Efecto del hipotiroidismo e hipertiroidismo sobre la actividad aminopeptidasa en plasma de ratas / Aminopeptidase activity and thyroid function in rats

Las alteraciones en la función del tiroides originan importantes cambios en la respuesta cardiovascular, en los que están implicados modificaciones en el sistema renina-angiotensina circulante (SRA) y otros péptidos vasoactivos. Las actividades aminopeptidasas (AP), a través del control de la hormona liberadora de la tirotropina (TRH), el SRA y otros péptidos vasoactivos como la vasopresina desempeñan un importante papel en el control de la función del tiroides y de la presión arterial. Con el fin de evaluar el papel de distintas aminopeptidasas plasmáticas en la función tiroidea, determinamos las actividades alanina (AlaAP), cistina (CysAP), piroglutamato (pGluAP), glutamato (GluAP) y aspartato (AspAP) aminopeptidasa, utilizando derivados de la naftilamida como sustratos en animales eu hipo e hipertiroideos. Los resultados demuestran que el hipertiroidismo disminuye significativamente las actividades pGluAP y CysAP, mientras que aumenta la actividad AlaAP.Sin embargo, no se observaron diferencias para las actividades AspAP y GluAP. El hipotirodismo incrementó significativamente los valores de AlaAP, no observándose diferencias en el resto de las actividades. Los presentes resultados apuntan a un papel preponderante de la actividad AlaAP (AP M) en lugar de la GluAP (AP A) en la regulación del SRA circulante, en modelos animales de hiper e hipotiroidismo (AU)

Soluble and membrane-bound pyroglutamyl-peptidase I activity in the developing cerebellum and brain cortex.

Developmental changes of soluble and particulate pyroglutamyl (pGlu)-peptidase I activities in the rat brain cortex and in the cerebellum are described in this work. The enzyme activity has been measured spectrofluorimetrically using pGlu-b-naphthylamide as substrate (in the presence and absence of EDTA and DTT, necessary activators of the enzyme) in both soluble and particulate fractions. In the soluble fraction of the cerebellum and brain cortex, pGlu-peptidase I activity is high in the perinatal period and decreases two or three folds subsequently, at a later stage in the cerebellum than in the brain cortex, reaching adult levels at the end of the first postnatal month. The decrease in the activity of pGlu-peptidase observed in this work coincides with increasing levels of brain thyroliberin concentration after the second postnatal week. The particulate pGlu-peptidase I activity, obtained after osmotic shock and high-salt treatment, shows less significant changes during brain development in the areas under study. It is suggested that cytosolic pGlu-peptidase I could play a part in the normal development of the rat central nervous system.

Pyroglutamyl peptidase: an overview of the three known enzymatic forms.

Pyroglutamyl peptidase can be classified as an omega peptidase which hydrolytically removes the amino terminal pyroglutamate (pGlu) residue from specific pyroglutamyl substrates. To date, three distinct forms of this enzyme have been identified in mammalian tissues. Type I is typically a cytosolic, cysteine peptidase displaying a broad pyroglutamyl substrate specificity and low molecular mass. Type II has been shown to be a membrane anchored metalloenzyme of high molecular mass with a narrow substrate specificity restricted to the hypothalamic releasing factor, thyrotropin-releasing hormone (TRH, pGlu-His-Pro-NH2). A third pyroglutamyl peptidase activity has also been observed in mammalian serum which displays biochemical characteristics remarkably similar to those of tissue Type II, namely a high molecular mass, sensitivity to metal chelating agents, and a narrow substrate specificity also restricted to TRH. This serum activity has subsequently been designated 'thyroliberinase'. This review surveys the biochemical, enzymatic, and structural properties of this interesting and unique class of peptidases. It also addresses the putative physiological roles which have been ascribed to these enzymes. Pyroglutamyl peptidase activities isolated and characterized from bacterial sources are also reviewed and compared with their mammalian counterparts.

Diurnal variation and left-right distribution of pyroglutamyl peptidase I activity in the rat brain and retina.

The thyroliberin and luliberin contents exhibit a diurnal rhythm within the brain and an asymmetrical distribution of both neuropeptides has been demonstrated in the hypothalamus. Since they have been described as substrates of pyroglutamyl peptidase I, this activity was analysed in several rat brain regions and other structures, in order to investigate its putative diurnal variations and changes in relation to the distribution of these neuropeptides and/or other susceptible substrates. Fluorometric activity was assayed in the retina, pituitary gland, superior cervical ganglia, pineal gland, some selected brain regions, and serum of adult male rats at six different time points of a 12:12 h light:dark cycle, using pyroglutamyl-beta-naphthylamide as substrate. A significant circadian rhythm was demonstrated in the retina, the hypothalamus, and the intermediate-posterior pituitary lobe. In addition, a small but significant asymmetrical distribution of this activity, at certain time points, was disclosed: The activity was higher in the left than in the right retina at 10 h of the light period, whereas it was predominant in the right side at 01 h of the dark period. Furthermore, the activity was higher in the left anterior than in the right hypothalamic area at 13 and 01 h. These results could be indicative of a role of this enzymatic activity in the control of the functional status of its endogenous substrates.

Possible role of neuropeptide degrading enzymes on thyroliberin secretion in fetal hypothalamic cultures grown in serum free medium.

In the present work, we have looked for the presence of two tissular neuropeptide degrading activities, the pyroglutamate aminopeptidase (PAP) and the post-proline cleaving enzyme (PPCE), in dissociated brain cell cultures. These two activities are present in extracts of cells grown in serum-free medium and are detected at a very low level in incubation media. Depolarization of hypothalamic neurons by 60 mM K+ does not specifically increase the level of PAP and PPCE in the medium. We have also used an inhibitor of PPCE: Z-Gly-ProCHN2. This compound can be left in contact with living cells without any toxicity, and in certain conditions of incubation blocks totally and irreversibly both PAP and PPCE. This blockade results in increased levels of TRH, intracellular as well as released into the medium, spontaneously and upon K+ depolarization. These results evidence the role of degradation processes in the mechanisms regulating peptide turn-over.