GH1 and proliferative diabetic retinopathy: Extrapituitary expression of GH has been detected in the human retina and vitreous fluid,94 and GH has been demonstrated to directly stimulate the proliferation of human retinal microvascular endothelial cells in vitro.95 In vivo, ischemia-induced retinal neovascularization was inhibited in transgenic mice expressing a GH antagonist gene.96 Increased serum levels of GH and IGF1 have been observed in type 2 diabetes mellitus (T2D) patients with proliferative diabetic retinopathy compared to T2D patients with nonproliferative retinopathy or with no evidence of this complication.97