Activators of protein kinase C potentiate electrically stimulated hormone secretion from the rat's isolated neurohypophysis.

Two activators of protein kinase C, phorbol 12,13-dibutyrate (PDBu) and 1-oleoyl-2-acetylglycerol (OAG), augment electrically stimulated vasopressin and oxytocin secretion from the nerve terminals of the isolated rat neurointermediate lobe. The increased hormone release produced by PDBu is specific to the beta-phorbol conformation, and is dependent upon electrical stimulation in the presence of calcium. Furthermore, the potentiation of release was evident during low frequency stimulation (4 Hz) but not when the same number of pulses were applied at 20 Hz. This occlusion of the phorbol ester's effect by high-frequency stimulation suggests that activation of protein kinase C may play a role in the normal process of frequency-dependent facilitation of secretion in the neurohypophysial system.