Follistatin treatment modulates glucagon secretion. Human islets were cultured for 0–24 hours on 804G matrix-coated dishes in the presence of 50 mM follistatin. (A) Insulin secretion: human islets were incubated for 60 minutes at 2.8 mM glucose (open bars) followed by 60 minutes at 16.7 mM glucose (closed bars) (n = 6). (B) Glucagon secretion: human islets were incubated for 60 minutes at 16.7 mM glucose (closed bars) followed by 60 minutes at 2.8 mM glucose (open bars) (n = 4). In sorted rat β cells, 24 hours of follistatin treatment at 10 or 50 ng/ml increases proliferation (C) and decreases cell death (D) (n = 4).*P < .05 compared to control as tested by ANOVA followed by Bonferroni post hoc test. †Significant by Student's t test. Data are presented as mean ± SEM.