Plasma endothelin-1 during central hypovolaemia in man

Endothelin-1 (ET-1) is a potent vasoconstricting peptide with effect on resistance as well as capacitance vessels. We followed ET-1 in arterial plasma together with heart rate (HR), central venous pressure (CVP), mean arterial pressure (MAP), and thoracic electrical impedance (TI) in seven men during central hypovolaemia induced by 50 degrees head-up tilt. During tilting plasma ET-1 increased from 1.1 +/- 0.2 to 1.4 +/- 0.3 pmol l-1 (mean +/- SE) concomitant with an increase in total peripheral resistance (TPR) (from 15 +/- 2 to 25 +/- 3 mmHg min l-1) (P < 0.01), and HR (from 67 +/- 2 to 94 +/- 5 beats min-1) (P < 0.01) while MAP remained unchanged. CVP decreased (from 1.8 +/- 0.9 to -1.6 +/- 1.0 mmHg) (P < 0.01) during tilting and remained unchanged during sustained tilt despite further reduction of central blood volume as recorded by TI. Presyncopal symptoms occurred after 28 +/- 6 min associated with decreases in HR (to 70 +/- 6 beats min-1), MAP (from 90 +/- 3 to 52 +/- 4 mmHg) and TPR (to 11 +/- 2 mmHg min l-1) (P < 0.01). At this time plasma ET-1 reached its highest level of 1.6 +/- 0.3 pmol l-1 (P < 0.01). Data show that head-up tilt is associated with increased plasma concentrations of ET-1 which may play a role in maintaining vascular tone in situations with a reduced central blood volume.