The Role of Protein Kinase C in LH Release

To investigate the postreceptor mechanism, especially the role of proteinkinase C (C-kinase), in luteinizing hormone (LH) release from anterior pituitarycells, dispersed rat anterior pituitary cells were stimulated with luteinizinghormone-releasing hormone (LH-RH), [D-Ser (tBu)]6 des-Gly-NH102 ethylamide (Buserelin), 12-0-tetradecanoyl phorbol-13-acetate (TPA) and trifluoperazine (TFP) and the LH released into the medium was determined by radioimmunoassay.LH released by combined stimulation with TPA and eitherLH-RH or Buserelin was significantly less than that released by LH-RH orBuserelin alone (LH-RH: p<0.05; Buserelin: p<0.01). It is thought thatthis paradoxical phenomenon occurred due to desensitization accompanied bydown-regulation of LH-RH receptors induced by TPA. This hypothesis wassupported by the finding indicating that the binding capacity of LH-RH receptorsdecreased in a time-course manner during incubation with TPA. Theamount of LH released by combined stimulation with TPA and TFP wassignificantly greater than with TPA alone (P<0.01). This suggests that TFP has dual actions, i.e., facilitating and inhibiting LH release.