EFFECTS OF THYROTROPIN RELEASING HORMONE AND ENVIRONMENTAL TEMPERATURE ON THE HYPOPHYSIAL-THYROID AXIS OF HYPOTHYROID, EUTHYROID AND CASTRATED WHITE LEGHORN CHICKENS

Persistent Link:
http://hdl.handle.net/10150/282002
Title:
EFFECTS OF THYROTROPIN RELEASING HORMONE AND ENVIRONMENTAL TEMPERATURE ON THE HYPOPHYSIAL-THYROID AXIS OF HYPOTHYROID, EUTHYROID AND CASTRATED WHITE LEGHORN CHICKENS
Author:
Carr, Bruce Leslie
Issue Date:
1981
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
Cyclic AMP-dependent protein kinase (cAMP-PK) is an important mediator of hormone action. Its activity ratio is an accurate indicator of cellular activity under various experimental conditions including: (1) age and sex, (2) hormone administration and (3) temperature and photoperiod. Pituitary activity in unstimulated birds is not altered by age, but thyroid activity is much higher in old birds than in young animals. Thyrotropin releasing hormone (TRH) increases pituitary, thyroid and liver activity of prepubescent chickens, but has no effect on aged males and increases only thyroid and liver activities in aged females, suggesting a reduction in pituitary-thyroid function with advancing age. In prepubertal females, TRH increases pituitary and thyroid cAMP-PK activity, plasma T₃ and T₄ levels and liver T₄ monodeiodination. Thyroid activity reaches maximum activity before the pituitary, while plasma T₄ and liver T₄ monodeodinating activity reach their highest levels 20 minutes before plasma T₃. These findings suggest that fluctuations in liver T₄ 5' monodeiodinating activity might be responsible for the cyclic response of plasma T₃ and T₄. Castrated cockerels have larger pituitaries than untreated birds, but contain the same amount of DNA. Methimazole-fed cockerels have pituitaries significantly smaller than controls, while castrated cockerels fed methimazole have pituitaries the same size as untreated birds. Pituitary DNA is less than controls in both groups of methimazole-fed birds. These results are considered to be due to a change in the thyrotroph population, without an increase in total cell numbers, and may indicate a transformation of basophils. Pituitary cAMP-PK activity during cold stress substantiates this conclusion. Thyroid glands of castrated and untreated cockerels are smaller in size, histological appearance and DNA content; however, cAMP-PK activity is much greater in the castrated birds. Methimazole-fed cockerels have enlarged thyroid glands, elevated cAMP-PK activity, increased DNA and cellular hypertrophy; however, these effects may be mitigated by castration. Seven days after removal of testosterone supplements, photostimulated castrates have a higher thyroid cAMP-PK activity ratio than short day castrates; however, both groups are elevated above control, suggesting that long photoperiods enhance the stimulatory effects of castration on thyroid activity. Pituitary activity is elevated in long and short day birds seven days after removal of testosterone, but remains high only in short day castrates. Therefore, a reduction in the sensitivity of the hypothalamic-pituitary axis to testosterone may occur only in long day cockerels.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Thyrotropin releasing factor.; Light -- Physiological effect.; Temperature -- Physiological effect.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Animal Physiology
Degree Grantor:
University of Arizona
Advisor:
Chiasson, Robert B.

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titleEFFECTS OF THYROTROPIN RELEASING HORMONE AND ENVIRONMENTAL TEMPERATURE ON THE HYPOPHYSIAL-THYROID AXIS OF HYPOTHYROID, EUTHYROID AND CASTRATED WHITE LEGHORN CHICKENSen_US
dc.creatorCarr, Bruce Leslieen_US
dc.contributor.authorCarr, Bruce Leslieen_US
dc.date.issued1981en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractCyclic AMP-dependent protein kinase (cAMP-PK) is an important mediator of hormone action. Its activity ratio is an accurate indicator of cellular activity under various experimental conditions including: (1) age and sex, (2) hormone administration and (3) temperature and photoperiod. Pituitary activity in unstimulated birds is not altered by age, but thyroid activity is much higher in old birds than in young animals. Thyrotropin releasing hormone (TRH) increases pituitary, thyroid and liver activity of prepubescent chickens, but has no effect on aged males and increases only thyroid and liver activities in aged females, suggesting a reduction in pituitary-thyroid function with advancing age. In prepubertal females, TRH increases pituitary and thyroid cAMP-PK activity, plasma T₃ and T₄ levels and liver T₄ monodeiodination. Thyroid activity reaches maximum activity before the pituitary, while plasma T₄ and liver T₄ monodeodinating activity reach their highest levels 20 minutes before plasma T₃. These findings suggest that fluctuations in liver T₄ 5' monodeiodinating activity might be responsible for the cyclic response of plasma T₃ and T₄. Castrated cockerels have larger pituitaries than untreated birds, but contain the same amount of DNA. Methimazole-fed cockerels have pituitaries significantly smaller than controls, while castrated cockerels fed methimazole have pituitaries the same size as untreated birds. Pituitary DNA is less than controls in both groups of methimazole-fed birds. These results are considered to be due to a change in the thyrotroph population, without an increase in total cell numbers, and may indicate a transformation of basophils. Pituitary cAMP-PK activity during cold stress substantiates this conclusion. Thyroid glands of castrated and untreated cockerels are smaller in size, histological appearance and DNA content; however, cAMP-PK activity is much greater in the castrated birds. Methimazole-fed cockerels have enlarged thyroid glands, elevated cAMP-PK activity, increased DNA and cellular hypertrophy; however, these effects may be mitigated by castration. Seven days after removal of testosterone supplements, photostimulated castrates have a higher thyroid cAMP-PK activity ratio than short day castrates; however, both groups are elevated above control, suggesting that long photoperiods enhance the stimulatory effects of castration on thyroid activity. Pituitary activity is elevated in long and short day birds seven days after removal of testosterone, but remains high only in short day castrates. Therefore, a reduction in the sensitivity of the hypothalamic-pituitary axis to testosterone may occur only in long day cockerels.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectThyrotropin releasing factor.en_US
dc.subjectLight -- Physiological effect.en_US
dc.subjectTemperature -- Physiological effect.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineAnimal Physiologyen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorChiasson, Robert B.en_US
dc.identifier.proquest8126168en_US
dc.identifier.oclc8712532en_US
dc.identifier.bibrecord.b13918163en_US
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