The effect of vasoactive intestinal peptide (VIP) on prolactin (PRL) secretion from pituitary cells is reviewed and compared to the effect of thyrotropin releasing hormone (TRH). These two peptides induced different secretion profiles from parafused lactotrophs in culture. TRH was found to increase PRL secretion within 4 s and induced a biphasic secretion pattern, while VIP induced a monophasic secretion pattern after a lag time of 45–60 s.

The secretion profiles are compared to changes in adenylate cyclase activity, production of inositol polyphosphates, changes in intracellular calcium concentrations and changes in electrophysiological properties of the cell membrane.

Abbreviations AC, adenylate cyclase; DG, diacyglycerol; GH, growth hormone; GTP, guanosine trisphosphate; Gi, GTP binding proteins that mediate inhibition of adenylate cyclase and that are pertussis toxin sensitive; Gs, GTP binding protein that mediates stimulation of adenylate cyclase; GH cells, clonal rat pituitary tumor cells producing PRL and/or growth hormone; GH3 GH4C1 and GH4B6, subclones of GH cells; PKA, protein kinase A; PKC, protein kinase C; PLC, phospholipase C; PRL, prolactin; TPA, 12-O-tetradecanoyl phorbol 13-acetate; TRH, thyrotropin releasing hormone; VIP, vasoactive intestinal peptide

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