Abstract
It is still undetermined which GTP-binding (G) protein is involved in the regulation of prolactin (PRL) release and through which effector. This study shows that, when compared to normal pituitary tissue, the levels of αo protein were very low in dopamine (DA)-resistant, PRL-secreting pituitary tumors 7315a and MtTW15, while αo mRNA was present in the two tumors. In the MtTW15 tumor αil, αi2 and αi3 levels were decreased while those of αs42 and αs47 were increased, and in the 7315a tumor αi2, αi3 and β levels were decreased and those of αs47 increased. In an estrone-induced, DA-sensitive prolactinoma the levels of ι3 were greatly reduced. DA was unable to inhibit basal PRL release by 7315a and MtTW15 and basal cAMP accumulation by adenomatous and MtTW15 cells. Vasoactive intestinal peptide (VIP) increased both cAMP accumulation and PRL release by all cell preparations which could be suppressed by DA with adenomatous and 7315a but not with MtTW15 cells. These and previously published results provide circumstantial evidence that αo, αil and αi3 are all involved in the transduction of the DA inhibitory message while αs47 transduces cAMP activating messages and αs42 is responsible for the constitutive activation of L-type Ca 2+ channels, adenylate cyclase and baseline PRL release.
Published Version
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