CHANGES IN PROLACTIN SECRETION IN POSTNATAL RATS AND EFFECT OF NEONATAL THYROIDECTOMY

The prolactin (PRL) gene expression and PRL accumulation in rat pituit aries during the neonatal period were measured by means of radioimmuno assay and Northern blot analyses. The effects of neonatal thyroidectom y (Tx) on PRL synthesis and release were also investigated. The pituit ary PRL mRNA level at 20 fetal days had already reached levels suffici ent to detect and was increased markedly in the early neonatal period. The PRL concentrations in sera were at almost the same level during t he early neonatal period, but the increases of PRL contents and PRL mR NA levels were marked in this period. Neonatal Tx effectively decrease d the PRL mRNA level and PRL contents in the pituitary after 10 postna tal 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. (C) 1997 Elsevier Science Ireland Ltd.