Bombesin stimulates prolactin secretion from cultured rat pituitary tumour cells (GH 4C 1) via activation of phospholipase C

Bombesin (BBS) stimulated prolactin (PRL) secretion from monolayer cultures of rat pituitary tumour cells (GH 4C 1) in a dose-dependent manner with half maximal and maximal effect at 2 nM and 100 nM, respectively. No additional stimulatory effect on PRL secretion was seen when BBS was combined with thyroliberin (TRH) used in concentrations known to tive maximal effects, while the effects of BBS and vasoactive intestinal peptide (VIP) were additive. Using a parafusion system, BBS (1 μM) was found to increase PRL secretion within 4 s and the secretion profiles elicited by BBS and TRH (1 μM) were similar. Both BBS and TRH increased inositoltrisphosphate (IP 3) as well as inositolbisphosphate (IP 2) formation within 2 s. BBS also induced the same biphasic changes in the electrical membrane properties of GH 4C 1 cells as TRH, and both peptides caused a rapid and sustained increase in intracellular [Ca 2+]. These results suggest that BBS stimulates PRL secretion from the GH 4C 1 cells via a mechanism involving the immediate formation of IP 3 thus resembling the action of TRH.