1
|
Ortiga-Carvalho TM, Chiamolera MI, Pazos-Moura CC, Wondisford FE. Hypothalamus-Pituitary-Thyroid Axis. Compr Physiol 2016; 6:1387-428. [PMID: 27347897 DOI: 10.1002/cphy.c150027] [Citation(s) in RCA: 200] [Impact Index Per Article: 25.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The hypothalamus-pituitary-thyroid (HPT) axis determines the set point of thyroid hormone (TH) production. Hypothalamic thyrotropin-releasing hormone (TRH) stimulates the synthesis and secretion of pituitary thyrotropin (thyroid-stimulating hormone, TSH), which acts at the thyroid to stimulate all steps of TH biosynthesis and secretion. The THs thyroxine (T4) and triiodothyronine (T3) control the secretion of TRH and TSH by negative feedback to maintain physiological levels of the main hormones of the HPT axis. Reduction of circulating TH levels due to primary thyroid failure results in increased TRH and TSH production, whereas the opposite occurs when circulating THs are in excess. Other neural, humoral, and local factors modulate the HPT axis and, in specific situations, determine alterations in the physiological function of the axis. The roles of THs are vital to nervous system development, linear growth, energetic metabolism, and thermogenesis. THs also regulate the hepatic metabolism of nutrients, fluid balance and the cardiovascular system. In cells, TH actions are mediated mainly by nuclear TH receptors (210), which modify gene expression. T3 is the preferred ligand of THR, whereas T4, the serum concentration of which is 100-fold higher than that of T3, undergoes extra-thyroidal conversion to T3. This conversion is catalyzed by 5'-deiodinases (D1 and D2), which are TH-activating enzymes. T4 can also be inactivated by conversion to reverse T3, which has very low affinity for THR, by 5-deiodinase (D3). The regulation of deiodinases, particularly D2, and TH transporters at the cell membrane control T3 availability, which is fundamental for TH action. © 2016 American Physiological Society. Compr Physiol 6:1387-1428, 2016.
Collapse
Affiliation(s)
- Tania M Ortiga-Carvalho
- Institute of Biophysics Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, UFRJ, Rio de Janeiro, Brazil
| | - Maria I Chiamolera
- Department of Medicine, Escola Paulista de Medicina, Universidade Federal de Sao Paulo, Sao Paulo, Brazil
| | - Carmen C Pazos-Moura
- Institute of Biophysics Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, UFRJ, Rio de Janeiro, Brazil
| | - Fredic E Wondisford
- Department of Medicine, Rutgers-Robert Wood Johnson Medical School, New Brunswick, New Jersey, USA
| |
Collapse
|
2
|
Malik V, Shukla GK, Bhatia N. Hearing profile in hypothyroidism. Indian J Otolaryngol Head Neck Surg 2012; 54:285-90. [PMID: 23119912 DOI: 10.1007/bf02993744] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
Abstract
The present study was carried on forty-five patients of confirmed hypothyroidism. Complete clinical examination and laboratory investigations were done regarding audiological and vestibular system. It was found that hypothyroidism affects the ear at multiple sites producing various types of hearing impairment viz. conductive, sensorineural and mixed. Vestibular system was found to be affected only minimally. The patients were then given levothyroxine and follow-up was done when they were euthyroid, which revealed statistically significant improvement in hearing threshold in 30% ears, in which conductive impairment was more common to be improved. The middle ear compliance and pressure, on impedance audiometry, also improved significantly in 50% and 87.50% ears respectively. Statistically significant change was also observed in acoustic reflex threshold. Improvement was also noted in wave I, V and interpeak (I-V) latencies, on Brain stem Evoked Response Audiometry (statistically not significant). The results of auditory investigations suggest a causal relationship between hypothyroidism and hearing loss. The site of.
Collapse
Affiliation(s)
- Vikas Malik
- Department of Otorhinolaryngology, KGMC, Lucknow, India
| | | | | |
Collapse
|
3
|
Richter CP, Münscher A, Machado DS, Wondisford FE, Ortiga-Carvalho TM. Complete activation of thyroid hormone receptor β by T3 is essential for normal cochlear function and morphology in mice. Cell Physiol Biochem 2011; 28:997-1008. [PMID: 22178950 DOI: 10.1159/000335812] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/19/2011] [Indexed: 12/16/2022] Open
Abstract
BACKGROUND/AIMS Thyroid hormones (THs) regulate many developmental processes, including the developmental onset of cochlear differentiation and function. TH action is mediated mostly by triiodothyronine (T3) bound to thyroid hormone nuclear receptors (TRs). At positive regulated genes and in the absence of THs, nuclear co-repressors are bound to TRs and decrease basal transcription rate. Ligand (T(3)) binding results in the dissociation of co-repressors and the recruitment of co-activators to the complex, which results in full transcriptional activation. METHODS We measured cochlear function in two knock-in mouse models: TRβ(E457A/E457A), with the TRβ co-activator binding surface (AF-2) disrupted to prevent co-activator binding; and TRβ(Δ337T/Δ337T), which is unable to bind T(3). Cochlear morphology and function were analyzed in 10-week-old normal and mutated mice. Cochlear function was determined by measuring auditory brainstem responses, cochlear tuning and compound action potential (CAP) thresholds. RESULTS All TRβ(Δ337T/Δ337T) and 85% of the TRβ(E457A/E457A) mice presented elevated CAP thresholds (P < 0.05 or less). Five percent of the TRβ(E457A/E457A) mice presented normal CAP thresholds with broadened cochlear tuning. TRβ(E457A/E457A) and TRβ(Δ337T/Δ337T) presented developmental defects that led to a decreased width (P < 0.01) and an increased thickness (P<0.01) of the tectorial membrane. In addition, TRβ(Δ337T/Δ337T) animals showed an increased tectorial membrane area (P<0.01). CONCLUSION Both mutations were deleterious to tectorial membrane development and led to important alterations in cochlear morphology and loss of cochlear function.
Collapse
Affiliation(s)
- Claus-Peter Richter
- Department of Otolaryngology-Head and Neck Surgery, Northwestern University, Feinberg School of Medicine, Chicago, IL, USA
| | | | | | | | | |
Collapse
|
4
|
Mann ZF, Kelley MW. Development of tonotopy in the auditory periphery. Hear Res 2011; 276:2-15. [PMID: 21276841 DOI: 10.1016/j.heares.2011.01.011] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/01/2010] [Revised: 01/18/2011] [Accepted: 01/19/2011] [Indexed: 10/18/2022]
Abstract
Acoustic frequency analysis plays an essential role in sound perception, communication and behavior. The auditory systems of most vertebrates that perceive sounds in air are organized based on the separation of complex sounds into component frequencies. This process begins at the level of the auditory sensory epithelium where specific frequencies are distributed along the tonotopic axis of the mammalian cochlea or the avian/reptilian basilar papilla (BP). Mechanical and electrical mechanisms mediate this process, but the relative contribution of each mechanism differs between species. Developmentally, structural and physiological specializations related to the formation of a tonotopic axis form gradually over an extended period of time. While some aspects of tonotopy are evident at early stages of auditory development, mature frequency discrimination is typically not achieved until after the onset of hearing. Despite the importance of tonotopic organization, the factors that specify unique positional identities along the cochlea or basilar papilla are unknown. However, recent studies of developing systems, including the inner ear provide some clues regarding the signalling pathways that may be instructive for the formation of a tonotopic axis.
Collapse
Affiliation(s)
- Zoe F Mann
- Laboratory of Cochlear Development, NIDCD, NIH, Bethesda, MD 20892, USA.
| | | |
Collapse
|
5
|
Song L, McGee J, Walsh EJ. The influence of thyroid hormone deficiency on the development of cochlear nonlinearities. J Assoc Res Otolaryngol 2008; 9:464-76. [PMID: 18855071 DOI: 10.1007/s10162-008-0140-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2007] [Accepted: 09/11/2008] [Indexed: 11/24/2022] Open
Abstract
It is well known that failure to treat severe congenital hypothyroidism leads to profound auditory disability, and it has been suggested that an intracochlear defect, or defects, associated with the condition diminishes the efficacy of an active, physiologically vulnerable nonlinear transduction process commonly referred to as cochlear amplification. We address this question directly by tracking the development of threshold-frequency (tuning) curves and two-tone suppression in hypothyroid, Tshr mutant mice born to hypothyroid dams and comparing those findings with findings observed in euthyroid mice. Like sharp tuning, two-tone suppression is a product of transduction nonlinearity and is a useful indicator of the functional status of cochlear amplification. In contrast to euthyroid mice that acquire sharp tuning, normal two-tone suppression, and adultlike sensitivity by the end of the third postnatal week, as shown in earlier studies, hypothyroid mice remained grossly insensitive to sound throughout life. In addition, tuning was generally broad in hypothyroid mice, tuning curve "tips" were frequently missing, and two-tone suppression was rarely observed. However, unlike tip thresholds, tuning curve "tail" thresholds, a feature that reflects the functional status of passive elements of transduction, acquired normal values over a roughly 2-month postnatal time period. These observations collectively suggest that active transduction micromechanics, at least in the frequency region studied here, are profoundly affected by thyroid hormone and support speculation that abnormal outer hair cell function may be the cause of the primary, enduring peripheral auditory defect associated with profound, congenital hypothyroidism in the Tshr mutant mouse.
Collapse
Affiliation(s)
- Lei Song
- Developmental Auditory Physiology Laboratory, Boys Town National Research Hospital, 555 North 30th Street, Omaha, NE 68131, USA
| | | | | |
Collapse
|
6
|
Sabini P, Sclafani AP. Efficacy of serologic testing in asymmetric sensorineural hearing loss. Otolaryngol Head Neck Surg 2000; 122:469-76. [PMID: 10740163 DOI: 10.1067/mhn.2000.102180] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
PURPOSE The goal of this study was to determine the efficacy of a detailed questionnaire, auditory brain stem response testing (ABR), MRI, and an extensive battery of serologic tests in diagnosing asymmetric sensorineural hearing loss (ASNHL). METHODS AND MATERIAL Patients with audiograms demonstrating ASNHL of 10 dB or greater in 2 consecutive frequencies or 15 dB in any 1 frequency between 250 and 6000 Hz were asked to participate. Patients underwent MRI scanning of the cerebellopontine angle, internal auditory canals, and posterior fossa with gadolinium contrast, ABR, and an extensive battery of tests. The causative diagnosis was made by the individual clinician based on each patient's history, physical examination, and test results. RESULTS Forty-five patients completed the study. A review of the data confirmed the utility of a detailed history and physical examination, MRI, and fluorescent treponemal antibody test in all cases. Erythrocyte sedimentation rate, glycosylated hemoglobin, Lyme antibody titers, and total hemolytic component (CH50) were helpful in selected cases. Thyroid function testing, complete blood count, Sequential Multiple Analysis-7, prothrombin time/partial thromboplastin time, lipid profile, and ABR were of no value in these patients. CONCLUSION A careful history and physical examination, MRI, and fluorescent treponemal antibody test should be performed for the evaluation of all patients with ASNHL; however, more extensive serologic testing, including sedimentation rate, glycosylated hemoglobin, Lyme antibody titers, and CH50, should be selectively performed, based on a suggestive history or suspicious physical findings.
Collapse
Affiliation(s)
- P Sabini
- Department of Otolaryngology-Head and Neck Surgery, Division of Facial Plastic and Reconstructive Surgery, New York Eye & Ear Infirmary, New York, NY 10003, USA
| | | |
Collapse
|
7
|
Abstract
Developing mammals are more sensitive to noise, chemical and drug-induced ototoxicity than adults, with maximum sensitivity occurring during periods of anatomical and functional maturation of the cochlea. Normal physiological development of resting potentials (the endocochlear potential) and sound-evoked potentials including cochlear microphonics, summating potentials, compound action potentials, auditory brainstem responses and more recently distortion-product otoacoustic emissions have been characterized in several species including rats, mice, kittens, gerbils and guinea pigs. All of these responses are significantly impaired following acoustic trauma and/or exposure to a variety of ototoxic agents including aminoglycoside antibiotics, loop diuretics, antithyroid and antitumor drugs (alpha-difluoromethylornithine) and excitatory amino acids. Coupled with physiological and anatomical development is the maturation of specific biochemical pathways, which may be vulnerable targets of environmental noise and chemicals, excitatory amino acids and therapeutic drugs with ototoxic potentials.
Collapse
Affiliation(s)
- C M Henley
- Department of Otorhinolaryngology/Communicative Sciences, Baylor College of Medicine, Houston, TX 77030, USA
| | | |
Collapse
|
8
|
Hald J, Milroy CM, Jensen KD, Parving A. Human temporal bone findings in acquired hypothyroidism. J Laryngol Otol 1991; 105:886-9. [PMID: 1761939 DOI: 10.1017/s0022215100117748] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Histological studies of the auditory organ in patients with acquired hypothyroidism are scarce. Thus the aim of the present study was to examine the temporal bones and the brain in subjects with hypothyroidism. Four temporal bones and two brains from clinically and biochemically hypothyroid subjects were removed and evaluated by light microscopy determine to the morphological changes and deposition of neutral and acid glycosaminoglycans. An audiogram from one of the patients showed a sensorineural hearing loss, which could be ascribed to occupational noise exposure. The study revealed histological changes compatible with age and infectious disease. No accumulation of neutral or acid glycosaminoglycans could be demonstrated in the temporal bones, or in the brains.
Collapse
Affiliation(s)
- J Hald
- Department of Audiology, Bispebjerg Hospital, Copenhagen, Denmark
| | | | | | | |
Collapse
|
9
|
Parving A, Ostri B, Bretlau P, Hansen JM, Parving HH. Audiological and temporal bone findings in myxedema. Ann Otol Rhinol Laryngol 1986; 95:278-83. [PMID: 3717854 DOI: 10.1177/000348948609500313] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Fifteen patients with confirmed myxedema at a median age of 48 years (range 32 to 60 years) were referred for audiological evaluation before and after treatment with levothyroxine. The median interval between the pretreatment and posttreatment investigations was 18 months (range 9 to 27 months). In addition, 13 patients at a median age of 78 years (range 64 to 95 years) were audiologically reexamined after long-standing levothyroxine treatment. The observation period upon treatment with levothyroxine was 40 months (range 32 to 46 months). No improvement in hearing sensitivity could be demonstrated either in the younger patients or in the elderly. When compared to an age- and sex-matched unscreened population, the myxedematous patients did not demonstrate any different degree of hearing loss. Histological investigation of the temporal bones from an 83-year-old woman with myxedema, however, showed no morphological changes or deposition of glycosaminoglycans, changes which are compatible with true age-related hearing loss. It is concluded that no association exists between myxedema and hearing impairment and that no morphological or structural changes due to myxedema can be demonstrated in the temporal bones.
Collapse
|
10
|
Uziel A, Legrand C, Ohresser M, Marot M. Maturational and degenerative processes in the organ of Corti after neonatal hypothyroidism. Hear Res 1983; 11:203-18. [PMID: 6619005 DOI: 10.1016/0378-5955(83)90079-5] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
In order to study the long-term effects of neonatal hypothyroidism on the organ of Corti, rats were given propylthiouracil (PTU) during the first 30 days after birth. Cochlear changes occurring after the cessation of antithyroid treatment were studied by both physiological (brainstem auditory evoked responses: BAERs, electrocochleography) and morphological techniques (transmission and scanning electron microscopy). The first appearance of BAERs was noted between days 37 and 45. Maturation of auditory potentials was achieved within 10-15 days but was incomplete since the animals definitely demonstrated elevated thresholds around 60-70 dB SPL. Morphological results indicated that some structures, like the inner sulcus epithelium, were able to restart maturational processes that had been interrupted during the period of hypothyroidism. However, these maturational changes were considerably limited and rapidLy accompanied by severe degenerative changes involving almost all cochlear structures. Degenerative changes included the deposition of an amorphous substance within the organ of Corti, severe alterations in pillar cells (absence of formation of the tunnel of Corti, distortion of microtubules), severe outer hair cell losses with abnormalities in their innervation (absence of development of efferents and loss of afferent dendrites).
Collapse
|