US EPA

1655818 

Journal Article 

Physiological concentrations of melatonin inhibit the nitridergic pathway in the Syrian hamster retina 

Sáenz, DA; Turjanski, AG; Sacca, GB; Marti, M; Doctorovich, F; Sarmiento, MI; Estrin, DA; Rosenstein, RE 

2002 

Yes 

Journal of Pineal Research
ISSN: 0742-3098
EISSN: 1600-079X 

33 

1 

31-36 

English 

12121483 

WOS:000176833300005 

In the present work, the effect of melatonin on the hamster retinal nitridergic pathway was examined. When the retinas were incubated in the presence of low concentrations (1 pM-10 nM) of melatonin for 15 min, a significant decrease of nitric oxide synthase (NOS) activity was observed. However, when crude retinal homogenates were preincubated with melatonin for 15 min, no changes in NOS activity were detected, despite the fact that under the same conditions trifluoperazine, a calmodulin inhibitor, significantly decreased enzymatic activity. Kinetic analysis showed that melatonin decreased the V(max) of retinal NOS without changes in the K(m). On the other hand, low concentrations (100 pM) of melatonin significantly reduced retinal L-arginine influx. A decrease in the V(max) of L-arginine uptake was observed in the presence of melatonin, whereas the K(m) remained unchanged. Melatonin significantly inhibited the accumulation of cyclic guanosine monophosphate (cGMP) levels induced by both L-arginine and sodium nitroprusside (SNP). In summary, the present results indicate that melatonin could be a potent inhibitor of the retinal nitridergic pathway. 

L-arginine uptake; melatonin; NOS; retina; Syrian hamster