Regulation of histidine decarboxylase activity in rat hypothalamus in vitro by ATP and cyclic AMP: enzyme inactivation under phosphorylating conditions.

In vitro, hypothalamic HD1 from rat, could strikingly be inhibited by ATP and cyclic AMP. The enzyme inhibition is partially dependent upon Mg2+ and the circumstances favourable for a cAMP-dependent phosphorylation. An almost complete inhibition could be achieved by incubating the homogenate of the hypothalamus under phosphorylating conditions (ATP, cAMP, Mg2+ and IBMX) in the presence of a cAMP-dependent protein kinase (obtained from bovine thymus). Cyclic nucleotides and ATP alone elicit only moderate inhibitions on the hypothalamic HD activity. Neither ATP, nor cAMP, added alone or in combinations, alter the total brain or the hypothalamic HNMT from guinea-pigs or rats in concentrations up to 10(-3) M. Results suggest that hypothalamic HD is regulated through a cAMP-dependent process, probable a direct phosphorylation, via a cAMP-dependent protein kinase.