CORTICOSTERONE RESPONSES OF ADULT LEWIS AND FISCHER RATS

Indwelling catheters were implanted into the inferior vena cava of adu lt male and female Lewis/N and Fischer 344 rats. Each animal was expos ed to ACTH, novelty stimulation, nicotine, lipopolysaccharide (LPS), a nd saline on 5 consecutive days. Blood was withdrawn before (baseline) and at several time points after the stimulus on each day. There were no differences in baseline corticosterone levels nor in responses to saline in any group. In general, responses to stimulation peaked at 15 -30 min and returned to baseline by 60-90 min. Corticosterone response s to LPS showed a different time course; maximal responses occur at 1- 2 h and return to baseline by 24 h. Fischer animals showed higher cort icosterone levels than Lewis rats during the response to stimulation, but returned to baseline at the same times. Females of each strain sho wed higher corticosterone responses than males at 15, 30, and 45 min a fter ACTH, but the sexes did not differ in response to the other stimu li. For individual; rats, the maximum response to ACTH was slightly co rrelated with the maximum response to novelty stimulation, nicotine, a nd saline but was not correlated with the response to LPS.