Preferential release of tri-iodothyronine following stimulation by thyrotrophin or thyrotrophin-releasing hormone in sheep of different ages

1992 ◽  
Vol 132 (1) ◽  
pp. 93-100 ◽  
Author(s):  
R. Peeters ◽  
N. Buys ◽  
D. Vanmontfort ◽  
J. Van Isterdael ◽  
E. Decuypere ◽  
...  
Keyword(s):  
Thyroid Gland ◽  
Thyroid Hormones ◽  
Plasma Concentrations ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone ◽  
Neonatal Injection ◽  
Different Ages ◽  
Neonatal Lambs

ABSTRACT The influence of TRH and TSH injections on plasma concentrations of tri-iodothyronine (T3) and thyroxine (T4) was investigated in neonatal (injection within 0·5 h after delivery) and growing lambs and in normal, pregnant and lactating adult ewes (all 2 years old and originating from Suffolk, Milksheep and Texal cross-breeds). Neonatal lambs had higher levels of T3, T4 and GH compared with all other groups, whereas prolactin and TSH were higher in lactating ewes. In all animals, injections of TRH increased plasma concentrations of prolactin and TSH after 15 min but not of GH at any time. Small increases in T3 and T4 were observed in neonatal lambs, without any effect on the T3 and T4 ratio, after prolactin administration, whereas prolactin did not influence plasma concentrations of T3 or T4 in all other experimental groups. Similar results for thyroid hormones were obtained after TRH or TSH injections. It was therefore concluded that the effects observed after TRH challenge were mediated by the release of TSH. With the possible exception of neonatal lambs, plasma concentrations of T3 after administration of TRH or TSH were always increased before those of T4; the increase in T3 occurred within 0·5–1 h compared with 2–4 h for T4 in all experimental groups. This resulted in an increased ratio of plasma T3 to T4 up to 4 h after injection. It is concluded that, in sheep, TRH and TSH preferentially release T3 from the thyroid gland probably by a stimulatory effect of TSH on the intrathyroidal conversion of T3 to T4. Journal of Endocrinology (1992) 132, 93–100

HYPOTHALAMIC SECRETION OF THYROTROPHIN RELEASING HORMONE IS DECREASED IN MALE JAPANESE QUAIL EXPOSED TO LONG DAILY PHOTOPERIODS

1982 ◽  
Vol 92 (2) ◽  
pp. 261-265 ◽  
Author(s):  
O. F. X. ALMEIDA
Keyword(s):  
Thyroid Gland ◽  
Japanese Quail ◽  
Adult Male ◽  
Plasma Concentrations ◽  
Thyroid Stimulating Hormone ◽  
Blood Concentrations ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone ◽  
Stimulating Hormone

Adult male Japanese quail held under short daily photoperiods (8 h light: 16 h darkness; 8L : 16D) had significantly higher plasma concentrations of thyroid-stimulating hormone (TSH), tri-iodothyronine (T3) and thyroxine (T4) than did those kept under long days (16L : 8D). When given a single s.c. injection of 50 μg thyrotrophin releasing hormone (TRH) the birds held under both the 8L : 16D and 16L : 8D photoperiods showed rapid increases in their blood concentrations of TSH, T4 and T3, the amplitude of the TSH response of the birds exposed to 16L : 8D being particularly marked. These results suggest that, in the male quail, long daily photoperiods produce a hypothyroid state as a result of diminished TRH secretion. The synthetic and secretory capacities of the thyroid gland and pituitary thyrotrophs are apparently unimpaired by long days.

PLASMA CONCENTRATIONS OF PROLACTIN AND THYROTROPHIN DURING SUCKLING: EFFECTS OF STIMULATION OF THE MEDIAN EMINENCE

1978 ◽  
Vol 76 (3) ◽  
pp. 557-558 ◽  
Author(s):  
J. B. WAKERLEY ◽  
M. B. TER HAAR
Keyword(s):  
Direct Effect ◽  
Median Eminence ◽  
Plasma Concentrations ◽  
Prolactin Release ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone ◽  
Animal Physiology ◽  
Inhibiting Factor ◽  
Hypothalamic Level ◽  
Stimulation Of

A.R.C. Institute of Animal Physiology, Babraham, Cambridge, CB2 4AT (Received 1 November 1977) Thyrotrophin releasing hormone (TRH) can have a stimulatory effect on the release of both prolactin and thyrotrophin (TSH; Deis & Alonso, 1973), although in the rat, supraphysiological doses of TRH are required to affect the secretion of prolactin (Burnet & Wakerley, 1976). A more important factor in the control of the release of prolactin is considered to be prolactin release inhibiting factor (PIF), which is thought to act through the catecholamine, dopamine (MacLeod, 1976). Stimuli which cause the concomitant release of TSH and prolactin are thought to have a direct effect at the hypothalamic level such that neurones releasing TRH are excited, whereas those releasing PIF are inhibited. In the present work, we have tested this hypothesis using the suckling stimulus to elicit the simultaneous release of prolactin and TSH (Blake, 1974; Burnet & Wakerley, 1976). If

PARTIAL FAILURE OF ANTERIOR PITUITARY AND THYROID PRESENTING AS MYXOEDEMA

1975 ◽  
Vol 79 (4) ◽  
pp. 688-690
Author(s):  
A. D. Toft ◽  
W. J. Irvine
Keyword(s):  
Thyroid Gland ◽  
Anterior Pituitary ◽  
Clinical Presentation ◽  
Present Report ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone ◽  
Partial Failure ◽  
Impaired Function ◽  
Precise Evaluation ◽  
Thyroid Axis

ABSTRACT The development of a sensitive radioimmunoassay of plasma thyrotrophin (TSH) and the isolation and synthesis of thyrotrophin-releasing hormone (TRH) allows a precise evaluation of the disordered brain-thyroid axis. The present report describes a patient who presented with myxoedema due to partial failure of both the anterior pituitary and the thyroid gland. The degree of impaired function of either gland alone would not have caused her clinical presentation.

Effects of infusion of thyrotrophin releasing hormone and dopamine either alone or in combination on plasma prolactin concentrations in the anoestrous ewe

1983 ◽  
Vol 96 (2) ◽  
pp. 353-357
Author(s):  
B. F. Fitzgerald ◽  
F. J. Cunningham
Keyword(s):  
Combined Treatment ◽  
Plasma Concentrations ◽  
Regulatory Role ◽  
Plasma Prolactin ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone

Plasma concentrations of prolactin in anoestrous ewes were respectively lowered or raised by the separate infusion of dopamine or thyrotrophin releasing hormone (TRH). Combined treatment with dopamine and TRH lowered the concentration of prolactin in plasma but the values increased markedly after the treatment was stopped and reached a level equivalent to that found in ewes treated with TRH alone. The results are interpreted as evidence that both dopamine and TRH play a regulatory role in determining the secretion of prolactin in the ewe.

Thyrotrophin-releasing hormone (TRH) and hormone secretion from the follicular and C-cells of perfused dog thyroid lobes

1985 ◽  
Vol 109 (4) ◽  
pp. 499-504 ◽  
Author(s):  
E. Iversen ◽  
P. Laurberg
Keyword(s):  
Thyroid Hormone ◽  
Thyroid Gland ◽  
Hormone Secretion ◽  
Inhibitory Effect ◽  
C Cells ◽  
Follicular Cells ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone ◽  
Direct Inhibitory Effect ◽  
Thyroid Secretion

Abstract. Recently we found small amounts of TRH immunoreactivity in the thyroid gland of dogs and pigs. In the present study we investigated if exogenous TRH influences the release of T4, T3 and cAMP from the follicular cells, and calcitonin and somatostatin from the C-cells of perfused dog thyroid lobes. 10−5 mol/l TRH inhibited the TSH induced iodothyronine and cAMP release from the thyroid while 10−8 mol/l TRH had no effect. The relative proportions of T4 and T3 in thyroid secretion were not altered by TRH infusion. TRH did not influence the basal or the Ca++ induced release of somatostatin and calcitonin. Hence TRH has a direct inhibitory effect on the hormone secretion from thyroidal follicular cells. This opens the possibility that TRH in the thyroid participate in the regulation of thyroid hormone secretion. Even though the concentration of TRH found to be effective is high our results may indicate that TRH in the thyroid participates in the regulation of thyroid hormone secretion as an antagonist to TSH.

The effects of insulin on TSH secretion and the morphology and physiology of the thyroid in the lizard Podarcis s. sicula

1996 ◽  
Vol 17 (1) ◽  
pp. 39-45 ◽  
Author(s):  
Anna Capaldo ◽  
Vincenza Laforgia ◽  
Rosaria Sciarrillo ◽  
Antimo Cavagnuolo
Keyword(s):  
Thyroid Gland ◽  
Thyroid Hormones ◽  
Plasma Concentrations ◽  
Thyroid Stimulating Hormone ◽  
Lizard Species ◽  
Podarcis Sicula ◽  
Tsh Secretion ◽  
Stimulating Hormone

AbstractInsulin was administered to Podarcis sicula in winter, when the thyroid gland is inhibited. The activity of the thyroid increased, plasma concentrations of thyroid hormones and hepatic 5'-monodeiodinase activity (MDA) increased, and thyroid stimulating hormone (TSH) concentrations fell to undetectable values. This result confirms the influence of insulin on the activity of the thyroid gland in the lizard species studied. The mechanisms are still unclear, although there is evidence which leads us to believe that insulin is directly responsible for thyroid activation.

Effects of antiserum to thyrotrophin-releasing hormone on the concentrations of plasma prolactin, thyrotrophin and LH in the pro-oestrous rat

1985 ◽  
Vol 104 (2) ◽  
pp. 205-209 ◽  
Author(s):  
A. M. Horn ◽  
H. M. Fraser ◽  
G. Fink
Keyword(s):  
Plasma Concentrations ◽  
Passive Immunization ◽  
Immune Serum ◽  
Female Rats ◽  
Plasma Prolactin ◽  
Thyrotrophin Releasing Hormone ◽  
Blood Samples ◽  
Releasing Hormone ◽  
Sheep Blood

ABSTRACT The possible role of thyrotrophin-releasing hormone (TRH) in causing the pro-oestrous surge of prolactin was investigated in conscious female rats by passive immunization with a specific anti-TRH serum raised in sheep. Blood samples were withdrawn through a previously implanted intra-atrial cannula. The i.p. injection of 1 ml anti-TRH serum, but not non-immune sheep serum, at 13.00 h of pro-oestrus delayed by about 1 h the onset of the prolactin surge, but the peak of the surge was similar to that in animals injected with the non-immune serum. The plasma concentrations of TSH were significantly reduced by the anti-TRH serum, but plasma concentrations of LH were not significantly affected. These results show that TRH may play an important role in the timing and initiation, but not the maintenance of the prolactin surge in the pro-oestrous rat. J. Endocr. (1985) 104, 205–209

Effects of prednisone on thyroid and gonadal endocrine function in dogs

1983 ◽  
Vol 96 (2) ◽  
pp. 293-NP ◽  
Author(s):  
R. J. Kemppainen ◽  
F. N. Thompson ◽  
M. D. Lorenz ◽  
J. F. Munnell ◽  
P. K. Chakraborty
Keyword(s):  
Hormone Secretion ◽  
Plasma Concentrations ◽  
Thyroid Tissue ◽  
Endocrine Function ◽  
Follicular Cell ◽  
Electron Microscopic ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone ◽  
Prednisone Treatment ◽  
Basal Plasma

To assess the effect of a glucocorticoid on thyroid and gonadal endocrine function, prednisone was administered on alternate days to dogs. The prednisone injections resulted in adrenocortical suppression, as shown by the response to ACTH. Basal plasma thyroxine and tri-iodothyronine concentrations were considerably reduced in prednisone-treated dogs. However, the thyroid response to injection of thyrotrophin-releasing hormone was not altered, indirectly demonstrating that pituitary release of TSH was not inhibited by prednisone. Similarly, the response of the thyroid to exogenous TSH was not reduced by prednisone treatment. Electron microscopic examination of thyroid tissue revealed accumulation of colloid droplets in the follicular cell cytoplasm of dogs treated with prednisone. It is postulated that prednisone may interfere with basal thyroid hormone secretion by inhibiting lysosomal hydrolysis of colloid in the thyroid follicular cell. Basal plasma concentrations of LH and testosterone, measured in the male dogs, were reduced by prednisone treatment. Responses of prednisone-treated dogs to luteinizing hormone releasing hormone were not significantly reduced. Prednisone administration did not alter testicular responsiveness to injection of human chorionic gonadotrophin. After orchidectomy, plasma LH values were significantly reduced in prednisone-treated dogs. Taken together, these results suggest that LH secretion in dogs is inhibited at the hypothalamic and/or pituitary level by prednisone administration, which consequently results in reduced testosterone concentrations.

scholarly journals Applicability of thyroxine measurements and ultrasound imaging in evaluations of thyroid function in turtles

2019 ◽  
Vol 63 (2) ◽  
pp. 267-273
Author(s):  
Joanna Pajdak-Czaus ◽  
Elżbieta Terech-Majewska ◽  
Dagmara Będzłowicz ◽  
Martyn Mączyński ◽  
Wioletta Krystkiewicz ◽  
...  
Keyword(s):  
Thyroid Hormone ◽  
Thyroid Gland ◽  
Thyroid Hormones ◽  
Thyroid Function ◽  
Ultrasound Imaging ◽  
Ultrasound Examination ◽  
Plasma Concentrations ◽  
Physiological Homeostasis ◽  
Low Levels ◽  
And Function

AbstractIntroduction: The thyroid and parathyroid glands play a major role in maintaining physiological homeostasis in all vertebrates. Reptiles have plasma concentrations of thyroid hormones far lower than mammals. Low levels of these hormones in reptiles impede thyroid hormone detection with assays designed for the higher levels of mammals. The aim of this study was to explore teaming this with ultrasound imaging of the thyroid to appraise glandular function. Material and Methods: Thyroid function of four pond sliders was evaluated based on the results of T4 analyses and ultrasound. Results: The concentrations of T4 varied considerably between the examined animals from <9 nmol/L to >167.3 nmol/L. Ultrasound examination revealed uniform echogenicity and a smooth outline of the thyroid gland in all animals. Conclusion: Monitoring of thyroid function based on T4 and electrolyte concentrations is helpful in assessing the health and living conditions of reptiles, which is important in veterinary practice but problematic. Ultrasound examinations are useful in diagnosing changes in gland structure, such as tumours and goitres, and a combination of both methods supports comprehensive assessments of the anatomy and function of the thyroid gland.

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