Effects of housing and chronic cannulation on plasma ACTH and corticosterone in the rat.

Effects of housing and cannulation on plasma ACTH and corticosterone levels were evaluated to validate a method for obtaining repeated blood samples for ACTH from conscious rats. Resting morning, evening, or noise-stimulated (4 min of metal rattling) levels of plasma ACTH or corticosterone obtained by decapitation were similar in rats housed alone or in pairs. Individually housed, cannulated rats had slightly elevated morning levels of plasma ACTH and corticosterone, but the evening and noise-stimulated increases in hormone levels were similar to those in unoperated, decapitated rats. A hemorrhage stimulus administered on separate days to cannulated rats evoked highly replicable elevations in plasma ACTH and corticosterone. These results demonstrate that 1) ACTH and corticosterone secretion are similar in rats housed alone versus in pairs, and 2) long-term cannulation permits multiple intra-animal comparisons of basal and acutely stimulated plasma ACTH and corticosterone levels that are useful reflections of those measured in decapitated rats.