Changes in prolactin secretion in postnatal rats and effect of neonatal thyroidectomy

The prolactin (PRL) gene expression and PRL accumulation in rat pituitaries during the neonatal period were measured by means of radioimmunoassay and Northern blot analyses. The effects of neonatal thyroidectomy (Tx) on PRL synthesis and release were also investigated. The pituitary PRL mRNA level at 20 fetal days had already reached levels sufficient to detect and was increased markedly in the early neonatal period. The PRL concentrations in sera were at almost the same level during the early neonatal period, but the increases of PRL contents and PRL mRNA levels were marked in this period. Neonatal Tx effectively decreased the PRL mRNA level and PRL contents in the pituitary after 10 postnatal days. A significant decrease in the serum PRL of the Tx group was first observed at 20 postnatal days. These data indicate that thyroid hormone dependent PRL secretion is established in the neonatal period.