Bombesin stimulates inositol polyphosphate production in GH4C1 pituitary tumor cells: comparison with TRH.
The hormones bombesin and thyrotropin-releasing hormone (TRH) stimulated formation of inositol- monophosphate, bisphosphate, trisphosphate and tetrakisphosphate with parallel time courses in GH4C1 cells, while a more polar inositol polyphosphate peak, consisting of inositol-pentakisphosphate and perhaps also inositol-hexakisphosphate, was unaffected by either hormone. Although bombesin and TRH had similar potencies in stimulating inositol trisphosphate production (Km = 30 nM and 40 nM, respectively), TRH was significantly more efficacious than bombesin. Maximal stimulation of inositol-1,4,5-trisphosphate formation by TRH was not further increased by addition of a maximally effective dose of bombesin, suggesting that the two hormones act through stimulation of a common pool of phospholipase C, and this enzyme pool can be fully stimulated by TRH, alone.
D000818:Animals; D001839:Bombesin / Q000494:pharmacology*; D002460:Cell Line; D007295:Inositol Phosphates / Q000096:biosynthesis*; D007700:Kinetics; D010911:Pituitary Neoplasms / Q000378:metabolism*; D051381:Rats; D013403:Sugar Phosphates / Q000096:biosynthesis*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*
D007295:Inositol Phosphates; D013403:Sugar Phosphates; D013973:Thyrotropin-Releasing Hormone; D001839:Bombesin