DOPAMINE INHIBITS THE ARACHIDONATE AND PROLACTIN-RELEASE STIMULATED BY THYROTROPIN-RELEASING-HORMONE THROUGH AN ISLET-ACTIVATING PROTEIN-SENSITIVE GTP-BINDING PROTEIN IN ANTERIOR-PITUITARY-CELLS

Coupling of the dopamine (DA) receptor to the pathway of arachidonate (AA) through the islet-activating protein (IAP)-sensitive GTP-binding (G) protein was examined in primary cultures of anterior pituitary cells. The inhibitions by 1 μΜ DA of the stimulations of prolactin (PRL) release by 100 nM thyrotropin-releasing hormone and by 10 μΜ calcium ionophore Λ23187 were blocked by 100 ng/ml IAP. DA at I μΜ did not inhibit the release of [3H]-AA induced by 100 mU/ml phospholipase A2 (PLA2), but it inhibited the release of PRL induced by 100 mU/ml PLA2. This inhibition was blocked by 100 ng/ml IAP. IAP also blocked the inhibitions by DA of the releases of PRL by 5 μΜ AA and by 5 μΜ 5-hydroxyeicosatetraenoic acid. These results suggest that the DA receptor on lactotrophs is coupled to the pathway following the release of AA (lipoxygenase) through the IAP-sensitive G protein. © 1990 S. Karger AG, Basel.