CALCITONIN GENE-RELATED PEPTIDE (CGRP) AND LEG VASCULAR-RESISTANCE DURING HEAD-UP TILT INDUCED HYPOVOLEMIC SHOCK IN MAN

Calcitonin gene-related peptide is a potent vasodilator and its distribution in perivascular nerves suggests a role in the regulation of vascular tone. We evaluated leg vascular resistance together with total peripheral resistance and the arterial plasma concentrations of calcitonin gene-related peptide and catecholamines during 50-degrees head-up tilt induced hypotension in 7 males. During tilt mean arterial pressure, heart rate, total peripheral resistance, leg vascular resistance and plasma noradrenaline increased, while cardiac output and leg blood flow decreased. After 45 +/- 9 min (mean + SE) presyncopal symptoms appeared together with decreases in mean arterial pressure (81 +/- 6 to 56 +/- 9 mmHg), heart rate (97 +/- 6 to 73 +/- 8 beats min-1), leg vascular resistance (158 +/- 9 to 109 +/- 8 mmHg min l-1) and total peripheral resistance (17 +/- 3 to 10 +/- 2 mmHg min l-1) (P < 0.01). Plasma calcitonin gene-related peptide increased from 32 + 3 to 35 +/- 3 pmol l-1 (P < 0.01) and adrenaline from 1.1 +/- 0.2 to 1.7 +/- 0.3 nmol l-1 (P < 0.01), while noradrenaline did not change. The results indicate that presyncopal symptoms induced by head-up tilt are associated with regional as well as total decreases in vascular resistance accompanied by moderate increases in arterial plasma concentrations of calcitonin gene-related peptide and adrenaline.