Ontogeny of glucagon messenger RNA in the rat pancreas.

The synthesis of proglucagon mRNA was studied in rat pancreas from day 11 of fetal gestation (E11) to maturity. Proglucagon mRNA was first detected on E11, the time that the pancreatic bud forms in developing rats. The synthesis of proglucagon mRNA and its translation product at this early time point in pancreatic development suggests an early differentiation of A cell function. Between E17 prenatally and day 10-14 postnatally, pancreatic proglucagon mRNA abundance was higher than in adult pancreas. Regulation of the abundance of pancreatic proglucagon mRNA therefore appears to underlie the previously documented increases in serum and pancreatic glucagon immunoreactivity in the late fetal and perinatal periods. By day 20 postnatally, pancreatic proglucagon mRNA declined to levels found in adult pancreas. Prenatally between E17 and E21, changes in proglucagon mRNA abundance did not parallel previously reported developmental changes in relative mass of proglucagon-producing pancreatic A cells. This suggests that changes in proglucagon mRNA abundance during these times may be attributed to changes in proglucagon gene transcription or proglucagon mRNA stability per cell. In contrast between E21 and maturity, changes in proglucagon mRNA abundance paralleled previously reported changes in relative A cell mass, suggesting no major changes in proglucagon gene transcription or mRNA stability per cell during these times.