Corticosterone concentrations in blood and excretion in faeces after ACTH administration in male Sprague-Dawley rats.

The aim of the present study was to analyse the corticosterone response to exogenous ACTH in the circulation of catheterised male rats and to investigate the sensitivity of faecal corticosterone output as a measure of preceding elevated levels in the circulation. A total of 21 adult male Sprague-Dawley rats permanently catheterised (v. jugularis externa for intravenous administration of ACTH and a. carotis communis for blood sampling), were used. Administration of both 10 and 100 microg/kg ACTH resulted in a rapid and pronounced corticosterone increase three minutes after injection (226 and 220 ng/ml, respectively), but the duration of the response was different. In the 10 microg/kg group, corticosterone levels were significantly elevated for 3-90 min after injection, while in the 100 microg/kg group, the levels remained elevated for 240 min after injection. In faeces, a significant increase during eight hours after ACTH injection was found in the group treated with 100 microg/kg, but not in the group treated with 10 microg/kg. In conclusion, quantification of faecal excretion of corticosteroids is a useful non-invasive measure of prior substantial stress (e.g. surgery), but not sufficiently sensitive to reveal minor stress or acute stress of short duration.