Nature of induction of tryptophan pyrrolase in cold exposure

1975-The activity of hepatic tryptophan pyrrolase in rats ex-posed to cold increased rapidly and reached a maximum of three-fold at 8 h. On continued exposure up to 48 h stress, the activity partly decreased but remained at a level higher than the initial. Withdrawal from the cold stress reversed the change. Adrenalec-tomy or treatment with inhibitors of protein synthesis abolished the increase in the enzyme activity during cold stress indicating a possible involvement of corticosteroids and de nova protein syn-thesis. Treatment with drugs known to block autonomic nervous system failed to inhibit the cold-mediated increase in enzyme ac-tivity. The results suggest that the increase in enzyme activity obtained on cold exposure is mediated by corticosteroids and not by either indolealkylamines or autonomic nervous system. The changes in the enzyme obtained under cold stress with respect to the overshoot phenomenon, relationship to the degree of stress an