the recovery period (mean 17.2 pmol I⁻¹ [sd 9.1]) but levels were significantly higher than control (P < 0.02). It is suggested that the natriuresis during recovery is mediated by elevated ANP levels, probably due to increased blood volume distending the atria.