DELAYED ACTIVATION OF PHOSPHOLIPASE-D BY GONADOTROPIN-RELEASING-HORMONE IN A CLONAL PITUITARY GONADOTROPE CELL-LINE (ALPHA-T3-1)

Stimulation of cultured pituitary cells from a gonadotrope lineage (alpha-T3-1) by the gonadotropin-releasing hormone agonist analog [D-Trp6]GnRH (GnRH-A) resulted in a manifold increase in accumulation of phosphatidylethanol, a specific product of phospholipase D phosphatidyl transferase activity when ethanol is the phosphatidyl group acceptor. Levels of the natural lipid product of phospholipase D, phosphatidic acid, were increased 2-3-fold. Activation of phospholipase D by GnRH-A was dose- and time-dependent and was blocked by a GnRH receptor antagonist [D-pClPhe2, D-Trp3.6]GnRH. GnRH-A stimulated phospholipase D activity after a lag of 1-2 min. We conclude that in alpha-T3-1 gonadotropes GnRH receptor occupancy results in delayed activation of phospholipase D which could participate in late phases of gonadotrope regulation by the neurohormone.