ABSENCE OF INCREASED TYROSINE HYDROXYLATION AFTER INDUCTION OF BRAIN TYROSINE-HYDROXYLASE FOLLOWING RESERPINE ADMINISTRATION

Reserpine was administered to rats by i.p. injection, and seven days later, with a control group, crude synaptosomal suspensions were prepared from hippocampus and cerebellum for the estimation of rates of synaptosomal tyrosine hydroxylation; additionally, samples of hippocampus, cerebellum and hypothala- mus were homogenized in a hypotonic buffer containing Triton for the 171 in vitro estimation of tyrosine hydroxylase. In the samples from reserpine pretreated animals, in vitro tyrosine hydroxylase activities were considerably elevated compared to controls (234 per cent of controls in the cerebellum, 154 per cent in hippocampus and 181 per cent in hypothalamus). However, the synaptosomal tyrosine hydroxylation rates were not elevated in the drug-treated group. The rate of product formation with time was linear in preparations from both control and reserpine pretreated animals. The results suggests that enzyme induction leads to an increased potential for tyrosine hydroxylation which may not be expressed due to interaction with regulatory mechanisms operating on the enzyme. © 1979.