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Adenosine 35'5'-Monophosphate Derivatives Increase Prolactin Synthesis and Prolactin Messenger Ribonucleic Acid Levels in Ergocryptine-Treated Pituitary Cells^*

RICHARD A. MAURER

Department of Physiology and Biophysics, University of Iowa, Iowa City, Iowa 52242

Abstract

Dopamine and dopamine agonists, such as ergocryptine, inhibit PRL synthesis and decrease PRL raRNA levels in pituitary cells. To examine the possible role of cAMP in mediating this response, cultures of dispersed rat pituitary cells were treated with ergocryptine and several cAMP analogs for 4 days, and the cells were then analyzed for PRL synthesis. Monobutyryl cAMP, 8-bromo cAMP, and chlorophenylthio cAMP were all found to partially block the ability of ergocryptine to inhibit PRL synthesis. Similar effects were obtained with the phosphodiesterase inhibitor isobutylmethylxanthine. Cholera toxin, which stimulates adenylate cyclase, also blocked ergocryptine effects on PRL synthesis. These findings demonstrate that increased levels of intracellular cAMP can prevent the dopaminergic inhibition of PRL synthesis. The effects of monobutyryl cAMP on PRL mRNA levels were also determined. Cells were treated with ergocryptine and various concentrations of monobutyryl cAMP for 4 days; then, the total cellular RNA was isolated, and PRL mRNA was quantitated by hybridization to a radiolabeled cDNA. Monobutyryl cAMP stimulated PRL synthesis and PRL mRNA levels in ergocryptine-treated cultures in a dose-dependent manner, and there was a very good correlation between increases in PRL synthesis and PRL mRNA levels. The effect of ergocryptine on cAMP levels in pituitary cells and the levels of cAMP secreted into the medium were also examined. Ergocryptine significantly inhibited cAMP secretion into the medium, and a much smaller inhibition of intracellular cAMP content was detected. When cells were treated with varying concentrations of ergocryptine, there was a very good correlation between the inhibition of cAMP levels and the inhibition of PRL synthesis. Thus, ergocryptine decreases cAMP levels in pituitary cells, and the addition of cAMP derivatives to pituitary cells can affect PRL synthesis and PRL mRNA levels. These results suggest that cAMP may have a role in mediating the dopaminergic inhibition of PRL synthesis and RL mRNA levels.

Footnotes

^* This work was supported by Grant AM-21803 from the NIH.

To whom requests for reprints should be addressed.

Received September 10, 1981.

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