| Abstract: | Summary. 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± head-up tilt. During tilting plasma ET-1 increased from 1.1 ±0.2 to 1.4 ± 0.3 pmol 1-1 (mean ± SE) concomitant with an increase in total peripheral resistance (TPR) (from 15 ± 2 to 25 ± 3 mmHg min 1-1) (P< 001), 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. |
