The origin and fate of histamine in the rabbit retina

The rabbit retina contained histamine, showed well expressed histamine-methyltransferase activity and marginal histidine decarboxylase activity. Slices of the rabbit retina and hypothalamus took up [(3)H]histamine against a concentration gradient in a temperature-dependent process. [(3)H]Histamine uptake by the rabbit retina was inhibited by ouabain, and was unaffected by imipramine, fluoxetine, nisoxetine and nomifensine (all at 10 ?M concentration). [(3)H]Histamine taken up by the retina was metabolized to tele-methylhistamine and methylimidazoleacetic acid. It is suggested that histamine in the retina may be of some functional importance.