Haemodynamic effects of adrenomedullin in human resistance and capacitance vessels

Aims: The haemodynamic effects of adrenomedullin and calcitonin gene-related peptide (CGRP) were studied in resistance and capacitance vessels of healthy volunteers. Methods: Adrenomedullin and CGRP were infused into the brachial artery of eight healthy subjects on two separate occasions at doses between 0.3-30 pmol min^-1. Forearm blood flow was measured using venous occlusion plethysmography. Venodilatation to adrenomedullin and CGRP was assessed in a further eight subjects by infusing the peptides at doses between 0.3-10 pmol min^-1 into a dorsal hand vein preconstricted with noradrenaline. Venodilator responses were measured as percentage reduction in noradrenaline preconstriction. Results Adrenomedullin and CGRP at a dose of 30 pmol min^-1, produced an increase in forearm blood flow of 288 ± 42% and 252 ± 30% respectively (mean ± s.e. mean, P < 0.001). At doses between 3 and 10 pmol min^-1 adrenomedullin was significantly more potent than CGRP. The vasodilatation to both peptides was of similar duration with a biological half-life of approximately 18 min. Adrenomedullin reversed constriction in dorsal hand veins by 84 ± 2% (P < 0.001) at a dose of 10 pmol min^-1. CGRP produced a similar effect reversing constriction by 72 + 12% at the same dose (P < 0.01). In veins, adrenomedullin was also more potent than CGRP at doses between 0.3 and 3 pmol min^-1. Conclusions: The lowest dose of adrenomedullin producing significant arteriolar dilatation was calculated to produce plasma levels similar to those found in heart failure. These findings suggest that in pathophysiological conditions such as heart failure circulating levels of adrenomedullin may be within a range capable of influencing vascular resistance directly.