[Effect of short-term space flights on the activity of the renin-angiotensin-aldosterone system and on the blood concentration of cyclic nucleotides and prostaglandins].

After short-term flights renal excretion of aldosterone increased, thus suggesting its enhanced production and metabolism. An adequate increase of aldosterone synthesis was accompanied by an increase of its concentration in blood. An inadequate activation of mineralocorticoids manifested as a lower concentration of blood aldosterone and a greater excretion of aldosterone in the urine. These differences in the mineralocorticoid activity were determined by the renin-angiotensin system whose activity was associated not only with fluid-electrolyte metabolism but also with changes in the concentration of cyclic nucleotides and prostaglandins that reflect the vascular tone and sympatho-adrenal activity. An increased activity of the renin-angiotensin system seen in most cosmonauts at an acute stage of readaptation was correlated with a higher concentration of cAMP and a lower concentration of depressor prostaglandins. The activity of the renin-angiotensin system declined in parallel with the decrease of the blood content of cAMP.