Effect Of IGF-1 On The Retinal Vascular Development And Neovascularization In The Neonatal Rat

Retinopathy of prematurity (ROP) continues to be a significant cause ofblindness wordwide. It is possible that further reductions in the prevalence andseverity of blindness caused by ROP can be made only with advancements inthe prevention of neovascularization (NV), rather than treatment of NV once itoccurs.Objective:The purpose of this study was to determine the effect of seruminsulin-like growth factor (IGF)-1 concentrations on retinal vasculardevelopment and neovascularization in neonatal rats. The emergence ofneovascularization (NV) and the associated changes in IGF-1 mRNA levels inmethimazole-induced retinopathy and oxygen-induced retinopathy in theneonatal rats were also concerned.Methods:SectionⅠ: Sprague-Dawley rats (n=75) were raised in expanded litters of25 in room air and were exposed to MMI from birth (given as a 0.1% solutionto nursing mothers for either 4 or 10 days).Experiments ended on day 4 (n=25)or 10 (n=50).Fifty control rats were analyzed on day 4 (n=25) or 10 (n=25) oflife. Right eyes were fixed, and retinas were removed and stained withadenosine diphosphatase (ADPase). Retinas were graded for presence andseverity of neovascularization (NV) in a masked manner, and retinal avascularareas and vascular density were quantified. Left eyes were processed foranalysis of IGF-1 mRNA.Serum IGF-1 level were measured byradioimmunoassay and IGF-1 were performed on pooled blood samples. Bodyweight were measured every day.SectionⅡ: Control and MMI-exposed newborn rats were raised either inroom air or variable oxygen (40/15) every 24 hours until P14. All groups were then exposed to room air between postnatal day P14 and P18. Dams drankeither tap water or water containing 0.1% MMI. Eyes in all groups were fixed,and retinas were dissected and stained with adenosine diphosphatase, thenanalyzed for retinal vascular areas, vascular density, and NV incidence andseverity. Serum IGF-1 level was measured by radioimmunoassay. Body weightwere measured every day.SectionⅢ: Sprague-Dawley rats (n=150) were raised in expanded littersof 25 in room air and were exposed to MMI from birth (given as a 0.1%solution to nursing mothers for either 4 or 10 days). Among them, 75 ratsreceived of rhIGF-1 and others received saline control beginning on day 1 oflife for 3days. Rat were sacrificed on either day 4 or day 10 of life. Righteyes were fixed, retinas dissected and ADPase-stained. Flat mounted retinaswere digitized and total retinal areas and retinal vascular density wereevaluated in a masked manner. Serum IGF-1 were measured at each time point.Body weight were measured every day.Results:SectionⅠ: Retinal NV occurred in 27% of rats exposed to 10 days ofMMI. None of the rats exposed to 4 days of MMI alone and none of thecontrol aninals was graded positive for NV. Retinal vascular areas weresignificantly reduced in rats exposed to 4 days of MMI compared with 4-daycontrol animals (P＜0.05). Serum IGF-1 levels were markedly reduced in4-day MMI rats compared with age-matched control animals (P＜0.05) and in10-day MMI rats compared with 10-day control animals (P＜0.05).SectionⅡ: Compared with non-MMI control pups, newborn rats raised inroom air and receiving MMI exhibited significant (P＜0.05) changes in bodyweight and vascular density. Retinal NV was not found in MMI control retinas,although retinal vascular density was significantly lower (P＜0.05) inMMI-treated pups than in the control group. Compared with untreated 40/15pups, 40/15 newborn rats receiving MMI exhibited significant (P＜0.05)changes in body weight, peripheral avascular area and severity, and NV incidence. Serum IGF-1 levels were markedly reduced in MMI treated controlrats compared with untreated control animals (P＜0.05) and in MMI treated40/15 rats compared with untreated 40/15 group (P＜0.05).SectionⅢ: Retinal vascular density was increased in animals receivingrhIGF-1 compared with saline controls (P＜0.05). But no significant differencein NV incidence was found between age-matched MMI and rhIGF-1 groups.Serum IGF-1 levels were increased after rhIGF-1 treatment for 3 days.Conclusion:MMI induces NV in neonatal rats. This may be mediated by the initialsuppression of serum IGF-1. The relationship between the temporal course ofserum IGF-1 and NV in immature retinas needs further investigation. SystemicrhIGF-1 supplementation was beneficial to retinal vascular development inneonatal animals.