Effects of immobilization on rat liver tryptophan pyrrolase and brain 5-hydroxytryptamine metabolism.

1. Rat liver tryptophan pyrrolase increased on immobilization. The concentration of 5-hydroxyindoleacetic acid in the brain also rose and that of 5-hydroxytryptamine fell.2. When adrenalectomized rats were immobilized pyrrolase activity did not rise and brain 5-hydroxytryptamine concentration fell to a lesser extent but the 5-hydroxyindoleacetic acid concentration rose as in intact animals.3. When intact rats were injected with the pyrrolase inhibitor Allopurinol both the increase of pyrrolase and the fall of 5-hydroxytryptamine on immobilization were less prominent but the concentration of 5-hydroxyindoleacetic acid rose as before. Allopurinol did not affect the changes in immobilized adrenalectomized rats.4. Immobilization thus appears to cause (a) decreased brain 5-hydroxytryptamine synthesis resulting from pyrrolase induction and (b) increased 5-hydroxytryptamine breakdown by a more direct effect on the brain. Results of experiments on rats injected with lysergic acid diethylamide, and with alpha-methyltryptophan or probenecid are consistent with the above interpretation.5. The 5-hydroxytryptamine and 5-hydroxyindoleacetic acid changes were maximal after 5-6 hours' immobilization and became less on more prolonged immobilization, which suggests regulatory changes.