Bromocriptine reduces rat thyrotropin beta-subunit mRNA stability

We have examined the effect of orally administered bromocriptine on TSH beta-subunit messenger (m)RNA in the anterior pituitary glands of Sprague-Dawley rats using in situ and dot-blot hybridization histochemistry. Quantitative in situ hybridization of pituitary sections demonstrated a 60% reduction in TSH beta-subunit mRNA probe binding from rats fed a diet containing bromocriptine 10 mg/kg/day. This was confirmed by dot-blot analysis of nuclear and cytoplasmic pituitary extracts from the same tissue. Hybridization of cytoplasmic extracts of pituitary cells cultured under actinomycin D-induced transcription arrest showed that part of the effect of bromocriptine appeared to be mediated through a change in TSH beta-subunit mRNA stability and implies that the acute influence of dopamine on TSH metabolism may be transduced by control of TSH beta-subunit mRNA catabolism. This suggests a mechanism by which cells with relatively stable tissue specific mRNAs appear to respond rapidly to hormonal effects at the transcriptional level.