Factors Affecting Glucocorticoid and Thyroid Hormone Production of Island Foxes

2019 ◽  
Vol 84 (3) ◽  
pp. 505-514
Author(s):  
Corinne P. Kozlowski ◽  
Helen Clawitter ◽  
Angela Guglielmino ◽  
Juliann Schamel ◽  
Stacy Baker ◽  
...  
Keyword(s):  
Thyroid Hormone ◽  
Hormone Production ◽  
Factors Affecting

Thyrotrophin-producing pituitary adenomas

1982 ◽  
Vol 57 (4) ◽  
pp. 515-519 ◽  
Author(s):  
Stephen A. Hill ◽  
James M. Falko ◽  
Charles B. Wilson ◽  
William E. Hunt
Keyword(s):  
Thyroid Hormone ◽  
Pituitary Adenomas ◽  
Preoperative Diagnosis ◽  
Pituitary Tumors ◽  
Recurrent Tumor ◽  
Hormone Production ◽  
Content Type ◽  
Aggressive Tumor ◽  
Tsh Levels ◽  
Fine Print

✓ Hyperthyroidism due to thyrotrophin (TSH)-secreting pituitary tumors is rare. Four cases are described, with the features that allow preoperative diagnosis. In all the patients, thyroid hormone production was consistently elevated despite antithyroid therapy, and TSH levels were inappropriately elevated. All patients were treated with both surgery and irradiation. Each patient had recurrent tumor with suprasellar, intrasphenoidal, or intraorbital spread. The combination of a recurrent, aggressive tumor complicated by thyrotoxicosis makes this a complex and difficult surgical problem.

In vivo effects of flavonoid EMD 21388 on thyroid hormone secretion and metabolism in rats

1991 ◽  
Vol 261 (2) ◽  
pp. E227-E232 ◽  
Author(s):  
J. P. Schroder-van der Elst ◽  
D. van der Heide ◽  
J. Kohrle
Keyword(s):  
Thyroid Hormone ◽  
Hormone Secretion ◽  
Male Rats ◽  
Intact Male ◽  
Hormone Production ◽  
Iodide Uptake ◽  
Brown Adipose ◽  
In Vivo Effects

In vitro, the synthetic flavonoid EMD 21388 appears to be a potent inhibitor of thyroxine (T4) 5'-deiodinase and diminishes binding of T4 to transthyretin. In this study, in vivo effects of long-term administration of EMD 21388 on thyroid hormone production and metabolism were investigated. Intact male rats received EMD 21388 (20 mumol.kg body wt-1.rat-1.day-1) for 14 days. [125I]T4 and 3,5,3'-[131I]triiodotyronine (T3) were infused continuously and intravenously in a double-isotope protocol for the last 10 and 7 days, respectively. EMD 21388 decreased plasma thyroid hormone concentrations, but thyrotropin levels in plasma and pituitary did not change. Plasma clearance rates for T4 and T3 increased. Thyroidal T4 secretion was diminished, but T3 secretion was elevated. Extrathyroidal T3 production by 5'-deiodination was lower. T4 concentrations were markedly lower in all tissues investigated. Total tissue T3 was lower in brown adipose tissue, brain, cerebellum, and pituitary, tissues that express the type II 5'-deiodinase isozyme due to decreased local T3 production. Most tissues showed increased tissue/plasma ratios for T4 and T3. These results indicate that this flavonoid diminished T4 and increased T3 secretion by the thyroid, probably in analogy with other natural flavonoids, by interference with one or several steps between iodide uptake, organification, and hormone synthesis.

Factors affecting folliculogenesis in ruminants

1999 ◽  
Vol 68 (2) ◽  
pp. 257-284 ◽  
Author(s):  
R. Webb ◽  
R. G. Gosden ◽  
E. E. Telfer ◽  
R. M. Moor
Keyword(s):  
New Technologies ◽  
Ovarian Function ◽  
Major Gene ◽  
Follicular Development ◽  
Oocyte Quality ◽  
Ovulation Rate ◽  
Follicular Growth ◽  
Stages Of Development ◽  
Hormone Production ◽  
Factors Affecting

AbstractThis review addresses the reasons for the lack of progress in the control of superovulation and highlights the importance of understanding the mechanisms underlying follicular development. The present inability to provide large numbers of viable embryos from selected females still restricts genetic improvement, whilst variability in ovarian response to hormones limit the present capacity for increasing reproductive efficiency.Females are born with a large store of eggs which rapidly declines as puberty approaches. If these oocytes are normal then there is scope for increasing the reproductive potential of selected females. Oocytes must reach a certain size before they can complete all stages of development and the final changes that occur late in follicular development. It is likely that oocytes that do not produce specific factors at precise stages of development will not be viable. Hence, it is important to characterize oocyte secreted factors since there are potential indicators of oocyte quality.The mechanisms that determine ovulation rate have still not been fully elucidated. Indeed follicular atresia, the process whereby follicles regress, is still not known. A better understanding of these processes should prove pivotal for the synchronization of follicular growth, for more precise oestrous synchronization and improved superovulatory response.Nutrition can influence a whole range of reproductive parameters however, the pathways through which nutrition acts have not been fully elucidated. Metabolic hormones, particularly insulin and IGFs, appear to interact with gonadotrophins at the level of the gonads. Certainly gonadotropins provide the primary drive for the growth of follicles in the later stages of development and both insulin and IGF-1, possibly IGF-2, synergize with gonadotrophins to stimulate cell proliferation and hormone production. More research is required to determine the effects of other growth factors and their interaction with gonadotropins.There is evidence, particularly from studies with rodents, that steroids can also modulate follicular growth and development, although information is very limited for ruminants. There may be a rôle for oestrogens in synchronizing follicular waves, to aid in oestrous synchronization regimes and for removing the dominant follicle to achieve improved superovulatory responses. However more information is required to determine whether these are feasible approaches.Heritability for litter size is higher in sheep than in cattle. Exogenous gonadotropins are a commercially ineffective means of inducing twinning in sheep and cattle. Although there are differences in circulating gonadotropin concentrations, the mechanism(s) responsible for the high ovulation appear to reside essentially within the ovaries. The locus of the Booroola gene, a major gene for ovulation rate, has been established but not specifically identified. However sheep possessing major genes do provide extremely valuable models for investigating the mechanisms controlling ovulation rate, including a direct contrast to mono-ovulatory species such as cattle.In conclusion, the relationship between oocyte quality, in both healthy follicles and those follicles destined for atresia, must be resolved before the future potential for increasing embryo yield can be predicted. In addition, a greater understanding of the factors affecting folliculogenesis in ruminants should ensure that the full benefits ensuing from the precise control of ovarian function are achieved. The improved use of artificial insemination and embryo transfer that would ensue from a greater understanding of the processes of folliculo genesis, coupled with the new technologies of genome and linkage mapping, should ensure a more rapid rate of genetic gain.

Effects of marginal iodine deficiency during pregnancy: iodide uptake by the maternal and fetal thyroid

1997 ◽  
Vol 273 (6) ◽  
pp. E1121-E1126 ◽  
Author(s):  
P. M. Versloot ◽  
J. P. Schröder-Van Der Elst ◽  
D. Van Der Heide ◽  
L. Boogerd
Keyword(s):  
Thyroid Hormone ◽  
Iodine Deficiency ◽  
Specific Activity ◽  
Hormone Production ◽  
Iodide Uptake ◽  
Deficient Diet ◽  
Pregnant Rats ◽  
Thyroid Hormone Metabolism ◽  
Fetal Thyroid ◽  
The Absolute

Iodide uptake by the thyroid is an active process. Iodine deficiency and pregnancy are known to influence thyroid hormone metabolism. The aim of this study was to clarify the effects of iodine deficiency and pregnancy on iodide uptake by the thyroid. Radioiodide was injected intravenously into nonpregnant and 19-day pregnant rats receiving a normal or marginally iodine-deficient diet. The uptake of radioiodide by the thyroid was measured continuously for 4 h. The absolute iodide uptake by the maternal and fetal thyroid glands at 24 h was calculated by means of the urinary specific activity. Pregnancy resulted in a decrease in the absolute thyroidal iodide uptake. Marginal iodine deficiency had no effect on the absolute iodide uptake by the maternal thyroid. The decreased plasma inorganic iodide was compensated by an increase in thyroidal clearance. A similar compensation was not found for the fetus; the uptake of iodide by the fetal thyroid decreased by 50% during marginal iodine deficiency. This can lead to diminished thyroid hormone production, which will have a negative effect on fetal development, especially of the brain.

scholarly journals Ontogeny of pituitary thyrotrophs and regulation by endogenous thyroid hormone feedback in the chick embryo

2005 ◽  
Vol 184 (2) ◽  
pp. 407-416 ◽  
Author(s):  
Michael Muchow ◽  
Ioannis Bossis ◽  
Tom E Porter
Keyword(s):  
Thyroid Hormone ◽  
Thyroid Hormones ◽  
Anterior Pituitary ◽  
Feedback Regulation ◽  
Thyroid Stimulating Hormone ◽  
Mrna Levels ◽  
Hormone Production ◽  
Negative Feedback Regulation ◽  
Cephalic Lobe ◽  
Whole Mount

Increased thyroid hormone production is essential for hatching of the chick and for the increased metabolism necessary for posthatch endothermic life. However, little is known about the ontogeny and distribution of pituitary thyrotrophs during this period or whether pituitary thyroid-stimulating hormone (TSH) production is regulated by endogenous thyroid hormones during chick embryonic development. This study assessed the abundance and location of pituitary thyrotrophs and the regulation of TSHβ peptide and mRNA levels by endogenous thyroid hormones prior to hatching. TSHβ-containing cells were first detected on embryonic day (e) 11, and the thyrotroph population increased to maximum levels on e17 and e19 and then decreased prior to hatching (d1). Thyrotroph distribution within the cephalic lobe of the anterior pituitary was determined on e19 by whole-mount immunocytochemistry for TSHβ peptide and by whole-mount in situ hybridization for TSHβ mRNA. Thyrotroph distribution within the cephalic lobe was heterogeneous among embryos, but most commonly extended from the ventral medial region to the dorsal lateral regions, along the boundary of the cephalic and caudal lobes. Inhibition of endogenous thyroid hormone production with methi-mazole (MMI) decreased plasma thyroxine (T4) levels and increased pituitary TSHβ mRNA levels on e19 and d1. However, control pituitaries contained significantly more TSHβ peptide than MMI-treated pituitaries on e17 and e19, suggesting higher TSH secretion into the blood in MMI-treated groups. We conclude that thyrotroph abundance and TSH production increase prior to hatching, that thyrotrophs are localized heterogenenously within the cephalic lobe of the anterior pituitary at that time, and that TSH gene expression and secretion are under negative feedback regulation from thyroid hormones during this critical period of development.

SIGNIFICANCE OF TRIIODOTHYRONINE FOR THYROID HORMONE SUPPLY DURING STIMULATION

1966 ◽  
Vol 53 (1) ◽  
pp. 151-161 ◽  
Author(s):  
Dieter Emrich ◽  
Peter Pfannenstiel ◽  
Günter Hoffmann ◽  
Walter Keiderling
Keyword(s):  
Thyroid Hormone ◽  
Thyroid Hormones ◽  
Thyroid Function ◽  
Hormone Production ◽  
Partial Inhibition

ABSTRACT The metabolism of the two thyroid hormones thyroxine (T4) and triiodothyronine (T3) and particularly the T4/T3 ratio was studied by the 131I technique in rats and rabbits during stimulation. Both exogenous TSH and experimentally increased endogenous TSH (secondary to the partial inhibition of thyroid function by sodiumperchlorate) caused a change in the T4/T3 ratio in favour of T3. This response of thyroid hormone production (in rats) and secretion (in rabbits) was found at different times after the use of 131I. It depended on the intensity of the direct or indirect thyrotrophic stimulation. From this observation it is suggested that the synthesis and the secretion of the biologically more effective T3 is more markedly increased during stimulation than is T4 probably in order to compensate more successfully for deficiencies in the peripheral thyroid hormone supply.

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