K 184Modulation of IGF-I production of cultured retinal endothelial cells by growth hormone, glucose and oxygen levels
N. Eter 1, M. Sahm 1, D. Klingmüller 2, M. Spitznas 1
Purpose: To evaluate the interaction of glucose, growth hormone (GH) and oxygen levels on IGF-I production of cultured bovine retinal endothelial cells (BREC).
Methods: Confluent cultures of BREC were incubated with either DMEM (including 1 g/l glucose) only or DMEM supplemented with 4.5 g/l glucose, with or without 10 ng/ml growth hormone under 3% or 20 % oxygen. After incubation times of 0, 24, 48 and 72 h IGF-I was measured in the supernatant using a radioimmunoassay and cells were counted by a counting chamber. All experiments were carried out in duplicate and repeated 6 times.
Results: In all samples IGF-I production increased over the period of 72 h. Highest levels of IGF-I were reached after 72 h with 4.5 g/l glucose and 10 ng/ml GH under 3% O2 (1.06 ± 0.54 ng/104 cells). IGF-I levels were 1.02 ± 0.54 ng/104 cells in samples with 4.5 g/l glucose without GH , 0.95 ± 0.6 ng/104 cells with 1 g/l glucose and 10 ng/ml GH and 0.87 ± 0.53 ng/104 cells with 1 g/l glucose without GH, all incubated under 3% O2. In the 20% O2 experiments, highest IGF-I levels were found with 4.5 g/l glucose and 10 ng/ml GH (0.46 ± 0.11 ng/104 cells). IGF-I levels were 0.39 ± 0.22 ng/104 cells in samples with 1 g/l glucose with 10 ng/ml GH, 0.38 ± 0.15 ng/104 cells with 1 g/l glucose without GH and 0.38 ± 0.17 ng/104 cells with 4.5 g/l glucose without GH.
Conclusions: IGF-I production of bovine retinal endothelial cells is stimulated by high levels of glucose and, especially, by low oxygen concentration. These findings confirm the clinical impression that retinal hypoxia resulting from non-perfused areas constitutes an important stimulus for retinal neovascularization in diabetic retinopathy.
1Dept. of Ophthalmology, 2Dept. of Clinical Biochemistry, University of Bonn, Germany