Effects of topical insulin administration on phosphorylated protein kinase B and nitric oxide levels in the rat retina

PurposeTo examine the effects of insulin treatment on the expression of phosphorylated protein kinase B (Akt or pAkt) and nitric oxide (NO), known targets of insulin action.MethodsRetinas from Lewis rats were treated with insulin in vitro, and the levels of pAkt and NO expression assessed in lysed tissue homogenates at various time points. In addition, rats were treated in vivo with a single eye drop containing 1% insulin after which the levels of pAkt and NO were assessed in their retinas at various time points.ResultsIncubation of retinas in media containing 10 or 100ng/mL of insulin resulted in a significant increase in their expression of pAkt 15–30min later. When insulin was topically applied in vivo, its levels peaked in the retina 35min. Topically applied insulin significantly increased retinal pAkt levels 10 and 15min post-treatment (p<0.02 and 0.01, respectively). NO levels were elevated 20min after insulin treatment both in vitro and in vivo (p<0.007 and 0.04, respectively).ConclusionsInsulin upregulated retinal expression of pAkt and NO both in vivo and in vitro, suggesting that topically applied insulin that accumulates in the retina may be physiologically active