An analogue of creatine increases TRH-stimulated prolactin secretion and phosphoinositide hydrolysis in rat pituitary tumor cells

Abstract

Prolactin (PRL)-secreting GH3 cells were grown, in vitro, with the creatine analogue beta-guanidinopropionic acid (GPA) added to the culture medium. After 5 days there was a small increase in basal and greatly increased thyrotropin-releasing hormone (TRH)-stimulated PRL secretion. The site of action of GPA is at the TRH-induced hydrolysis of phosphoinositides, since increased amounts of mono, bis and tris/tetrakis inositol phosphates were found in treated cells, while the PRL secretion induced by a phorbol ester or a calcium ionophore, treatments which mimic the second messages generated by inositol phospholipid hydrolysis, were not enhanced by GPA. The mechanism by which GPA increases phospholipase C activity has not been fully elucidated but may involve the activity of a controlling G protein.