Role of the Hypothalamus in the Induction of Tryptophan Pyrrolase Activity in Rabbit Liver*

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Abstract
Induction of tryptophan pyrrolase activity of rabbit liver by hypothalamic lesion or stimulation was studied. When the sympathetic area of the hypothalamus was bilaterally destroyed, tryptophan pyrrolase activity of liver homogenates increased to about 3 times the normal value 1 day after the destruction, and returned to the normal level 3 to 6 days after the destruction. Bilateral hypothalamic lesions of the parasympathetic area had little influence on the activity. An increase in activity of liver homogenates of about 8 fold was observed after electric stimulation of the sympathetic area of the hypothalamus. An increase of nearly 5 fold in activity of liver homogenates was also observed after electric stimulation of the parasympathetic area of the hypothalamus. Electrical stimulation of the sympathetic area resulted in a marked elevation of the total tryptophan pyrrolase activity and one-half of this enzyme was saturated with respect to its cofactor, in vivo. When the parasympathetic area of the hypothalamus was stimulated, the total amount of enzyme also increased markedly but only one-fifth of this enzyme was combined with cofactor. The induction of enzyme activity by hypothalamic stimulation was also observed in an adrenalectomized rabbit. These studies indicate that 2 further influences, namely the sympathetic and parasympathetic areas of the hypothalamus, are involved in the induction of tryptophan pyrrolase activity in mammalian liver.