The role of pregnancy hormones in the regulation of Pdx-1 expression.

During pregnancy, pancreatic beta cells undergo changes that are probably due to an increase in the lactogenic hormones prolactin (PRL) and placental lactogen (PL). Since the transcription factor PDX-1 is involved in the regulation of the beta cell function and phenotype, we tested the possibility that the effect of PRL on beta cells was mediated by PDX-1. Exposure of islet cells to PRL in vitro resulted in increased levels of PDX-1 protein and mRNA and a stimulation of pdx-1 transcription. However, PDX-1 levels in islets exposed in vivo to high concentration of prolactin was similar to controls. In vitro studies suggested that the up-regulation of PDX-1 by PRL was opposed by glucocorticoids (GC) at concentrations similar to those present in pregnant and control female mice. We conclude that, although pdx-1 is a key regulator of beta cell specific genes, it does not appear to play a central role in the up-regulation of islet cell function during pregnancy.