Hormone-stimulated redistribution of gonadotrope protein kinase C in vivo: dependence on Ca2+ influx.

In the present study we show that natural sequence gonadotropin-releasing hormone (GnRH) and a high affinity, metabolically stable agonist (Buserelin) promote redistribution of protein kinase C (PKC) activity to a particulate fraction prepared from anterior pituitary. The action of the agonists, administered in vivo to ovariectomized rats, is both time and dose dependent. GnRH antagonist alone does not measurably alter distribution of this enzymatic activity but inhibits the ability of GnRH to do so and to stimulate luteinizing hormone release. This finding indicates that receptor occupancy alone is insufficient to cause PKC redistribution. Redistribution of PKC in response to Buserelin is inhibited by the calcium ion channel antagonist methoxyverapamil (D600), suggesting that redistribution of PKC activity, like GnRH-stimulated gonadotropin release, requires the influx of extracellular calcium.