Abstract
Hydrocortisone sodium succinate (5 mg/kg i.p.) led to a larger absolute increase in hepatic tryptophan pyrrolase activity in younger (26, 46 and 66 days) than older (107 and 225 days) rats. Activity in control animals was lower in the older rats and there was no obvious correlation between percentage change and age. Responses of male and females were comparable. Consistent with previous findings brain 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) decreased 6 hr after hydrocortisone only at ages when a large absolute increase of pyrrolase activity occurred (26, 46 and 66 days). Brain 5-HT and 5-HIAA levels both before and after hydrocortisone were comparable in males and females. Immobilization led to pyrrolase induction and brain 5-HT changes in 66-day but not in 225-day old rats. Studies with different hydrocortisone preparations showed that the soluble succinate salt caused a more rapid increase of pyrrolase activity than the insoluble acetate salt or free base and a more marked brain 5-HT decrease. Results are discussed in relation to the suggested association between liver tryptophan pyrrolase activity and the subsequent changes in brain 5-HT and 5-HIAA.
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