Evidence for the kidney as an important source of 5′-monodeiodination activity and stimulation by somatostatin in Oreochromis niloticus L

Byamungu, N.; Mol, K.; Kohn, Elise

doi:10.1016/0016-6480(92)90251-e

Cited by 24 publications

(16 citation statements)

References 30 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The fact that total trout liver 5Ј-deiodinase activity saturates at low T 4 concentrations (10 nm) is probably the explanation for the previous failure to clearly identify type I activity in teleostean liver and for the observation that ORD had a low (7,26) or ultra-low T 4 -K m type I activity (8). Nevertheless, present results in trout liver and previous reports in tilapia kidney (22,25) have clearly shown the presence of rT 3 -ORD activity with the kinetic characteristics of mammalian type I. Of note is the fact that, when used at high substrate concentrations, both rT 3 (present results, 22,25) and T 4 -ORD (6) consistently exhibit a conspicuous, albeit partial, resistance to PTU.…”

Section: Discussioncontrasting

confidence: 56%

“…Nevertheless, present results in trout liver and previous reports in tilapia kidney (22,25) have clearly shown the presence of rT 3 -ORD activity with the kinetic characteristics of mammalian type I. Of note is the fact that, when used at high substrate concentrations, both rT 3 (present results, 22,25) and T 4 -ORD (6) consistently exhibit a conspicuous, albeit partial, resistance to PTU.…”

Section: Discussioncontrasting

confidence: 36%

“…On the contrary, the single component is a reflection of the relatively low type I-mediated T 4 ORD and of the limitations imposed by the specific activity of 125 I-T 4 to measure the release of 125 I when the predominant pathway of deiodination is the type II. Thus, it has been demonstrated previously that T 4 -ORD can be detected in trout liver at higher substrate concentrations if the activity is measured by the production of T 3 by RIA (7,21,22), which would not be possible if the activity were measured by the release of 125 I, because, at high substrate concentrations, the fractional rate deiodination is very low (Fig. 2).…”

Section: Discussionmentioning

confidence: 99%

See 2 more Smart Citations

Rainbow Trout Liver Expresses Two Iodothyronine Phenolic Ring Deiodinase Pathways with the Characteristics of Mammalian Types I and II 5'-Deiodinases

Orozco¹

1997

Endocrinology

View full text Add to dashboard Cite

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 T 3 (rT 3 ) and T 4 as substrates. The use of rT 3 disclosed two enzymatic components with the characteristics of mammalian types I and II 5Ј-deiodinases. The high rT 3 -K m type I 5Ј-deiodinase activity (180 nM) has a low cofactor requirement (5 mM dithiothreitol) and is relatively sensitive to propylthiouracil inhibition, whereas the low rT 3 -K m activity was akin to the outer ring deiodination of T 4 in these regards. The use of T 4 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 V max of this enzyme is as high as that found in comparable homogenates from hypothyroid mammalian tissues, whereas the V max of the type I activity is lower than that of mammalian liver. These findings are in consonance with the peculiar kinetics of T 3 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. (Endocrinology 138: 254 -258, 1997) T HE THYROID gland secretes predominantly T 4 , which functions primarily as a prohormone because it is largely converted to T 3 in peripheral tissues. T 3 is about 10 times more active than T 4 and is produced in an organspecific manner by enzymatic outer ring deiodination (ORD) of its precursor. In mammalian species, ORD is catalyzed by two distinct enzymes, well characterized in operational terms and tissue distribution: the type I and type II 5Ј-deiodinases (1-3).The complement of deiodinases present in vertebrate liver varies with the species and developmental stage of the organism. In fetal rats, for example, the liver expresses both type II and type III (an inner ring deiodinase), whereas, after birth, type I activity predominates (Aceves, C., unpublished data from our laboratory). Chicken embryo liver exhibits types I and II (4), whereas, in developing tadpoles, only type III is expressed (5). However variable the expression of deiodinases could be during ontogeny, adult liver of vertebrate species expresses predominantly, if not exclusively, type I deiodinase activity. In fish liver, it seems that two ORD processes are present, but it is not clear whether they correspond to the types I and II mammalian deiodinase activities (6 -8). In trout, for example, enzyme kinetic analyses have demonstrated vastly differing K m values for hepatic T 4 -ORD. Whereas initial studies reported K m values of 190 nm (6) and 13 nm (7), a subsequent report by Mac Latchy and Eales (8) has suggested that tw...

show abstract

Section: Discussioncontrasting

confidence: 56%

Section: Discussioncontrasting

confidence: 36%

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Rainbow Trout Liver Expresses Two Iodothyronine Phenolic Ring Deiodinase Pathways with the Characteristics of Mammalian Types I and II 5'-Deiodinases

Orozco¹

1997

Endocrinology

View full text Add to dashboard Cite

show abstract

“…However, recently Sweeting and Eales (1992) found no direct effect of GH on the conversion of T 4 into T 3 in isolated hepatocytes of rainbow trout. In Oreochromis, administration of ovine GH raises only plasma T 4 , but not T 3 concentrations, while somatostatin can increase the conversion of T 4 into T 3 (Byamungu et al 1991(Byamungu et al , 1992. Furthermore, deiodinating enzymes in tilapia liver and kidney show common characteristics to the mammalian type II and I, respectively ) and, as in higher vertebrates, a T 3 -degrading enzyme (possibly type III) is present in liver and gill of rainbow trout (MacLatchy and Eales 1993).…”

Section: Maymentioning

confidence: 99%

Hormonal profile of growing male and female diploids and triploids of the blue tilapia,Oreochromis aureus, reared in intensive culture

Mol

Byamungu

Cuisset

et al. 1994

Fish Physiol Biochem

Self Cite

View full text Add to dashboard Cite

Triploidy as a result of thermal shock exposure of fertilized eggs decreases the growth rate ofOreochromis aureus as compared to their diploid controls, but this is due to the higher female ratio present in triploids (86%) and the lower growth rate of females. When females and males are considered separately, the growth rate is not significantly different in diploids and triploids. Since triploidy results in a malfunctioning steroidogenesis in females (mainly testosterone (T) and 17β-estradiol (E2)), but does not affect the growth rate, it is concluded that female gonadal steroids do not influence growth unless in pharmacological concentrations. These low levels of gonadal steroids are generally accompanied by higher levels of gonadotropin (GtH), but the difference is not always significant.Despite their lower growth rate diploid females have higher plasma concentrations of growth hormone (GH) during several months compared to the triploid females and diploid males. 3,5,3'-triiodo-L-thyronine (T3) levels, however, are comparable between diploid and triploid females (except for 1 month), but higher in diploid males in 4 of the 5 months studied. 11-ketotestosterone (11kT) is always higher in males. These results indicate that the higher growth rate of males may be related to the high circulating levels of T3 and 11kT.

show abstract

“…Free T 4 enters cells of peripheral tissue (brain, liver, gill, kidney, heart and muscle) and is then deiodinated to form triidothyronine, (T 3 ) by L-thyroxine 5'monodeiodinase (MDI), the enzyme responsible for peripheral conversion of T 4 to T 3 Leatherland et al 1990;Byamungu et al 1992;Eales, 1990, 1992;Eales et al 1993a,b). Eales and Brown (1993) suggest that in teleosts the 'peripheral model' of plasma T 3 regulation by MDI activity predominates over the 'central model' via the hypothalamic-hypophyseal-thyroidal axis.…”

Section: Plasma Thyroid Hormonesmentioning

confidence: 99%

Endocrine, Physiological and Histopathological Responses of Fish and their Larvae to Stress with Emphasis on Exposure to Crude Oil and Various Petroleum Hydrocarbons

Alkindi

Brown

Waring

2000

SQU Journal for Science

View full text Add to dashboard Cite

ABSTRACT:Various endocrine and physiological responses of fish exposed to forceful physical and chemical stimuli are reviewed with emphasis on the effects of crude oils and their hydrocarbon constituents. The chemistry and toxicity of petroleum hydrocarbons are examined and methods for experimental exposure of fish to crude oil and petroleum hydrocarbons are considered. A variety of blood-borne parameters recognized as reliable tools in determining the relative severity of stress in fish are reviewed. The effects of stress and petroleum hydrocarbons on endocrine responses including changes in plasma AL-KINDI, BROWN, and WARING catecholamines, corticosteroids, and thyroid hormones are reviewed. The physiological responses: changes in plasma glucose, osmotic and ionic regulation, blood oxygen, hematocrit and hemoglobin concentration are explored, and histopathological effects of crude oil on fish are reviewed. Recent studies of the effects of petroleum hydrocarbons on fish larvae are considered and the increased sensitivity of the early life stages of fish are highlighted.

show abstract

Evidence for the kidney as an important source of 5′-monodeiodination activity and stimulation by somatostatin in Oreochromis niloticus L

Cited by 24 publications

References 30 publications

Rainbow Trout Liver Expresses Two Iodothyronine Phenolic Ring Deiodinase Pathways with the Characteristics of Mammalian Types I and II 5'-Deiodinases

Rainbow Trout Liver Expresses Two Iodothyronine Phenolic Ring Deiodinase Pathways with the Characteristics of Mammalian Types I and II 5'-Deiodinases

Hormonal profile of growing male and female diploids and triploids of the blue tilapia,Oreochromis aureus, reared in intensive culture

Endocrine, Physiological and Histopathological Responses of Fish and their Larvae to Stress with Emphasis on Exposure to Crude Oil and Various Petroleum Hydrocarbons

Contact Info

Product

Resources

About