CHANGES IN THE ULTRASTRUCTURAL DISTRIBUTION OF PROLACTIN AND GROWTH-HORMONE MESSENGER-RNAS IN PITUITARY-CELLS OF FEMALE RATS AFTER ESTROGENAND BROMOCRIPTINE TREATMENT, STUDIED USING IN-SITU HYBRIDIZATION WITHBIOTINYLATED OLIGONUCLEOTIDE PROBES

The expression and distribution of prolactin (PRL) mRNA and their alte rations induced by estrogen and bromocriptine were investigated using non-radioisotopic in situ hybridization (ISH) at the electron microsco pic (EM) level. Our EM-ISH studies using biotinylated oligonucleotide probes showed that estrogen induced whirling changes of the rough endo plasmic reticulum (RER) of female rat PRL cells and increased transcri ption of PRL genes located on the polysomes of the whirling RER. The p resence of mammosomatotroph cells in the rat pituitary gland was also verified in our EM-ISH studies. After bromocriptine administration, PR L cells contained many secretory granules due to the inhibition of sec retion. Pre- and post-embedding EM-ISH and northern hybridization stud ies revealed that bromocriptine induced the distorted, vesiculated, an d dilated RER, and also the suppressed PRL mRNA expression. The activi ty of protein kinase C (PKC), which mediates PRL gene expression, tend ed to be elevated by estrogen and suppressed by bromocriptine. Therefo re, it is considered that the ultrastructural and quantitative changes in PRL mRNA expression evoked by estrogen and bromocriptine may be me diated by the intracellular signal transduction system, including PKC.