[3-Me-His(2)]-TRH combined with dopamine withdrawal rapidly and transiently increases pyroglutamyl aminopeptidase II activity in primary cultures of adenohypophyseal cells.

TRH is hydrolyzed by pyroglutamyl aminopeptidase II (PP II), a highly specific ecto-enzyme which is localized on the surface of lactotrophs. To study whether PP II activity may be rapidly regulated during a burst of prolactin secretion, we used an in vitro model in which primary cultures of adenohypophyseal cells were incubated with 500 nM dopamine (DA) for 24 h prior to treatments. We observed a rapid increase of PP II activity when 100 nM [3-Me-His(2)]-TRH, a TRH agonist, was added at removal of DA.

Multiple hypothalamic factors regulate pyroglutamyl peptidase II in cultures of adenohypophyseal cells: role of the cAMP pathway.

In the adenohypophysis, thyrotrophin-releasing hormone (TRH) is inactivated by pyroglutamyl peptidase II (PPII), a TRH-specific ectoenzyme localized in lactotrophs. TRH slowly downregulates surface PPII activity in adenohypophyseal cell cultures. Protein kinase C (PKC) activation mimics this effect.