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C Valverde-R

Publications and source records attributed to C Valverde-R.

10 recordsLinked to original sources
PubMed2004

Comparative kinetic characterization of rat thyroid iodotyrosine dehalogenase and iodothyronine deiodinase type 1.

The initial characterization of a thyroid iodotyrosine dehalogenase (tDh), which deiodinates mono-iodotyrosine and di-iodotyrosine, was made almost 50 years ago, but little is known about its catalytic and kinetic properties. A distinct group of dehalogenases, the so-called iodothyronine deiodinases (IDs), that specifically remove iodine atoms from iodothyronines were subsequently discovered and have been extensively characterized. Iodothyronine deiodinase type 1 (ID1) is highly expressed in the rat thyroid gland, but the co-expression in this tissue of the two different dehalogenating enzymes has not yet been clearly defined. This work compares and contrasts the kinetic properties of tDh and ID1 in the rat thyroid gland. Differential affinities for substrates, cofactors and inhibitors distinguish the two activities, and a reaction mechanism for tDh is proposed. The results reported here support the view that the rat thyroid gland has a distinctive set of dehalogenases specialized in iodine metabolism.

Animals↗
PubMed2000

Hepatic outer-ring deiodinase in a Mexican endemic lizard (Sceloporus grammicus).

The kinetic characterization of the outer-ring deiodination pathway using rT(3) (rT(3)-ORD) in male, female, and pregnant female livers of an endemic lizard, Sceloporus grammicus, is reported. The ORD pathway does not have the characteristics of deiodinase type II; it is exclusively carried out by deiodinase type I (DI). DI enzymatic activity in lizard liver contains one of the highest activities reported in vertebrates. This activity is sexually dimorphic, with males presenting the highest activity during the reproductive season. The properties of this enzyme correspond to those described in mammals, such as specificity for rT(3), susceptibility to inhibition by 6-n-propyl-2-thiouracil and gold-thioglucose, cofactor requirement, and kinetic pattern. Unlike other vertebrates, the lizard DI exhibits conspicuous stability in the thermal range of 15 to 42 degrees C and in the pH range of 5.0 to 9.0. Male true kinetic constants exhibit a direct correlation with temperature. This is in agreement with short-term adaptation to microenvironmental changes and the feasible expression of enzymatic forms/variants which, together, endow this lizard species with a greater adaptation to natural daily ambient thermal fluctuations.

Animals↗
PubMed1997

Rainbow trout liver expresses two iodothyronine phenolic ring deiodinase pathways with the characteristics of mammalian types I and II 5'-deiodinases.

Deiodinases are major determinants of thyroid hormone tissue availability and disposal. The knowledge of the expression of these enzymes in lower species is important to understand evolutionary and ontogenetic aspects of thyroid hormone action and metabolism. Here we have studied outer ring deiodination in the trout liver using both reverse T3 (rT3) and T4 as substrates. The use of rT3 disclosed two enzymatic components with the characteristics of mammalian types I and II 5'-deiodinases. The high rT3-K(m) type I 5'-deiodinase activity (180 nM) has a low cofactor requirement (5 mM dithiothreitol) and is relatively sensitive to propylthiouracil inhibition, whereas the low rT3-K(m) activity was akin to the outer ring deiodination of T4 in these regards. The use of T4 exhibited only a single type of activity with a low K(m) (0.63 nM), a relatively high cofactor requirement (25 mM dithiothreitol), and propylthiouracil-resistance. Teleosts constitute a unique example of type II activity expression in the liver of an adult vertebrate. Furthermore, the Vmax of this enzyme is as high as that found in comparable homogenates from hypothyroid mammalian tissues, whereas the Vmax of the type I activity is lower than that of mammalian liver. These findings are in consonance with the peculiar kinetics of T3 in trout liver, kinetics remarkably similar to those of the mammalian pituitary, cerebral cortex, and brown adipose tissue, which also preferentially express type II deiodinase.

Animals↗
PubMed1997

Mammary gland type I iodothyronine deiodinase is encoded by a short messenger ribonucleic acid.

Lactating rat mammary gland expresses a deiodinating activity that, on the basis of kinetic characteristics, corresponds to the so-called 5'-deiodinase type I (D1). In the present study we amplified and sequenced several D1 complementary DNA (cDNA) fragments from rat lactating mammary gland. The mammary cDNA was found to be identical to the previously reported rat liver cDNA in the coding region, but 465 nucleotides shorter on its 3'-untranslated region, suggesting that the D1 is the same in both tissues. D1 messenger RNA (mRNA) was also detected by reverse transcriptase-PCR in mammary glands from puberal and late pregnant rats, but not in virgin animals. Densitometric analysis showed a close and direct correlation between mRNA content and enzyme specific activity in mammary gland. Our results also show that rat liver contains both D1 mRNA forms and that the large form may respond to the thyroid status. These data suggest a differential and organ-specific expression of these mRNA forms, which could play a role in the functional regulation of D1 activity.

Animals↗
PubMed1993

Ontogenesis of iodothyronine deiodinase activities in brain and liver of the chick embryo.

The ontogeny of 5'-monodeiodinase activity (5'-MA) was analyzed in chick embryo brain and liver tissue. The enzymatic type predominant in this path and the activity of the deactivating pathway (5 MA-III) were determined during certain periods of neural development in both organs. Results show that T3 is predominantly formed in both organs during the first third of embryogenesis (from day 5) until neuroblast proliferation (day 13). Within this lapse, the slow type II enzyme (insensible to propylthiouracil) is present in the brain, whereas in the liver the predominating enzyme is type I (the rapid enzyme). Further along the synaptogenesis period (day 14-17), 5' deiodination virtually disappears in the brain, the hepatic type I enzyme switches to the slow autoconsume enzyme (type II), and 5 MA-III levels increase significantly in both organs. Finally, on days 18-20 (perinatal period) the 5' pathway reaches the highest levels observed throughout the study in both tissues. Associated to this increase, liver enzymatic activity returns to type I. During this period, 5 MA-III is reduced by 40% in the brain and disappears from the liver. Together, these data strengthen the notion of a protective mechanism against brain overexposure to T3 during synaptogenesis and suggest that the protective mechanism also involves the regulation of extraneural deiodinases.

Animals↗
PubMed1978

Serum growth hormone and ultrastructural studies of adenohypophysial tissue in bromocriptine treated acromegalic patients.

The therapeutic effectiveness of bromocriptine as well as the post-operative ultrastructural aspects of treated pituitary adenomas were investigated in five acromegalic patients. Although concentrations of GH basal decreased and the glucose tolerance test and the TSH responses were significantly improved, the release of GH induced by TRH was not prevented by the dopaminergic agonist. Adenomatous cells were densely granulated and contained a dilated endoplasmic reticulum. Misplaced exocytosis was frequently observed. These findings clearly indicate that bromocriptine inhibits the spontaneous release of GH but does not interfere with the abnormal GH response to TRH. This suggests a separate site of action. The drug seems not to block the synthesizing activity of the adenomatous cell, a finding in accordance with clinical observations that warns against its use as a single therapeutic agent.

Acromegaly↗