[Influence of the redistribution of liquid volumes on atrial natriuretic factor]

Several studies evidence that volume or pressure increase stimulates atrial natriuretic factor (ANF) secretion by atrial cardiocyte stretch. In order to study the relationship between plasma renin activity (PRA) and ANF plasma level in experimental weightlessness, six healthy male subjects were submitted to antigravity (anti-g) suit inflation which shifts fluid in the thoracic region. Firstly, blood samples were taken at rest after 15 mn in supine position, secondly after 25 mn in upright position with and without anti-g suit. During the tilt test, plasma ANF decreased from 35 +/- 4.1 to 28 +/- 6.6 pg/ml (p less than 0.05) without anti-g suit and rose to 38 +/- 4.1 pg/ml (p less than 0.05) with anti-g suit. This demonstrates the stimulating effect of weightlessness on the ANF release. During the same tilt test PRA increased from 2.69 +/- 0.29 to 4.76 +/- 0.83 ng/ml/h that evidences the perfusion pressure fall on the intrarenal baroreceptors. Anti-g suit inflation abolished this PRA response to the orthostatism, since PRA increase was only 3.23 +/- 0.79 ng/ml/h (p less than 0.05). ACTH and aldosterone levels do not change significantly. These results demonstrate that ANF and PRA which have opposite effects on aldosterone release and Na excretion, change in opposite sens during fluid shifts, to produce antinatriuresis in upright position, or natriuresis in experimental weightlessness.