Blood collection and processing for measurement of catecholamines in exercising rats

We have studied the time course of the decline in plasma catecholamines in the postexercise period in rats. Male Sprague-Dawley rats were run on the treadmill for 5 min at 31 m/min up a 15% grade. At the end of the exercise the rats were quickly anesthetized by intravenous injection of pentobarbital. Blood samples were collected as soon as possible (average of 43 s), at 2 and 7 min postexercise. Plasma epinephrine decreased from 0.79 +/- 0.09 ng/ml to 0.51 +/- 0.05 after 2 min and to 0.35 +/- 0.09 after 7 min. Plasma norepinephrine decreased from 0.89 +/- 0.16 ng/ml to 0.61 +/- 0.05 after 2 min and to 0.50 +/- 0.07 after 7 min. We also studied the effect of time of centrifugation with respect to time of blood collection on plasma catecholamines. If blood samples were kept on ice no significant change in plasma epinephrine occurred over a period of 1 h. A small (14%) but significant decrease in norepinephrine was observed after 15 and 60 min. These studies emphasize the importance of collecting rat blood samples as quickly as possible after the end of exercise. Catecholamines decline very quickly in the rat after intravenous pentobarbital anesthesia.