Adenosine 3',5'-monophosphate derivatives increase gonadotropin-releasing hormone receptors in cultured pituitary cells.

In this study the GnRH receptors (GnRH-R) in cultured rat pituitary cells were examined after treatment with GnRH and cyclic nucleotide derivatives. GnRH at doses of between 10(-11) and 10(-8) M caused GnRH-R increases, 10(-9) M resulting in a 50% stimulation of both GnRH-R and LH release. (Bu)2cAMP increased GnRH-R in a dose dependent manner, with a maximal 2-fold increase at 1 mM, with no effect on LH release in serum-containing medium. The time-course of both the GnRH and (Bu)2cAMP stimulation of GnRH-R was similar, with maximal levels being reached between 6-12 h. There was no difference in the GnRH receptor affinity subsequent to either GnRH or (Bu)2cAMP treatment. GnRH-R increases of 70% were observed when pituitary cells were treated with 1 mM cAMP and 8- bromocAMP , but n-butyric acid, adenosine, and cyclic guanosine monophosphate (all 1 mM) were not effective. Fifty eight millimolar KCl resulted in a 2-fold elevation of GnRH-R. Isobutylmethylxanthine (0.2 mM) did not affect basal receptor levels and slightly enhanced the GnRH-and potassium-stimulated increase of GnRH-R, whereas the increase caused by (Bu)2cAMP was completely prevented. Simultaneous treatment of cultured pituitary cells with either GnRH, KCl, or (Bu)2cAMP and cycloheximide completely prevented GnRH-R increases, while not affecting either basal or GnRH and KCl-stimulated LH secretion. None of the cyclic nucleotides stimulated LH release under the culture conditions employed to examine receptor regulation. However, when incubated in medium not containing serum, both (Bu)2cAMP and cyclic guanosine monophosphate stimulated significant LH release. When the pituitary cells were treated with GnRH in medium without serum, no increase in GnRH-R was measured, although LH release was unaffected. However, absence of serum in the medium did not affect either the K+ or (Bu)2cAMP stimulation of GnRH-R. The GnRH antagonist ( DpGlu1 , D-Phe2, D-Trp3,6) GnRH (1 microM) prevented both GnRH- and (Bu)2cAMP-induced increases in GnRH-R, although not that of 58 mM KCl. The antagonist also inhibited GnRH-stimulated LH secretion, although not that caused by KCl.(ABSTRACT TRUNCATED AT 400 WORDS)