Non‐invasive measure of corticosterone in food restricted rats

Abstract

Fecal corticosterone (CORT) metabolites (FCM) have been measured in laboratory animals and wildlife populations because they avoid handling‐induced stress response. Here we test whether FCM provide a measure of acute and chronic stress induced by an adrenocorticotropic hormone (ACTH) challenge and food restriction (FR), respectively in 4 month old female Wistar rats. Blood and fecal samples were collected before and after 7 days of FR to 88% baseline body mass (FR n = 10) or ad libitum feeding (CON n = 8) and after ACTH challenge. Enzyme immunoassays showed greater FCM after FR compared with baseline (419.1 ± 250.5 vs. 294.6 ± 145.6 ng.g−1). Serum CORT increased from baseline in response to ACTH challenge in both FR (79.7 ± 45.5 ng.ml−1vs. 610.6 ± 253.4 ng.ml−1) and CON (62.2 ± 46.2 ng.ml−1vs. 227.2 ± 78.1 ng.ml−1), with a greater response in FR. There was no difference in FCM measured at 2 h intervals over the 24 h period post ACTH injection between groups and the increase in 24h‐average FCM post ACTH only reached significance for CON (384.1 ± 29.1 vs. 521.5 ± 26.3 ng.g−1) and not FR (419.1 ± 250.5 vs. 523.8 ± 405.2 ng.g−1). Thus FCM provide a measure of the response to a chronic stress, however this measure is less sensitive than serum CORT for describing the acute response. These data support the use of FCM for measurement of long‐term adaptive response to physiologic stressors in rats and demonstrate increased adrenal sensitivity in FR. Funded by Kinesiology & Physical Education