SIGNALING PATHWAYS MEDIATING SECRETORY AND MITOGENIC RESPONSES TO GALANIN AND PITUITARY ADENYLATE CYCLASE-ACTIVATING POLYPEPTIDE IN THE 235-1 CLONAL RAT LACTOTROPH CELL-LINE

The neuropeptides galanin and pituitary adenylate cyclase-activating p eptide (PACAP) have been implicated in the physiological regulation of lactotroph function. Using the 235-1 clonal lactotroph rat cell line we have studied the signalling pathways mediating the secretory and mi togenic responses to galanin and PACAP. Both peptides stimulated prola ctin release to a similar maximal extent. PACAP (100 nM) stimulated an increase in the proliferation rate of 235-1 cells, but was significan tly less effective than 100 nM galanin (161.8+/-2.3% vs 296.1+/-9.1% o f control). PACAP stimulated cAMP accumulation with an ED(50) of 3.2 n M, and a maximal effect of almost two-fold at a concentration of 100 n M. Galanin depleted cAMP, by 30% at a concentration of 100 nM. The ami nosteroid phospholipase C (PLC) inhibitor U-73122 virtually abolished maximal peptide stimulated prolactin release. Depletion of inositol ph osphates or downregulation of protein kinase C reduced maximal peptide stimulated prolactin release from about 260% to about 160% of unstimu lated release. Both peptides at a concentration of 100 nM caused a sus tained increase in intracellular calcium when incubated with cells for 30 min. These results demonstrate that both peptides stimulate prolac tin release and the proliferation rate of 235-1 cells. The most import ant signalling pathway for prolactin release activated by both peptide s is via PLC, although they also regulate cAMP levels, which are incre ased by PACAP and decreased by galanin. Despite maximal peptide stimul ated prolactin release being equal,galanin has a greater mitogenic eff ect on 235-1 cells than PACAP, raising the possibility that it activat es an additional mitogenic signalling pathway.