Physical conditioning in rats influences the central and peripheral catecholamine responses to sustained exercise

We have investigated the effect of treadmill running in rats (25m · min^–1 using a 3 % gradient; for 1 h or 2 h) on the cortical extracellular concentrations of noradrenaline (NA) and its main metabolites — 3,4-dihydroxyphenylglycol and 3-methoxy-4-hydroxyphenylglycol-and the plasma adrenaline (A) and NA concentrations in relation to prior physical conditioning (1 or 2-h running -day-¹ for 12 days). Cortical microdialysates and peripheral blood were collected during 1-h resting, 1-h or 2-h running and for 1 h after exercise. Catecholamines and their metabolites were quantitated using high performance liquid chromatography with electrochemical detection. Treadmill running stimulated concomitantly peripheral catecholamine secretion and central noradrenergic activity, i.e. NA turnover and release. The effect extended into the recovery period even more as the duration of the run increased. Prior physical conditioning greatly influenced the central and peripheral catecholamine responses: the 1-h trained rats experienced the 2-h run as a stressful new event eliciting great long-lasting catecholamine responses, whereas the 2-h trained rats exhibited a progressive sustained catecholamine increase with an earlier onset of the central NA release. The data are discussed in relation to the psychological and intellectual effects of exercise and physical fitness in humans. In addition, the positive correlation found between the central noradrenergic activation and peripheral A secretion confirmed and extended our previous observations in exercising men and gave support to the hypothesis that the elevation of circulating A can be a relevant factor mediating — directly or indirectly — the exercise-induced central effects.