1. To investigate the possible role of adrenaline as a modulator of noradrenaline release from the sympathetic nervous system, the responses of cardiac and whole-body noradrenaline kinetics to intravenous infusions of adrenaline (30 ng min−1 kg−1) and matching saline placebo were determined at rest and during supine bicycle exercise in 16 patients undergoing cardiac catheterization, in whom β-adrenoceptor antagonists had been discontinued for 72 h.
2. At rest and compared with placebo, infusion of adrenaline was associated with a small increase in arterial plasma noradrenaline from 211 ± 129 pg/ml to 245 ± 29 pg/ml (P < 0.05). Increases in whole-body noradrenaline spillover to arterial plasma were larger (from 282 ± 40 ng min−1 m−2 to 358 ± 41 ng min−1 m−2, P < 0.01) and there was a trend towards an increase in whole-body noradrenaline clearance. Cardiac noradrenaline clearance was modestly increased during adrenaline infusion, but cardiac noradrenaline spillover was not altered despite increases in heart rate and coronary sinus plasma flow. Adrenaline infusion was associated with symptomatic myocardial ischaemia in four of 14 patients with coronary heart disease.
3. Supine bicycle exercise was associated with significant increases in peripheral noradrenaline concentrations and in cardiac and whole-body noradrenaline spillover. The increases on exercise were not significantly different for these variables during saline and adrenaline infusions.
4. Infusion of adrenaline to produce ‘physiological’ increases in plasma adrenaline concentration was associated with an increase in total noradrenaline release, as assessed by whole-body noradrenaline spillover to plasma. This is consistent with the hypothesis that adrenaline may modulate noradrenaline release by acting upon pre-junctional β-adrenoceptors, but could also be explained by reflexogenic responses to the haemodynamic effects of adrenaline.
