Changes of plasma renin activity and aldosterone level during 21 d headdown bedrest with and without cuffs.

bjective To investigate changes of plasma renin activity (PRA) and aldosterone (ALD) level during 21 d -6headdown bedrest (HDT) with and without cuffs. Methods The -6 head down bedrest 21 d was used to simulate weightlessness. Twelve volunteers were divided into 2 groups, control group and cuffs group. In cuffs group, cuffs on the upper parts of thighs and arms were inflated 12 h/d during 110 d,1821 d of bedrest. No countermeasures were used in control group. Samples of plasma were taken before and during HDT. Plasma renin activity and aldosterone were measured by radioimmunoassay. Results PRA levels were elevated and the peak values revealed at D4, D10 respectively in control and cuffs groups, and then declined to the preHDT level by the end of 21 d HDT in both groups. In control group, plasma aldosterone level decreased at D2, and then increased at D4, D10, D21.No significant difference was observed between two groups. Conclusions HDT induces the initial hormonal response with a decrease in plasma aldosterone. The long term effects of HDT are linked to increase of plasma renin activity and aldosterone. The change of plasma aldosterone can be alleviated by using cuffs during HDT.