Figure 3.
Effect of IGF-1 on insulin secretion is potentiated by 8-Br-cAMP but not N6-benzoyl-cAMP (6-Bnz-cAMP). Newborn rat pancreatic islets in monolayer cell culture were preincubated in low-glucose medium (1.6 mM) for 2 hr before being switched to high glucose (11.1 mM). The cAMP analogs and/or 10 nM IGF-1 were added together with the high-glucose medium. After incubation for 30 min the medium was analyzed for immunoreactive insulin (IRI). Experiments under each set of conditions were carried out in triplicate. IGF-1 suppressed insulin secretion potentiated by 8-Br-cAMP (a relatively good PDE3B substrate) but had little or no effect on the insulin secretion potentiated by N6-benzoyl-cAMP, an analog highly resistant to hydrolysis by PDE3B. Twenty-five units of IRI = 1 mg of insulin.