Comparison between men and women of volume regulating hormones and aquaporin-2 excretion following graded central hypovolemia.

Central hypovolemia induced by orthostatic loading causes reno-vascular changes that can lead to orthostatic intolerance. In this study, we investigated volume regulating hormonal responses and reno-vascular changes in male and female subjects as they underwent central hypovolemia, induced by graded lower body negative pressure (LBNP). Aquaporin-2 (AQP2) excretion was measured as a biomarker for the renal system response to vasopressin. 37 young healthy subjects (n = 19 males; n = 18 females) were subjected to graded LBNP until - 40 mmHg LBNP. Under resting conditions, males had significantly higher copeptin (a stable peptide derived from vasopressin) levels compared with females. Adrenocorticotropin (ACTH), adrenomedullin (ADM), vasopressin (AVP) and brain natriuretic peptide (BNP) were not affected by our experimental protocol. Nevertheless, an analysis of ADM and BNP with the data normalized as percentages of the baseline value data showed an increase from baseline to 10 min after recovery in the males in ADM and in the females in BNP. Analysis of BNP and ADM raises the possibility of a preferential adaptive vascular response to central hypovolemia in males as shown by the normalized increase in ADM, whereas females showed a preferential renal response as shown by the normalized increase in BNP. Furthermore, our results suggest that there might be a difference between men and women in the copeptin response to alterations in orthostatic loading, simulated either using LBNP or during posture changes.