1. On three separate occasions, at least 1 week apart, seven young healthy male subjects received intravenous infusions of either adrenaline, 50 ng min−1 kg−1 (high A), adrenaline, 10 ng min−1 kg−1 (low A) or sodium chloride solution (saline :154 mmol of NaCl/1) plus ascorbic acid, 1 mg/ml (control), over 30 min.

2. Venous adrenaline concentrations of 2.19 ± 0.15 nmol/l, 0.73 ± 0.08 nmol/l and 0.15 ± 0.03 nmol/l were achieved during the high A, low A and control infusions respectively.

3. Heart rate rose significantly by 19 ± 3 beats/min (high A) and by 6 ± 1 beats/min (low A). Heart rate remained significantly elevated 30 min after cessation of the high A infusion, despite venous plasma adrenaline concentration having fallen to control levels.

4. The diastolic blood pressure fell during the high A and low A infusions, but the systolic blood pressure rose only during the high A infusion.

5. Vasodilatation occurred in the calf vascular bed during both high A and low A infusions. The changes in hand blood flow and hand vascular resistance were not statistically significant, although there was a tendency to vasoconstriction during the infusion of adrenaline.

6. Metabolic rate rose significantly by 23.5 ± 1.8% (high A) and by 11.8 ± 1.6% (low A). Metabolic rate remained elevated between 15 and 30 min after termination of the high A infusion. There was an initial transient increase in respiratory exchange ratio (RER) during the adrenaline infusions. During the later stages of the adrenaline infusions and after their cessation, RER fell, probably reflecting increased fat oxidation.

7. Blood glucose, glycerol and lactate concentrations all rose significantly during the high A infusion, but only the blood glycerol concentration rose during the low A infusion. Plasma potassium concentration fell during and after the high A infusion but only after cessation of the low A infusion.

8. When adrenaline was infused intravenously at rates that elevated the plasma adrenaline concentration within the physiological range, peripheral circulatory effects were observed similar to those previously described for larger doses of adrenaline. The persistent tachycardia noted after stopping the high A infusion may, at least in part, have been a consequence of the concomitantly elevated metabolic rate.

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