Lack of effect of chronically administered thyrotropin-releasing hormone (TRH) on regional rat brain tyrosine hydroxylase activity.
Chronic treatment of adult male rats with TRH (1 or 10 mg/kg IP) for 5 or 9 days failed to alter the activity of tyrosine hydroxylase (TH), the enzyme regulating the rate-limiting step in catecholamine biosynthesis. In contrast, as previously described, chronic reserpine administration (0.5 mg/kg IP: 9 days) resulted in a significant rise in TH activity in midbrain, hypothalamus, pons-medulla and forebrain. These results suggest that the enhanced brain norepinephrine turnover reported to occur after treatment with TRH is not due to synthesis of new TH enzyme protein.
Lack of effect of chronically administered thyrotropin-releasing hormone (TRH) on regional rat brain tyrosine hydroxylase activity. Chronic treatment of adult male rats with TRH (1 or 10 mg/kg IP) for 5 or 9 days failed to alter the activity of tyrosine hydroxylase (TH), the enzyme regulating the rate-limiting step in catecholamine biosynthesis. In contrast, as previously described, chronic reserpine administration (0.5 mg/kg IP: 9 days) resulted in a significant rise in TH activity in midbrain, hypothalamus, pons-medulla and forebrain. These results suggest that the enhanced brain norepinephrine turnover reported to occur after treatment with TRH is not due to synthesis of new TH enzyme protein.