EFFECTS OF COCAINE, EXERCISE, AND RESTING CONDITIONS ON PLASMA-CORTICOSTERONE AND CATECHOLAMINE CONCENTRATIONS IN THE RAT

Cocaine and exercise are both known as stressors, but little is known about the combined effects of these two treatments. In this study, rats under the influence of cocaine (12.5 mg/kg, intraperitoneally [IP]) or saline were exposed to a variety of resting conditions, as well as exercise (running, 26 m/min, 10% grade, for 30 minutes), to evaluate the amount of stress imposed by these conditions as determined by the changes in the plasma concentrations of corticosterone (C) and catecholamines (norepinephrine [NE], epinephrine [E], dopamine [DA]). After injection of saline, resting near the operating treadmill for 30 minutes caused the concentration of C to increase from 0.07 ± 0.03 to 0.30 ± 0.05 μg/mL (P < .05), compared to the increase to only 0.15 ± 0.04 μg/mL after resting in a cage. This increase due to proximity to the treadmill subsided after 50 minutes. After cocaine, the 30-minute resting values were 0.70 ± 0.15 (treadmill) and 0.55 ± 0.13 (cage) (P < .05), and did not subside after 50 minutes. Cocaine also increased levels of E, NE, and DA above those in saline under all rest conditions. With exercise, the value for C in saline increased to 0.61 ± 0.18, but, in cocaine, the value went to 0.93 ± 0.05 (P < .05). The concentrations of E (946 ± 74 v 603 ± 101 pg/mL, cocaine v saline) and NE (1,027 ± 102 v 440 ± 153, cocaine v saline) during exercise also were exaggerated by cocaine treatment (P < .05). These results show that cocaine by itself imposes a stress response, and that when an additional stress factor is added (eg, exercise or altered rest conditions), the increases in plasma C, E, and NE (used as indices of stress) are greater than those associated with either stress alone. © 1991.