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Mary B Dratman - One of the best experts on this subject based on the ideXlab platform.
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film autoradiography identifies unique features of 125i 3 3 5 Reverse Triiodothyronine transport from blood to brain
Journal of Neurophysiology, 1994Co-Authors: Lan Ying Cheng, L V Outterbridge, N D Covatta, Diana A Martens, Janice T Gordon, Mary B DratmanAbstract:: 1. Steady-state iodothyronine profiles in plasma are composed of thyroid gland-synthesized hormones (mainly thyroxine) and tissue iodothyronine metabolites (mainly Triiodothyronine and Reverse Triiodothyronine) that have entered the bloodstream. The hormones circulate in noncovalently bound complexes with a panoply of carrier proteins. Transthyretin (TTR), the major high-affinity thyroid hormone binding protein in rat plasma, is formed in the liver. It is also actively and independently synthesized in choroid plexus, where its function as a chaperone of thyroid hormones from bloodstream to cerebrospinal fluid (CSF) is undergoing close scrutiny by several groups of investigators. Because TTR has high-affinity binding sites for both thyroxine and retinol binding protein, its potential role as a mediator of combined thyroid hormone and retinoic acid availability in brain is of further interest. 2. While they are in the free state relative to their binding proteins, iodothyronines in the cerebral circulation are putatively subject to transport across both the blood-brain barrier (BBB) and choroid plexus CSF barrier (CSFB) before entering the brain. Previous autoradiographic studies had already indicated that after intravenous administration the transport mechanisms governing thyroxine and Triiodothyronine entry into brain were probably similar, whereas those for Reverse Triiodothyronine were very different, although the basis for the difference was not established at that time. Intense labeling seen over brain ventricles after intravenous administration of all three iodothyronines suggested that all were subject to transport across the CSFB. 3. To evaluate the role of the BBB and CSFB in determining iodothyronine access to brain parenchyma, autoradiograms prepared after intravenous administration of [125I]-labeled hormones (revealing results of transport across both barriers) were compared with those prepared after intrathecal (icv) hormone injection (reflecting only their capacity to penetrate into the brain after successfully navigating the CSFB). 4. Those studies revealed that thyroxine and Triiodothyronine were mainly transported across the BBB. They shared with Reverse Triiodothyronine a generally similar, limited pattern of penetration from CSF into the brain, with circumventricular organs likely to be the main recipients of iodothyronines (with or without retinol) transported across the CSFB. 5. Analysis of all of the images obtained after intravenous and icv hormone administration clarified the basis for the unique distribution of intravenously injected Reverse Triiodothyronine. The hormone is excluded by the BBB but may be subject to limited penetration into brain parenchyma via the CSF. 6. Overall the observations single out Reverse Triiodothyronine as the iodothyronine showing the most distinctive as well as the most limited pattern of transport from blood to brain.(ABSTRACT TRUNCATED AT 400 WORDS)
Lan Ying Cheng - One of the best experts on this subject based on the ideXlab platform.
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film autoradiography identifies unique features of 125i 3 3 5 Reverse Triiodothyronine transport from blood to brain
Journal of Neurophysiology, 1994Co-Authors: Lan Ying Cheng, L V Outterbridge, N D Covatta, Diana A Martens, Janice T Gordon, Mary B DratmanAbstract:: 1. Steady-state iodothyronine profiles in plasma are composed of thyroid gland-synthesized hormones (mainly thyroxine) and tissue iodothyronine metabolites (mainly Triiodothyronine and Reverse Triiodothyronine) that have entered the bloodstream. The hormones circulate in noncovalently bound complexes with a panoply of carrier proteins. Transthyretin (TTR), the major high-affinity thyroid hormone binding protein in rat plasma, is formed in the liver. It is also actively and independently synthesized in choroid plexus, where its function as a chaperone of thyroid hormones from bloodstream to cerebrospinal fluid (CSF) is undergoing close scrutiny by several groups of investigators. Because TTR has high-affinity binding sites for both thyroxine and retinol binding protein, its potential role as a mediator of combined thyroid hormone and retinoic acid availability in brain is of further interest. 2. While they are in the free state relative to their binding proteins, iodothyronines in the cerebral circulation are putatively subject to transport across both the blood-brain barrier (BBB) and choroid plexus CSF barrier (CSFB) before entering the brain. Previous autoradiographic studies had already indicated that after intravenous administration the transport mechanisms governing thyroxine and Triiodothyronine entry into brain were probably similar, whereas those for Reverse Triiodothyronine were very different, although the basis for the difference was not established at that time. Intense labeling seen over brain ventricles after intravenous administration of all three iodothyronines suggested that all were subject to transport across the CSFB. 3. To evaluate the role of the BBB and CSFB in determining iodothyronine access to brain parenchyma, autoradiograms prepared after intravenous administration of [125I]-labeled hormones (revealing results of transport across both barriers) were compared with those prepared after intrathecal (icv) hormone injection (reflecting only their capacity to penetrate into the brain after successfully navigating the CSFB). 4. Those studies revealed that thyroxine and Triiodothyronine were mainly transported across the BBB. They shared with Reverse Triiodothyronine a generally similar, limited pattern of penetration from CSF into the brain, with circumventricular organs likely to be the main recipients of iodothyronines (with or without retinol) transported across the CSFB. 5. Analysis of all of the images obtained after intravenous and icv hormone administration clarified the basis for the unique distribution of intravenously injected Reverse Triiodothyronine. The hormone is excluded by the BBB but may be subject to limited penetration into brain parenchyma via the CSF. 6. Overall the observations single out Reverse Triiodothyronine as the iodothyronine showing the most distinctive as well as the most limited pattern of transport from blood to brain.(ABSTRACT TRUNCATED AT 400 WORDS)
Eduard Kuhn - One of the best experts on this subject based on the ideXlab platform.
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stimulation of thyroid function by several pituitary hormones results in an increase in plasma thyroxine and Reverse Triiodothyronine in tilapia tilapia nilotica
General and Comparative Endocrinology, 1990Co-Authors: N Byamungu, S Corneillie, Veerle Darras, Eduard KuhnAbstract:Abstract In this study, intravenous injection of several doses of porcine follicle stimulating hormone (pFSH: 0.002, 0.01, 0.05, and 0.5 μg/g body wt), bovine TSH (bTSH: 0.5 μg/g body wt), and ovine growth hormone (oGH: 0.04, 0.02, and 0.4 μg/g body wt) stimulated an increase in plasma thyroxine (T4) and Reverse Triiodothyronine (rT3) in tilapia. This effect occurred in a dose-dependent manner. pFSH was the most potent in stimulating thyroid function. The dose of 0.002 μg pFSH/g body wt increased plasma levels of T4 over control levels (2.59 ± 0.16 ng/ml) about 2.5-fold within 4 hr, whereas a concentration of 0.5 μg/g body wt caused a great and prolonged increase of T4 and rT3 levels. Control levels (2.59 ± 0.16 ng/ml for T4 and 40.37 ± 8.60 pg/ml for rT3) were increased 19- and 22-fold respectively, over 24 hr. An increase of T4 and rT3 levels occurred also after injection of total hypophyseal extract and a Con A II glycoprotein fraction of a tilapia pituitary homogenate, whereas the protein fraction failed to alter plasma concentrations of T4 and rT3. rT3 levels were also significantly increased at 2 hr, but not at 1 hr, after injection of T4. Basal T3 levels (1.90 ± 0.22 ng/ml) were reduced by half over 24 hr in all experiments. These results suggest the existence, in tilapia, of a 5-D pathway deiodination of T4 which is pituitary independent. Stimulation of T4 release is always followed by an increase in plasma rT3 levels.
N D Covatta - One of the best experts on this subject based on the ideXlab platform.
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film autoradiography identifies unique features of 125i 3 3 5 Reverse Triiodothyronine transport from blood to brain
Journal of Neurophysiology, 1994Co-Authors: Lan Ying Cheng, L V Outterbridge, N D Covatta, Diana A Martens, Janice T Gordon, Mary B DratmanAbstract:: 1. Steady-state iodothyronine profiles in plasma are composed of thyroid gland-synthesized hormones (mainly thyroxine) and tissue iodothyronine metabolites (mainly Triiodothyronine and Reverse Triiodothyronine) that have entered the bloodstream. The hormones circulate in noncovalently bound complexes with a panoply of carrier proteins. Transthyretin (TTR), the major high-affinity thyroid hormone binding protein in rat plasma, is formed in the liver. It is also actively and independently synthesized in choroid plexus, where its function as a chaperone of thyroid hormones from bloodstream to cerebrospinal fluid (CSF) is undergoing close scrutiny by several groups of investigators. Because TTR has high-affinity binding sites for both thyroxine and retinol binding protein, its potential role as a mediator of combined thyroid hormone and retinoic acid availability in brain is of further interest. 2. While they are in the free state relative to their binding proteins, iodothyronines in the cerebral circulation are putatively subject to transport across both the blood-brain barrier (BBB) and choroid plexus CSF barrier (CSFB) before entering the brain. Previous autoradiographic studies had already indicated that after intravenous administration the transport mechanisms governing thyroxine and Triiodothyronine entry into brain were probably similar, whereas those for Reverse Triiodothyronine were very different, although the basis for the difference was not established at that time. Intense labeling seen over brain ventricles after intravenous administration of all three iodothyronines suggested that all were subject to transport across the CSFB. 3. To evaluate the role of the BBB and CSFB in determining iodothyronine access to brain parenchyma, autoradiograms prepared after intravenous administration of [125I]-labeled hormones (revealing results of transport across both barriers) were compared with those prepared after intrathecal (icv) hormone injection (reflecting only their capacity to penetrate into the brain after successfully navigating the CSFB). 4. Those studies revealed that thyroxine and Triiodothyronine were mainly transported across the BBB. They shared with Reverse Triiodothyronine a generally similar, limited pattern of penetration from CSF into the brain, with circumventricular organs likely to be the main recipients of iodothyronines (with or without retinol) transported across the CSFB. 5. Analysis of all of the images obtained after intravenous and icv hormone administration clarified the basis for the unique distribution of intravenously injected Reverse Triiodothyronine. The hormone is excluded by the BBB but may be subject to limited penetration into brain parenchyma via the CSF. 6. Overall the observations single out Reverse Triiodothyronine as the iodothyronine showing the most distinctive as well as the most limited pattern of transport from blood to brain.(ABSTRACT TRUNCATED AT 400 WORDS)
Diana A Martens - One of the best experts on this subject based on the ideXlab platform.
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film autoradiography identifies unique features of 125i 3 3 5 Reverse Triiodothyronine transport from blood to brain
Journal of Neurophysiology, 1994Co-Authors: Lan Ying Cheng, L V Outterbridge, N D Covatta, Diana A Martens, Janice T Gordon, Mary B DratmanAbstract:: 1. Steady-state iodothyronine profiles in plasma are composed of thyroid gland-synthesized hormones (mainly thyroxine) and tissue iodothyronine metabolites (mainly Triiodothyronine and Reverse Triiodothyronine) that have entered the bloodstream. The hormones circulate in noncovalently bound complexes with a panoply of carrier proteins. Transthyretin (TTR), the major high-affinity thyroid hormone binding protein in rat plasma, is formed in the liver. It is also actively and independently synthesized in choroid plexus, where its function as a chaperone of thyroid hormones from bloodstream to cerebrospinal fluid (CSF) is undergoing close scrutiny by several groups of investigators. Because TTR has high-affinity binding sites for both thyroxine and retinol binding protein, its potential role as a mediator of combined thyroid hormone and retinoic acid availability in brain is of further interest. 2. While they are in the free state relative to their binding proteins, iodothyronines in the cerebral circulation are putatively subject to transport across both the blood-brain barrier (BBB) and choroid plexus CSF barrier (CSFB) before entering the brain. Previous autoradiographic studies had already indicated that after intravenous administration the transport mechanisms governing thyroxine and Triiodothyronine entry into brain were probably similar, whereas those for Reverse Triiodothyronine were very different, although the basis for the difference was not established at that time. Intense labeling seen over brain ventricles after intravenous administration of all three iodothyronines suggested that all were subject to transport across the CSFB. 3. To evaluate the role of the BBB and CSFB in determining iodothyronine access to brain parenchyma, autoradiograms prepared after intravenous administration of [125I]-labeled hormones (revealing results of transport across both barriers) were compared with those prepared after intrathecal (icv) hormone injection (reflecting only their capacity to penetrate into the brain after successfully navigating the CSFB). 4. Those studies revealed that thyroxine and Triiodothyronine were mainly transported across the BBB. They shared with Reverse Triiodothyronine a generally similar, limited pattern of penetration from CSF into the brain, with circumventricular organs likely to be the main recipients of iodothyronines (with or without retinol) transported across the CSFB. 5. Analysis of all of the images obtained after intravenous and icv hormone administration clarified the basis for the unique distribution of intravenously injected Reverse Triiodothyronine. The hormone is excluded by the BBB but may be subject to limited penetration into brain parenchyma via the CSF. 6. Overall the observations single out Reverse Triiodothyronine as the iodothyronine showing the most distinctive as well as the most limited pattern of transport from blood to brain.(ABSTRACT TRUNCATED AT 400 WORDS)