title: Modulation of retinal aromatic L-amino acid decarboxylase via alpha 2 adrenoceptors.
abstract: Aromatic L-amino acid decarboxylase (AAAD) activity of the rat retina increases when animals are placed in a lighted environment from the dark. The rise of activity can be inhibited by administering alpha 2 adrenoceptor agonists. In the dark, the enzyme activity can be made to increase by administering alpha 2 adrenoceptor antagonist drugs. Kinetic analysis indicates that the maximum velocity of the enzyme increases with little change of the Km for the substrate L-3,4-dihydroxyphenylalanine or the cofactor pyridoxal-5'-phosphate. The rise of activity in the light and in the dark after alpha 2 antagonists can be blocked by administering cycloheximide, suggesting that protein synthesis is needed for the response. We speculate that epinephrine released in the dark from a subpopulation of retinal amacrine cells onto alpha 2 receptors suppresses AAAD activity that is associated with dopaminergic amacrines.
authors.affiliation: Department of Pharmacology, Ohio State University College of Medicine, Columbus 43210-1239.
authors.forename: Z
authors.initials: Z
authors.lastname: Rossetti
authors.forename: D
authors.initials: D
authors.lastname: Krajnc
authors.forename: N H
authors.initials: NH
authors.lastname: Neff
authors.forename: M
authors.initials: M
authors.lastname: Hadjiconstantinou
mesh_terms: D000818:Animals; D001142:Aromatic-L-Amino-Acid Decarboxylases / Q000378:metabolism*; D003000:Clonidine / Q000494:pharmacology; D003513:Cycloheximide / Q000494:pharmacology; D003624:Darkness; D004295:Dihydroxyphenylalanine / Q000378:metabolism; D007700:Kinetics; D008027:Light; D008297:Male; D010109:Oxymetazoline / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D010883:Piperoxan / Q000494:pharmacology; D011732:Pyridoxal Phosphate / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D012160:Retina / Q000201:enzymology*; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; D011732:Pyridoxal Phosphate; D004295:Dihydroxyphenylalanine; D010109:Oxymetazoline; D003513:Cycloheximide; D010883:Piperoxan; D001142:Aromatic-L-Amino-Acid Decarboxylases; D003000:Clonidine; D010646:Phentolamine