Effect of streptozotocin injection on expression of immunoreactive follistatin and beta A and beta B subunits of inhibin/activin in rat pancreatic islets.

The effect of streptozotocin (STZ) on expression of immunoreactive follistatin and beta-subunits of inhibin/activin in pancreatic islets was studied by immunohistochemistry. To localize immunoreactive follistatin in pancreatic islets, two different anti-follistatin sera were used. Anti-follistatin (300-315) serum detects only long-form follistatin, while anti-follistatin(123-134) serum detects both long- and C-terminal truncated short-form follistatin in sodium dodecyl sulfate polyacrylamide gel electrophoresis and immunoblotting. Although an intense reaction with anti-follistatin(123-134) was found in pancreatic B cells, a reaction with anti-follistatin(300-315) was not present in any type of cells. This result suggests that only short-form follistatin is expressed in pancreatic islets. It was confirmed that immunoreaction with anti-beta A(1-10)-Tyr serum was found in pancreatic B cells. The anti-beta B(1-10)-Tyr reaction was intense in A cells but weak in B cells. These findings suggest that the expression pattern of each beta-subunit differs in each type of islet cells. At 2 weeks after STZ injection (65 mg/kg), insulin immunoreaction still remained in B cells, although most pancreatic B cells were destroyed. In contrast, immunoreactions of follistatin and beta-subunits in B cells disappeared 24h after STZ treatment. These results indicate that STZ affects the production of follistatin or beta-subunits of inhibin/activin in pancreatic B cells rather than insulin secretion.