FIGURE 1.

TNF-α action on primary beta cell proliferation, survival, and glucose-stimulated insulin secretion. A, effect of TNF-α on proliferation of rat primary beta cells. Proliferation was measured by BrdU incorporation. Cells were grown under standard culture conditions (20% fetal calf serum, 11.2 mm glucose) and treated for 48 h with TNF-α (20 ng/ml), and BrdU was added the last 24 h. Beta cells were identified by insulin immunofluorescence. n = 5 independent experiments. B and C, effect of TNF-α on rat and human primary beta cell apoptosis. Cell death was measured in insulin-positive (immunofluorescence) cells by TUNEL after 24 h of treatment with TNF-α. n = 5 independent experiments. D and E, effect of TNF-α treatment on insulin secretion from rat and human primary beta cells. Insulin secretion was measured using rat and human primary beta cells incubated for 1 h at 2.8 mm glucose (white bars, basal secretion) following by 1 h at 16.7 mm glucose (dark bars, stimulated secretion). n = 5 independent experiments. *, p < 0.05 versus basal secretion: #, p < 0.05 versus stimulated secretion under control conditions.