Gonadotropin-releasing hormone modulation of protein kinase-C activity in perifused anterior pituitary cell cultures.

The ability of GnRH to modulate protein kinase-C (PKC) activity was examined in perifused rat pituitary cell cultures. Under these conditions, LH release and GnRH receptor number remained unchanged after repeated pulses of 1 nM GnRM, whereas PKC (measured both enzymatically and by radioligand assay) showed an initial increase in kinase activity after the first pulse of GnRH (approximately 2-fold), followed by down-regulation of PKC activity with subsequent pulses of the releasing hormone. It was also observed that the GnRH-stimulated down-regulation of PKC was dependent on the presence of extracellular calcium, which was not the case for the initial up-regulation of PKC. These findings are consistent with a modulating role of the GnRH receptor on PKC activity through a Ca2(+)-dependent process. This study also provides further evidence that GnRH-stimulated LH release and PKC activity can be uncoupled.