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  • Bioscientifica  (8)
  • 1995-1999  (8)
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  • Bioscientifica  (8)
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  • 1995-1999  (8)
Year
  • 1
    Online Resource
    Online Resource
    Characterization of the binding of 3,3′-di-iodo-l-thyronine to rat liver mitochondria
    Bioscientifica ; 1997
    In:  Journal of Endocrinology Vol. 154, No. 1 ( 1997-07), p. 119-124
    Details
    In: Journal of Endocrinology, Bioscientifica, Vol. 154, No. 1 ( 1997-07), p. 119-124
    Abstract: The binding of labelled 3,3′-di-iodo-l-thyronine (3,3′-T 2 ) to isolated rat liver mitochondria has been characterized. Specific binding could be detected only in the inner mitochondrial membrane, not in other mitochondrial subfractions. The composition of the incubation medium influenced the binding capacity, the best combination of high specific binding and low non-specific binding being observed in phosphate buffer, pH 6·4. The specific binding of 3,3′-T 2 to mitochondria requires low ionic strength: concentrations of K + and Na + higher than 10 mmol/l and 0·1 mmol/l respectively resulted in a decreased binding capacity. The optimal calcium ion concentration was in the range 0·01–1·0 mmol/l. Varying magnesium ion, over the range of concentrations used (0·1–100 mmol/l), had no effect. Both ADP and ATP, at over 1 mmol/l, resulted in an inhibition of the specific binding. Incubation with protease resulted in a decrease in specific binding and an increase in non-specific binding, thus indicating the proteic nature of the binding sites. In addition to the above factors in the local environment the thyroid state of the animal might influence the 3,3′-T 2 -binding capacity. In fact, the thyroid state of the animal seemed not to have an influence on the affinity constant, but it did affect binding capacity. Journal of Endocrinology (1997) 154, 119–124
    Type of Medium: Online Resource
    ISSN: 0022-0795 , 1479-6805
    URL: Article
    DOI: 10.1677/joe.0.1540119
    Language: Unknown
    Publisher: Bioscientifica
    Publication Date: 1997
    detail.hit.zdb_id: 1474892-7
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  • 2
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    Online Resource
    Tissue-specific changes in angiotensin II receptors in streptozotocin-diabetic rats
    Bioscientifica ; 1997
    In:  Journal of Endocrinology Vol. 154, No. 2 ( 1997-08), p. 355-362
    Details
    In: Journal of Endocrinology, Bioscientifica, Vol. 154, No. 2 ( 1997-08), p. 355-362
    Abstract: While there have been reports on changes in the renin–angiotensin system and angiotensin II (AT) receptors in diabetes, there is no agreement on the nature of these changes. This study has characterised specific AT receptors in the heart, kidney, liver and adrenal glands of the streptozotocin (STZ)-diabetic rat using radioligand binding studies with the radioligand 125 I-[Sar 1 ,Ile 8 ]-angiotensin II. Left ventricular AT receptor density increased by 135% 4 weeks after treatment and by 206% 12 weeks after treatment; in the liver, AT receptor density increased by 476% (4 weeks) and 263% (12 weeks) and in the adrenal gland by 236% (4 weeks) and 109% (12 weeks). In contrast, renal AT receptor density decreased by 49% (4 weeks) and 36% (12 weeks). Competition-displacement assays with losartan, an AT1-selective ligand, showed that the proportion of AT receptor subtypes remained unchanged. STZ treatment decreased plasma angiotensinogen by 72% (4 weeks) and 67% (12 weeks) and increased plasma renin concentration after 12 weeks; plasma renin activity and aldosterone concentrations remained unchanged. Treatment with human insulin (5 U/day) attenuated changes in plasma angiotensinogen and AT receptor density except in the left ventricle. We conclude that there are major changes in AT receptors in the STZ-diabetic rat that are tissue-specific and time-dependent. Plasma angiotensinogen and renin secretion change in directions that result in the maintenance of plasma renin activity and aldosterone concentration. Journal of Endocrinology (1997) 154, 355–362
    Type of Medium: Online Resource
    ISSN: 0022-0795 , 1479-6805
    URL: Article
    DOI: 10.1677/joe.0.1540355
    Language: Unknown
    Publisher: Bioscientifica
    Publication Date: 1997
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  • 3
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    Online Resource
    Type II thyroxine 5′-deiodinase in the rat thymus
    Bioscientifica ; 1995
    In:  Journal of Endocrinology Vol. 146, No. 1 ( 1995-07), p. 105-111
    Details
    In: Journal of Endocrinology, Bioscientifica, Vol. 146, No. 1 ( 1995-07), p. 105-111
    Abstract: In the present study we have shown type II thyroxine 5′-deiodination (5′D) in the rat thymus. The enzyme activity was identified in crude extract homogenates by measuring the 125 I released from [3′,5′- 125 I]thyroxine which is used as a substrate of the reaction. The release of 125 I is dependent on protein tissue concentration, time, temperature and pH, and is saturable by increasing the substrate concentration, indicating its enzymatic nature. Characteristics of the enzyme activity also include a low K m (9·1 nm), its dependence on dithiothreitol, and its inhibition by iopanoic acid, but not by propylthiouracil. Experiments to investigate the cellular location of the enzyme in the thymic gland showed that the enzyme is present in both stromal cells and thymocytes. At the subcellular level, 5′D activity was associated with cellular membranes. Thyroid status appears to regulate 5′D activity in rat thymus. Hypothyroidism caused an increase in thymus 5′D activity. The K m value remained unchanged (9·1 vs 10·5 nm) during hypothyroidism, but V max increased significantly from 17·7 fmol/mg protein per h in euthyroid rats to 53·5 fmol/mg protein per h in hypothyroid rats. 5′D activity was also modulated by catecholamines through β-adrenergic receptors because isoproterenol, but not methoxamine or clonidine, could activate the enzyme. Because these characteristics define the type II iodothyronine-deiodinating pathway in other tissues, we suggest that the rat thymus also shares this pathway. Journal of Endocrinology (1995) 146, 105–111
    Type of Medium: Online Resource
    ISSN: 0022-0795 , 1479-6805
    URL: Article
    DOI: 10.1677/joe.0.1460105
    Language: Unknown
    Publisher: Bioscientifica
    Publication Date: 1995
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  • 4
    Online Resource
    Online Resource
    Prolactin-like protein-B: heterologous expression and characterization of placental and decidual species
    Bioscientifica ; 1997
    In:  Journal of Endocrinology Vol. 152, No. 2 ( 1997-02), p. 291-302
    Details
    In: Journal of Endocrinology, Bioscientifica, Vol. 152, No. 2 ( 1997-02), p. 291-302
    Abstract: Prolactin-like protein-B (PLP-B) is a member of a family of proteins expressed by the rat placenta and/or decidua with characteristics similar to prolactin (PRL). In this report, we present the heterologous expression and characterization of PLP-B. Recombinant PLP-B heterologously expressed in Chinese hamster ovary cells exhibited similar immunoreactive and electrophoretic characteristics with PLP-B produced by rat placental and decidual tissues. N-terminal sequencing verified the identity and purity of the recombinant PLP-B species and the site of cleavage of the signal peptide from the mature secreted PLP-B species. Polyclonal antibodies were generated to the recombinant PLP-B and used for Western blot and immunocytochemical analyses. Recombinant and native PLP-B migrated as a doublet at 30–31 kDa in SDS-PAGE under reducing conditions. Treatment of recombinant and native PLP-B with N-glycanase accelerated their electrophoretic mobility, indicative of their glycoprotein nature. PLP-B was localized exclusively to decidual cells in the developing deciduum and spongiotrophoblast cells in the placental junctional zone. The level of PLP-B protein expression dramatically declined prior to parturition. Potential PRL-like biological actions of PLP-B were also investigated. PLP-B bound weakly to ovarian and liver PRL receptors and did not stimulate the proliferation of lactogen-dependent Nb2 lymphoma cells. In conclusion, recombinant PLP-B possesses characteristics similar to native decidual and placental PLP-B and may represent a hormone/cytokine that has important modulatory actions during the establishment of pregnancy and the initiation of parturition. Journal of Endocrinology (1997) 152, 291–302
    Type of Medium: Online Resource
    ISSN: 0022-0795 , 1479-6805
    URL: Article
    DOI: 10.1677/joe.0.1520291
    Language: Unknown
    Publisher: Bioscientifica
    Publication Date: 1997
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  • 5
    Online Resource
    Online Resource
    Agonist-induced internalisation of the angiotensin II-binding sites from plasma membranes of isolated rat hepatocytes
    Bioscientifica ; 1997
    In:  Journal of Endocrinology Vol. 152, No. 3 ( 1997-03), p. 407-412
    Details
    In: Journal of Endocrinology, Bioscientifica, Vol. 152, No. 3 ( 1997-03), p. 407-412
    Abstract: Angiotensin II (Ang II) provokes rapid internalisation of its receptor from plasma membranes in isolated rat hepatocytes. After 10 min stimulation with Ang II, plasma membrane lost about 60% of its 125 I-Ang II-binding capacity. Internalisation was blocked by phenylarsine oxide (PhAsO), whereas okadaic acid, which markedly reduced the sustained phase of calcium mobilization, did not have a preventive effect on Ang II–receptor complex sequestration. These data suggest that Ang II receptor internalisation is probably independent of a phosphorylation/dephosphorylation cycle of critical serine/threonine residues in the receptor molecule. To establish a relationship between sequestration of the Ang II receptor and the physical properties of the Ang II-binding sites, 125 I-Ang II–receptor complex profiles were analysed by isoelectric focusing. In plasma membrane preparations two predominant Ang II-binding sites, migrating to pI 6·8 and 6·5 were found. After exposure to Ang II, cells lost 125 I-Ang II-binding capacity to the Ang II–receptor complex migrating at pI 6·8 which was prevented in PhAsO-treated cells. Pretreatment of hepatocytes with okadaic acid did not modify Ang II–receptor complex profiles, indicating that the binding sites corresponding to pI 6·5 and pI 6·8 do not represent a phosphorylated and/or non-phosphorylated form of the Ang II receptor. The results show that the Ang II–receptor complex isoform at pI 6·8 represents a functional form of the type-1 Ang II receptor. Further studies are necessary to identify the Ang II-related nature of the binding sites corresponding to pI 6·5. Journal of Endocrinology (1997) 152, 407–412
    Type of Medium: Online Resource
    ISSN: 0022-0795 , 1479-6805
    URL: Article
    DOI: 10.1677/joe.0.1520407
    Language: Unknown
    Publisher: Bioscientifica
    Publication Date: 1997
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  • 6
    Online Resource
    Online Resource
    Inhibition of 5α-reductase in genital skin fibroblasts and prostate tissue by dietary lignans and isoflavonoids
    Bioscientifica ; 1995
    In:  Journal of Endocrinology Vol. 147, No. 2 ( 1995-11), p. 295-302
    Details
    In: Journal of Endocrinology, Bioscientifica, Vol. 147, No. 2 ( 1995-11), p. 295-302
    Abstract: Isoflavonoids and lignans, constituents of many plant foods, have been proposed as protective agents in those populations with a low incidence of hormone-dependent cancers. They may act by their inhibition of the metabolism of growth-promoting steroid hormones. This report describes the inhibition of 5α-reductase and 17β-hydroxysteroid dehydrogenase by six isoflavonoids and two lignans in human genital skin fibroblast monolayers and homogenates, and in benign prostatic hyperplasia tissue homogenates. In genital skin fibroblasts, genistein, biochanin A and equol were the most potent inhibitors of 5α-reductase activity, each resulting in greater than 80% inhibition at a concentration of 100 μm. The IC 50 values for genistein and a seven-compound mixture were approximately 35 μm and 20 μm (2·9 μm of each compound) respectively. Of the lignans, enterolactone was the most potent inhibitor. Inhibition by biochanin A was shown to be reversible. When genital skin fibroblast homogenates were used, biochanin A was found to inhibit 5α-reductase isozymes 1 and 2 to differing extents (30% and 75% respectively). Genistein was shown to inhibit 5α-reductase 2 in a non-competitive nature (V max and K m values without and with inhibitor were 30 and 20 pmol/mg protein per h and 177 and 170 nm respectively). All of the compounds tested inhibited 17β-hydroxysteroid dehydrogenase activity in genital skin fibroblast monolayers. When prostate tissue homogenates were used, the compounds tested were better inhibitors of 5α-reductase 1 than 2. It is possible that a life-long dietary exposure to these lignans and isoflavonoids may have a significant influence on the development of hormone-dependent tumours. Journal of Endocrinology (1995) 147, 295–302
    Type of Medium: Online Resource
    ISSN: 0022-0795 , 1479-6805
    URL: Article
    DOI: 10.1677/joe.0.1470295
    Language: Unknown
    Publisher: Bioscientifica
    Publication Date: 1995
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  • 7
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    Online Resource
    Blockade of the neonatal increase in testosterone by a GnRH antagonist: the free androgen index, reproductive capacity and postmortem findings in the male marmoset monkey
    Bioscientifica ; 1997
    In:  Journal of Endocrinology Vol. 154, No. 1 ( 1997-07), p. 125-131
    Details
    In: Journal of Endocrinology, Bioscientifica, Vol. 154, No. 1 ( 1997-07), p. 125-131
    Abstract: Male marmoset monkeys which had received gonadotrophin-releasing hormone (GnRH) antagonist treatment as neonates to block the postnatal increase in testosterone were studied, with the object of determining potential long-term effects of treatment on the reproductive system, including tests of fertilising capacity. To obtain information on the nature of the circulating testosterone during this neonatal period, sequential blood samples were collected from a further control group of ten neonates, aged between birth and 3 months, and from 11 adult, normally fertile males, to examine the relative proportions of free, sex-hormone-binding globulin (SHBG)-bound, and non-SHBG-bound testosterone. In control neonates, 11% of the circulating testosterone was free, and a further 19% non-SHBG-bound, and therefore presumed to be biologically available. The remaining 70% was SHBG-bound and considered to be biologically inert. This indicates that the neonatal increase in marmoset testosterone has a biological function. After pairing with females, time to first positive vaginal lavage and first delivery was similar for females, whether they were with control or treated male partners. Pregnancy outcome, in terms of number of young delivered and sex ratio, did not differ. This indicates that there appear to be no long-term sequelae in terms of procreative ability in male marmosets treated neonatally with a GnRH antagonist. Autopsy revealed no gross changes, except in the thymus, which was significantly heavier in the treated group. These results indicate that, although the circulating testosterone is in a biologically active form during the neonatal period, inhibition of testicular function in the neonate is without major effect on the adult male reproductive system. Treatment with a GnRH antagonist may have long-term effects on the immune system. Journal of Endocrinology (1997) 154, 125–131
    Type of Medium: Online Resource
    ISSN: 0022-0795 , 1479-6805
    URL: Article
    DOI: 10.1677/joe.0.1540125
    Language: Unknown
    Publisher: Bioscientifica
    Publication Date: 1997
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  • 8
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    Online Resource
    Induced luteal regression: differential effects on follicular and luteal inhibin/activin subunit mRNAs in the marmoset monkey
    Bioscientifica ; 1995
    In:  Journal of Endocrinology Vol. 144, No. 2 ( 1995-02), p. 201-208
    Details
    In: Journal of Endocrinology, Bioscientifica, Vol. 144, No. 2 ( 1995-02), p. 201-208
    Abstract: During the luteal phase of the primate ovulatory cycle the predominant inhibin/activin subunit mRNAs produced by the corpus luteum and antral follicles are those for the α- and β B -subunits respectively. The control of expression of these mRNAs and the resultant nature of the endocrine and paracrine signals which they may potentially generate has yet to be elucidated. Inhibin/activin subunit mRNAs may have a role in both the paracrine regulation of follicular and luteal function and modulation of FSH secretion. The aim of this study was to investigate the expression of inhibin/activin subunit mRNAs following luteal regression induced by either withdrawal of LH support (GnRH antagonist treatment), or by a direct inhibitory action (prostaglandin administration). Marmoset monkeys with regular ovulatory cycles were treated on day 8 and 9 of the luteal phase with either GnRH antagonist, prostaglandin or vehicle ( n =3 per group). Ovaries were studied 48 h after onset of treatment (on day 10 of the luteal phase) by hybridizing frozen tissue sections with radiolabelled riboprobes specific to the inhibin/activin α-, β A - and β B -subunit mRNAs. After autoradiographic exposure, grain concentrations were quantified by image analysis. In corpora lutea from control marmosets there was high expression of α-mRNA with only marginal expression of β B -mRNA. Corpora lutea in animals treated with GnRH antagonist or prostaglandin had markedly reduced expression of α-mRNA while β B -mRNA was unchanged. In controls, all healthy antral follicles exhibited a high level of expression of β B -mRNA in the granulosa cells and low expression of α-mRNA in theca cells. This was unaffected by either treatment. β A -mRNA was found at a low level in granulosa cells but was not evident at a significant level in the corpora lutea of any of the groups. These results demonstrate (1) the marmoset corpus luteum is a source of high expression of α-subunit mRNA, (2) this α-mRNA is dependent upon LH support, (3) the process of luteal regression takes place without alteration of β B -mRNA. Antral follicle α- and β B -mRNAs are independent of the process of luteal regression or gonadotrophic withdrawal during the period of the luteal-follicular phase transition. Journal of Endocrinology (1995) 144, 201–208
    Type of Medium: Online Resource
    ISSN: 0022-0795 , 1479-6805
    URL: Article
    DOI: 10.1677/joe.0.1440201
    Language: Unknown
    Publisher: Bioscientifica
    Publication Date: 1995
    detail.hit.zdb_id: 1474892-7
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