[3-Me-His2]-TRH combined with dopamine withdrawal rapidly and transiently increases pyroglutamyl aminopeptidase II activity in primary cultures of adenohypophyseal cells

• Published in: Neuropeptides (Edinburgh) 2000-04, Vol.34 (2), p.83-88
• Main Authors: Bourdais, J., Romero, F., Uriostegui, B., Cisneros, M., Joseph-Bravo, P., Charli, J.-L.
• Format: Article
• Language: English
• Subjects: Aminopeptidases - metabolism; Animals; Biological and medical sciences; Cells, Cultured; Dopamine - pharmacology; Female; Fundamental and applied biological sciences. Psychology; Hormones and neuropeptides. Regulation; Hypothalamus. Hypophysis. Epiphysis. Urophysis; Pituitary Gland, Anterior - cytology; Pituitary Gland, Anterior - enzymology; Pyrrolidonecarboxylic Acid - analogs & derivatives; Rats; Rats, Wistar; Thyrotropin-Releasing Hormone - agonists; Thyrotropin-Releasing Hormone - analogs & derivatives; Thyrotropin-Releasing Hormone - pharmacology; Vertebrates: endocrinology
• ISSN: 0143-4179; 1532-2785
• DOI: 10.1054/npep.2000.0796

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 500nM dopamine (DA) for 24h prior to treatments. We observed a rapid increase of PP II activity when 100nM [3-Me-His2]-TRH, a TRH agonist, was added at removal of DA. PPII activity was maximal after 20min of treatment and reduced to time 0 activity at 30min. Dopamine withdrawal alone, slightly and transiently, modified the enzyme activity: an initial activation at 15min was followed by a transient inhibition at 20min. The specific contribution of [3-Me-His2]-TRH in this paradigm was a transient enhancement of PP II activity. If DA was not removed, [3-Me-His2]-TRH was ineffective. These data demonstrate that during in vitro conditions that mimic a suckling episode, adenohypophyseal PP II activity is rapidly and reversibly adjusted.