The Relationship between Plasma Catecholamine Concentration and Pulse Rate during Exercise and Standing

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Abstract
Plasma catecholamine concentrations (PCA) were measured during standing and exercise using a precise and sensitive double‐isotope derivative technique. By plotting the increase in PCA in the standing position on the y‐axis of a coordinate system against the increase in pulse rate, PCA was resolved into two components: one corresponding to the intercept of the y‐axis where rise in pulse rate equals zero (CAP) while the other (CAH) was calculated by multiplying the slope of the regression line by the mean increase in pulse rate.–The rise in PCA, mainly noradrenaline, was considerably less during light to moderate exercise than during standing. Thus there was no rise in PCA during exercise until the increase in pulse rate exceeded approximately 30 beats/min and there was no rise in the CAP component during exercise. When PCA began to rise during exercise the increase in PCA per increment in pulse rate was similar to that observed in the standing experiments. There was no difference between the increments in PCA observed during exercise in the supine and the sitting positions but resting PCA was doubled in the sitting position.–It is suggested that 1. the initial rise in pulse rate during exercise is due to withdrawal of parasympathetic activity on the heart 2. the increase adrenergic in vasoconstrictor activity is considerably less during moderate exercise than during standing 3. the increase in plasma noradrenaline during moderate exercise is of cardiac origin.