Effect of thyroxine on pancreatic digestive enzymes and ornithine decarboxylase gene expression in neonatal rats

Background: Thyroxine has been shown to play a role in the development of exocrine pancreatic enzymes in neonatal rats. Methods: To further evaluate the regulatory mechanisms for thyroxine in pancreatic development, we examined the changes in the expression of pancreatic enzymes (amylase and trypsinogen) and ornithine decarboxylase (ODC) genes following daily injection of thyroxine for 5 and 10 days to neonatal rats (5 days old). Results: Total pancreatic proteins and DNA contents as well as the activity of ODC and exocrine enzymes were signifi cantly increased after 5 and 10 days of thyroxine treatment. These increases were associated with parallel alterations (to three to fourfold rise) in steady-state mRNA levels of both amylase and trypsinogen. In contrast, thyroxine only produced a 57-68% increase in steady-state ODC mRNA levels. Conclusions: These data suggest that thyroxine stimulated the express of amylase and trypsinogen genes partly due to increased transcriptional rate and/or decreased mRNA turnover. Thyroxine also stimulated ODC gene expression. However, the stimulatory mechanisms may involve transnational or posttranslational regulation of ODC and are independent of thyroxine effects.