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Three TRH-like molecules are released from rat hypothalamus in vitro
1Departamento de Genética y Fisiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, MEXICO.
Neurochemical Research
|July 14, 1999
Summary
The hypothalamus secretes TRH-like molecules, including authentic TRH and two novel forms, possibly pglu-phe-proNH2. Pyroglutamyl aminopeptidase II degrades TRH in the hypothalamus.
Area of Science:
- Neuroendocrinology
- Molecular Endocrinology
- Hypothalamic-pituitary axis research
Background:
- Thyrotropin-releasing hormone (TRH) has known functions, but TRH-like immunoreactivity exists beyond authentic TRH.
- The secretion and nature of TRH-like molecules from the hypothalamus remain incompletely understood.
Purpose of the Study:
- To investigate the secretion of TRH-like molecules by the hypothalamus.
- To characterize novel TRH-like substances released from hypothalamic tissue.
- To explore the metabolic fate and enzymatic degradation of TRH in the hypothalamus.
Main Methods:
- Incubation of hypothalamic slices in Krebs Ringer bicarbonate solution under basal and high KCl conditions.
- Analysis of secreted TRH-like molecules using reverse-phase high-performance liquid chromatography (RP-HPLC) and TRH radioimmunoassay.
- Gel filtration chromatography to assess molecular weights of TRH-like forms.
- Incubation of hypothalamic slices with radiolabeled TRH ([3H-Pro]-TRH) to study post-secretory metabolism and identify degradation products.
- Enzyme inhibition studies to identify the specific aminopeptidase involved in TRH degradation.
Main Results:
- Three TRH-like molecules were detected in the media from incubated hypothalamic slices.
- Peak I corresponded to authentic TRH, while Peaks II and III exhibited different retention times on RP-HPLC.
- Peaks II and III were not detected in hypothalamic tissue or olfactory bulb samples.
- Gel filtration indicated that Peaks II and III have molecular weights similar to TRH.
- Peak II's retention time was comparable to pglu-phe-proNH2.
- [3H-Pro]-TRH incubation led to rapid degradation into [3H-Pro]-his-prodiketopiperazine ([3H]-HPDKP), not Peaks II or III.
- Inhibitor profiles implicated pyroglutamyl aminopeptidase II (not I) in [3H]-HPDKP production.
Conclusions:
- The hypothalamus actively secretes TRH-like molecules, including authentic TRH and at least two additional forms.
- One secreted TRH-like molecule may be pglu-phe-proNH2, potentially influencing adenohypophyseal secretions.
- Pyroglutamyl aminopeptidase II is likely the primary enzyme responsible for TRH degradation in the hypothalamic extracellular fluid.