Effect of methytimidazole-induced hypothyroidism in a model of low retinal neovascular incidence

PURPOSE. To determine the effect of methylimidazole (MMI)-induced hypothyroidism in a newborn rat model of low retinal neovascular (NV) incidence. METHODS. Control and MMI-exposed newborn rats were raised either in room air or variable oxygen (40/15) until P14. All groups were then exposed to room air between postnatal day (P)14 and P20. Dams drank either tap water or water containing MMI. Eyes of animals in all groups were enucleated, and retinas were removed and stained with adenosine diphosphatase and analyzed for peripheral avascularity, vascular density, and NV incidence and severity. RESULTS. In the control group, MMI treatment did not promote the development of retinal NV although a linear relationship (r = 0.99, P < 0.01) was found between increased MMI dose and lower peripheral retinal vascular densities. In all the 40/15 groups, peripheral retinal vascular densities were lower (P < 0.05) than normal and were not a function of MMI dose. Increased MMI dose produced increased retinal incidence of NV (r = 0.99, P < 0.05). CONCLUSIONS. These data are consistent with the notions that thyroid function contributes to normal retinal vascular density and that hypothyroidism can play a permissive role in the development of retinal NV.