Presence and regulation of a truncated proopiomelanocortin gene transcript in rat pancreatic islets.

The demonstration of proopiomelanocortin-(POMC-) derived peptides in the endocrine pancreas suggests a local biosynthesis of these peptides. Using Northern blot analysis we demonstrated a 800 nucleotide POMC-like mRNA species. The POMC-like mRNA was demonstrable in a part of the pancreatic islets by the in situ hybridization technique. A small number of single cells within the exocrine pancreas were also found to give positive hybridization signals. Isolated islets were incubated under normoglycemic conditions with dibutyryl-cAMP (3mM) or dexamethasone (0.1mM) for 4 h. Dibutyryl-cAMP significantly (p < 0.01) increased the POMC-like mRNA content to 177 +/- 39.1% of the control whereas dexamethasone decreased it to 66.9 +/- 11.4% of the control. In vivo treatment of adult rats with 80 micrograms dexamethasone over 3 days showed also a reduction of the POMC-like mRNA level in the islets. In conclusions, the POMC gene is expressed in adult rat islets and can be regulated by dexamethasone and dibutyryl-cAMP. Whether the truncated POMC-like mRNA reported here is the source of the biosynthetic POMC-like products detected in the islets is not yet known.