AGE-RELATED-CHANGES IN TETRAHYDROBIOPTERIN AND GTP-CYCLOHYDROLASE ACTIVITY IN THE BRAIN AND ADRENAL-GLAND OF RATS

In the present study, we observed that tetrahydrobiopterin (BH4) level s were decreased significantly in the striatum, substantia nigra, fron tal cortex, hypothalamus, and cerebellum of 25-month-old and in the ce rebellum only in case of 18-month-old rats as compared to 4-month-old rats. In contrast, BH4 levels in adrenal glands of 25-month-old rats w ere increased significantly. Kinetic analysis of GTP-cyclohydrolase re vealed a decrease in the apparent K-m along with an increase in V-max value in the adrenal of 25-month-old rats compared to 4-month-old rats . Whereas, in cerebellum we observed that the apparent K-m of the high affinity form of the enzyme was increased and a decrease in the V-max value of the low affinity form only in case of 25-month-old rats comp ared to the young animals. These alterations in the BH4 levels and its synthesizing enzyme kinetics in specific brain areas and adrenal glan ds of aged rats are consistent with the reported changes in the catech olamine function in central and peripheral nervous system with aging.