Plasma norepinephrine, epinephrine and corticosterone stress responses to restraint in individual male and female rats, and their correlations.

Norepinephrine (NE), epinephrine (E), and corticosterone (C) levels were determined in the same male and female rats before and during a 30-min period of restraint. Individual values were compared within and among NE, E and C. Individual rats responded differently to immobilization and females usually showed higher stress values. NE and E levels rose smoothly and simultaneously in all animals and peaked early. The early (5 min) NE and E levels, but not the baseline values (0 min), predicted the total extent of the NE and E stress responses in both sexes. The C response was relatively independent of either E or NE. The male C response, but not the female C response, was strongly predicted by the C 5-min level, and significantly predicted by the C 15-min level. Additionally, the male C response, unlike the E, NE or female C response, was biphasic, dropping significantly below baseline at 5 min before rising to peak levels at the end of immobilization (30 min).