Thyrotropin-releasing hormone and lysine-bradykinin stimulate arachidonate liberation from rat anterior pituitary cells through different mechanisms.
TRH and lysine-bradykinin (Lys-bradykinin) increase PRL release and arachidonate liberation from anterior pituitary cells. We investigated whether the arachidonate liberation stimulated by TRH and Lys-bradykinin originates in pituitary lactotropes and whether these events are accomplished through similar mechanisms. Lys-bradykinin and TRH rapidly (0.5 min) increased the intracellular [3H]arachidonate content of rat anterior pituitary cells. Lys-bradykinin also increased [3H]arachidonate liberation and PRL release from lactotrope-enriched pituitary cells, but not from a pituitary cell preparation with a diminished number of lactotropes. In contrast, TRH increased [3H]arachidonate liberation from both lactotrope-enriched and lactotrope-diminished preparations; this increased [3H]arachidonate liberation stimulated by TRH in the lactotrope-diminished cells may originate in the thyrotropes. The effects of TRH and Lys-bradykinin on [3H]arachidonate and [14C]stearate liberation in perfused pituitary cells also were determined. Both secretagogues increased arachidonate and stearate liberation in a biphasic manner, characterized by a transient spike, followed by a lower magnitude wave of fatty acid release. The spike phase produced by Lys-bradykinin was more pronounced than that produced by TRH. The calcium dependence of TRH- and Lys-bradykinin-stimulated arachidonate liberation also was investigated. Cobalt and the low calcium medium containing ionomycin were used to block the secretagogue-induced increase in intracellular calcium concentrations. These conditions blocked TRH-stimulated arachidonate liberation, but only marginally decreased Lys-bradykinin-stimulated arachidonate liberation, indicating that the two peptides act through different mechanisms. Therefore, TRH stimulation of arachidonate liberation is linked to an increase in intracellular calcium. In contrast, Lys-bradykinin increases arachidonate liberation through a calcium-independent intracellular mediator. This calcium-independent increase in arachidonate liberation may involve the bradykinin receptor being coupled directly to a phospholipase, a G-protein that provides a link between the bradykinin receptor and the phospholipases that liberate arachidonate, or bradykinin-induced activation of a protein kinase-C that activates the phospholipases and subsequently liberates arachidonate.
Judd
A M
AM
Department of Internal Medicine, University of Virginia Health Sciences Center, Charlottesville 22908.
MacLeod
R M
RM
D000818:Animals; D001095:Arachidonic Acids / Q000378:metabolism*; D002478:Cells, Cultured; D005260:Female; D007609:Kallidin / Q000494:pharmacology*; D007700:Kinetics; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D011388:Prolactin / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013229:Stearic Acids / Q000378:metabolism; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*; D013997:Time Factors; D014316:Tritium
D001095:Arachidonic Acids; D013229:Stearic Acids; D014316:Tritium; D007609:Kallidin; C031183:stearic acid; D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin