Fatty acid and tryptophan changes on disturbing groups of rats and caging them singly

The effects of disturbing groups of 24 hr fasted rats on plasma unesterified fatty acid (UFA) and tryptophan concentrations and brain tryptophan concentrations were investigated. Removing rats from cages rapidly increased plasma UFA and corticosterone and decreased plasma and whole blood tryptophan of cage mates. The disturbance also appeared to influence biochemical values of rats in other cages within the same chamber. Effects specific to individual cages were also suggested. In subsequent experiments 24 fasting rats caged together were rapidly transferred to 24 separate cages and killed at intervals. Plasma UFA rose to a maximum by 12 min and then fell toward initial values. Plasma total tryptophan concurrently fell then rose. Its percentage in the free (ultrafilterable) state, and in some experiments the absolute values of free tryptophan rose then fell. When the latter rise was marked then brain tryptophan and the 5-HT metabolite 5-hydroxyindoleacetic acid rose. Tyrosine changes were negligible. Thus altered brain tryptophan level and 5-HT metabolism may be associated with plasma tryptophan changes caused by brief environmental disturbance.