Dopamine stimulated increase of GTP levels in the rat retina.
Dopamine stimulates a 7-10-fold increase of GTP concentration in whole rat retina maintained in vitro. Half-maximal stimulation of GTP levels were obtained with 10(-6) M dopamine, and significant increases in GTP levels were seen with 10(-7) M dopamine. Intracellular GTP levels were significantly increased within 4 min after exposure to dopamine and maximal effects were reached within 30 min. Dopamine agonists, apomorphine and bromocriptine, also stimulate a 7-10-fold increase in GTP concentration, whereas other catecholamines (norepinephrine, epinephrine, and isoproterenol) were less potent. Several other neurotransmitters present in rat retina (gamma-aminobutyric acid, glycine, glutamine, and taurine) had no effect on GTP levels. Although dopamine also stimulates increases in cyclic AMP levels in the retina, dibutyryl cyclic AMP and 8-bromo-cyclic AMP had no effect on GTP levels, indicating that the dopamine-stimulated increase of GTP is independent of the catalytic production of cyclic AMP by adenylate cyclase. Since dopamine-stimulated adenylate cyclase activity requires GTP, the dopamine-stimulated increase in GTP concentration described in this report may serve to facilitate dopamine stimulation of adenylate cyclase activity.
Schaeffer
J M
JM
Anderson
S M
SM
D000818:Animals; D001058:Apomorphine / Q000494:pharmacology; D001971:Bromocriptine / Q000494:pharmacology; D002069:Butaclamol / Q000494:pharmacology; D004298:Dopamine / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006160:Guanosine Triphosphate / Q000378:metabolism*; D007536:Isomerism; D007545:Isoproterenol / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012160:Retina / Q000187:drug effects / Q000378:metabolism*
D001971:Bromocriptine; D006160:Guanosine Triphosphate; D002069:Butaclamol; D007545:Isoproterenol; D001058:Apomorphine; D004298:Dopamine