Circadian rhythm of histamine metabolism in the rabbit central nervous system (CNS): analysis of brain and ocular structures.

The circadian rhythm of the level of histamine (HI) and histidine decarboxylase (HD) and histamine-methyltransferase (HMT) activity in 6 brain and 5 ocular structures of the rabbit was studied. Clear circadian variations of the histaminergic parameters in two brain (hypothalamus and lateral geniculate body) and two ocular (retina and iris-ciliary body) tissues were found. It is suggested that HI in some brain and ocular structures may be functionally involved in activity that depends on circadian rhythm.