Quantitative in-situ hybridization histochemistry in the rat pituitary gland: effect of bromocriptine on prolactin and pro-opiomelanocortin gene expression.

The temporal effect of orally administered bromocriptine on pro-opiomelanocortin (POMC) and prolactin gene expression in male Sprague-Dawley rats was examined using in-situ hybridization histochemistry. Messenger RNA in the anterior and intermediate lobes could be clearly delineated in each section. Administration of bromocriptine resulted in a reduction in hybridization of 35S-labelled cDNA probe to prolactin mRNA from 0.69 x 10(12) to 0.29 x 10(12) copies bound/g after 150 h. POMC mRNA in the anterior lobe remained unchanged with 0.08 x 10(12) copies of probe bound/g for the duration of the experiment, while in the intermediate lobe it decreased from 2.44 x 10(12) to 0.44 x 10(12) copies of probe bound/g at 150 h. The rate of reduction in intermediate lobe POMC mRNA was similar to that of prolactin mRNA for the first 24 h but was subsequently more rapid and more profound, falling to 20% of the control value at 84 h and to 18% at 150 h.